Pfeiffer Vacuum

4.2.2 Application

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

Vapors that can condense entirely or partially in the pump during the compression phase must also be displaced during distillation and drying processes. Opening the gas ballast valve helps in this case to displace the vapor through the pump without condensation. However the vapor compatibility is not always sufficient to prevent condensation. Condensates mix with the oil and cause the ultimate pressure to increase and diminish the lubricating capacity of the operating fluid. These factors can cause corrosion inside the pump. Before evacuating the vapors, the pump must be warmed up for at least half an hour with gas ballast. The higher temperature of the operating fluid reduces condensation. Additional measures to reduce condensation include obtaining the lowest possible outlet pressure and separate removal of condensates. A condensate separator at both the inlet and outlet sides should be used for this purpose. Back pressure at the outlet must be prevented with an oil mist filter and a vertical exhaust gas line. If an extraction system is available, the outlet should be connected to it.

Dust, particles and chemicals

Within certain limits, filters and separators can protect the vacuum pump against wear and corrosion. Separators that are filled with polyester (SAS) or epoxy glass microfiber (DFT) filter inserts bind dust. Activated carbon filters (FAK) bind inorganic vapors, and their filter filling is replaceable. Inflowing hydrocarbons (oil vapor) can be catalytically incinerated in the heated catalytic trap (URB), and zeolite traps (ZFO or ST) adsorb various vapors. When saturated, they can be regenerated by baking them out. Condensates can be collected in the condensate separator (KAS or CT) 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 when operated with gas ballast, oil mist is entrained out of the pump. An oil loss of 4 ml at a gas throughput of 100 kPa · m³ can be assumed. The oil vapor can be separated in an oil mist filter (ONF or OME) and returned to the pump’s oil circulation system through an additional return line (ORF or ODK).

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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