# Piston Pumps (DD-072)

> A piston diaphragm (membrane) pump is a reciprocating positive-displacement pump. In most designs a crank-driven piston doesn't push the diaphragm directly: it moves a sealed hydraulic fluid, and that fluid flexes the diaphragm. On the suction stroke the pump chamber expands, the inlet check valve opens and liquid flows in. On the discharge stroke the diaphragm pushes into the chamber, the inlet valve closes and the outlet valve opens. Only the diaphragm, chamber and check valves touch the pumped liquid, so the pumps are used for slurries, acids and shear-sensitive products. Large mining models handle slurries of up to 85% solids at up to 250 °C.

- Department: Tech (also Science)
- First published: 2026-02-02
- Last updated: 2026-02-02
- Permalink: https://detailenjoyer.com/case/piston-pumps/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## Quick facts

- **DD-072-F01**: In most piston diaphragm pumps, the piston pushes hydraulic oil, and the oil flexes the diaphragm. _(Write-up · Exhibit B (Piston, oil, diaphragm))_
- **DD-072-F02**: In a piston diaphragm pump, only the chamber, the diaphragm and the check valves touch the pumped liquid. _(Write-up · Exhibit D (What touches the liquid))_

## 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. **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. **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. **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. **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. **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. **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.

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## Reel vs. record

- **Nuance**: in most piston diaphragm pumps the piston doesn't drive the membrane directly. It moves a hydraulic fluid, and that fluid flexes the diaphragm. [Emmerich; ABEL; Universal Pumping]
- **Missing context**: the inlet and outlet check valves are what make the flow one-way. They touch the liquid too, so they, not the piston, are the main wear parts. [Star Pump Alliance; Weir]
- **Terminology**: in English the part is usually called a diaphragm, so the pump is usually called a piston diaphragm pump. Manufacturers also use 'membrane'. [Star Pump Alliance; Emmerich]
- **Confirmed**: it is a positive-displacement pump with suction and discharge strokes, and the pumped liquid doesn't touch the piston or drive. 'Sensitive' liquids include shear-sensitive products. [ABEL; Star Pump Alliance]
- **Context on scale**: big mining versions, such as Weir's GEHO pumps, move slurries of up to 85% solids at up to 250 °C, for example through ore pipelines and tailings lines. [Weir]

## Video: Piston Pumps: A Pump Whose Piston Never Touches the Fluid

- Duration: 24.5 s · Published: 2026-02-02
- File: https://detailenjoyer.com/assets/videos/DUQzo7rkY2t.mp4

### Transcript

DID YOU KNOW? A piston membrane pump is a type of positive displacement pump that combines a mechanical piston with a flexible membrane to move fluids efficiently and safely. The piston drives the membrane back and forth, creating suction on the intake stroke, and pressure on the discharge stroke, while the fluid itself never comes into direct contact with the piston or drive mechanism. This separation makes the pump ideal for handling corrosive, abrasive, or sensitive liquids. NOW YOU KNOW!

## Questions & answers

**Q: What type of pump is a piston diaphragm pump?**  
A: It moves a fixed volume with each stroke. _(Source: Write-up · Exhibit A (Positive displacement) · Piston diaphragm pumps (Star Pump Alliance))_

**Q: In most designs, what actually flexes the diaphragm?**  
A: The piston works on a sealed hydraulic fluid. _(Source: Write-up · Exhibit B (Piston, oil, diaphragm) · Piston diaphragm pumps: technology (Emmerich GmbH); HMQ quadruplex piston diaphragm pump flyer (ABEL Pumps); How do piston diaphragm pumps work? (Universal Pumping))_

**Q: What makes the flow go one way?**  
A: The inlet valve opens on suction and the outlet valve on discharge. _(Source: Write-up · Exhibit C (Suction and discharge) · Piston diaphragm pumps: technology (Emmerich GmbH); HMQ quadruplex piston diaphragm pump flyer (ABEL Pumps))_

**Q: Which parts touch the pumped liquid?**  
A: The valves are the main wear parts. _(Source: Write-up · Exhibit D (What touches the liquid) · Piston diaphragm pumps (Star Pump Alliance); GEHO piston diaphragm pumps brochure (Weir Minerals))_

**Q: Up to what solids concentration can GEHO pumps handle?**  
A: They also handle temperatures up to 250 °C. _(Source: Write-up · Exhibit E (What they pump) · HMQ quadruplex piston diaphragm pump flyer (ABEL Pumps); Piston diaphragm pumps (Star Pump Alliance); GEHO piston diaphragm pumps brochure (Weir Minerals))_

## Sources

- [Piston diaphragm pumps: technology (Emmerich GmbH)](https://je-pumpen.de/en/technology/piston-diaphragm-pumps)
- [HMQ quadruplex piston diaphragm pump flyer (ABEL Pumps)](https://abelpumps.com/wp-content/uploads/HMQ-Flyer_EN.pdf)
- [Piston diaphragm pumps (Star Pump Alliance)](https://www.starpumpalliance.com/pumps/displacement-pumps/piston-diaphragm-pumps/)
- [GEHO piston diaphragm pumps brochure (Weir Minerals)](https://www.global.weir/globalassets/resources/product-pdfs/geho/geho-piston-diaphragm-pumps-brochure.pdf)
- [How do piston diaphragm pumps work? (Universal Pumping)](https://www.universalpumping.com/how-do-piston-diaphragm-pumps-work/)

## Cite this case file

Easterling, Marcus. "Piston Pumps." The Detail Department (DetailEnjoyer), case file DD-072, last updated Feb 2, 2026. https://detailenjoyer.com/case/piston-pumps/