Welch Vacuum 8925 Direct Drive Rotary Vane Pump - Manual (Page 7)

7
1.06 Vacuum Connections
The pump inlet is equipped with a UNIBARB TM 7/16” and 13/16” hose fitting. The inlet is located
next to the pump handle. It contains a screen to collect any debris from getting into the pump. An
extensive line of vacuum pump ISO fittings, hoses, traps, etc. is available from Welch to meet the
requirements of most vacuum systems. For the best vacuum, use a hose clamp in conjunction with a
vacuum hose to hose nipple connections. Welch offers a number of different types of vacuum tubing
and connectors.
See Section 9 - Accessories or call Welch customer support (847) 676-8800, Extension 1.
The choice of connections and fittings can have a very marked effect on the pumping speed at the
vacuum chamber. Any connection placed between the pump and the chamber creates an impedance to
the flow of gas. This is particularly true at low pressures in the millitorr range where the gas flow is
substantially molecular in character. The gas flow is then dependent upon the kinetic activity of the
molecules to bring it to the pump intake. This impedance is described by the term “conductance”.
The conductance of a tube is proportional to the cube of its diameter and inversely proportional to its
length. Therefore, connecting lines should be as large in diameter and as short in length as practical.
For best results the diameter of the connecting tube should be at least as large as the diameter of the
pump intake. To avoid a large reduction in pumping speed at the vacuum chamber, the conductance of
the line must be considerably greater than the speed of the pump. Sharp bends in vacuum lines also
contribute to conductance. To avoid reductions in pumping speed, minimize the number of 90º angles
in the vacuum system.
1.07 Vacuum Gauges
The type of vacuum gauge to be used in a system is determined largely by the pressure range to be
measured. A thermocouple or pirani gauge is recommended for measuring pressures in the range
produced by these pumps. See Website or call for additional information.
1.08 Vacuum Pump Oil
Filling with Fresh Oil
Be sure the pump is filled with oil to the level indicated on the oil fill window. When additional oil is
required, use only DIRECTORR® Gold Vacuum Oil , pump performance is not guaranteed with other
brands of oil. Do not overfill the pump, and be sure to replace the oil fill plug.
Remove the oil fill plug located on the top of the oil case and add the oil supplied in a bottle packaged
with each pump.
The fill plug has a raised middle section and a center slot for easy turning either by hand or with a
screwdriver. After the pump has been running for at least 15 minutes, check the oil level again. The oil
level should be maintained at the “full” mark on the oil level window while the pump is operating. Do
not overfill, excess oil tends to be splashed out the pump exhaust.
Guidelines for the frequency of oil changes and the oil changing procedure can be found in
Section 6-2: Oil Change
WARNING
The vacuum pump is shipped witout oil inside to prevent possible
spillage during shipment. Oil must be added prior to use.
WARNING
Use only DIRECTORR® Premium or Gold Vacuum Pump Oil.