Metering Pump Selection Checklist: What to Send Before You Order

The most common enquiry we get reads something like "need a metering pump, a few dozen liters an hour." Flow alone is not enough for metering pump selection. What a supplier really needs is a duty sheet covering the chemical, flow, pressure, suction conditions, control and power. Leave any of it out and the questions come back to you anyway.

Below is the metering pump selection list we run through with customers. Fill it in before you send an enquiry and you will save several rounds of phone calls.

Metering Pump Selection Starts With the Chemical

The chemical sets the materials of the head, valves and seals, so this is the part of the metering pump selection sheet you cannot be vague about. Provide:

• the chemical name, preferably the chemical name rather than a trade name;
• concentration, both before and after any dilution;
• liquid temperature, as a range if summer and winter differ a lot;
• viscosity, flagged clearly if the product is thick;
• whether it carries solids, crystallizes or gives off gas.

The NEWDOSE mechanical pump manual points out that during the suction stroke the pressure inside the head must stay above the liquid's vapor pressure, otherwise cavitation sets in and performance suffers. For volatile or gassing chemicals, get the temperature right.

If your chemical supplier has given you a safety data sheet, just attach it. Composition, concentration, flash point and corrosiveness are all there. Customers often ask what metering pump selection really depends on, and the honest answer is that a complete chemical data page gets you most of the way. Flow and pressure are easy to check after that.

Flow Data for Metering Pump Selection

Quote flow in L/h. One number is not enough. Give the maximum, the minimum and the usual flow so the supplier can see where stroke length and frequency will sit in normal running.

One point gets missed all the time: is the chemical diluted before dosing, or pumped neat? The two can differ several times over in flow, so state clearly whether the figure is solution volume or pure product.

Pressure and Piping: Look at the Injection Point

For metering pump selection, what matters is the actual pressure at the injection point, the pipe or vessel the chemical is going into. The manual requires that maximum working pressure at the pump head outlet stays at or below the rated pressure on the nameplate.

Too little pressure is a problem too. When the pressure difference across the pump is under 1 bar, fit a back pressure valve to create discharge pressure, or metering accuracy suffers. If you are dosing into an open basin or an unpressurized tank, say so, and the supplier will include a back pressure valve.

While you are at it, describe the discharge line: length, elevation change and pipe material.

Suction Conditions: Is the Tank Above or Below the Pump?

Suction is where most site problems start, and it is the item most often missing from metering pump selection sheets. The manual recommends that the pump suction sits below the lowest liquid level in the tank, so chemical flows into the pump under gravity. For the mechanical pumps the maximum suction lift is 2 m of water.

So tell the supplier where the tank level sits relative to the pump, and how long and how wide the suction line is, with how many bends. The suction line bore should be no smaller than the pump inlet, and with viscous liquids the inlet line should be sized up.

Control, Power and Site Conditions for Metering Pump Selection

The earlier items decide whether a pump can do the job at all. This part decides how it is wired and controlled. The second half of the sheet we give customers usually lists:

1. Control: manual adjustment, or a pulse signal, a 4–20 mA current signal or RS485. For mechanical pumps, whether electric stroke adjustment is needed.
2. Power: single phase 220 V or three phase 380 V, 50 Hz or 60 Hz.
3. Explosion protection: where it is required, NEWDOSE mechanical pumps offer an explosion-proof motor rated Exd Ⅱ BT4.
4. Site: indoors or outdoors, and ambient temperature. The manual notes the mechanical pumps should not run unprotected in the open, so outdoor installs need a canopy.
5. Number of injection points: how many points one pump is feeding.

Don't underestimate that last item in metering pump selection. The manual recommends a separate pump for every injection point. Even a tiny pressure difference between points sends most of the chemical to the one with the lowest pressure.

Accessories: Don't Assume They Are Included

The NEWDOSE mechanical pump manual says it plainly: the pump ships without accessories. A typical installation drawing shows a back pressure valve, pulsation damper, safety valve and diaphragm pressure gauge on the discharge, a Y strainer on the suction, plus a calibration column.

List which of these you need and which are already on site, and add that list to your metering pump selection sheet. Don't skip the safety valve in particular. If a discharge valve is closed by mistake, it is what protects the pump and pipework.

Conclusion

Metering pump selection comes down to six blocks of information: chemical, flow, pressure, suction, control and power, and accessories. Give the chemical name with concentration and temperature, quote maximum and normal flow, use the real injection point pressure, and describe where the tank sits. Send a complete sheet and the proposal you get back will be one you can rely on.

FAQ

What if I don't know the injection pressure?

Fit a gauge near the injection point and measure it, or ask the piping designer. If neither is possible, at least say whether you are dosing into a pressurized pipe or an open basin.

I only know daily chemical usage. Is that enough?

It works, but convert it to L/h and say how many hours a day the pump runs. Dosing around the clock for 24 hours and dosing a few hours a day lead to different pumps.

The formulation is confidential. What can I share?

At minimum the main component type, whether it is acidic or alkaline, concentration and temperature. Material choice is where the risk lies, and the less you share the more likely a mistake.

Summer and winter differ. Which metering pump selection data do I quote?

Both. Temperature and viscosity changes affect suction and material compatibility, and the supplier will size for the worse case.

Do accessories have to come with the pump?

No, existing items on site can be reused. But anything matched to the pump's pressure, such as the back pressure valve and safety valve, is safer chosen together with the pump. Use this as your dosing pump sizing checklist every time.

Can't fill in every line? Send what you have through our contact page and we'll work through it with you.