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6
Adjusting the Opening Closing Velocities
Circuit breaker timing tests are performed routinely as part
of circuit breaker maintenance. Contact velocity measure-
ments are a part of this testing. The velocity of the HMB-8
mechanism is factory-set and should not significantly
change over the life of the circuit breaker. However, provi-
sions are available for adjusting the opening and closing
velocities if necessary. The location of the open velocity
throttle and close velocity throttle are shown in Plate 4.
Plate 4: Open and close velocity throttles
To increase or decrease either the open or close velocity:
1.
Equalize the hydraulic pressure as described in sec-
tion 4.1.1.
2.
Loosen the locking nut of the respective throttle (open
or close)
3.
Turn the throttle counter-clockwise to increase the
speed; turn the throttle clockwise to decrease the
speed. Never turn the throttle more than one turn
without re-verifying the speed through timing tests.
7
Adjusting the Onboard Auxiliary Switches
The auxiliary switches 97604 (Figures 1 and 1b) are preset
in the factory and should not require readjustment for the
life of the mechanism. However, if switch replacement,
addition or adjustment does become necessary, the aux-
iliary linkage will need to be adjusted. Adjustment is done
by resetting the length of the adjustable link 97608 (Figures
1 and 1b). When complete, apply Loctite 242 to both end
threads and tighten the 2 nuts.
HMB-8 / HMB-8.7 Mechanism
Pilot Valves
Close velocity throttle
Open velocity throttle
641P026-008
(formerly HMB-11)
©
Page 15
High
Pressure
Access
4 November 2005
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