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Quickly learn about water-sealed vacuum pumps

The principle of water-sealed vacuum pump has been studied as early as 1890, that is, "water ring pump". Due to their simple and robust construction, water-sealed vacuum pumps (fig. ) are suitable for creating a vacuum in applications where moist gases or vapors are evacuated, or where condensation may form inside the vacuum pump during compression processes.


Water-sealed vacuum pumps are particularly suitable for humidification processes and can therefore be used for rough vacuum generation in process technology (such as during chemical industry and petroleum production and processing), steam turbine condenser exhaust as well as in the plastics industry, paper industry, food industry technology industry and many other industrial applications.


How it works

Water-sealed vacuum pumps use water or a liquid compatible with the gas or vapor to be vacuumed as the working fluid. Glycols, mineral oils or organic solvents can be used as working fluids as other fluids in process components. The basic principle is the same for all construction sizes and versions.


The eccentrically mounted impeller rotates in a cylindrical pump casing (see figure). Fill the pump casing with working fluid so that the blades of the impeller are submerged in the working fluid. The rotational movement of the impeller and the resulting centrifugal force cause the liquid in the pump casing to form a so-called liquid ring. The pumped medium is transferred to the space between each vane and water seal. Due to the eccentric design of the impeller, the volume of the space changes as the gas is sucked in, compressed and discharged again. The liquid ring seals the space of each stage as the pump chamber. For this reason, it is sometimes called a sealing fluid rather than a working fluid.



There is a fundamental difference between a single-stage water-sealed vacuum pump and a two-stage water-sealed vacuum pump. In single-stage water-sealed vacuum pumps, the above compression process is performed in one compression stage. Whereas in a two-stage vacuum pump, the pumped medium pre-compressed in the first stage is conveyed to the second compression stage and compressed again. The single-stage water-sealed vacuum pump can achieve an ultimate pressure of 130 hPa (mbar), and the two-stage water-sealed vacuum pump can reach an ultimate pressure of up to 33 hPa (mbar).


Run mode

The supply and removal of working fluid can be achieved in three ways:


Non-reloop operation

This is the easiest way to run a water-sealed vacuum pump, and is available when sufficient working fluid is available. Continuous supply of working fluid to the compression stage. The working fluid is then discharged together with the gas and condensed water.


Open liquid circuit

In an open circuit, the working fluid exits the vacuum pump and is transferred to the liquid separator along with the gas. Liquid and gas are separated here. Gas is vented or diverted when new working fluid is supplied to the liquid separator. This ensures that there is sufficient working fluid in the circuit and that the temperature does not rise. Open circuit saves up to 50% of hydraulic fluid compared to non-recirculating operation.


Closed liquid circuit

in closed loop There is also a liquid separator downstream of the pump (Figure 5). Gas is exhausted from it while being diverted through the heat exchanger before the working fluid flows again into the vacuum pump. This continuously cools the working fluid. This configuration saves up to 95% of working fluid. This means that only a small amount of fresh working fluid needs to be added through the liquid separator. Therefore, when there is not enough working fluid, or when it is necessary to save working fluid as much as possible, we recommend using a closed circuit.




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