2.2.2 Application notes
Rotary vane vacuum pumps can be employed universally throughout the entire low and medium vacuum ranges. Either a single- or double-stage pump can be used, depending upon the pressure range in question. Ideal operating conditions always exist if the medium to be pumped down will not condense at pump operating pressure and atmospheric pressure.
Vapors that can condense entirely or partially in the pump during the compression phase must also be displaced for distillation and drying processes. Here, opening the gas ballast valve helps to displace the vapor through the pump without condensation. However vapor compatibility is not always sufficient to prevent condensation. Condensates mix with the oil and cause ultimate pressure to increase and diminish the lubricating capacity of the operating fluid. These factors can cause corrosion inside the pump.
Within certain limits, filters and separators can protect the vacuum pump against wear and corrosion. Separators that are filled with paper filter inserts (STP), Raschig rings (STR) or additionally with cyclone (STZ) bind dust. Activated carbon filters (FAK) bind inorganic vapors, and Fuller's earth filters (FBL) can be connected upstream for absorption of organic vapors. The fillings are replaceable. Inflowing hydrocarbons (oil vapor) can be catalytically incinerated in the heated catalytic trap (URB), and zeolite traps adsorb various vapors. When saturated, they can be regenerated by baking them out. Condensates can be collected in the condensate separator (KAS) and drained manually. Chemical oil filters (OFC) clean the pump oil with the aid of the oil pump that is integrated in the rotary vane pump.
At high gas throughputs and in connection with gas ballast operation, oil mist is entrained out of the pump. 4 ml of oil loss at a throughput of 1 bar · m3 gas can be assumed. The oil vapor can be separated in an oil mist separator (ONF) and returned to the pump's oil circulation system by means of an additional return line.
However if substances are also displaced that chemically attack the pump oil or that have such low vapor pressure that condensation in the pump cannot be avoided, in spite of gas ballast and the above-mentioned accessories, a different type of backing pump should be selected.
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