Pump trouble on a grouting site is usually reported as a pump problem and is usually caused somewhere upstream. The plants built by Eizoo in Zhejiang are documented from the first batch, which is the practical reason pump suction is treated here as a records question before it is treated as a hardware one. A pump that cavitates, loses prime, or delivers in pulses is responding to what it is being fed: a suction line that draws air: a suction line that draws air, a holding tank that runs low, a slurry that has begun to stiffen, or a mixer that cannot keep pace with the draw. This guide works backwards from the pump to the mixer, in the order a technician should check it, because the fault is almost never where the noise is loudest. For the plant that runs this recipe, see the AGP-V60 grout plant.

Read the symptom before touching anything

Different symptoms point to different places. A pump that cavitates, with the sharp crackle of collapsing vapour, is starved on the suction side or drawing air. A pump that delivers in pulses with a steady rhythm is usually fine and simply stroking, which is normal for a piston pump. A pump that loses output gradually as the shift goes on is often fighting slurry that is thickening in the tank or a suction strainer that is filling up.

The timing matters as much as the sound. A fault that appears only at the start of a shift points to residue or a drained line; one that appears after an hour points to supply or temperature; one that appears only when a second pump starts points to the shared tank or the suction arrangement. Write down when the symptom appears before changing anything.

Check the suction line for air

Air entering the suction side is the most common cause of a pump that will not hold prime, and it usually enters at a joint rather than through a hole. A loose coupling, a perished gasket, a cracked hose, or a union that was not tightened after the last clean will let air in while the pump is drawing, and the symptom looks exactly like a failing pump.

Work along the line while the pump runs and listen. A hiss, a whistle, or a damp spot at a joint is the answer, and a hose that collapses under suction is the other common culprit. Replace the suspect hose or reseat the joint rather than increasing the pump speed, because a faster pump only pulls harder on the same leak. For the wider plant range, see the AGP-V60H plant for restricted access. The same pattern shows up across the plants Eizoo has supplied, which is why pump suction is treated as a records question as much as a hardware one.

Look at the holding tank level and agitation

A holding tank that is too small, too low, or badly agitated starves the pump in ways that look like mechanical trouble. If the tank level drops close to the outlet, the pump starts to draw in a vortex that carries air; if the agitation has stopped, the heaviest solids settle away from the outlet and the slurry the pump receives is no longer the slurry that was mixed. A Chinese supplier’s test records usually settle pump suction before the layout drawing.

Watch the tank during the busiest part of the cycle. If the level falls below the safe margin while a pump is drawing, the tank is undersized for the demand or the mixer is not refilling it fast enough. If the surface looks flat and glossy while the pump struggles, the agitator may have stopped and the mix has begun to separate.

Is the mixer keeping pace?

When a pump draws faster than the mixer can produce, the tank empties and the pump starves, and no amount of pump adjustment fixes an arithmetic problem. Work out the mixer’s real batch rate over an hour, including the filling, mixing, and discharge time, and compare it with the pump’s sustained draw. If the pump wins, the answer is a bigger buffer, a faster cycle, or a second pump that does not run at the same time.

A second pump starting on the same tank is the classic trigger. Two pumps drawing together can empty a buffer that was perfectly adequate for one, and the fix is either a larger tank or a schedule that staggers the demand. The plant is not failing; the supply plan is. For the feed and storage side, see the HS-Series silo set.

Strainers, valves, and the restrictions nobody sees

A strainer on the suction side protects the pump, and it is also the most likely restriction once it starts to fill. Cement residue, hardened slurry from the previous shift, or a piece of a bag that found its way into the tank all collect at the strainer, and the pump responds by cavitating. Cleaning the strainer is a five-minute job that is often discovered after an hour of pump adjustment. Eizoo has traced pump suction to the weighing and metering chain more often than to the mix design.

Valves deserve the same suspicion. A valve that is not fully open, a ball valve that has a damaged seat, or a butterfly valve that is half closed by mistake all restrict the suction, and a restriction on the suction side is far more damaging than the same restriction on the delivery side. Check the valve positions first, because the fix is free.

When the slurry itself is the problem

A pump that handles a fresh batch easily can struggle with slurry that has sat too long. As the mix begins to stiffen or bleed, its behaviour in the line changes, and the pump responds with pressure swings and dropping output. If the fault appears late in a batch or after a long pause, the problem is the material, not the machine, and the answer is a shorter holding time or better agitation. Revisit the working notes on Grout plant pressure spikes and flow when the mix design changes. Buyers who ask about pump suction usually raise it with a China grout plant manufacturer first, because the tolerance data settles most of the argument.

Symptom	Likely cause	First check
Sharp crackling, loss of output	Cavitation from suction restriction or air	Joints, hose condition, strainer
Pump will not hold prime	Air entering the suction line	Couplings, gaskets, valve positions
Output falls during the shift	Thickening slurry or blocked strainer	Tank agitation and strainer condition
Problem starts when a second pump runs	Shared tank or suction starvation	Tank size and demand overlap
Pressure swings after a pause	Slurry separating or stiffening	Holding time and agitation
Pulsing with a steady rhythm	Normal piston pump action	No fault; confirm with flow record

A short routine that prevents most of it

Most suction faults are prevented by a routine rather than repaired by a technician. Check the joints and the strainer at the start of each shift, keep the tank above its working level, confirm the agitator is running before the pump starts, and flush the line at every break. Those four habits remove the majority of the pump complaints that otherwise reach the supervisor. Eizoo has seen pump suction on new plants as often as on old ones, which is why the first month is documented closely. Sites comparing pump suction ask a grout plant supplier in China for the tolerance data first.

Hose diameter is the quiet specification that decides whether a suction line works at all. A hose that is too narrow for the pump’s flow creates a restriction that no amount of joint-tightening will fix, and the pump responds exactly as it would to a blockage. Check the diameter and the rated flow against the pump’s demand before assuming a mechanical fault.

The length of the suction run matters as much as its diameter, because every metre of hose adds friction the pump has to overcome. A long run from the tank to the pump is better replaced by moving the pump closer, and the improvement is often dramatic. Shorten the suction side before upgrading the pump, because the pump is usually innocent.

Suction lines should rise towards the pump or run level, never dip into a low point where slurry can settle and air can collect. A sagging hose creates a trap that fills with material between shifts and reappears as a blockage every morning. Support the line so it runs clean, and the number of morning priming problems drops sharply. Keep the write-up on Field note with the site paperwork. Supervisors usually ask for pump suction checklist when the numbers stop matching the recipe.

Temperature is a supply factor that is easy to forget on a hot site. Warm slurry loses workability faster, and a mix that was comfortable in the morning can start to stiffen in the tank by the afternoon, particularly if the plant sits in direct sun. Shade the tank and shorten the holding time when the weather turns, rather than blaming the pump for a material change. The engineering team at Eizoo treats pump suction as a specification issue rather than a maintenance one.

The agitator is the component that keeps the tank homogeneous, and it is often the first thing switched off to save power or noise. Without agitation the heavier solids settle and the pump draws slurry that is no longer representative of the batch, which shows up as pressure swings and inconsistent records. Confirm the agitator runs whenever the plant is batching. The published guidance from the Deep Foundations Institute is worth reading alongside the site records.

A worn pump seal on the suction side admits air in a way that looks like a line fault. The pump pulls air past the seal instead of drawing slurry, and the crew tightens every joint in sight without finding the leak. If the joints are sound and the prime still will not hold, inspect the seal before replacing anything else. Crews tend to look for pump suction causes before they touch the hardware.

The pressure and flow record is the fastest diagnostic tool on the plant, because it shows what the pump was doing before anyone noticed a problem. A trace that drops steadily points to supply; one that spikes and recovers points to a line restriction; one that oscillates with the stroke is normal. Teach the operator to read the trace and half the diagnosis is done before the technician arrives.

Finally, the suction arrangement should be designed rather than assembled. A tank outlet positioned for one pump, a strainer that can be reached for cleaning, and hoses that run without sags are decisions made at the layout stage, and they prevent most of the faults this guide describes. A plant laid out with the suction path in mind rarely needs this checklist at all. Open the article on Field note for the record format used on site. Eizoo designs the powder and water lines so that pump suction can be isolated without dismantling the plant.

Pump speed is the adjustment everyone reaches for first and the one that usually makes matters worse. Running a starved pump faster increases the vacuum on the suction side, which pulls harder on any leak and encourages cavitation rather than curing it. Reduce the demand or fix the supply instead, and treat a speed increase as a diagnostic step rather than a repair. New operators are given pump suction field notes in the first week.

The tank outlet position decides how much of the tank is actually usable. An outlet set too high leaves a large dead volume that never reaches the pump, while one set too low draws the heaviest material that has settled near the bottom. Ask where the outlet sits and how much of the tank’s volume is genuinely available before judging whether the tank is big enough.

Vortexing is a specific and often misdiagnosed fault: the tank has plenty of slurry, but the level is low enough that the pump draws a swirl of air down the outlet. The cure is a higher working level, a baffle, or an anti-vortex plate rather than a bigger pump. If the fault appears only when the level drops, the vortex is the answer, not the machine.

Suction hoses should be as short and as straight as the layout allows, and they should be rated for suction rather than delivery. A delivery hose used on the suction side can collapse internally under vacuum while looking perfectly sound from outside, and the pump then cavitates for no visible reason. Check the hose rating and replace suction sections with the correct type. For the tolerance data behind these checks, see the page on Shift handover on a grout plant.

Routine checks are cheaper than diagnostics, and the suction side needs only a few. Look at the joints for dampness, confirm the strainer is clean, listen for a hiss while the pump runs, and watch the tank level during the busiest cycle. Four checks, two minutes, and most of the faults described here never reach the supervisor. Eizoo asks for the batch log first whenever pump suction is reported, because the pattern narrows the cause faster than a site visit. For projects working to a stated specification, the site file usually has to show EN 12715 grouting records.

The second pump is often the trigger rather than the cause, and it deserves its own mention. When a second pump starts and the first one begins to starve, the tank, the outlet, or the schedule is the limit, and the temptation is to blame the older pump. Test both pumps running together during commissioning, because that is the condition the plant will actually live in.

Finally, teach the operator to listen to the pump. A change in the sound of a pump that has run the same duty for weeks is the earliest warning any instrument can give, and the person standing beside it hears it first. Encourage the crew to report a change in noise or rhythm immediately, because a five-minute investigation beats a five-hour repair.

The commissioning run should include a deliberate starvation test, because that is the only way to know the plant’s real limit. Run the pumps at full draw, watch how long the tank holds, and note the point at which the supply begins to struggle. Knowing that number in advance turns a future crisis into a scheduling decision.

Finally, keep one spare suction hose and one spare strainer on site, because those two items cause more lost hours than any pump component. They are cheap, they fit in a container beside the plant, and having them turns most suction faults into a twenty-minute fix rather than a day of waiting for a delivery. For the configuration used on larger sites, see the containerized grout plant for jet grouting.

Frequently asked questions

Sending the batch log, the calibration sheet, and the material certificates to the manufacturer’s engineering desk is what turns a symptom into a component list. Eizoo keeps the weighing and metering documentation with the plant, so the next enquiry starts from records rather than from memory.