Data Sheet

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Fisherr 644 and 645 Differential Pressure
Pump Governor Actuators
Fisher 644 and 645 actuators are used in combination
with any of several sliding-stem valves to automatically
control steam-driven boiler feedwater pumps
(reciprocating or turbine). The 644 or 645 actuator
(see figure 2), when used in combination with one of
several push-down-to-close sliding-stem valves, forms
a pump governor.
644 and 645 actuators may also be combined with
push-down-to-open valves to be used as relief
governors. Relief governors are used to divert excess
pump discharge back to the suction side of the pump.
Features
 Rugged Construction–Steel and cast iron
construction provides long service life.
 Ease of Maintenance–Few moving parts and easy
access reduce maintenance and downtime.
 Ease of Adjustment–Spring adjustment is readily
accessible without removing any parts.
 Fast Acting– Direct-operated configuration provides
fast speed of response.
Determining Buildup or
Droop
To determine the buildup (for relief applications) or
droop (for pressure reducing applications):
1. Find a pressure setting limit range that includes the
required pressure setting from table 1.
Fisher 644 Actuator Mounted on easy-et Valve Body
W2265-1
2. Find the sensitivity factor for the desired spring and
actuator casing combination from table 1.
3. Use the formula below to determine the buildup or
droop required for normal actuator travel.
X
Y
P=
where,
P = Buildup (for pressure relief) or Droop (for pressure
reduction), bar (psig)
Y = Normal actuator travel, mm (inches)
X = Sensitivity factor from table 1 mm/newtons
(inches/psig)
644 and 645 Pump Governors
D100185X012
Product Bulletin
61.9:644
December 2012