การใช้งาน (Application)
The rotary piston vacuum pump has become the major workhorse for a number of vacuum applications where relatively large chamber volumes have to be evacuated, where there is a large volume of outgassing from chamber walls or the process product or when the process has a high gas throughput due to gas being fed into the process chamber.
They are excellent if the process requires a vacuum range between a few mm Hg (also called torr after Mr. Torricelli) down to about 50 microns. The pumps are generally rated to give an ultimate vacuum of 10 microns. (1 micron = 1/1000th of 1 mm Hg) Remember that the vacuum level in the process chamber will always be higher than the ultimate or blank-off vacuum at the pump inlet.
Prior to the 1980s, when “dry” vacuum pumps started to enter the market, the rotary piston pump was a popular option when there was a large industrial or scientific process chamber to be evacuated. They were not used much in the chemical process industry, as the vacuum levels needed there were not as high and large volumes of gas and vapor could be handled better by steam ejectors combined with liquid ring type vacuum pumps. (A “dry” vacuum pump has no lubricant in the pumping volume, but still requires lubrication for gears and bearings.) Oil sealed rotary vane pumps, originally vee-belt driven and later mostly direct drive, were used but were not particularly suited to dirty applications, especially the faster running direct drive designs. In some applications with either a very harsh process or where the process requires a “cleaner” pump with less chance of contamination by oil vapor the newer designs of dry vacuum pumps have been used successfully.
In the heat treating and vacuum furnace industry rotary piston vacuum pumps are still an economical choice for many applications. The basic pumping capacity is often 150 cfm or 300 cfm and either size can be combined with a Roots design blower on the inlet side to give a variety of higher pumping speeds (and higher vacuum) depending on the pumping speed of the Roots blower. Also, the pumps are relatively easy to maintain or service by either in-house maintenance crews, local third-party service shops or by the pump manufacturer depending on the ability or choice of the user. A number of vacuum pump industry companies have the ability to manufacture and sell the basic piston, piston sleeve and hinge bars for this type of pump.
