Leybold Vacuum Products, TRIVAC A, Dual Stage, Rotary Vane ...

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EXHAUST HOLES
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NOTE: This photograph is for illustration purposes only. When assembled, the cap end of the gas ballast valve
(17) is attached outside the top of the oil casing (12) (see Figure 1·1), and an oil filter (35) and other parts fit
around the valve (17) stem (see Figure 5·10B).
Figure 2-3. Gas Ballast Valve and Second Stage Pump Cylinder With Front End Plate Removed
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2-3-2 Purpose and Function of the Gas Ballast Valve
All systems contain moisture. Some processes have large quantities of condensable vapors in the process gas.
When these vapors condense in the pump, they degrade the lubricating and sealing qualities of the pump fluid
(see Section 2-4) resulting in excessive pump wear, higher base pressure, and sometimes pump seizure.
The gas ballast valve allows removal of condensable vapors and condensate such as water, alcohol, gasoline.
benzene, carbon tetrachloride, etc. from the pump. It also enables high levels of water vapors to be pumped
without condensation. The water vapor tolerance for your pump is listed in Table4-1. If the partial pressure of
water vapor in the gas being pumped exceeds the tolerance of your pump, the vapor will condense. We
recommend installing an AK condensate trap on the pump when pumping saturated vapors (see Section 1 of
our catalog for more information on condensate traps).
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When the gas ballast valve (17) is open, it admits a controlled amount of air into the second stage pump cylinder
(46) just before the exhaust holes (see Figure 2-3). The open gas ballast valve prevents vapors from condensing
by reducing the partial pressure of the condensable vapors and by increasing the operating temperature of the
pump.
The gas ballast valve is not fully effective until the pump is warm to the touch. When using the gas ballast valve
to remove condensate from the pump fluid, it is best to seal off the intake tube (1). Sealing off the intake tube
(1) prevents additional vapors from entering the pump while the condensate is being vaporized and the vapor is
being ejected. See Sections 4-1-2 and 4-2 for instructions for using the gas ballast valve during start-up and operation.
In addition to increasing the operating temperature, running the pump with the gas ballast valve open also results
in higher ultimate pressure (see Table 4-1), higher pump fluid consumption, and a pump fluid mist in the exhaust
stream. If you run the pump with the gas ballast valve open continuously, we recommend an SE smoke eliminator
or an AF exhaust filter with an oil return line. After closing the gas ballast valve the pump normally reaches ultimate
pressure as soon as it cools to operating temperature.
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TRIVAC "A" Manual, Edition L