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Servicing
Vacuum Pump Diaphragm and Valve Replacement
Valve Replacement
7-12
Model 42i Trace Level Instruction Manual
8. Rotate the counterweight until the connecting rod is in mid-stroke and
then tighten the clamping disc. Do not over tighten the clamping disc.
Note Over tightening of the clamping disc will significantly reduce
diaphragm life. Tighten enough to avoid contact with the head. If a
significant amount of torque is required to tighten, first re-check to see if
the threads are clear, then check that the connection rod support disc ("H")
is properly seated on the connection rod. Over-torque of the clamping disc
must never be a way to avoid contact with the hea d .
9. Remove the two temporary aligning screws and re-install the heads on
to the pump body. The correct head bolt torque range is 20-30 inch-
pounds.
10. Turn the counterweight ("M") through at least one full revolution to
check for smooth operation.
11. Re-install the housing cover and check the pump for correct
performance.
Use the following procedure to replace the valve.
1. With the head off the pump, unscrew the socket head cap screws with
M4 lock washers ("S") to remove the head lid ("T") and gasket ("V").
2. Loosen the single pan head screw, washers and nut ("P") and remove
the two stainless steel reed valves ("Q"). If necessary, hold the nut in
place with a nut-driver.
3. Lightly clean the valve seat area of debris or deposits with fine-grade
steel wool. This area must be clean and smooth, without pits or
scratches. Do not scratch the head plate. Finish the cleaning with
alcohol and then air-dry the parts.
4. Lay the two replacement reed valves on a flat surface to the direction of
any slight bend.
5. Lay the replacement reed valves in place, center bowed out (see valve
installation), and tighten the pan head screw, both washers, and the
nut. Be certain that the reed valves lay straight and smooth with
clearance from the recessed edge to prevent sticking. If a reed valve
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Thermo Fisher Scientific
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Troubleshooting
