Chemglass AF-0349 Welch Vacuum Pump - Manual (Page 10)

10
2.07 Pump Lubrication
To ensure efficient operation and proper maintenance, and to minimize noise and oil vapors, it is important to use the
correct type and quantity of oil. Welch DIRECTORR® Premium or Gold Vacuum Pump Oil has been developed to
have the proper viscosity, low vapor pressure, and chemical stability needed to produce peak pumping efficiency. The
ultimate vacuum guarantee on Welch pumps applies only when this oil is used. Therefore, DIRECTORR® Premium
or Gold Oil is the only oil recommended for use with these pumps. Each pump is supplied with a bottle of oil sufficient
for filling. Additional oil is available. See Section 9 - Accessories.
2.08 Exhaust Filter
Any oil-sealed vacuum pump tends to discharge oil mist from its exhaust port when the pump operates under high-flow
conditions, such as when the pump’s intake is at or near atmospheric pressure. Typically, oil mist in the form of a white
puff of “smoke” can be seen from the exhaust port when no filter is used. Once the vacuum level and the correspond-
ing air flow through the pump are reduced, very little, if any, oil mist will be emitted.
An optional exhaust filter is recommended for any vacuum pump installation where the pump operates at high intake
pressures for a prolonged period of time. Oil droplets entrained in the pump’s exhaust are removed by the exhaust
filter element. Use of an exhaust filter typically reduces or baffles pump noise as well. Exhaust filters are sometimes
referred to as Oil Mist Eliminators. See Section 9 - Accessories.
2.09 Gas Ballast Valve
The gas ballast valve can increase the pump’s water vapor tolerance. (The gas ballast valve is sometimes referred to
as a vented exhaust valve.) In many vacuum pump applications the gases being pumped from a system are a
combination of permanent gases and undesirable vapors such as water vapor. Under some conditions, the vapors
condense in the second stage of the pump and contaminate the oil. The gas ballast valve reduces oil contamination by
decreasing or eliminating vapor condensation. Vapor condensation usually takes place in the compression stroke of the
second stage of the vacuum pump when the compression ratio between the initial pressure and the end pressure is
high. Opening the gas ballast valve will admit air to the second stage of the vacuum pump thereby reducing the partial
pressure of any vapor in the gas mix (Dalton’s Law). Diluting the vapor with air increases the condensation pressure.
Depending on the amount of air added, condensation of the vapor is either entirely avoided or substantially reduced.
When the gas ballast valve is open, the pump has to work a little harder, resulting in a slight increase in operating
temperature. The increase in temperature is small, however, and is not harmful to the pump. Also, the pump is slightly
noisier, and the pump’s ultimate pressure is somewhat reduced. Therefore, the gas ballast valve should be kept closed
when it is not needed. Note that the gas ballast is not equally effective on all vapors, so it does not always eliminate
condensation completely.
2.10 UNIBARB TM Intake Fitting - Simplifies Small Hose Connections
The UNIBARB TM intake fitting allows the user to be able to use 2 sizes of ID hose to connect to this system.
However, the choice of hose size can have a very marked difference on pumping speed. It is the best to have the
largest connection I.D.(internal diameters) as possible. However, we recognize many lab appliances use hose
barbs accepting small I.D. hose.The conductance of a tube is proportional to the cube of its diameter and inversely
proportional to its length. Therefore, connecting line should be as large in diameter and short in length as practical.
Included is a free hose clamp to hold the hose in place.