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TM 10-4310-391 -13&P
charge to prevent unnecessary contamination An additional supply of ail Is furnished with each pump with
Instructions to drain and discard the ail contain- In the pump and replace with the fresh ail DuoSeal ail has been
especially prepared and Is ideally suited for use m mechanical vacuum pumps because of bits desirable
viscosity, low vapor pressure and chemical stability. The vacuum guarantee on all Sargent-Welch pumps
applies only when DuoSeal ail Is used Other lubricants for special applications are available Including venous
lubricants for oxygen compatibility lubricants for use with diffusion pumps as well as other special requirements.
II. OPERATION
II-1.
STARTING PROCEDURES
II-1a.
Starting a DuoSeal Pump
Before attaching the pump to a system it Is well to familiarize yourself with the function and action of the pump
which you have now acquired Remove the Intake and exhaust port plugs and temporarily provide a stopper for
the intake and a dust cap for the exhaust Review the power requirements as described In Paragraph 1-6
II-1b. Cleanliness
Take every precaution to prevent foreign particles from entering the pump A fine mesh screen Is provided for
this purpose In the Intake passage of all the DuoSeal pumps
II-1c. Oil Level Determination
The amount of ail suitable for efficient and satisfactory performance should be deter mined after the pump has
reached bits operating temperature In-t-ally, however, the pump should be filled with fresh ail while the pump is
Idle fill the pump until the ail level falls between the two ail level marks If after a short period of operation the
level should fall, it Is likely the result of ail entering some of the interior pockets of the pump if a burgling sound
occurs, additional ail must be added In general, the ail level will be higher during high pressure operation
Mechanical pumps will gurgle In varying degrees under four conditions of performance. [a] when operating at
high pressure as m the beginning cycles of evacuation of a chamber, [b] when the ail level in the pump
reservoir Is lower than required, [c] when a large leak Is present In the system; and Ed.] when the vented
exhaust valve is open Awareness of these possibilities will save time In setting up a system Best performance
of a mechanical pump Is generally obtained after sufficient time has been allowed for the pump to come to
operating temperature
II- 2. LEAK DETECTION
II-2a. 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
II-2b. Small Leaks
Small leaks In glass systems may be located by probing with a high frequency coil of the Tesla type This
Instrument Is an ungrounded, high-potential spark coil with a pointed electrode The discharge spark from the
coil will seek and pass through any minute opening and produce a faint pink glow at the location of the hole In
using a Tesla coil, the electrode point should be held about ½ Inch from the glass and should be kept In
constant motion It is not recommended for use In very thin-walled systems or m locations adjacent to glass-to-
metal seals. 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 m 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 flammable!
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