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Types 644 and 645
8. If discharge pressure is too high, slightly open
equalizing valve (F). If the pressure does not fall low
enough, turn the lower spring seat counterclockwise
out of the yoke.
9. Open or close valve (B) to a point where very slight
movement (approximately 1/64-inch) of the stem is
noticeable with each stroke of the pump. Greater stem
movement will result in erratic operation and shorten
the life of the diaphragm.
Adjustment
No adjustment is required other than that described in
the procedure for putting the governor into operation.
If it is necessary to change the setting, turn the lower
spring seat clockwise into the yoke to increase the
pressure setting. Turn the lower spring seat counter-
clockwise, out of the yoke, to decrease the pressure
setting.
Principle Of Operation
Figure 3 shows Type 645-ED being used to directly
maintain a differential setting between the pump dis-
charge pressure and the boiler steam pressure in a
boiler feedwater system.
If pump discharge pressure increases, the change is
registered on the top of the actuator diaphragm. The
increased pressure forces the diaphragm and valve
plug downward. With the steam supply thus restricted,
less steam reaches the pump. This causes the dis-
charge pressure to drop so that a difference between
the discharge pressure and the boiler pressure will
return to the desired differential setting.
In figure 4, Type 644-EDR is being used as a relief
governor maintaining a differential pressure between
the boiler and pump discharge.
An increase in the pump discharge pressure is regis-
tered on the top of the actuator diaphragm. The in-
creased pressure forces the diaphragm and valve plug
downward. Since this governor is reverse acting, this
action opens the valve and allows the excess pump
discharge to flow to the pump suction line. The pump
discharge pressure drops and the difference between
the boiler pressure and the pump discharge pressure
returns to the desired level.
4
Maintenance
Actuator parts are subject to normal wear and must be
inspected and replaced when necessary. The frequen-
cy of inspection and replacement depends on the se-
verity of service conditions. Because of the care
Fisher Controls takes in meeting all manufacturing re-
quirements (such as heat treating and dimensional
tolerances), use only replacement parts manufactured
or furnished by Fisher Controls.
WARNING
Avoid personal injury or property dam-
age from sudden release of process
pressure or bursting of parts. Before
performing any maintenance opera-
tions:
Disconnect any operating lines pro-
viding air pressure, electric power, or a
control signal to the actuator. Be sure
the actuator cannot suddenly open or
close the valve.
Use bypass valves or completely
shut off the process to isolate the valve
from process pressure. Relieve process
pressure from both sides of the valve.
Drain the process media from both
sides of the valve.
Vent the power actuator loading
pressure and relieve any actuator spring
precompression.
Use lock-out procedures to be sure
that the above measures stay in effect
while you work on the equipment.
WARNING
To avoid personal injury and equipment
damage, isolate the pump governor
from all pressure before beginning dis-
assembly. The pump governor can be
isolated by throttling valve (D) and clos-
ing the shut-off valves (A, B, C and E).
Directions for lubricating the packing and disassem-
bling the actuator are given below. Refer to figures 5
and 6.
Lubricating the Packing
Keep the packing box nuts (key 9) tightened firmly in
order to prevent leakage. However, do not over-tighten
these nuts. This increases friction and results in unsat-
isfactory service.
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