Metering pump

A metering pump moves a precise volume of liquid in a specified time period providing an accurate volumetric flow rate.

[1] Delivery of fluids in precise adjustable flow rates is sometimes called metering.

They are typically made to meter at flow rates which are practically constant (when averaged over time) within a wide range of discharge (outlet) pressure.

Low pressure in the chamber causes liquid to enter and fill the chamber through the inlet check valve, but higher pressure at the outlet causes the outlet valve to shut.

If the piston's suction and discharge strokes occur at the same speed and liquid is metered out half the time the pump is working, then the overall metering rate averaged over time equals half the average flow rate during the discharge stroke.

To produce good chromatograms, it is desirable to have a pumping flow rate as constant as possible.

In order to avoid leakage at the packing or seal particularly when a liquid is dangerous, toxic, or noxious, diaphragm pumps are used for metering.

Such motion changes the volume of a chamber in the pump head so that liquid enters through an inlet check valve during decompression and exits through an outlet check valve during compression, in a manner similar to piston pumps.

Peristaltic pumps use motor-driven rollers to roll along flexible tubing, compressing it to push forward a liquid inside.

The relief valve setting should be below the maximum pressure rating that the piping, tubing, or any other components there could withstand.

Since a liquid can be only slightly compressed during a discharge stroke, it is forced out of the pump head.

This situation can be avoided by placing a correctly rated positive pressure differential check valve downstream of the pump.