What matters most when choosing between Dry Screw Pumps & Liquid Ring Vacuum

When using vacuum technology, it is important to select the right tool for the job. There are many vacuum technologies that can be used in different industries. You may find yourself in a situation where you need to choose between a liquid ring vacuum pump or a dry screw vacuum pump for your process industry. The right vacuum pump will ensure smooth operation, improve consistency, and maximize return on investment. Both the Dry Screw Vacuum pump as well as the Liquid Ring Vacuum pumps are positive displacement pumps. The main difference is that the dry screw vacuum pumps do not use fluids to create vacuum, while the liquid ring vacuum pumps uses liquid to create vacuum.Many apprentices confuse the two. Let's clarify the differences between a dry screw vacuum and a liquid-ring vacuum pump.

There advantages and shortcomings are as follows:

1. Based upon the working principle : The liquid ring vacuum pumps consist of a cylindrical housing that is partially filled with sealing fluid to create a vacuum. Vacuum generation takes place through a rotating impeller with multi-blades that is mounted on an eccentric shaft within the housing. A centrifugal force is created by the rotation of the impeller, which creates a liquid ring. This liquid ring creates a vacuum that is necessary for the operation. Two screw rotors rotate in opposite directions to create vacuum. Dry screw vacuum pumps produce vacuum by rotating two screw rotors. The movement of the rotor reduces the volume of trapped gas, which results in compression and exhaust. The compression chamber does not require lubrication as the rotors are not in direct contact with each other during compression. This is known as dry technology.
2. Based upon discharge temperature: A liquid ring pump's inherent design allows for the use of many liquids as sealants. This includes solvents, oils, and other compatible fluids. The gas compression is considered to be isothermal because the liquid comes in direct contact with the compressed gases/vapors during the process. The outlet discharge temperature is controlled between 45 to 150 degrees F. The liquid ring vacuum pump allows for great flexibility because different gases can either be condensed or passed through. The constant-pitch or progressive pitch design of dry screw vacuum pumps ensures that the gas/vapor is transported at constant volume to its discharge port. The compression process is considered adiabatic with discharge temperatures up to 450°F. This pump technology is also popularly termed as HOT Pumping as it ensures minimum condensation within the pump casing because of this high operating temperature and thus promotes solvent recovery at the pump discharge.
3. Based upon operation conditions : The liquid ring vacuum pumps can withstand the most difficult applications and are highly resistant to harsh environments, saturated air, and vapor loads. The gas compression process is isothermal so the pump can pump flammable, explosive and toxic gasses.The dry screw vacuum pump cannot be used to pump gasses contaminated by oil, dust, water vapor, or other contaminants. Only a dry, clean stream of gas can be used.
4. Based upon operation and maintenance costs : The liquid ring vacuum pumps need heavy utilities to operate such as high quantity of sealing water, this sealing water gets contaminated with process vapours wherein it creates 2 problems, first being treatment of the water and the second one being, loss of solvent from that water.Dry Screw Vacuum pump however has no such issue, all internal components are non contact type only. This makes its maintenance relatively easier and operation cost substantially lower as compared to a Liquid Ring Vacuum pump.

Dry screw pumps have low maintenance & lesser requirement of utilities, there NET carbon footprint on the environment is substantially lower as compared to any other type of vacuum pump and they are thus becoming a very popular choice owing to clean operation and high return on investment.

We conclude that the differences between the dry screw and liquid ring vacuum pumps make it easy to choose the right vacuum pump for your industrial application. The right vacuum pump will give you smooth operation and a high return on investment.

Dhruv Malhotra is the director and expert author of the Dry Vacuum Pump website, and the website having lot of information about all dry screw vacuum pumps, roots vacuum pumps, rotary vane vacuum pumps, oil syst vacuum systems.