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III.
OPERATION
III-1.
STARTING PROCEDURES
III-1a. STARTING THE PRESSURE/VACUUM PUMP.
Before attaching the pump to a system we recommend you familiarize yourself with the function and action
of the Pressure/Vacuum pump which you have acquired. Review the power requirements as described in
Section II-6. We recommend running the pump for a few minutes to warm it up before use. The warm-up
improves the pump ability to handle humid air.
III-1b. CLEANLINESS
Take every precaution to prevent foreign particulate from entering the pump. Particulates will damage the
pump's performance. If you fi nd that particulates will come off the process during evacuation, a particulate
trap in the foreline will work. Placing glass wool in a glass or plastic tube may make a simple, inexpensive
trap. Screens must be inserted to hold the glass wool in place.
III-2.
LEAK DETECTION
The importance of eliminating all leaks in a vacuum system is obvious. The pump must remove this added
volume of leaked gas to maintain the desired vacuum. Leaks for these pumps can be located by slightly
pressuring the system and painting the suspected area with a thick soap solution. Escaping air will produce
soap bubbles.
III-3.
OPERATING PRESSURE RANGE
The pressure/vacuum pump is designed to be run from slightly below atmospheric to their maximum
vacuum level on the vacuum side. The pumps also may be run from atmospheric to 10 PSIG continuously,
to 33 PSIG intermittent. Consult the Specifi cation Table in the back of this manual for the ratings for your
specifi c model.
III-4.
SHUTDOWN PROCEDURES
After use, we recommend 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 water condensate that
may have formed on the inside of the pump. This purge of the pump mechanism helps extend the pumps
service life.
IV.
MAINTENANCE
Welch dry pressure/vacuum unit is oil-free. The pump employs a PTFE piston sleeve and cylinder. No
maintenance is necessary for the bearings. All bearings are sealed and permanently lubricated. Lubrication
should not be attempted. The units are built for continuos and intermittent duty operation with the quietness
and durability of a diaphragm, but with piston performance. The Compressor/Pump has a service free
lifetime of 2,000 to 3,000 hours. The Compressor/Pump in the plastic housing is not fi eld serviceable.
V.
TROUBLESHOOTING
V-1.
VACUUM PROBLEMS
Leakage, contamination and unusual outgassing are the general causes of problems associated with poor
vacuum. To operate at maximum effi ciency a system must be thoroughly clean. If the system is completely
clean and free from leaks, and unwarranted vacuum problems still exist, the pump should be checked. A
simple criterion for the condition of the pump is the determination of its maximum vacuum capability. This
can be accomplished by blocking of the intake and reading the vacuum level on the dial gauge.
V-2.
PRESSURE PROBLEMS
Leakage and contamination are the general causes of problems associated with poor pressure. To operate
at maximum effi ciency a system must be thoroughly clean. If the system is completely clean and free from
leaks, and unwarranted pressure problems still exist, the pump/compressor should be checked by a service
technician.
3
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