Two Stage Liquid Ring Vacuum Pump

Single stage liquid ring vacuum pumps discharge the compressed gases to the atmosphere. The discharge from two-stage liquid ring vacuum pumps does not let out to the atmosphere. The first stage discharges through the manifold leading to the second stage as well as through a discharge port located in the intermediate plate between the first- and second-stage impellers. This compression process repeats itself in the second stage, allowing deeper vacuum and finally discharging the gas to the atmosphere. Because of the two stages of impellers, this type of vacuum pump is called a two-stage liquid ring vacuum pump.

The working principle of a two-stage water ring vacuum pump is simple. An eccentric rotor is placed in a cylindrical housing and water is fed into this housing. When the rotor is rotated by a motor, centrifugal force is applied on the water in the housing which creates a void in the center. The void created draws in gases. These gases are compressed and sent to the second stage through the discharge port. The same process is repeated in the second stage and the compressed gases are discharged out into the atmosphere.

Once-through System

• This is the simplest module. It comprises a pump complete with electric motor, drive, and base frame.
• These systems are ideal where an ample supply of seal liquid is available, which can be subsequently discharged to drain. The liquid/gas mixture is discharged to drain through the discharge line.

Partial Recirculation

• In this case, the liquid/gas mixture is separated in the discharge separator. The recovered service liquid is then mixed with fresh seal fluid to maintain a constant temperature in the pump.
• The excess liquid, equivalent to the make-up supply, goes into the drain.
• The minimum amount of fresh make-up fluid is used to ensure cavitation-free operation at the required suction pressure.
• It offers typical water savings of 50% compared to once-through operation.
  

Total Recovery

• Total recovery is a closed loop system that is used when the seal fluid is in short supply or when contamination may be a problem.
• To enable total re-circulation of the seal liquid, the recovered liquid must be cooled prior to re-use.
• In this case, a heat exchanger is utilized between the discharge separator and the pump.
• It offers typical water savings of up to 95% compared to once-through operation.