Metering Pumps: What’s Your Type?

Metering pumps move precise volumes of liquid in a specified time period to provide accurate flow rates. This class of pumps moves liquids in two stages: the suction stroke and the discharge stroke. During the suction stroke, liquid is pulled into the pump cavity past the inlet check valve. During the discharge stroke, the inlet valve closes; the outlet valve opens, and the liquid is pushed out. Vary the flow either by changing the stroke length or by adjusting the cycle frequency.

Described below are a few types of metering pumps—bellows, cylinder, diaphragm, peristaltic, piston, and syringe.

Bellows Pumps move a bellows back and forth to displace liquid. These pumps do not require seals. Special nonclogging valves are available for abrasive or particulate applications. Bellows pumps produce a maximum pressure of 50 psi (3.4 bar).

Diaphragm Pumps pulse a flexible membrane to displace liquid with each stroke. These pumps require no seals, so you can pump abrasives and slurries if the valves are kept clean. Diaphragm pumps produce pressures to 5000 psi (344.7 bar).

Peristaltic Pumps are designed so that the only material in contact with the fluid being pumped is the tubing. This allows the fluid to not contaminate the pump and the pump to not contaminate the fluid. These pumps provide flexibility through the wide variety of tubing materials available.

Piston Pumps use a reciprocating plunger to move liquid through the pump. These pumps require a seal to prevent leaks and are not recommended for use with abrasive fluids. Piston pumps produce pressures to 18,000 psi (1241 bar).

Syringe Pumps either draw in or push out liquid through a syringe to obtain a known volume as determined by the size of the syringe. Up to ten syringes may be used on one pump. With the programmable pumps, up to eight commands may be programmed to perform a variety of functions. Syringe pumps are great for low flow, low pressure applications. With the addition of the high pressure version, much higher back pressure can be overcome.