Metering Pump Specifications Explained: Flow, Pressure and Material Codes

Metering pump specifications boil down to a short list: maximum flow, maximum discharge pressure, stroke rate, stroke length, motor data and the wetted materials. Reading the numbers is easy. Knowing the conditions behind them is what keeps you out of trouble. A catalog flow figure is normally measured with clean water at ambient temperature, 100% stroke length, top stroke rate and rated pressure. Put a viscous chemical on the suction side or change the back pressure, and the pump will not deliver that figure. This guide is for buyers comparing quotes, consulting engineers checking submittals and operators who need to make sense of a nameplate.

If you need to decode the model number itself, see our guide on how to read a metering pump model number. Here we focus on what each value in the metering pump specifications actually means and where people misread it.

Flow rate in metering pump specifications

Flow is usually given in L/h or GPH, and larger pumps may list m³/h. In most metering pump specifications, the value is the maximum capacity at full stroke length, maximum stroke rate and rated discharge pressure.

Three mistakes come up again and again:

1. Treating maximum flow as the working dose. Your normal dose should sit in the middle of the pump's range so you have room to adjust both ways. A pump that lives at a very short stroke setting repeats poorly.
2. Ignoring supply frequency. A motor-driven diaphragm pump runs at a different speed on 50 Hz and 60 Hz power, so stroke rate and flow change. Many datasheets list both columns. Copy the right one.
3. Forgetting pressure. On some designs, delivered flow drops slightly as discharge pressure approaches the rating. The manufacturer's performance curve is the reference.

Maximum pressure is a pump limit, not your line pressure

Pressure is shown in bar, psi or MPa. In metering pump specifications, this figure is the highest discharge pressure the pump is built to work against. The pump rating must exceed the pressure at the injection point plus line losses plus any back pressure valve setting.

A common trap: the chemical goes into an open tank, so someone decides pressure does not matter. Low discharge pressure is exactly when siphoning happens, and the chemical flows through the pump on its own, overdosing the process. Fit a back pressure valve, and include its setting when you check the pressure side of the metering pump specifications.

Stroke rate and stroke length in metering pump specifications

A stroke is one full back-and-forth movement of the diaphragm or plunger. Stroke rate, in strokes per minute (spm), sets how often it happens. Stroke length, in millimeters or percent, sets how much liquid each stroke pushes out. Multiply the two and convert units, and you have flow.

High-speed pumps are compact, but the suction stroke is short and fast, so thick chemicals may not fill the head completely. For polymer solutions or strong sodium hypochlorite that tends to gas off, a lower stroke rate model is the safer choice. For reading the stroke dial, our article on reading a metering pump stroke dial covers the main scale and vernier.

Wetted material codes in metering pump specifications

Material codes describe only the parts that touch the liquid: pump head, diaphragm, check balls, valve seats and seals. Typical heads are PVC, PP, PVDF or 316 stainless steel. Diaphragms are usually PTFE-faced, and balls may be ceramic, glass, stainless steel or PTFE. Each brand uses its own shorthand, and one code often fixes the whole set of head, ball and seal materials.

The usual error is reading the head material as the chemical rating of the whole pump. A PVDF head with EPDM seals will still leak on some solvents. Send the chemical name, concentration and temperature to the manufacturer and ask them to confirm every wetted part. The Cheonsei KD range is a good example of how codes bundle materials: see PTC, FTC and STS liquid ends explained.

Motor, enclosure and hazardous area data

Metering pump specifications and nameplates also list motor power, voltage, phase, enclosure rating and, where relevant, explosion protection marking. Motor-driven pumps are usually three-phase, while solenoid pumps run on single-phase power. In a classified area, check the explosion protection category and temperature class. Outdoors, look at the IP rating. The first digit covers dust and the second covers water, and higher numbers mean better protection.

Accuracy and suction lift

Accuracy in metering pump specifications normally means steady-state repeatability under rated conditions after calibration. It does not promise the same result at every stroke setting. Suction lift is quoted for water. Heavy, viscous or gassing liquids lift less, so use flooded suction where you can.

How to check metering pump specifications before you order

Work through the sheet in this order:

1. Every wetted part is compatible with the chemical, concentration and temperature.
2. Rated pressure exceeds injection pressure plus back pressure.
3. Maximum dose falls in the middle of the flow range.
4. Supply frequency, voltage, hazardous area and IP rating match the site.
5. Connection size and type match your tubing or pipe.

If your duty data is incomplete, use our metering pump selection checklist. You can compare models across our metering pump range and mechanical diaphragm pumps.

Conclusion

Good use of metering pump specifications comes down to test conditions. Flow is water at rated pressure and full stroke, pressure is the pump's ceiling, and material codes cover wetted parts only. Line those facts up against your own chemical, pressure and dose, and the right model usually becomes obvious. Send us your flow, pressure, chemical and power supply, and contact our engineers to have the datasheet checked line by line.

FAQ

The nameplate and the datasheet show different flow. Which is right?

Trust the nameplate. The datasheet covers a whole series, while the nameplate reflects your exact build, including motor frequency and head size. If the gap is large, ask the supplier.

How do bar, psi and MPa compare?

One MPa is about 10 bar, and one bar is about 14.5 psi. Keep the unit with the number when you copy values between documents.

Is it safer to pick a bigger pump?

No. An oversized pump spends its life at a short stroke setting, where repeatability suffers. Aim for your dose to sit mid-range.

I cannot decode the material code. What should I do?

Give the supplier the chemical, concentration and temperature and ask for written confirmation of head, diaphragm, ball and seal materials.

Can I compare a solenoid pump and a motor-driven pump on the same metering pump specifications?

Only roughly. Drive type, stroke rate range and pressure behavior differ, so compare delivered flow at the same pressure with the same liquid.