Dosing Pump Foot Valve and Strainer: Why the Suction Sits Off the Tank Bottom

A dosing pump foot valve sits on the end of the suction tube inside the chemical tank. It is a check valve with a strainer: the screen keeps particles out, and the ball lets chemical move only toward the pump, so the suction line stays full when the pump stops and you do not have to re-prime on every start. It should sit some distance above the tank bottom because that is where sediment, crystals and undissolved product collect. Sit the dosing pump foot valve on the floor of the tank and the screen blinds quickly, while whatever gets through ends up lodged under the pump's own check balls. This guide is for operators who check chemical tanks on their rounds and for installers fitting out dosing skids.

What is inside a dosing pump foot valve

Take apart a typical solenoid pump foot valve and you will find three parts:

1. A strainer screen at the bottom that blocks larger particles.
2. A ball and seat forming a check valve, so chemical can only travel upward.
3. A weight that keeps the valve sunk and vertical instead of floating up with the tubing.

NEWDOSE solenoid pumps ship with a filter foot valve and 2 m of clear PVC suction tubing as standard accessories. Nanfang supplies an injection valve, foot valve and weight with some of its small PVC and PVDF head models. Whether your model includes one is shown on the packing list.

Dosing pump foot valve vs the pump's check valves

People often call the foot valve "the check valve", which is fair, but the location matters. The pump head already has its own suction and discharge check valves, and those do the work on every stroke. The dosing pump foot valve is an extra check at the far end of the suction line, and its job is to hold the column of liquid in that line.

So a foot valve cannot replace a worn pump-head valve, and a good foot valve will not cover for a failed one. For what happens when a check valve goes in the wrong way round, see metering pump check valve direction.

Why the dosing pump foot valve sits off the tank bottom

The bottom of a chemical tank is where the dirt lives. Undissolved polymer granules, insolubles from coagulant, crystals from sodium hypochlorite and general sludge all settle there. A foot valve resting on the floor pulls that material onto its screen every stroke.

Too low and the screen clogs; too high and the pump draws air as the level drops. There is no universal number, so in the field the height is set like this:

• Keep the screen above the sediment layer. On a cone-bottom tank or one with a drain, allow for the depth of sludge it builds.
• Set the low-level switch above the foot valve so the pump stops before the valve is uncovered.
• In a mixing tank, keep the foot valve clear of the agitator so it is not swung around by the flow.

The tank drawing or skid layout takes priority where it specifies a height.

A trap on jobs without a level switch

Some small installations skip the low-level switch. The tank runs nearly empty, nobody notices, the dosing pump foot valve breaks the surface and the suction line fills with air. The pump keeps clicking but nothing is delivered until someone bleeds it. Foot valve height and the low-level alarm should be designed together, not left to wherever the tube happens to land.

Dosing pump foot valve or inline strainer?

A small solenoid pump drawing through a tube from the top of the tank only needs a dosing pump foot valve with a strainer. Larger mechanical diaphragm pumps are usually fed with flooded suction from a side outlet on the tank through rigid pipe. There is nowhere to hang a foot valve, so fit a Y-strainer in the suction line with isolation valves either side for cleaning. The NEWDOSE mechanical pump manual calls for a filter on the suction line, regular checks for blockage, suction pipe no smaller than the pump inlet, and a larger suction line for viscous liquids.

The Cheonsei KD manual is blunter: a foot valve with a strainer must be fitted at the bottom of the suction line to keep particles out of the pump head, and it must be checked often. A screen that is too fine is a problem too, because viscous chemicals struggle to pass it and the pump starves. For polymer feeds, read why a PAM dosing pump will not pump.

Signs of a clogged or failing dosing pump foot valve

Trouble at the foot valve usually shows up in one of these ways:

• Flow falls off gradually and dosing concentration drops as the screen blinds.
• After every stop the pump needs bleeding again before it delivers, because the ball no longer seals and the line drains.
• In clear suction tubing you can watch the liquid column sink after the pump stops, which is the most direct evidence.

The NEWDOSE solenoid pump manual recommends regular cleaning of check valves and filters, with the interval set by the user according to the chemical. Stop the pump and isolate the discharge first. With hypochlorite, acids or caustics, wear gloves and eye protection, lift the foot valve out, rinse it in clean water and do not poke the screen with anything sharp. For spares to keep on the shelf, see our metering pump spare parts list.

Conclusion

A dosing pump foot valve does two jobs: the screen stops particles and the ball holds the suction line full. Keeping it off the tank bottom avoids sediment and crystals, while the low-level alarm should trip before the valve is uncovered. Small pumps use a strainer foot valve, larger flooded-suction pumps use an inline strainer. Find foot valves, strainers and fittings in our dosing accessories range and NEWDOSE standard accessories on the NEWDOSE pump page. Send us the chemical, flow and tank type and contact our engineers.

FAQ

Can a dosing pump foot valve rest on the tank bottom?

It is not recommended. Resting on the floor draws sludge onto the screen, clogs it fast and can carry particles into the pump-head check valves.

How often should I clean the dosing pump foot valve?

There is no fixed interval. Clean it when flow drops or concentration falls, and more often with chemicals that crystallize.

Will the pump still draw without a foot valve?

Yes, but the suction line tends to drain when the pump stops, so you bleed it on every start, and particles go straight into the pump head.

Can I fit a foot valve in the middle of the suction line?

A dosing pump foot valve is designed for the end of the line. Mid-line, use an inline check valve, and on larger pumps fit a Y-strainer on the suction side.

The foot valve ball is stuck. What now?

Remove it and rinse with clean water, then check the seat for crystals or scratches. If it will not come clean or the seat is damaged, replacing the foot valve is quicker.