Pd pump Systems neslab p/N 000878 Rev. 08/15/96 Service Manual

Pressure Gauge Fittings
Figure 22

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34
 Relief Valve (Internal)
The relief valve built into the pump temporarily protects against
dangerous overpressure. The relief valve is set at the pump factory
and confirmed at NESLAB. The relief valve setting appears
stamped in the brass as shown. (The illustration shows the posi-
tion of the stamping only - your actual value may differ). The flow
will fully bypass from the outlet to the inlet at the specified relief
valve setting. The relief valve actually begins to crack open and
allow bypass flow approximately 50 PSI (345 kPa) below the
stamped relief valve setting.
Turning the pressure adjustment screw clockwise will increase the
relief valve setting.
NESLAB supplies an additional external relief valve, set to a lower
setting, to provide primary pressure control. The internal relief
valve is a safety feature and should not be relied on to provide
primary pressure control. Changing the setting on this internal
relief valve is not recommended.
See PRESSURE ADJUSTMENT for details on balancing the
settings of both internal and external relief valves.
Figure 23

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35
Pressure Adjustment
The fluid system contains two relief valves: An internal one in the
pump, and an external one on the pump discharge line. Because
of their ability to interact, adjustment must be done in a certain
sequence.
Figure 24

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36
1. Turn unit off. Locate the external relief valve. Loosen the
locknut. Turn the threaded stem all the way in (clockwise).
This manually closes the valve by setting it to an infinite
value.
2. If the unit is not plumbed to an application, install a loop of
hose between the supply and return fittings. Turn unit on.
NOTE: The external relief valve may drip
while the locknut is loose. This is normal.
3. CFT units: Crimp the loop of hose flat using a pair of vise-
grips. HX units: Turn flow control valve completely clockwise
if a round handle, or fully - if a lever handle. The pressure
gauge should rise to a high value. It is now indicating the
internal relief valve setting.