WELCH-ILMVAC DUOSEAL 1374, Руководство пользователя

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2.225 Controlled Ballast Flow
Some degree of variation in ballast fl ow may be obtained by the amount of opening applied tot he gas ballast.
Two or more turns of the gas ballast are suffi cient to open it wide. With the gas ballast open, the sound of
the exhaust is similar to that of a pump operating against a large leak. Because of the increased pressure
introduced into the compression stroke, the pump must work a little hard to function, thus resulting in an
increased operating temperature of approximately 8°C over a prolonged period of time. Tests have shown that
continuous and prolonged operation for several weeks under these conditions is not injurious to the pump.
2.226 Other Forms of contamination control
The application of the gas ballast is a moderate and very successful method for the removal of condensable
vapors. For very heavily laden systems, other means of removal such as oil separators may be required. For
mild cases of contamination the simple expedient of a cold trap or a change of oil serve the purpose.
2.23 System Leaks - Impact & Detection
2.231 Large Leaks
The importance of eliminating all leaks in a vacuum system is obvious when it is realized that a leak into the
system, at atmospheric pressure, expands in volume by a factor of 750,000 to 10,000,000 or more. The pump
must remove this added volume to maintain the desired vacuum. Fortunately a number of effective techniques
for leak detection have been developed. Large leaks can be located by pressurizing the system and painting
the suspected area with a thick soap solution. Escaping air will produce soap bubbles.
2.232 Small Leaks
Small leaks may also be detected by spraying a suspected area with acetone or gases rich in hydrogen, and
observing a sudden change in pressure on an electrical gauge. The difference in calibration of these gauges,
for air and other gases, will produce a distinct change in the pressure reading. To use this method of detection,
the system must be under vacuum and the gauge sensing tube must be located between the pump and the
area to be probed. Use extreme caution, as these materials are highly fl ammable!
2.233 Fine Leaks
Locating very fi ne leaks requires a helium-sensitive, mass-spectrometer leak detector. This instrument will
locate leaks which cannot be detected by any other method. Numerous fi ne leaks can have the total effect of a
large leak.
2.30 Shutdown Procedures
2.301 DuoSeal Shutdown
A few simple precautions are all that is necessary when shutdown is in order. If a gauge is connected to the
system, fi rst isolate the gauge, then turn off the power and open the system to atmosphere. If the pump is
removed from the system, cover the intake port with a rubber stopper or suitable cover to protect the pump
against contamination and loose particles. If the pump has been contaminated in service and is going to be
shelved for a prolonged period it is best to drain the oil and refi ll with a fresh charge.