Guide to Peristaltic Pumps

Here’s a quick guide to peristaltic pumps. They are a precise, effective type of pump with a host of advantages for specialist applications, particularly at lower volumes.

There are dozens of types of pumps, but the vast majority belong to one of four families - positive displacement, impulse, velocity and gravity. Positive displacement pumps work by trapping fluids in an enclosed volume and moving it from the inlet to the outlet in a continuous motion. Peristaltic pumps belong to this type.

In theory, once a positive displacement pump is stopped, the flow will stop, in that fluid won’t be allowed to flow backwards or forwards, rather like closing a valve. In practice, there might be tiny gaps that could potentially let small amounts of fluid through, which might be necessary to prevent abrasion of moving parts. However, these narrow gaps should be so disruptive as to effectively stop flow. In many pump types, by contrast, if it is switched off, there is still a route through for the fluids, which means that flow may continue through it given a source of pressure somewhere in the system, and that could mean that flow could go backwards, which is often undesirable.

Peristaltic pumps come with a number of advantages for certain applications. Here are the key benefits of this type of pump:

• The fluid only comes into contact with the tube. In most pump designs, the fluid will touch the outer casing, blades, gears, valves, seals, diaphragms and possibly even lubricants as it passes through. Each one of these is a source of potential contamination of the fluid, which in many industrial, medical and pharmaceutical processes is unacceptable. In the peristaltic pump, the tube can run continuously from one part of the process to the other and merely passes through the pump. It also means there is no means of escape for the fluid to the outside world
• They can run very slowly. This type of pump does not require enormous amounts of energy or momentum to get the fluid moving. The shoes can move around very slowly and deliver a gentle supply of fluid, where desired
• They are good for viscous fluids. Viscous fluids that can’t be pumped by a velocity pump can often pass smoothly through a peristaltic one
• Precise measurement is possible. Because the volume within the chamber between shoes is a known quantity, precise volume measurements can be achieved simply by counting revolutions or fractions of a revolution
• They can run dry. There’s no risk of damage if the tube runs dry as the system doesn’t rely on the fluid for cooling or preventing the motor from overspeeding
• They are reversible. The process is exactly the same in whatever direction the shoes are moving, so it can be reversed, which might be useful in some applications, but is also good for flushing and clearing blockages
• No need for external valves. Although valves can be incorporated into the tubing to ensure flow is stopped, stopping the motion automatically stops the flow, rather like a diaphragm valve
• Tubing can be transparent. Although they are often opaque, tubes can be transparent to keep an eye on the flow and colour of the fluid

The system is not without its drawbacks, which can rule it out of some applications:

• The tube can fatigue. After hundreds of thousands of compression and release cycles, the walls of the tube can perish and potentially split. In mitigation, however, they do tend to run relatively slowly, and modern tubing materials have phenomenal durability. With a well-observed inspection and maintenance regime, this downside can be discounted
• The flow tends to be pulsed rather than smooth. The constant injection of single batches of fluid, and the inevitable gap where the shoe or roller is, tends to cause a pulsating flow. This is sometimes desirable, however
• The tubing needs to be unreactive with the fluid. Certain fluids will react with certain tubing materials, so the material has to be chosen carefully to avoid contamination or corrosion

Within peristaltic pumps, there are a few main types.

Peristaltic Dosing Pumps

Where very precise (and often small) doses of a fluid need to be injected into another fluid, the peristaltic dosing pump is a good way of delivering controllable and measurable amounts in a short burst, rather than continuously. Low-flow peristaltic pumps are vital in medicine and many chemical processes.

Peristaltic Hose Pumps

While many peristaltic pumps can fit in the palm of your hand and connect small-volume tubing, there are some that have higher volume delivery, namely peristaltic hose pumps.

Small Peristaltic Pumps

This type of pump comes into its own at a small scale, where incredibly precise volumes can be delivered by measuring and controlling the motor’s rotation, by fractions of a rotation if necessary.

Industrial Peristaltic Pumps

There are some applications where peristaltic pumps are useful at the large industrial scale, for example when moving thick sludges and sewage with lumps of solid matter in them. Many other types of pumps simply cannot handle such fluids.

When you’re choosing a peristaltic pump, it’s essential that you know its maximum flow rate, head, pressure and operating temperature. You need to ensure any pump you choose can handle the specifications set by the engineers for its proposed use. Choosing a pump that will work near or outside its intended flow rate will adversely affect its efficiency, and could even prevent it from delivering fluid anywhere near your required levels. Always check the specifications to ensure you choose a suitable pump for your requirements.