What Is a Liquid Ring Vacuum Pump?
A liquid ring vacuum pump is a rotary pump that creates a vacuum by filling the pump casing with water and rotating the impeller inside.
To create a vacuum, the space between the impeller and the casing must change in volume. The Elmo type (eccentric type) is known to generate this volume change by shifting the impeller’s mounting position from the center, and the Nash type (symmetric type) is known to generate it by making the casing elliptical in shape.
The Nash type can be smaller than the Elmo type for the same capacity. However, the pressure produced by the Elmo type is superior, so the Elmo type is widely used in vacuum pumps today.
Uses of Liquid Ring Vacuum Pumps
The general use of vacuum pumps is to create a vacuum by removing gas from a container. However, liquid ring vacuum pumps are often used for suctioning gases, especially those mixed with water.
This is because water sealing is already used in the pump to create a vacuum, so any moisture in the suction and exhaust does not affect the pump.
The sealed water in the system also acts as a sealant, allowing the pump to be used under conditions where flammable or corrosive gases are present.
On the other hand, compared to other vacuum pumps, the vacuum attainment is considered to be low, but the two-stage structure of the pump can be used at a high vacuum to some extent.
Due to these features, specific applications of liquid ring vacuum pumps include priming of turbo pumps, vacuum pumps for condensers, vacuum pumps for extruders, and industrial uses of liquids in general.
Principle of Liquid Ring Vacuum Pumps
As the name implies, liquid ring vacuum pumps create a vacuum by changing the volume between the impeller and the casing by rotating the impeller to form a ring of sealed water.
Liquid ring vacuum pumps are considered a type of positive displacement pump, meaning that the enclosed water acts as a piston to push the gas out. The water seal forms a ring-shaped liquid film that seals the inside of the pump, thereby preventing almost any gas leakage.
In this way, the water seal inside the pump plays an important role in liquid ring vacuum pumps, and the condition of the sealed water, especially its temperature, must be properly controlled.
Since the sealed water is enclosed in the casing that performs gas compression, the temperature of the sealed water rises as the pump continues to operate, resulting in a drop in the vacuum attained and a drop in the gas displacement rate.
Generally, there are several methods to maintain the temperature of the sealing water, including the method of running cooling water so that the sealing water is constantly replaced, the method of circulating and reusing the sealing water, and the method of cooling the sealing water using a heat exchanger.