Piston Pumps

The write-up

A pump whose piston never touches the fluid. A flexible diaphragm walls off the liquid, so acids and slurries can't reach the piston.

1. Exhibit A

   Positive displacement

   A piston diaphragm pump moves a fixed volume of liquid with each stroke, like a piston pump. The difference is that a flexible diaphragm, also called a membrane, separates the pumped liquid from the piston.

2. Exhibit B

   Piston, oil, diaphragm

   In most designs the piston doesn't push the diaphragm directly. It moves a hydraulic fluid, and the fluid flexes the diaphragm.

3. Exhibit C

   Suction and discharge

   On the suction stroke the chamber expands, the inlet check valve opens and liquid flows in. On the discharge stroke the diaphragm presses into the chamber, the inlet valve closes and the outlet valve opens.

4. Exhibit D

   What touches the liquid

   Only the inside of the pump chamber, the diaphragm and the check valves touch the pumped liquid. That protects the piston and seals, and it leaves the valves as the main wear parts.

5. Exhibit E

   What they pump

   The pumps are used for abrasive slurries, acids, toxic media and shear-sensitive products. Weir's GEHO mining pumps handle slurries of up to 85% solids at temperatures up to 250 °C.

6. Exhibit F

   Leak detection

   Diaphragms are often built in two layers with a sensing port between them. A pressure switch on that port can detect a rupture and shut the pump down.