By Travis Merrill, Chemical Feed Pump Specialist, Ti-SALES.
Peristaltic and diaphragm pumps make up the majority of chemical feed pumps used by the water industry, primarily in water and wastewater treatment centers. Each has distinct advantages and disadvantages compared to the other: for example, diaphragm pumps require a base level of understanding to ensure success, where peristaltic pumps are simpler to set up and use successfully.
Left: Diaphragm pump. Right: Peristaltic pump.
For those unfamiliar with either type of pump, a diaphragm pump uses the bi-directional stroke of a diaphragm with a series of check valves to move liquid through the pump. This is referred to as a pulsation. A peristaltic pump, on the other hand, uses a set of rollers that squeeze a flexible tube against a fixed housing and rotates to move the liquid solution through the pump. This produces a very smooth movement with no pulsation. (This is the same way that your throat works while swallowing.)
Diaphragm Pumps Pros and Cons
Since a diaphragm pump works with a series of check valves, you can run into challenges when trying to pump a solution with worn check valves or when there are particulates present – that is, undissolved solids. If the particulate manages to foul or clog the valves, the pump will no longer be able to accurately meter and performance will suffer, if not completely fail.
Diaphragm pumps can also be difficult to prime, particularly if there is backpressure on the line. They can also have difficulty priming at a low stroke length and speed rate. These challenges are helped with the use of priming or multi-function valves along with higher speed and stroke settings when priming is needed. A poorly maintained diaphragm pump may lose its prime and have difficulty pumping the required amount of liquid for the application.
On the upside, a well-maintained diaphragm pump is more cost-efficient to operate over time, as well as more energy-efficient – they use more power on the discharge stroke, but very little on the suction stroke. Diaphragm pumps, when properly primed, are also well-suited for pumping into pressures higher than 100 to 125 PSI.
Peristaltic Pumps Pros and Cons
A peristaltic pump has no check valves, meaning that it works well with high levels of particulate in the pumped solution. Additionally, backpressure and chemical composition both have little effect on the rate of a peristaltic pump, making them very easy to set up properly. This style of pump is also superior at priming and has excellent suction capabilities.
Peristaltic pumps do have their down sides since their method of operation requires more power, as the motor is under a constant load. Additionally, the constant squeezing of the pump tube will degrade the tube over time, which can affect the feed rate. Most pump tubes are rated in hours of operation, which requires careful monitoring with new installations to find the perfect balance for getting the longest life out of the tube before failure occurs.
Finally, a poorly maintained peristaltic pump is at risk of leaking, which can damage the pump and create a hazard, depending on what substance is being pumped.
In conclusion, there’s no one right answer to the question of which pump is better, peristaltic or diaphragm: it entirely depends on your specific application and needs. A diaphragm pump is more energy-efficient but requires a skilled installation and maintenance technician – and may not be appropriate to all situations. A peristaltic pump is extremely easy to set up and effective in a wide range of uses, but users must adhere to the pump’s maintenance and tube replacement schedule.
When faced with a decision on the best pump for your application, consult with a qualified expert to ensure the correct pump is installed for the best long-term performance and outcome.
Travis Merrill is the Chemical Feed Pump Specialist for Ti-SALES, a leading distributor of water and wastewater supplies and the exclusive supplier for Blue-White Industries’ line of municipal chemical feed pump solutions. Blue-White manufactures both diaphragm and peristaltic metering pumps as well as flowmeters (variable-area, paddlewheel, ultrasonic) and water treatment accessories.