Understanding the functionality of oil-sealed rotary vane vacuum pumps
Oil-sealed rotary vane vacuum pumps are the standard, tried and tested technology for numerous industrial applications due to their streamlined design, traditional reliability and efficiency. These single and double stage pumps are coveted for their simplicity and robustness, making them an integral part of various industrial operations worldwide.
Let's look into the mechanics of a rotary vane vacuum pump:
At its core, the oil-sealed rotary vane vacuum pump can achieve pressures as low as 10-2 mbar. With a housing (stator) and a cylindrical rotor, lubricated by oil, this mechanism operates seamlessly. The eccentric rotor, fitted snugly against the stator, houses two to three blades within completely opposite slots.
As the rotor makes its revolution, the blade tips maintain constant contact with the stator wall, initiating a cycle of induction, isolation, compression, and exhaust phases. When in action, gas molecules entering the pump inlet flow into the volume created by the rotor's eccentric positioning within the stator. This gas volume is then compressed, prompting the exhaust valve to open and allowing the discharge of gas.
To ensure a tight seal, a continuous thin film of oil is maintained between the components, drawn from the oil reservoir into the pump interior. The circulating oil, along with the pumped gas, is then expelled back into the reservoir via the exhaust valve. The pump's ultimate pressure is restricted by back-leakage between the suction and discharge compartments and the outgassing of the lubricating oil.
Managing vapor load, particularly when dealing with gas containing water vapor, becomes crucial. Condensation of vapor during pump compression can mix with the pump oil, resulting in compromised performance, reduced lubrication, and potential corrosion of pump components. Traditional solutions like frequent oil changes are expensive and inconvenient. However, a modern-day solution lies in the integration of a "gas ballast" feature within the pump mechanism.
The gas ballast serves as a safeguard against vapor contamination of the pump oil. By admitting atmospheric air during the compression stage, it increases the non-condensable gas proportion within the pump. Consequently, vapor is discharged without condensing, mitigating the risks of performance deterioration and oil properties degradation.
In essence, the gas ballast feature in oil-sealed rotary vane vacuum pumps acts as a shield, enabling these machines to handle vapor-containing gases, without compromising efficiency or risking oil contamination.