Metering Pump Installation Diagram: Suction and Discharge Accessories in the Right Order

A metering pump installation diagram is easiest to read if you ignore the valve count and follow the arrows. On the suction side the usual order is tank outlet, isolation valve, strainer, calibration column tee, then the pump. On the discharge side it is relief valve, bleed valve, pressure gauge, pulsation dampener, back pressure valve, isolation valve, and finally the injection point. Get that sequence into your head and even a crowded drawing makes sense.

This guide is written for two groups: engineers who draw the metering pump installation diagram for a project, and installers who have to build from it on site. It covers standard mechanical diaphragm and solenoid diaphragm pumps. Plunger and hydraulic diaphragm pumps follow the same discharge logic.

What a Metering Pump Installation Diagram Must Show

Before any accessory, a usable metering pump installation diagram needs three reference points: the minimum liquid level in the tank, the elevation of the pump inlet, and the location and pressure of the injection point. Those three numbers decide most of what follows.

If the pump inlet sits below the lowest tank level, you have flooded suction. Chemical flows into the head by gravity and the pump primes easily. If the pump sits above the liquid, it has to lift, and you are limited by the rated suction lift in the manual. The NEWDOSE mechanical diaphragm pump manual, for example, gives a maximum suction height of 2 m water column, and real chemicals that are viscous or gassy do worse than water. If the injection point is lower than the tank level, or it is an open basin, siphoning becomes a risk and a back pressure valve goes on the drawing.

Suction Side Order on a Metering Pump Installation Diagram

The suction line has few parts, but it decides whether the pump delivers at all. In flow order, as a metering pump installation diagram should show it:

1. Tank outlet, set a little above the tank floor so settled sludge stays behind.
2. Isolation valve, so the pump head can be serviced without draining the tank.
3. Strainer, to protect the check balls and seats. Put it where someone can actually open it.
4. Calibration column, teed in before the pump with its own valve, closed in normal service.
5. Pump inlet. The suction pipe should be no smaller than the pump connection.

Keep the line short and straight with long-radius bends. Never let the suction pipe rise into a hump before dropping to the pump. An inverted U traps air, and the pump will deliver one minute and lose prime the next. After assembly, test joints with soapy water; a tiny suction leak shows up as lost flow on the discharge side.

For viscous chemicals, go one pipe size larger than the pump inlet. For slurries or liquids that settle, use crosses with plugs at the bends so lines can be flushed without cutting pipe.

Discharge Side: Why Each Accessory Sits Where It Does

This is the part of a metering pump installation diagram that people get wrong most often.

The relief valve goes right at the pump outlet, with no valve between it and the pump. If any valve downstream is closed by mistake, the relief valve has to open first. Pipe its return to the tank or the suction line and keep the outlet visible so a leaking relief valve is obvious. On mechanical diaphragm pumps the relief valve is not optional.

A bleed valve near the outlet helps with first start-up and after a chemical change. The pressure gauge and pulsation dampener come next. The dampener absorbs the flow peak of each stroke, which is why the gauge stops jumping. For sizing and precharge, see our guide on pulsation dampener placement and precharge.

The back pressure valve goes after the dampener. Without a dampener, the back pressure valve snaps open and shut on every stroke and its diaphragm wears fast. With one, it floats half open and lasts much longer. The downstream isolation valve sits after the relief valve. If you inject into a boiler or a pressurised vessel, add a check valve just before the vessel.

Back Pressure Valve: At the Pump or at the Injection Point?

You will see both versions on a metering pump installation diagram. The choice depends on the line:

• In most systems, keep the back pressure valve close to the pump outlet.
• With high flow and a long, small-bore discharge line, or when injecting into a vacuum or an open tank, move it near the injection point to stop siphoning.

The NEWDOSE manual gives a simple trigger: when the pressure difference between pump inlet and outlet is below 1 bar, install a back pressure valve to create artificial discharge pressure. Without it, accuracy suffers. The differences between the two valves are covered in back pressure valve vs relief valve.

Details a Metering Pump Installation Diagram Often Leaves Out

A few site details rarely make it onto the drawing but save trouble later:

• A drip tray under the pump head, so a diaphragm failure does not spread chemical across the floor.
• A tee and valve at the pump inlet and outlet, so the head can be flushed without breaking pipe.
• Drain valves at the low points of the suction and discharge lines in unheated rooms, so the lines can be emptied before a freeze.
• Pipe supports. The pump head should never carry the weight of the piping, and plastic PVC heads are the least forgiving.

One mistake we see repeatedly is one pump feeding several injection points. Even a tiny pressure difference sends most of the chemical to the lowest-pressure point. One pump per injection point is the reliable layout.

Before changing any pipework, stop the pump, close the valves and open the bleed valve to release pressure. Wear goggles and chemical gloves. Opening a line under pressure is where most dosing injuries happen. Mark the bleed points on the metering pump installation diagram so the crew knows where to relieve pressure.

Conclusion

Read any metering pump installation diagram along the flow line. Suction side: isolation valve, strainer, calibration column, pump, with a short, airtight line and no humps. Discharge side: relief valve first with nothing between it and the pump, dampener before the back pressure valve, isolation valve after the relief valve. Put the back pressure valve at the pump or at the injection point depending on pressure difference and line length. Browse our dosing accessories and the metering pump range, or send tank level, injection pressure and line length and contact our engineers for a marked-up metering pump installation diagram.

FAQ

Can the calibration column go on the discharge side?

No, and a metering pump installation diagram that shows it there should be corrected. A calibration column works by letting the pump draw from it while you time the level drop, so it must be teed into the suction side.

Which comes first, the relief valve or the isolation valve?

The relief valve, on every metering pump installation diagram we draw. The isolation valve sits downstream, so if someone closes it, the relief valve can still open.

Can I fit a back pressure valve without a dampener?

It will work, but the valve cycles on every stroke and wears quickly. On long lines or higher flows, fit both.

Do I need an extra check valve on the suction line?

Usually not. The pump head already has inlet and outlet check valves, and an extra one adds suction loss. If in doubt about direction, read check valve installation direction.

Where should the relief valve return line go?

Back to the tank or the pump suction, or to a drain. Wherever it goes, the outlet must be visible so leakage is easy to spot.