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

Pressure Gauge Replacement
1.  Disconnect the unit from line voltage.
2. Remove fitting nut from the rear of the adapter fitting. The
fitting nut will be held captive to the capillary tube by the
ferrule.
3. Remove the adapter fitting.
4. Remove clamp bracket(s).
5. Pull the gauge out of the panel hole from the outside.
6. Apply Teflon® tape to the nipple of the new gauge.
7. Mount the new gauge using the clamp bracket(s).
8. Install the adapter fitting.
9. Retighten fitting nut. (Do not use Teflon® tape here).
10. Turn unit on and check for leaks.
Figure 14

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26
 Pressure Gauge Orifice
The mini style pressure gauge, 1 1/2 in ( 4 cm) diameter, has a
small orifice plate between the gauge nipple and the diaphragm.
This is intended to dampen any needle vibration. The orifice can
become clogged by a small piece of dirt. If this happens, the
gauge will read zero all the time.
Before disassembly, confirm that the needle is on the correct side
of the stop pin. If incorrect, the gauge has been destroyed by
overpressure and will require replacement.
To clean the orifice, remove the adapter fitting from the gauge.
Insert a small needle or similar probe into the gauge nipple. Lo-
cate the orifice and twirl the needle in the opening. This should
push any debris inside the gauge where it will be trapped out of
trouble. (System pressure will prevent any such trapped dirt from
"backing up" into the orifice). Reconnect fittings and test the
gauge.
Figure 15
Figure 16

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27
Check Valve
(Installed on HX units only)
The check valve is intended to keep the tank from siphoning dry
if the hose is removed from the return fitting. The valve is lo-
cated upstream from the return fitting.
There are two styles of checkvalves used. The mechanism of
the style shown in Figure 17 consists of a Teflon® seat on a
weighted hinged flapper; the one shown in Figure 18 is of a
spring-loaded metal-to-metal design. The mechanism is acces-
sible through the access cover. This need not be opened under
normal use, as there is no periodic maintenance required on
either style checkvalve.