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

Relief valve adjustment (external)
Leaks occurring at the locknut generally may be solved by tighten-
ing the locknut. The locknut serves two functions: It prevents the
adjustment stem from moving, and it tightens against the packing
gland inside the valve to prevent leaks. Leaks occurring at the
large nut (labelled "DO NOT ADJUST" in the diagram) should be
solved by replacing the valve.
Replacement of the valve is done by removing any hoses, then
transferring the fittings to a new valve. Teflon® tape should be
used on the threaded fittings. Replacement of the valve will re-
quire the system pressure to be reset.
Refer to ADJUSTMENTS and MAINTENANCE: PRESSURE
ADJUSTMENT for details on setting the system pressure.
Relief valve adjustment
Figure 21

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32
 Capillary Tube
The pressure gauge is connected to the pump discharge line by a
capillary tube of 0.075" (0.191 cm) I.D. (Inside Diameter). The
length is determined by measuring the distance of the path from
the discharge line to the pressure gauge and adding 27" ( 68 cm ).
This additional length will allow a 3 turn coil of approximately 3" (
7.6 cm ) diameter to be included. This coil will dampen any needle
vibration and allow future service.
TIP: A 3" (7.6 cm) diameter coil may be
formed easily using an aerosol can as a
winding form.
The capillary tube I.D. 0.075" (0.191 cm) was chosen because the
O.D. (Outside diameter) of 0.125" (0.32 cm ) provides a snug fit in
the adapter fitting.
The gauge indicates system back pressure, not pump capacity. A
unit connected to a low back-pressure system (parallel manifolds,
or short lines of large diameter) may indicate 0 or a very low
pressure. In other words, the gauge indication reflects reflects
system 
demand, not pump supply.

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33
Priming
The pumps are self-priming only if plumbed in a flooded-suction
configuration, i.e. the fluid flows continually downhill from the
tank to the pump inlet. NESLAB CFT and HX applications are
not plumbed flooded-suction, so priming may not be automatic.
If flow does not start immediately, shut the unit off. Remove the
fitting nut from the rear of the adapter fitting on the pressure
gauge. (The fitting nut is held captive to the cap tube by a ferrule.)
This allows the cap tube to become a vent for the discharge line,
providing an escape path for air trapped in the pump. Place a rag
over the end of the cap tube. Start the unit. When fluid is observed
flowing steadily from the cap tube, reseat it in the adapter fitting
and tighten the fitting nut.
When installing a new pump, add a small amount of fluid to the
inlet of the pump during installation to assist priming. See
PUMP REPLACEMENT for details.