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6. Lock the counterweight lock nut securely and spread the end of the screw
slightly to prevent the nuts backing off.
3.7.5.5. Inspection for Loose Counterweights and Loose Trunnion Screw Locknuts
The following procedure involves the opening of a vital relay.
Only individuals qualified to work on vital relays should
perform this procedure.
1. Remove the bottom cover from the relay. This exposes the contact assembly.
Exercise extreme caution not to disturb the adjustment of the contacts.
2. Remove nameplate to gain access to the counterweight assembly on the vane
crank.
3. Rotate the vane so that the counterweight assembly is visible. This will reveal
one or more counterweights, with or without a locknut, on the counterweight
screw.
4. As shown in the figure below, check to determine if:
a. The counterweight and locknut are tight.
b. At least two threads are visible on the counterweight screw end.
c. The split screw end is slightly spread apart. Tighten any loose counterweights
and locknut.
5. Conduct a visual inspection of the relay. Check for:
a. Rubbing vane.
b. Debris inside the relay.
c. Obviously misaligned contacts.
d. Check to see that the vane is approximately centered and that it has the
correct amount of end play (0.010 to 0.016 inch). Readjust if required.
e. Check the vane for freedom of movement.
f. Check to see that the operating arms, clips, and bushings are in the proper
position and are free to move.
g. Using a wrench, check the trunnion locknuts for tightness. Tighten any that are
loose.
Copyright 2019
WARNING
SM 4574F, Rev. 4, March 2019
PV-250 Track Relay
3-17
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