Chemglass AF-0349 Welch Vacuum Pump User Manual
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Changing the Lip Seal and Gasket for 8920 and 8925
When the shaft seal in the mounting plate shows signs of excessive oil leakage, it should be replaced. Before
attempting replacement of the seal, the pump must be disconnected from the vacuum system and from the power
outlet. New lip seal (P/N 61-8378A) and new gasket (P/N 41-0643) or seal replacement kit (for Model 8920:
Cat. No. 8915K-06, for Model 8925: Cat. No. 8925K-03) should be available before attempting repair.
1.
DRAIN OIL by opening the drain plug. The pump may be titled to remove residual oil out of the oil case.
2.
SEPARATE THE BASE the pump may be turned on its oil case face and REMOVE BASE with four
socket head screws 5/16-18x1.
3.
SEPARATE THE PUMP FROM THE MOTOR ASSEMBLY by removing four socket head screws
5/16-18x1-1/4 and washers from the motor adapter plate and carefully separate the pump from the motor
subassembly. Set aside the motor assembly with the coupling sleeve.
4.
REMOVE COUPLING and woodruff key from the pump shaft by loosening the setscrew. Next unscrew
three socket head screws #10-32x7/8 and three split lock washers holding outer lip seal assembly to the
mounting plate. Remove and discard outer lip seal assembly and gasket.
5.
WIPE OIL AND CLEAN the shaft surface and gasket sealing area. Inspect all sealing surfaces. These
must be thoroughly cleaned and free of any scratches.
6.
ASSEMBLE OUTER LIP SEAL ASSEMBLY WITH GASKET. Use a little oil on seal and shaft.
IMPORTANT: Assemble the part with the mark “up” in proper position.
Tighten gradually the three socket head screws #10-32x7/8 and washers.
7.
ATTACH COUPLING BODY to the pump shaft end by means of a woodruff key and a setscrew.
Tighten setscrew lightly.
8.
PLACE COUPLING SLEEVE inside pump coupling body.
9.
Insert two dowel pins into the mounting plate and place motor assembly over the mounting plate.
IMPORTANT: Check and adjust the coupling on pump shaft to insure 0.03 in. minimum total clearance
between coupling elements. Tighten setscrews on both coupling bodies. It is important that no axial thrust
is transmitted through the coupling from motor shaft.
10.
SECURE MOTOR TO THE PUMP by using four socket head screws 5/16-18x1-1/4 and four
lock washers.
11.
ATTACH THE BASE by means of four-socket head screws 5/16-18x1-1/4 and four lock washers.
12.
SCREW IN DRAIN PLUG with o-ring to oil case and fill oil.