9
Section 4: OPERATION
4.10 Starting a Welch Dry Vacuum Pump
Before attaching the pump to a system it is well to familiarize yourself with the function and action
of the pressure vacuum pump which you have acquired. Review the power requirements as
described in Section 3.16. Welch recommends running the pump for a few minutes to warm it up
before use. The warm-up improves the pumps ability to pass water and organic vapor. A warm
pump will handle more vapor without liquefying it than a cold pump.
4.11
Cleanliness
Take every precaution to prevent foreign particulates or liquid from entering the pump. Particulates
will damage the pump’
s performance. If you fi nd that particulates or liquid will come off during
the process of evacuation, a simple liquid trap can be made out of readily available material for
protecting the pump. The trap would consist of a fi ltering fl ask placed between the pump and the
vacuum chamber.
4.12 Leak Detection
Eliminating all leaks in a vacuum system is a key to obtaining maximum vacuum. The pump must
remove this added volume of leaked gas to maintain the desired vacuum. Leaks can be located
by slightly pressuring the system and painting the suspected area with a thick soap solution.
Escaping air will produce soap bubbles.
4.13 Operating Pressure Range
Vacuum pumps are designed to be run from slightly below atmospheric to their maximum vacuum
level on the intake side. Consult the Specifi cation Table in the back of this manual for the ratings
for your specifi c model.
4.14 The Effects of Unwanted Vapor
Systems which contain undesirable vapors cause diffi culty both from the standpoint of attaining
desirable ultimate pressures. A vapor is defi ned as the gaseous form of any substance which is
usually a liquid or a solid. Water, oil, and mercury vapors are three of the more common vapors
encountered in typical vacuum systems. When such vapors exist in a system, the vapors or
mixtures of gas and vapors are subject to condensation within the pump; the precipitated liquid
may thus ultimately solidify on the heads and diaphragm causing corrosion.
4.15 Shutdown Procedures
After use, Welch recommends the pump be run for about 2 minutes disconnected from the
vacuum process. The air pumped through the mechanism will purge out water vapor or droplets of
condensate that may have formed on the inside of the pump. This purge of the pump mechanism
helps prevent build up of solute crystals inside of the pump head. Over time, these crystals will
shorten pump lifetime.
