Thick, abrasive or solids-laden liquids such as sludge, polymer, grease, resins or food products are hard on pumps. Two designs are often compared for this work: the progressive cavity pump and the air-operated double diaphragm (AODD) pump. Here is how they differ.
How each one works
A progressive cavity pump uses a single helical rotor turning inside a rubber or elastomer-lined stator. It moves the fluid in sealed cavities, giving a smooth, steady, low-shear flow that is proportional to speed.
An AODD pump uses two flexible diaphragms moved by compressed air. Flow is pulsating, and capacity depends on the air supply.
Where progressive cavity pumps are the better choice
- Very viscous fluids and pastes, where steady positive displacement keeps the flow moving.
- Continuous duty at a steady flow rate.
- Metering-type accuracy. Flow is proportional to speed, so a drive with variable speed gives good control.
- Gentle handling. Low shear is useful for fluids with fibres, soft solids or shear-sensitive products.
- High discharge pressure compared with an air-operated pump.
- Efficiency. An electric drive is cheaper to run than compressed air.
Where AODD pumps are the better choice
- Intermittent or portable duty, such as emptying tanks, pits and sumps.
- Dry running without damage. A progressive cavity pump should not run dry, because the stator can burn in seconds.
- Abrasive slurries and larger solids, with easy replacement of simple wear parts.
- Hazardous areas where electric drives are a concern.
- Lower purchase cost for small duties.
Comparison
| Factor | Progressive cavity | AODD |
|---|---|---|
| Flow pattern | Smooth, steady | Pulsating |
| Very high viscosity | Excellent | Good, with reduced flow |
| Dry running | Not allowed | Safe |
| Running cost | Lower (electric) | Higher (air) |
| Flow control | Variable speed drive | Air supply |
| Wear parts | Rotor and stator | Diaphragms, balls, seats |
Practical tips
- Fit dry-run protection on any progressive cavity pump.
- For abrasive fluids, run progressive cavity pumps at lower speed to extend stator life.
- Choose the stator elastomer for the chemical and the temperature, not just for the abrasion.
- Stock a spare set of wear parts. Downtime costs more than the parts.
Power Energy Gulf supplies both pump types in Saudi Arabia and the GCC. See our progressive cavity pumps and AODD pumps pages, or contact us with your fluid details for a recommendation.
[…] also our comparison of progressive cavity and AODD pumps and our progressive cavity pumps […]