29 Apr The Principle of Diaphragm Pumps and Their Uses

Pumping equipment takes many different forms, and its mode of operation varies accordingly. The type known as a diaphragm pump is one of a group of related devices that depend for their performance on a principle known as positive displacement. All such devices work by mechanically drawing in successive, fixed volumes of fluid and then expelling them. Therefore, the resulting action is cyclic and will not necessarily depend on the action of diaphragms, as there are several other ways to achieve the same effect. Alternative mechanisms for producing positive displacement include gears, rollers, pistons, screws, and vanes.

How They Operate

While the effect remains the same, the operation of diaphragm pumps can be achieved in two ways. In some versions of the device, compressed air will provide the motive power for the mechanical action. In other models, an electric motor serves to produce the same activity.

Compressed air models are the more environmentally friendly option and utilise a pair of rubber or PTFE diaphragms mounted on a communal shaft. Air under pressure is fed alternately to chambers at each end, resulting in a back-and-forth motion. This movement successively draws fluid in and expels it and is aided by a system of automated valves.

Electrically operated diaphragm pumps have the same basic assembly as the air driven models. However, the back-and-forth motions are generated by an electric motor. The normally rotary motion of the motor’s driveshaft must first be converted to a reciprocating movement. The transition is achieved by a cam on the driveshaft which, in turn, drives a piston to move the assembly backwards and forwards. The effect is that one diaphragm is drawing in fluid while that at the opposite end is discharging fluid.

Regardless of how these machines are powered, diaphragm pumps offer the end-user several valuable benefits. Firstly, the air-operated models have few components to become worn or damaged. Similarly, low friction materials used to manufacture the shafts and bushings also add to the durability of electric models. Consequently, both tend to give long service while also requiring minimal downtime for maintenance. Together, these factors make them a particularly cost-effective choice. Furthermore, unlike most other types of pump, they are self-priming, submersible and their operating mechanisms allow them to be run dry without any danger of damage.

Some Common Applications

Typically, diaphragm pumps are easy to install and adjust and also provide the end-user with infinitely variable control over the flow rate. Such qualities have led to numerous applications across a broad spectrum of industries that range from petrochemicals and water treatment to power generation, paper pulp and food and beverages, to name just a few. In the F&B sector, there is a need for exceptional hygiene. Hence, the air-operated models can be a particularly beneficial choice. For example, they are a preferred option for food processing companies where it is often necessary to transport viscous slurries such as pureed fruits and ketchup while maintaining stringent standards.

Another virtue of diaphragm pumps is their exceptional versatility. They are equally effective in handling liquids of widely differing viscosity, including oils, gels and creams, and some models can develop a discharge pressure of up to 1 200 bar. They are also suitable for both clean and dirty applications.

By varying the materials used to manufacture their working parts, it is possible to create units that are highly resistant to the abrasive and corrosive actions of the most aggressive slurries and liquids. This ability has earned them an invaluable role in mining for conducting vital dewatering, with the producers of chemicals for commercial and industrial use and the manufacturers of paints and varnishes.

As well as transporting liquids and slurries, the characteristic action of diaphragm pumps also offers a means to dispense a measured volume of fluid on demand. This ability has been leveraged by water treatment plants where it assists several of the processes involved in producing potable water.

During the preliminary clarification stage, solids in colloidal suspension do not settle out under gravity. Consequently, the addition of flocculants is often necessary to achieve clarity. Similar additions are required later during the processing to adjust the pH and to ensure adding just the right amount of chlorine to preserve the finished product. In each case, the precise doses required can be measured and delivered using suitably calibrated diaphragm pumps.