There is no established calculation for estimating the time frame of oil change of a vacuum pump. Oil is changed in a vacuum pump if oil is contaminated or vacuum pumps fail to produce required vacuum levels. Contamination of vacuum pump oil can be identified from its colour and viscosity. Black colour and milky white oil are indicators of dirt contamination and water contamination respectively. Failure to obtain requisite pressure levels is one of the indicators that the vacuum pump oil is not as per specification of the pump OEM. In chemical applications, one can conduct a litmus test of the oil to conclude if oil change is evitable.
When to change oil in vacuum pump? Why to change vacuum pump oil? How to change oil in a vacuum pump?
Oil change in the pump is carried out when the pump is at ambient temperature. In case of top up of oil first oil is drained from the drain of the vacuum pump. Vacuum pumps used in wet application (salt drying/ paper drying), often tend to condense water vapour in the exhaust cycle which emulsifies in the oil and turns milky. One may keep the pump idle over-night and next morning, drain the oil. Often water that is settled overnight is drained initially followed by oil. If the later is acceptable in form of contamination, then top up of oil can be opted. Pump should not be rotated either by hand/motor, since water settled overnight may mix with oil.
In case of total oil change, first the oil from pump is drained completely. Later pump is filled with flushing oil. The pump is rotated by hand or its motor is inched (turned ON-OFF). This aids to circulate flush oil in the pump and gather dirt accumulation from the pump. Flushing is done twice or thrice as the contamination demands. Flushing oils are generally less viscous and compatible to vacuum pump oils. One may opt to mix benzene or carbon tetra-cholride with vacuum pump oil for better results. However, it is strongly recommended that the pump be rotated by hand in such scenarios. Followed by flushing the vacuum pump is filled with a new charge of oil.
What is Oil consumption of a vacuum pump, how much oil is consumed by a vacuum pump?
There is no equation that suggests an estimate of consumption. Individual pump manufacturers may however, lend information on oil consumption rate in cc (cubic centimeter) per mbar-cu.m of the pump which is helpful in estimating the oil consumption rate. General figures are 1.8 to 2.3 cc per 1000 mbar-cu.m of air for gas ballast pumps. Gas ballast contributes to 10% consumption in total oil consumption.