Industrial Positive Displacement Pumps: Types and Features

Diaphragm Pumps: Features and Applications

Diaphragm pumps resemble piston pumps but differ because the mobile membrane consists of a flexible metal, rubber, or plastic material. These pumps can be operated by mechanical action or pneumatically.

The primary advantage of this design is that it requires no packing gland to prevent the leakage of fluids between fixed and mobile parts. Consequently, they are frequently used to transport:

• Toxic or hazardous liquids
• Sterile liquids

The main disadvantages include the relatively short life of the diaphragm, the risk of rupture, and high maintenance costs.

Rotary Positive Displacement Pumps

Rotary pumps are a type of positive displacement pump. The pumping action is caused by the relative motion between the rotating elements of the pump and the stationary components. Their rotary motion distinguishes them from reciprocating positive displacement pumps, where the motion of moving parts is alternative.

In this type of pump, fluid displacement is produced by the rotation of one or more moving parts inside a casing, forming cavities where the liquid is housed. The liquid moves from the pump inlet to the discharge area. The volume displaced with each revolution is generally independent of the pump speed. Notably, these arrangements do not require inlet and outlet valves.

Rotary Gear Pump Mechanisms

Rotary gear pumps consist of two wheels that mesh perfectly inside a casing. One wheel is the driving wheel, which receives movement from a shaft, while the other is the driven wheel, carried by the movement of the conductor. The gears can be:

• Straight or helical
• External or internal teeth

When the teeth unmesh, a partial vacuum is created at the entrance, drawing fluid into the chambers. These chambers carry the fluid until it is expelled when the gears mesh again, resulting in a high level of hydraulic pressure. However, these pumps are often unbalanced because the high-pressure outlet imposes an asymmetrical load on the gears and bearings.

Lobe Pumps and Archimedean Screws

Lobe Pumps

Lobe pumps offer more displacement than gear pumps because each of the two rotors has only two or three teeth. These teeth are much broader and more rounded than those of an external gear pump. This type of pump has a relatively low pressure capacity and produces a more pulsatile flow.

Archimedean Screw Pumps

The rotating Archimedean screw is a special type of worm pump designed specifically for the removal of large volumes of water or for industrial liquid discharges.