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Maintenance
B344-21-880 Issue N
5.7 Lubricate/inspect the high-vacuum isolation-valve
(M- and P-model pumps)
If the high-vacuum isolation-valve is difficult to operate (that is, it sticks because it has been left in the closed
position for long periods, or it is stiff), we recommend that you lightly lubricate the valve-plate seal with Fomblin
RT15 grease. If you think that the valve-plate seal or shaft ‘O’ ring seals may be defective, inspect and replace them
if necessary.
To inspect/lubricate the high-vacuum isolation-valve, use the procedure below.
1. Allow the Diffstak to cool and open it to atmospheric pressure.
2. Drain the pump fluid as detailed in Section 5.4. Disconnect the cooling-water supply and return pipelines, the
electrical supply to the heater and the backing, roughing and system connections.
3. Remove the pump from the system and remove the valve-plate from the shaft (refer to Sections 5.5.2 and
Section 5.5.3).
4. Examine the valve-plate seal and the ‘O’ rings on the valve-shaft. If they are worn or damaged, use new
replacement parts (see Section 7). Lightly lubricate replacement ‘O’ rings and the valve-shaft roller-bearings
with pump fluid prior to reassembly. Lightly lubricate replacement valve-plate seals with Fomblin RT15 grease.
5. Reassemble the valve and refit the pump as detailed in Section 5.5.6.
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