Chemglass AF-0349 Welch Vacuum Pump - Manual (Page 7)

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1.06 Vacuum Connections
The pump inlet is equipped with a UNIBARB hose fitting. See table in section 3 for UNIBARB sizes and I.D. hoses
needed for each pump. 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. 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 vacuum 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. There-
fore, 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.
WARNING
The vacuum pump is shipped without oil inside to prevent possible
spillage during shipment. Oil must be added prior to use.
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® Premium or Gold Vacuum Pump 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.
WARNING
Use only Welch DIRECTORR® Premium or Gold Vacuum Pump Oil.
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.