Centrifugal pump maintenance that really extends pump life comes down to two habits: routine checks while the pump runs, and a precision rebuild when it is opened. In a rebuild, the wet end decides the result. New bearings and a new seal will not last if the impeller, casing and stuffing box cover go back with worn faces and open clearances. This guide follows Crane Engineering's precision maintenance video and adds the routine checks, wear limits and fits you need to bring a pump back to as-new condition.

Joe Frank of Crane Engineering inspects the wet end of a back pull-out end-suction pump. Video: Crane Engineering on YouTube (10:20).

What the video covers:

• 0:42 Casing inspection: face grooves, gasket area and cutwater
• 1:32 Impeller inspection: vanes, back pump-out vanes and fits
• 2:07 Stuffing box cover inspection
• 3:00 Wear limits for reusing each part
• 4:22 Impeller clearance, thrust and seal life
• 6:43 Worn parts from real pumps
• 8:32 An abrasive wear example
• 9:22 Wear rings on split-case pumps

Most pump failures give warning first: noise, heat, leakage or vibration. Routine centrifugal pump maintenance catches them while the fix is still cheap. The schedule below draws on a widely used preventive maintenance guide for centrifugal pumps and on the U.S. Department of Energy's pumping system tip sheets. Adapt the intervals to your duty, and follow your pump manual where it differs.

Do not keep tightening packing to stop a leak. Overtightened packing wears the shaft sleeve and raises power consumption. If it has to be tightened excessively, replace it.

A centrifugal pump relies on small gaps between rotating and stationary parts to keep high-pressure liquid at the discharge from flowing back to the suction. As those gaps wear open, more liquid recirculates inside the pump. The pump keeps running, but it delivers less flow and head for the same power.

The losses are significant. The U.S. Department of Energy notes that erosion of wear rings and the rotor can reduce a pump's wire-to-water efficiency by 10% or more. In a worked example by pump engineer Lev Nelik, doubling the wear ring clearance on a double-suction pump rated at 8,000 gpm and 400 ft (about 1,800 m³/h at 122 m) lets about 4% of the rated flow leak back. At roughly 900 hp, that wastes about 27 kW, or around $23,600 a year at $0.10/kWh in continuous service.

Energy is only part of the cost. As the video explains, open clearances also raise thrust loads and seal chamber pressure, which shortens bearing and seal life.

In a back pull-out end-suction pump, the wet end has three parts: the casing (volute), the impeller and the stuffing box cover, also called the seal chamber cover or back plate. When a back pull-out assembly is exchanged, the casing usually stays bolted into the piping, so it is easy to skip. Inspect it anyway: it is often the oldest part of the pump.

• Grooves across the face that runs next to the impeller.
• Cracks, irregularities or washouts at the gasket surface.
• The cutwater. It should be smooth and straight across; a worn or washed-out cutwater lets more liquid recirculate around the volute.

• Grooves or general wear on the face that runs next to the casing.
• Bent vanes.
• The back pump-out vanes: their height and whether the edges are still sharp.
• The threads, and the face that seats against the shaft sleeve.

• Wear, grooves or pitting on the face that runs next to the impeller.
• The gasket surface against the casing.
• The bore where the shaft sleeve passes through.
• The face where the mechanical seal mounts.
• The register that locates the cover on the frame adapter.

The video gives clear limits for reusing wet-end parts on an end-suction pump. Lay a straight edge across each face to judge the depth of grooves and general wear.

Where your pump manufacturer gives tighter limits, use those. A part just inside the limit can go back in, but expect some extra leakage and a small loss of efficiency. The video shows a stuffing box cover with grooves just under 1/8 in that falls into exactly this category, and a suction side plate with grooves deep enough that it should not be reused.

Open and semi-open impellers run with a small axial gap to the casing. For the mid-size ANSI pump in the video, the operating manual calls for 0.008 in (0.20 mm) at service temperatures of 200 °F (93 °C) or below. With the impeller set there, the gaps in front of and behind the impeller typically add up to 0.060–0.085 in (1.5–2.2 mm) between the casing and the stuffing box cover.

The right setting depends on temperature. Parts grow as they heat up, so hot service needs a larger cold setting. One of the casings in the video came from a pump set at the standard 0.008 in while the process ran above 300 °F (about 150 °C). The impeller grew into the casing, the two rubbed, and the casing was heavily worn.

On pumps that adjust with jack bolts and locking bolts on the bearing housing, the usual procedure is:

1. Lock out the driver, then remove the coupling guard and the coupling.
2. Mount a dial indicator with its button on the end of the shaft.
3. Back out the jack bolts, then tighten the locking bolts evenly until the impeller just touches the casing. Zero the indicator.
4. Back off the locking bolts, then tighten the jack bolts evenly to push the housing out until the indicator shows the specified clearance.
5. Tighten the locking bolts evenly while the jack bolts hold the setting, and check that the shaft turns freely by hand.

Some designs adjust with shims or an adjusting nut instead. Follow the manual for your pump. For more on the impeller types themselves, see open, semi-open and closed impellers.

Because an open impeller is adjustable, it is tempting to keep moving it toward the casing as the faces wear. That restores the front clearance, but the impeller moves the same distance away from the stuffing box cover, and the back gap grows. The back pump-out vanes are designed to work across a small back gap, so a wider one causes trouble.

Once the faces are worn past their limits, the fix is to restore or replace the parts, not to keep resetting the impeller.

Closed impellers, including the double-suction impellers in split-case pumps, seal against the casing with wear rings rather than an axial gap. The video notes that on split-case pumps the total clearance between the impeller ring and the casing ring is typically only 0.020–0.040 in (0.5–1.0 mm), depending on pump size and ring material. Wear rings cannot be adjusted, so the only cure for wear is new rings.

One fits-and-clearances checklist based on Hydraulic Institute standards gives this guide for the new diametral clearance between impeller ring and casing ring, for rings up to 12 in (305 mm) in diameter:

Clearance = 0.010–0.012 in + 0.001 in per inch of ring diameter
Example, 8 in (203 mm) ring: 0.018–0.020 in (0.46–0.51 mm)

Add 0.005 in (0.13 mm) for materials that tend to gall, such as stainless steel.

• When to renew them. The same checklist says to renew the rings when the clearance reaches twice the original value. Some manufacturers replace them sooner, when the clearance has grown by 40%.
• Rear rings. Excessive clearance at the rear rings raises axial thrust and can damage the thrust bearing.
• Fitting. Rings are pressed on with 0.002–0.003 in (0.05–0.08 mm) interference and locked with dowels or tack welds in at least two places. Do not bore out a casing ring seat by more than 3% of its original diameter.

A precision rebuild also restores the fits that keep the rotor running true. The values below come from the same checklist. Use the pump maker's figures where they differ.

The last end-suction example in the video is a back pull-out assembly from abrasive service, and every wet-end surface shows it. The vanes and the impeller face are worn and uneven. The back pump-out vanes are nearly gone. The stuffing box cover is cupped from the center outward, and the casing has heavy washout near the cutwater.

In abrasive duty, plan for faster wear:

• Shorten the inspection interval and trend performance, so parts are replaced before they pass their limits.
• Keep the pump near its best efficiency point. At low flow, liquid recirculates inside the pump and wears it faster.
• Choose harder materials, or a pump designed for solids, such as a slurry pump.
• Protect the mechanical seal from solids with a suitable flush, and keep the back pump-out vanes in good condition.

A rebuild makes sense when the casing is sound and the wet-end parts can be brought back within limits. Consider a new pump or a new back pull-out assembly instead when:

• The casing is cracked, washed out at the gasket face or grooved beyond 1/8 in, and cannot be repaired by building up and re-machining.
• The impeller has bent vanes or wear beyond the limits, and the parts would cost close to a new assembly.
• The pump runs far from its best efficiency point. A pump that does not suit its duty will keep wearing the same way, so check the operating point on the pump performance curve and reselect if needed. Our guide on how to select a centrifugal pump covers the process.
• Failures keep returning at short intervals even after careful rebuilds. Find the root cause first, whether it is the operating point, the piping or the liquid.

If you are sourcing a replacement, see our comparison of centrifugal pump suppliers in China.

The pump layout decides how quickly and accurately centrifugal pump maintenance can be done.

• IS horizontal clean water centrifugal pump. Built to ISO 2858 dimensions with a back pull-out layout: the casing and cover separate behind the impeller. Remove the coupling spacer and the rotor comes out without disturbing the casing, the suction and discharge piping or the motor. Flows up to 400 m³/h and heads up to 125 m, for clean water up to 80 °C.
• IH stainless steel chemical centrifugal pump. The same back pull-out layout for corrosive liquids.
• Horizontal split-case pump. The casing splits along the shaft line, so the upper half lifts off for access to the rotor and wear rings while the pipework stays connected.

Shinjo supports its pumps with spare parts, remote technical support and video installation guidance.

Planning a pump rebuild or a replacement? Send SHINJO the pump model, the duty and photos of the worn parts, and we will recommend spare parts or a replacement pump. See our full ranges of centrifugal pumps and split-case pumps.

Check noise, bearing temperature and leakage daily, lubrication monthly, and alignment and the coupling once a year. Open the pump for a rebuild when trends show falling performance, rising vibration or repeated seal leaks, rather than on a fixed calendar.

Use the value in the pump's operating manual for your service temperature. For example, the video quotes 0.008 in (0.20 mm) for a mid-size ANSI pump at 200 °F (93 °C) or below. Hot service needs a larger cold setting to allow for thermal growth.

A common rule is to renew them when the clearance reaches twice its original value. Some manufacturers replace them sooner, when the clearance has grown by 40%. Wear rings cannot be adjusted, so new rings are the only way to restore the clearance.

Check the back clearance. If the impeller was moved toward the casing to make up for front wear, the gap to the stuffing box cover grows. The back pump-out vanes then stop clearing solids from the seal area and the stuffing box pressure rises. Worn pump-out vanes have the same effect.

Only within limits. In the video, casing grooves up to 1/8 in (3.2 mm) and impeller face wear up to 1/16 in (1.6 mm) are acceptable, while any bent vane means a new impeller. Parts close to the limit still work, but with some extra leakage and lower efficiency.

Run it near its best efficiency point, keep lubrication and alignment in order, and trend vibration and performance. When the pump is opened, rebuild it to as-new clearances instead of replacing only the bearings and the seal.

Multistage pump selection comes down to five numbers: the flow, the total head, the head each stage adds at that flow, the NPSH available at the first stage, and the highest pressure the casing will see. Divide the required head by the stage head to get the number of stages. Then check three things: the pump runs near its best efficiency point, the first stage will not cavitate, and suction pressure plus shut-off head stays within the casing rating. Shinjo's DF multistage pump covers 15–336 m³/h and 144–690 m. For very small flows at high head, a partial emission pump is often the better fit.

State the minimum, normal and maximum flow, and how long the pump runs at each. If two pumps share a header, work out the real combined demand rather than adding up the maximum of every user. Say whether a standby pump must carry the full duty alone.

Record the liquid's temperature, density, viscosity and vapor pressure as well. Water-based pump curves do not apply directly to viscous oils, and abrasive solids rule out most multistage pumps, which have close running clearances.

Do not add a margin to every number. A safety factor on flow, another on friction losses and a third on head lead to a pump that spends its life throttled, far from its best efficiency point.

For a pump moving liquid between two vessels, the required head is:

H = Δz + Δp ÷ (ρ × g) + h_L

Δz is the elevation difference, Δp the pressure difference between the vessels, ρ the liquid density, g gravity and h_L the friction loss in pipes, fittings, valves and equipment. For large tanks, the velocity difference is negligible.

Example: water at 20 °C is pumped from an open tank to a vessel at 2.2 MPa gauge, 25 m higher, with 20 m of friction loss at 28 m³/h:

H = 25 + 2,200,000 ÷ (998 × 9.81) + 20 ≈ 25 + 224.7 + 20 ≈ 270 m

Two common mistakes: adding the discharge pressure again when it is already counted in Δp, and forgetting to subtract the pressure in a pressurized suction vessel. For more on the terms, see total head and total dynamic head and pump head loss.

In a multistage pump, the impellers work in series. The same flow passes through every stage, and their heads add up. So the number of stages is roughly the required head divided by the head of one stage at the duty flow.

Shinjo's DF46-50 adds 57.5 m per stage at 28 m³/h. For the 270 m example: 270 ÷ 57.5 = 4.7, so five stages are needed. The published data for this model at 28 m³/h:

Five stages give 287.5 m, which is 17.5 m more than needed. In practice, the pump will run slightly further out on its curve, where the system curve crosses it. Alternatively, the impellers can be trimmed, or a variable-frequency drive can reduce speed. Do not add a sixth stage "for margin". It adds 57.5 m of head that would be burned off in a throttling valve, plus about 8 kW of shaft power.

You can check the shaft power from the head, flow and efficiency (53% for this model):

P = ρ × g × Q × H ÷ η = 998 × 9.81 × (28 ÷ 3,600) × 287.5 ÷ 0.53 ≈ 41.3 kW

Select the motor for the highest power anywhere on the allowable operating range, not just at the duty point. Read the pump performance curve out to maximum flow and, for liquids heavier than water, scale the power with density.

Only the first impeller sees the suction conditions, so the first stage decides whether the pump cavitates. Adding stages raises the discharge pressure but does nothing for the suction.

Manufacturers publish NPSH required as NPSH3: the suction head at which cavitation has already cut the first-stage head by 3%. The pump is cavitating at that point, so NPSH available must be higher, with a margin. Calculate NPSH available at the lowest liquid level, the highest temperature and the lowest suction vessel pressure together, using absolute pressures. Hot water is the usual problem. Its vapor pressure rises steeply, which is why feed pumps on deaerators sit far below the tank.

If NPSH is short, raise the tank, enlarge and shorten the suction pipe, cool the liquid, choose a lower-speed pump, or add a low-head booster pump in front.

The casing must hold the highest pressure it can ever see. That is the maximum suction pressure plus the pump's shut-off head, at maximum speed and maximum liquid density. It is not just the discharge pressure at the duty point. Compare it with the allowable working pressure of the casing, nozzles and seal at operating temperature. The hydrostatic test pressure, usually 1.5 times the allowable working pressure, is a factory test, not an operating limit.

Check the inlet pressure as well. The DF pump is rated for an inlet pressure below 0.6 MPa. That matters when it takes suction from a pressurized vessel or runs in series behind another pump.

Every impeller pushes the rotor toward the suction end, and in a multistage pump these forces add up. Ring-section multistage pumps usually balance them with a balance disc or drum and a thrust bearing. Balance devices rely on close clearances, so abrasive particles wear them and let the rotor shift. Keep the liquid clean, and fit a suction strainer where needed.

Ask the supplier what pressure the shaft seal sees. It depends on the design and is not always full discharge pressure.

At low flow, most of the motor's power turns into heat in a small amount of liquid, and the liquid recirculates inside the impellers. Ask for the minimum continuous flow. If the process can demand less, fit a minimum-flow bypass that returns liquid to the suction tank, not directly to the pump inlet.

For small clean-water duties of 2–32 m³/h, the compact cast iron multistage pump has stainless steel impellers and inner parts in a cast iron frame, with motors of 0.37–3 kW. It handles water from −15 to 70 °C, or up to 120 °C in its hot-water version.

Choose the material from the liquid. Cast iron suits clean, cold water at moderate pressure. Cast steel suits higher pressures and hot water up to the DF's 105 °C limit. Stainless steel suits corrosive liquids, demineralized water, which attacks cast iron, and hygienic duties.

A multistage pump sized for a very small flow ends up with small, inefficient stages, or with a larger pump running far below its best efficiency point and relying on a bypass. For flows up to 15 m³/h and heads up to 120 m, Shinjo's high head partial emission pump reaches the head in a single stage. Its data table lists motor sizes for liquid densities of 1.0, 1.4 and 1.86, which shows how strongly power depends on density. Compare both options on curves, power and NPSH before deciding. For more on general selection, see how to select a centrifugal pump.

• Minimum, normal and maximum flow, and the running time at each.
• Total head, or the system details to calculate it: elevations, vessel pressures and pipe layout.
• Liquid, temperature, density, viscosity and vapor pressure.
• Suction conditions: tank level, suction pressure and NPSH available.
• Maximum suction pressure, for the casing pressure check.
• Material requirements, power supply and any required standard, such as API 610 or ISO 9906 test grades.

Need a pump for a high-head duty? Send your duty data to SHINJO and we will select the stages, material and motor for you. See our full range of multistage pumps.

No. Stages in series add head while carrying the same flow. The operating flow is where the pump curve crosses the system curve, so more stages shift that point only because the head rises.

Divide the required total head by the head of one stage at the duty flow, then round up. For example, 270 m at 28 m³/h with a DF46-50, which adds 57.5 m per stage, needs five stages. Then check efficiency, power and NPSH for that selection.

Because cavitation happens at the first impeller, which sees only the suction conditions. Extra stages raise the discharge pressure, not the suction pressure. Improve NPSH available, or choose a pump with a lower NPSH requirement.

The DF pump is rated for an inlet pressure below 0.6 MPa. Check this when it takes suction from a pressurized vessel or runs in series behind a booster pump.

When the flow is very small compared with the head: up to about 15 m³/h at heads up to 120 m. A single-stage partial emission pump then avoids a multistage pump running far below its best efficiency point.

Choose a non-clogging pump around whatever is most likely to block it, not just around flow and head. Hard lumps need a free passage larger than the biggest lump. Long fibers and rags need an impeller they cannot wrap around, or a cutter that shreds them. Grit and sand rarely block a pump, but they wear it, so they call for harder materials. Shinjo's non-clogging sludge pump passes particles of 15–80 mm and fibers of 150–1,000 mm, depending on size. For rags, ropes and plastic sheet, the submersible non-clogging pump with a shredder cuts them up before they reach the impeller.

"Dirty water" is not a specification. Different solids block a pump in different ways, and each calls for a different design.

Look at the worst case, not the average. A batch discharge at the end of a shift, or the first flush after a rainstorm, can block a pump that handled weeks of normal flow.

Most sewage pumps use single- or double-vane impellers with large channels. The JYWQ, for example, uses a double-channel non-clogging impeller. For a deeper look at impeller construction, see open, semi-open and closed impellers.

Free passage is the diameter of the largest sphere that can pass through the pump. It tells you about hard lumps, and nothing about fibers. A strip of cloth far thinner than the free passage can still catch on a vane edge and wrap.

Fiber rating is the longest fiber the pump can pass. Across Shinjo's non-clogging sludge pump range, particle tolerance runs from 15 to 80 mm and fiber tolerance from 150 to 1,000 mm. Both rise with pump size, so check the values for the model you select. The ZW self-priming non-clogging pump passes suspended solids up to 60% of its bore and fibers up to five times its bore. A DN100 ZW therefore passes solids of about 60 mm and fibers of about 500 mm.

The whole route counts. A large pump passage is wasted if a check valve, reducer or strainer downstream is smaller. Oregon's design rules for wastewater pump stations, for example, require raw sewage pumps to pass at least a 63 mm (2½ in) sphere and preferably 76 mm (3 in), and require the piping and valves to pass 76 mm.

Many blockages blamed on the pump are caused by how it runs.

• Stay near the best efficiency point. At low flow, liquid recirculates inside the pump, solids settle in the casing, and single-vane impellers vibrate. Calculate the total dynamic head at both high and low pit levels, and check both points on the pump performance curve.
• Keep the velocity up in the discharge line. Slow flow lets solids settle in the pipe. Oregon's rules call for 3.5–8 ft/s (about 1.1–2.4 m/s) in force mains. With a variable-frequency drive, they require at least 3.5 ft/s once in each pumping cycle and never less than 2 ft/s (0.6 m/s).
• Do not slow a variable-speed pump too far. Below a certain speed, solids stop moving and the impeller loses its ability to shed fibers.
• Do not oversize the motor to fight clogging. A bigger motor does not change the passage geometry. Size it for the full operating range of the curve.

The wet well decides much of what the pump sees. Bring the incoming flow in away from the pump inlet, and avoid dead corners where solids collect. Slope the floor toward the pump. Where sludge settles, a mixer keeps it in suspension. The JYWQ has a built-in mixing device, with a stirring diameter of 1,200–3,000 mm, that turns settled sediment back into a slurry the pump can carry away.

If rags are a constant problem and a cutter pump does not suit the duty, a screen upstream of the pit removes them. The screen then needs regular cleaning, or the blockage just moves upstream.

Choose materials for both corrosion and wear. On the ZW, cast iron suits liquids from pH 6 to 9 and stainless steel from pH 2 to 13. Abrasive grit needs hard wear surfaces and moderate speed. Where corrosion and abrasion occur together, as in many industrial effluents, the combined effect is worse than either alone.

Shinjo's non-clogging sludge pumps use two sets of hard-alloy mechanical seals. Hard faces matter in wastewater, because grit grinds away softer seal faces. Submersible versions run the seals in an oil chamber that protects the motor.

• Flow, and the head at high and low pit levels.
• Solids: largest lump, fiber length, rags or wipes, grit, and solids concentration.
• A photo or sample of the worst material, if available.
• Liquid temperature, pH and chemical content.
• Pit dimensions and how the pump will be installed.
• Discharge pipe size and length, including valves and reducers.

Need a pump that will not block on your wastewater? Send a description of the solids to SHINJO and we will recommend a non-clogging pump and impeller. See our full range of sewage pumps.

Yes. "Non-clogging" describes a design aim, not a guarantee. Oversized lumps, long rags, grease build-up, low-flow operation and undersized valves downstream can all stop a non-clogging pump.

It depends on the pump size and impeller. Shinjo's non-clogging sludge pumps pass particles of 15–80 mm and fibers of 150–1,000 mm across the range. The ZW self-priming pump passes solids up to 60% of its bore.

A vortex impeller keeps most solids away from the impeller and copes well with stringy material, but it is less efficient. A channel impeller is more efficient and passes large solids. For rags and plastic film, a cutter pump is often the most reliable answer.

When the wastewater carries rags, wipes, ropes or plastic sheet, and the flow and head are within the cutter pump's range: 15–145 m³/h and 4–25 m for Shinjo's shredder model. Cutter pumps are not suited to hard objects such as metal or stones.

No. Extra power does not change the passage size or stop fibers from wrapping. Prevent clogging with the right impeller, free passage, operating point and pit design, and size the motor for the full operating range.

Choose a self-priming sewage pump when the lowest liquid level is within about 4.5 m of the pump and you want the pump and motor above ground, where they are easy to reach. Choose a submersible sewage pump when the pit is deeper, space is tight or the suction line would be long. There is also a middle option: a vertical submerged pump, with the pump in the liquid and the motor above the pit. In Shinjo's range these are the ZW self-priming non-clogging sewage pump (8–800 m³/h), the WQ submersible sewage pump (10–6,000 m³/h) and the YW vertical submerged sewage pump (8–1,000 m³/h).

A self-priming pump does not pull liquid up. It lowers the pressure at its inlet, and atmospheric pressure pushes the liquid up the suction pipe. At sea level, atmospheric pressure equals about 10.3 m of water, and that is the theoretical limit. In practice, vapor pressure, friction in the suction pipe and the pump's own NPSH requirement use up much of it. The ZW is rated for a self-priming height of 4.5–5.5 m with a suction pipe up to 10 m long.

Two site conditions reduce the usable lift:

• Altitude. At 1,000 m above sea level, atmospheric pressure is about 9.2 m of water, so you lose more than a meter compared with sea level.
• Temperature. Warm wastewater has a higher vapor pressure and boils more easily at the low pressure inside the pump inlet.

Check the lift with an NPSH calculation at the lowest liquid level and the highest liquid temperature. Example: a pump station at 500 m altitude, wastewater at 30 °C, the lowest level 4.0 m below the pump inlet, and 0.8 m of friction loss in the suction pipe:

NPSHa = atmospheric head − vapor pressure head − static lift − suction losses
NPSHa = 9.77 − 0.43 − 4.0 − 0.8 ≈ 4.5 m

Oregon's design rules for wastewater pump stations require a safety margin of at least 6 ft (1.8 m) above the pump's NPSH required at suction-lift stations. In this example, the pump's NPSH required at the duty point must therefore be no more than about 2.7 m. If it is higher, lower the pump, shorten the suction line or choose a submersible pump.

The ZW uses an external-mixing, axial back-flow design. Its casing holds a reserve of liquid. When the pump starts, the impeller mixes this liquid with the air in the suction pipe, separates the air in the casing, discharges it and returns the liquid to the impeller. After a few cycles, the suction pipe is full and the pump delivers normally. It needs no foot valve.

The casing must be filled with liquid before the first start. After that it keeps its reserve between starts. Reliable priming depends on the installation:

• Keep the suction pipe short, no longer than 10 m, and completely airtight. A small leak lets in air without dripping, so it is easy to miss.
• Run the suction pipe so that it rises steadily to the pump, with no high points where air collects.
• Fit a check valve in the discharge, and give the air a way out during priming.

A submersible pump avoids suction lift entirely, but it brings its own conditions.

• Liquid temperature. The WQ is rated for liquids from 0 to 55 °C. For hotter industrial effluent, use the ZW or YW, which are rated to 80 °C.
• Motor cooling. Most submersible motors are cooled by the surrounding liquid, so the stop level must keep the motor covered. Some designs, such as the JYWQ, have an internal cooling circuit and can run down to the lowest pit level.
• Seals. A double mechanical seal in an oil chamber protects the motor. Where a moisture sensor is fitted in the oil chamber, it warns of seal wear before water reaches the windings.
• Retrieval. Guide rails and an automatic discharge coupling let you lift the pump out without entering the pit. Plan the lifting gear and overhead clearance before ordering. Never lift the pump by its cable.
• Hazardous gas. Sewage pits can contain flammable gas. A pump in the pit needs explosion-proof certification. A motor above the pit, as on the ZW and YW, avoids the problem.

Whichever layout you choose, the impeller and passages must pass the solids in the wastewater. Oregon's wastewater design rules, for example, require raw sewage pumps to pass at least a 63 mm (2½ in) sphere and preferably 76 mm (3 in), with piping and valves passing 76 mm. The ZW passes suspended solids up to 60% of the pump bore and fibers up to five times the bore. In a self-priming installation, also check the suction pipe, elbows and any strainer, because a blockage there stops the pump just as surely.

Match the material to the chemistry. On the ZW, cast iron suits liquids from pH 6 to 9 and stainless steel from pH 2 to 13. The liquid density must not exceed 1,240 kg/m³. For more on the basics, see what a sewage pump is and how it works.

The liquid level changes as the pit fills and empties, so the static head and the operating point change too. Calculate the total dynamic head at both high and low levels and compare pump curves across that range, not at one rated point. A submersible pump avoids suction losses. A self-priming pump costs less to maintain because nothing has to be lifted out of the pit. Include lifting equipment, civil works and the cost of an overflow when a pump is out of service, not just the purchase price.

• Flow, and the head at high and low pit levels.
• Pit depth, the lowest liquid level and the site altitude.
• Liquid temperature, pH and chemical content.
• Solids: maximum particle size, fibers, rags and grit.
• Whether flammable gas may be present in the pit.
• Power supply and control requirements.

Deciding between a self-priming and a submersible pump? Send your pit layout to SHINJO and we will recommend the right sewage pump. See our full ranges of sewage pumps and self-priming pumps.

The ZW is rated for a self-priming height of 4.5–5.5 m with a suction pipe up to 10 m long. The usable lift is lower at high altitude and with warm liquid, so confirm it with an NPSH calculation at the lowest pit level.

Yes. Fill the casing with liquid before the first start. The pump then keeps a reserve of liquid in the casing for later starts. Self-priming does not mean it can start or run dry.

Only within its rating. The WQ is rated for liquids up to 55 °C. For hotter industrial effluent, use a pump with the motor out of the liquid, such as the ZW or YW, which are rated to 80 °C.

A self-priming pump, because the pump, seal and motor are above ground. A submersible pump has to be lifted out on its guide rails, which needs lifting equipment and clear access above the pit.

A submersible or vertical submerged pump. A self-priming pump cannot lift more than about 4.5–5.5 m, so a deeper pit would need the pump to be installed below ground, which loses its main advantage.

A high temperature magnetic drive pump for 300–350 °C liquids has to do three things the liquid makes difficult. It must keep its magnets cooler than the liquid, keep its internal bearings wet, and keep its pressure boundary within rating at temperature. Shinjo's CQB-G is rated for liquids up to 300 °C and the MT-HTP for liquids up to 350 °C. Both cover 3.2–100 m³/h in stainless steel. Choose the rating from the hottest temperature the pump can see, then check NPSH, cold-start torque, cooling and warm-up. If a small seal leak is acceptable on hot thermal oil, a sealed hot oil pump is the simpler alternative.

Choose the rating from the highest temperature the pump can reach, including upsets, not from the normal operating temperature. If the liquid normally runs at 290 °C but can reach 320 °C when a control loop fails, the duty needs the MT-HTP. Never assume a 300 °C pump will survive "short" excursions above its rating. The parts that set the limit, the magnets, bearings and gaskets, do not recover when the temperature falls.

The liquid temperature and the magnet temperature are not the same thing, and the magnets usually set the real limit. Typical operating ranges are 150–220 °C for high-temperature neodymium magnets and 250–350 °C for samarium-cobalt magnets. A coupling that pumps a 350 °C liquid therefore has to keep its magnets well below the liquid temperature.

Heat reaches the magnets in three ways: by conduction through the casing, from the liquid circulating inside the pump, and from eddy currents in the metal containment shell, which add heat of their own. Overheated magnets lose torque. Above their limit, the loss becomes permanent, and the coupling slips under load.

That is why the cooling design matters as much as the temperature rating. On the CQB-G, cooling vanes on the outer magnet rotor and several internal circulation paths carry heat away from the magnets. The MT-HTP uses an external circulation cooling system. In both cases, the cooling only works if air can reach the bearing frame and coupling housing. Do not cover them with insulation, even if the rest of the pump is insulated.

Vapor pressure rises steeply with temperature. Some heat transfer fluids are used above their atmospheric boiling point. For example, the common diphenyl/diphenyl oxide fluids boil at about 257 °C at atmospheric pressure. At 300 °C or more, such a system must be pressurized, usually through the expansion tank, or the liquid flashes at the pump suction.

Calculate NPSH available at the highest temperature and the lowest system pressure, using absolute pressures and the vapor pressure of the actual fluid. Compare it with the pump's NPSH required: 3.2–4.5 m across the CQB-G range. Then leave margin. A magnetic drive pump also needs liquid to stay liquid inside the pump, in the passages around the shell and bearings, where the eddy-current heat raises its temperature further. If it flashes there, the bearings run dry even though the pump still delivers flow.

Thermal oils are many times more viscous cold than hot. At start-up the pump has to turn a thick liquid, so the torque demand can be far higher than at operating temperature. If the magnetic coupling is sized only for hot duty, it slips at a cold start. A slipping coupling heats its own magnets and can damage them before the system ever reaches temperature.

Give the supplier the viscosity at the coldest start-up temperature as well as at operating temperature. The motor and the coupling must both handle the cold case. Alternatively, preheat the loop, or start at reduced speed through a variable-frequency drive until the oil thins.

Hot liquid hitting a cold pump, or cold liquid hitting a hot one, causes uneven expansion. The containment shell, the close-clearance silicon carbide bearings and the casing gaskets suffer most. Bring the pump up to temperature with the system, and do not flush a hot pump with cold liquid.

Metals lose strength when hot, so the allowable pressure of flanges, casings and containment shells falls as temperature rises. A Class 150 flange holds roughly half as much pressure at 300 °C as at ambient temperature. Work out the highest discharge pressure, which is suction pressure plus the pump's shut-off head, and check it against the casing and shell rating at the maximum temperature, not at 20 °C.

Piping loads also grow with temperature. Thermal expansion of the connected pipework can push the pump out of alignment or overload its nozzles. Support the pipes independently, and do not pull them into place with the flange bolts.

A magnetic drive pump is the right choice when no leakage is acceptable, as with toxic, flammable or valuable hot liquids. For hot thermal oil in a heating loop, where a small weep from a seal is acceptable and larger flows are needed, the LQRY thermal oil pump is simpler and covers a wider range.

Both need a clean liquid. Aged thermal oil carries carbon and sludge, which wear the bearings of a magnetic drive pump. Filter the loop, and replace degraded oil before it damages the pump.

• The liquid, its grade, and its vapor pressure and viscosity at both start-up and operating temperature.
• Normal temperature, maximum temperature, and how long any upset lasts.
• Flow, head and system pressure, including how the system is pressurized.
• NPSH available at the hottest condition.
• Ambient temperature and the cooling utilities available.
• Start-up procedure, including whether the loop is preheated.
• Hazardous-area classification.

Pumping a hot liquid above 200 °C? Send the details to SHINJO and we will confirm the right high temperature model and coupling for your duty. See the full range of magnetic drive pumps, or read how to select a magnetic drive pump.

No. Magnets, bearings and gaskets can be damaged permanently above their rating, even briefly. If the liquid can reach 350 °C in any operating state, specify a pump rated for 350 °C, such as the MT-HTP.

Samarium-cobalt magnets are typically used at high temperature because they work at about 250–350 °C. Neodymium magnets are stronger but typically limited to about 150–220 °C even in high-temperature grades. The cooling design must still keep the magnets below the liquid temperature.

It depends on the design. The CQB-G cools itself through internal circulation paths and cooling vanes on the outer magnet rotor. The MT-HTP uses an external circulation cooling system. Ask which utilities the quoted model requires and what happens if they fail.

Yes, if the oil is clean and the pump is rated for its maximum temperature. Check NPSH at the hottest condition and size the coupling for cold-start viscosity. For large heating loops where a small seal leak is acceptable, a sealed thermal oil pump is often the simpler choice.

Usually because the oil is too viscous when cold and the coupling torque is too low for that condition. Preheat the loop, start at reduced speed, or ask for a stronger coupling. Do not keep restarting a slipping pump, because each slip heats the magnets.

A magnetic drive pump and a canned motor pump both remove the shaft seal, the most common leak path in a centrifugal pump. The difference is how they drive the impeller. A magnetic drive pump uses a standard motor and turns the impeller through a magnetic coupling, across a sealed containment shell. A canned motor pump puts the motor rotor inside the liquid, behind a thin can that protects the stator windings. For most chemical transfer, a magnetic drive pump is easier to own because the motor is standard and the pump can be repaired on site. A canned motor pump is more compact and suits clean liquids in closed loops, but it usually needs specialist repair.

Magnetic drive pump. An outer magnet rotor sits on the motor shaft. An inner magnet rotor is fixed to the impeller shaft. Between them is a stationary containment shell, also called an isolation sleeve, that closes off the liquid completely. The magnetic field passes through the shell and turns the impeller without any contact, so no shaft passes through the pressure boundary. The impeller runs on sleeve bearings lubricated by the pumped liquid.

Canned motor pump. The pump and motor form one sealed unit on a common shaft. The motor rotor turns in the pumped liquid, and a thin corrosion-resistant liner, the "can", separates the liquid from the stator windings. Some of the liquid circulates through the motor to cool it and to lubricate the sleeve bearings. There is no coupling and no separate motor.

Both are sealless designs. Static joints such as casing gaskets and flanges remain, so "zero leakage" means no leakage at the shaft, not that the installation can never leak.

A metal containment shell sits in a rotating magnetic field, so eddy currents flow in it and turn into heat. That heat is carried away by the liquid flowing through the inside of the pump. Ceramic shell suppliers report that switching from a metal shell to a non-conductive one cuts power input by 10–15%. That figure gives an idea of the loss in a metal shell. Hastelloy is a common metal choice because its low electrical conductivity keeps the loss down.

The heat matters most for liquids close to their boiling point. As an example, take a 15 kW pump on toluene. Here 10–15% is 1.5–2.3 kW. If only 1 m³/h of liquid circulates past the shell and bearings, the liquid there warms by about 4–5.5 °C:

ΔT = P ÷ (ṁ × c_p) = 1.5 kW ÷ (0.24 kg/s × 1.7 kJ/kg·K) ≈ 3.7 °C

If that pushes the liquid above its boiling point at the local pressure, it flashes to vapor in the bearing passages and the bearings run dry. A canned motor pump has the same problem with motor heat. For volatile liquids, ask the supplier for the temperature rise in the internal circulation and the margin above vapor pressure.

Both designs depend on the pumped liquid to lubricate and cool their bearings. That gives them the same three weaknesses.

• Dry running. Without liquid, the bearings overheat in minutes. A magnetic drive pump also loses cooling at the shell, and overheated magnets lose strength.
• Solids. Abrasive particles wear the bearings and can block the small internal circulation passages. Sealless pumps need clean liquids.
• Gas. Entrained gas or vapor breaks the liquid film in the bearings.

The best protection is a motor power monitor, which detects dry running, a closed valve and a decoupled magnetic drive. A temperature sensor at the containment shell and a low-level or flow switch add further protection.

Shinjo builds both types, but they serve different jobs.

The PBG canned motor pump is designed for clean water: HVAC circulation, booster sets, fire pressurization and hot and cold water loops. It mounts directly in a horizontal or vertical pipe. Because it never draws in air, it also suits vacuum systems. For corrosive, toxic or flammable chemicals, Shinjo supplies magnetic drive pumps, with the wetted material matched to the liquid.

Choose a magnetic drive pump when:

• You want a standard or explosion-proof motor that your site can replace.
• Maintenance will be done on site.
• The liquid needs a lined or plastic wet end, such as acids and chlorides.
• The duty may change later.
• The pump must lift from below, which the self-priming ZCQ and ZBF can do.

Choose a canned motor pump when:

• The liquid is clean water or a similar clean liquid in a closed loop.
• Space is tight or the pump has to sit in the pipeline.
• Low noise matters, as in buildings.

Choose neither when the liquid carries solids, the pump may run dry often, or the viscosity is high. In those cases, a sealed pump with a double mechanical seal or an air-operated diaphragm pump is more reliable. For sizing details on magnetic drive pumps, see how to select a magnetic drive pump.

• The liquid, its concentration, density, viscosity and vapor pressure at operating temperature.
• Normal and maximum temperature.
• Flow, head and suction conditions, including whether the pump must self-prime.
• Solids content, if any.
• Hazardous-area classification and the motor protection required.
• Whether secondary containment or leak detection is required.

Comparing sealless options for a chemical duty? Send the details to SHINJO and we will recommend a magnetic drive pump with the right material and coupling. See the full range of magnetic drive pumps.

It depends on the design. A metal containment shell can cost around 10–15% of input power in eddy-current losses, while a plastic or ceramic shell avoids most of that. Canned motors lose power in the can and the motor. Compare the absorbed power each supplier quotes at your duty point.

No. Both rely on the pumped liquid to lubricate and cool their bearings, and dry running can destroy the bearings within minutes. Fit a power monitor or flow switch that stops the pump when it loses liquid.

Both remove the shaft seal. A magnetic drive pump is easier to maintain because it uses a standard motor. A canned motor pump often provides a second containment barrier in the motor housing. Specify the containment and leak detection you need, and compare the offers against that.

Shinjo's PBG canned motor pump is a cast iron design for clean water up to 90 °C. For chemicals, we recommend a magnetic drive pump in stainless steel, fluoroplastic lining or polypropylene, depending on the liquid.

API 685 covers sealless centrifugal pumps, both magnetic drive and canned motor, for petroleum, petrochemical and gas industry service. Many general chemical duties do not require it. If your project does, state it in the enquiry.

Choose a PTFE-lined pump when the liquid attacks stainless steel: hydrochloric acid, hydrofluoric acid, dilute sulfuric acid, aqua regia, mixed acids and strong oxidizers. Choose a stainless steel pump when the liquid stays within the resistance of the grade and the duty is hotter, higher in head or pressure, or carries solids. In Shinjo's range, that means the IHF lined centrifugal pump (up to 80 °C and 87 m) or the sealless CQB-F on one side, and the IH stainless steel chemical pump (up to 150 °C, 132 m and 1.6 MPa) on the other.

Start with the liquid. For many common chemicals, one of the two options is ruled out before flow and head are even considered.

For 98% sulfuric acid, where cast iron is also an option, see our guide to the concentrated sulfuric acid pump.

In the pump trade, "PTFE-lined" and "Teflon-lined" usually mean any fluoroplastic lining: PTFE, FEP (also called F46) or PFA. PTFE cannot be melt-processed, so molded pump linings are usually FEP or PFA, which flow when heated. The IHF is lined with FEP. Its impeller and pump cover are metal inserts with fluoroplastic sintered over them.

The metal casing carries the pressure and the pipe loads, and the lining resists the chemicals. This is why a lined pump can handle hydrochloric acid, hydrofluoric acid, aqua regia, strong alkalis, strong oxidizers and most organic solvents. These are all listed on the IHF product page. Doing the same with solid metal would mean a far more expensive nickel alloy casing.

The fluoroplastics themselves tolerate high temperatures: PFA is rated for continuous service up to 260 °C. The pump's limit is much lower because the lining is locked into a steel casing, and plastic expands many times more than steel when heated. Heat and rapid temperature changes stress the bond between the two. That is why the published liquid temperature for the IHF and CQB-F is 80 °C.

The IHF uses an external bellows mechanical seal, so the springs and metal parts of the seal sit outside the liquid. The stationary face is 99.9% alumina ceramic or silicon carbide, and the rotating face is filled PTFE or silicon carbide.

Stainless steel resists corrosion because of a thin chromium oxide film. Anything that breaks that film down faster than it can reform will corrode the pump, and some chemicals do this from the first day.

• Hydrochloric acid. Standard 304 and 316 are considered non-resistant at any concentration and temperature.
• Chlorides. A widely used guideline for immersed stainless steel puts the chloride limit at about 200 ppm for 304L, 1,000 ppm for 316L and 3,600 ppm for duplex 2205. Above that, pitting and crevice corrosion start. Crevices, deposits and heat lower these limits.
• Hot chlorides. Chloride stress corrosion cracking of 304 and 316 is rare below 60 °C but becomes a real risk above it. Duplex grades resist it much better.
• Dilute reducing acids. Sulfuric acid between about 5% and 80% attacks 316 actively.

The grade matters as much as the word "stainless". The IH pump and the CQ magnetic drive pump are offered in 304, 316 and 316L. For flue gas desulfurization slurry, which combines chlorides, acidity and abrasion, the cast steel desulfurization pump uses a duplex ("two-phase") alloy for the casing and impeller.

A lining resists chemicals well. It fails mechanically and thermally, and these failures usually come from operating conditions rather than from the chemical itself.

• Heat and thermal cycling. Running near the top of the range, or heating and cooling the pump quickly, can blister the lining or separate it from the casing. Steam cleaning is a common cause, because steam is well above 80 °C.
• Vacuum. If the suction can fall below atmospheric pressure, for example when a line drains or siphons, the lining can be pulled away from the casing. Tell the supplier if vacuum is possible.
• Solids and cavitation. Hard or sharp particles cut and wear the lining, and collapsing cavitation bubbles erode it. Once the metal behind it is exposed, it corrodes quickly.
• Permeation. Small molecules such as hydrogen chloride, chlorine and bromine slowly diffuse through fluoroplastics. They can condense behind the lining and cause blisters. A thicker lining slows this down.
• Mechanical damage. Pipe strain, overtightened flanges and careless tools during maintenance all crack linings.

Lined pumps also reach lower heads. The IHF goes up to 87 m and the CQB-F up to 32 m, while the IH stainless steel pump reaches 132 m.

The IH has a back pull-out design. The rotating assembly comes out after removing the coupling spacer, without disturbing the casing, piping or motor. That shortens maintenance on a pump that sees regular seal changes.

The casing material is only half the decision. If a leak would be dangerous, toxic or costly, choose a magnetic drive pump with no shaft seal: the CQB-F for liquids that need a lining, or the CQ for liquids stainless steel can handle. For cool, mildly corrosive liquids, the CQF polypropylene magnetic drive pump is a lower-cost option up to 60 °C.

Magnetic drive pumps have their own limits. Their internal bearings are lubricated by the pumped liquid, so they must never run dry, and they need a clean liquid. For more on sizing them, see how to select a magnetic drive pump.

For hydrochloric acid, the real comparison is not lined pump against 316, because 316 fails. It is lined pump against a nickel alloy such as Hastelloy, and the lined pump is usually much cheaper. For a liquid that stainless steel handles well, a stainless pump avoids every lining risk above and tolerates upsets, solids and hot cleaning. In that case, the lining adds cost without adding life.

Count the failures, not just the purchase price. A lined pump that blisters after every steam-out costs more than a stainless pump in the right grade. A 316 pump that pits through in brine costs more than a lined pump that would have lasted.

• The liquid and its concentration range, including trace chlorides or fluorides.
• Normal and maximum temperature, and any steam or hot-water cleaning.
• Flow, head and suction conditions, including whether vacuum is possible.
• Solids content, particle size and hardness.
• Whether a leak is acceptable, which decides between a sealed and a sealless pump.
• Operating pattern: continuous, batch or frequent starts.

Not sure whether your liquid needs a lining? Send the details to SHINJO and we will recommend a pump and material for your duty. Our full range is in the chemical process pumps category.

Yes. Teflon is a brand name for PTFE and related fluoroplastics. In practice, "PTFE-lined" and "Teflon-lined" pumps are often lined with FEP or PFA, which can be molded. The IHF is lined with FEP (F46).

Yes. Fluoroplastic linings resist hydrochloric acid at all concentrations within the pump's temperature rating, while 304 and 316 stainless steel do not. Over time, hydrogen chloride can permeate the lining, so avoid running at the top of the temperature range.

The limit protects the bond between the lining and the steel casing. Plastic expands many times more than steel, so heat and rapid temperature changes can blister or loosen the lining long before the plastic itself degrades.

Usually not. A common guideline limits 316L to about 1,000 ppm chloride, and seawater contains about 19,000 ppm. Use a lined pump, a duplex or super duplex steel, or a plastic pump for seawater and strong brines.

Only fine, soft solids in low concentration. Hard or sharp particles cut and wear the lining. For corrosive slurries, a duplex steel pump such as the desulfurization pump is usually the better choice.

For a concentrated sulfuric acid pump handling 80% to 98% acid at moderate temperature, a centrifugal pump in gray cast iron or carbon steel is the standard and most economical choice. The acid itself forms a protective iron sulfate film on the metal. Below 80%, above 60 °C, or wherever the concentration can drop, that film breaks down, and a fluoroplastic-lined pump is the safer choice. This guide gives the limits for each option, shows how to size the motor for an acid that weighs 1.84 times as much as water, and lists what to put in the purchase order.

Concentrated sulfuric acid (sulphuric acid in British English) is a strong oxidizer. When it touches iron or carbon steel, it forms a thin layer of iron sulfate that separates the metal from the acid and slows further attack. That film is what protects a GBW pump. Its gray iron is ordinary HT200 or HT250 without large alloy additions; the protection comes from the acid, not from the alloy.

The film only survives in strong acid. Below 80% it dissolves, and the corrosion rate rises sharply. The range from 65% to 80% is the worst of all for iron. The concentration therefore has to stay above 80% in every operating state, including startup, shutdown, flushing and upsets. For the longest life, keep it at the strong end of the range.

Water is the usual cause of trouble. A water flush, a leaking cooler or moist air drawn into a tank can dilute the acid inside the pump. Dilution also releases a great deal of heat, so acid must always be added to water, never water to acid. Do not leave water or weak acid standing in an iron pump: drain it fully, and follow your site procedure for any flush.

High-silicon cast iron (STSi15R) is a different material. It resists sulfuric acid across the whole concentration range, but it is expensive, very brittle and hard to machine. It is used in other pump types, not in GBW.

The iron sulfate film is soft, and fast flow wears it away. Industry guidance for carbon steel piping in concentrated acid limits the flow velocity to about 0.9 m/s. Inside a pump the speeds are far higher: at 2,900 rpm, the tip of a GBW impeller between 100 mm and 250 mm in diameter moves at roughly 15 to 38 m/s.

GBW pumps are designed for this, but they are not suited to very high-velocity duties, and anything that adds turbulence shortens their life:

• Gas bubbles and cavitation, which scour the film. Keep a clear margin between NPSH available and NPSH required.
• Running far from the best efficiency point, especially when throttled close to shutoff.
• Solids in the acid, which abrade the film.

For the hydraulic side of selection, see our guide on how to select a centrifugal pump.

The GBW is a horizontal centrifugal pump built on ISW-type hydraulics for concentrated sulfuric acid.

Where the concentration can fall below 80% or the temperature exceeds 60 °C, use a fluoroplastic-lined pump instead, as described in the next section. The full range is in our chemical process pumps category.

The IHF and CQB-F are lined with FEP (F46), a fluoroplastic that resists 98% sulfuric acid without being oxidized by it. Chemical resistance is not the whole story, though. Temperature, water and the extra weight of the acid still decide how long a lined pump lasts.

Three conditions apply to both pumps:

• Temperature protects the lining bond, not just the plastic. FEP and the steel casing expand at very different rates, so high temperature and rapid heating or cooling can blister the lining or separate it from the steel. Do not run at the top of the range, and avoid thermal shock.
• Keep water out. Water or weak acid entering the pump dilutes the acid locally and releases heat, and that local hot spot can blister the lining.
• Size the motor for SG 1.84. Published motor ratings are for water, as the next section explains.

The CQB-F has two further requirements. Its internal bearings are lubricated and cooled only by the pumped acid, so a few minutes of dry running, cavitation or entrained gas can melt the bearings, overheat the containment shell and demagnetize the magnets. Concentrated acid is heavy and viscous, which makes cavitation more likely, so check NPSH with a clear margin and fit dry-running protection, such as motor power monitoring or a flow switch. The magnetic coupling must also be rated for the acid: a coupling sized for water can slip and lose its magnetism at SG 1.84, so both the coupling torque and the motor power have to be increased. Keep the liquid at or below 80 °C, because the risk of demagnetization rises with temperature. For more on sealless pumps, see how to select a magnetic drive pump.

Density does not change the head a centrifugal pump develops, but it raises the discharge pressure and the power in direct proportion. Sulfuric acid at 93% to 98% has a density of about 1.83 to 1.84 kg/L, and acid at 78% to 80% about 1.70 to 1.73. Size the motor for the strongest acid the pump will see. For how head and pressure relate, see what pump head means.

Catalogue tables, including the GBW table, are rated on water (SG 1.0) unless they say otherwise. Take the GBW65-160 as an example: 25 m³/h at 32 m, listed with a 5.5 kW motor. Assuming a pump efficiency of 60%:

Shaft power = ρ × g × Q × H ÷ η
Water: 1,000 × 9.81 × (25 ÷ 3,600) × 32 ÷ 0.60 ≈ 3.6 kW
98% acid: 1,840 × 9.81 × (25 ÷ 3,600) × 32 ÷ 0.60 ≈ 6.7 kW

The 5.5 kW motor is fine for water and overloaded on 98% acid. With a service margin added, the next standard size is 7.5 kW, or 11 kW if your standard applies a 15% margin. Concentrated acid is also about 25 times as viscous as water at 20 °C, which lowers efficiency a little further. Before ordering any concentrated sulfuric acid pump, ask the supplier to confirm in writing that the motor has been sized for SG 1.84.

The GBW's standard seal is a WB2-type external PTFE bellows single seal. It sits outside the acid and needs no cooling water. Seal configurations vary between manufacturers, so specify these items in the contract:

The same seal configuration applies to the IHF lined pump.

• Acid concentration: minimum, normal and maximum, including startup, cleaning and upset conditions.
• Liquid temperature: normal and maximum.
• Flow rate and total head, with the suction conditions and NPSH available.
• Impurities and solids, and whether water can enter the system.
• Operating pattern: continuous, batch, or intermittent transfer.
• Installation: horizontal pump with flooded suction, or transfer from a tank or sump.
• Motor standard, voltage and frequency, and a request to confirm the motor for SG 1.84.
• Seal configuration: SiC/SiC faces, PTFE secondary seals and Hastelloy C-276 springs.
• For a magnetic drive pump: a magnetic coupling rated for SG 1.84, and dry-running protection.

Need a pump for sulfuric acid? Send these details to SHINJO and we will recommend a model and material for your concentration and temperature.

For 80% to 98% acid, gray cast iron is suitable up to 50 °C and WCB carbon steel up to 60 °C, because the acid forms a protective iron sulfate film on them. Above those temperatures, or where the concentration can fall below 80%, a fluoroplastic-lined pump is the safer choice.

No. Below 80% the protective film dissolves, and the range from 65% to 80% is the most aggressive for iron. Use a fluoroplastic-lined pump for that range.

Only within narrow concentration and temperature windows. Common grades such as 316 corrode badly in the middle of the concentration range, so stainless steel is not a default choice for sulfuric acid pumps.

Yes, chemically. FEP and PTFE linings resist 98% sulfuric acid. The limits are temperature, published as 80 °C for the IHF and CQB-F to protect the bond between lining and steel; keeping water out of the pump; and sizing the motor for SG 1.84.

No. Its internal bearings are lubricated and cooled by the acid itself, so dry running, cavitation or gas bubbles can destroy the bearings and demagnetize the coupling within minutes. Fit dry-running protection and make sure the coupling is rated for SG 1.84.

No. The head stays the same, but the discharge pressure and the power rise in proportion to density, so 98% acid needs about 1.84 times the shaft power of water.