SANDPIPER ST25A - Manual (Page 5)

520-005-000 1/04 Models ST1-A, ST25A Type 4 Page 5
To re-install the sleeve and spool set, lightly lubricate the o-rings on the sleeve with an
o-ring assembly lubricant or lightweight oil (such as 10 wt. air line lubricant). Press the set
into the valve body easily, without shearing the o-rings. Re-install one end cap, and retaining
ring on the valve body. Using the arbor press or bench vise that was used in disassembly,
press the sleeve back into the valve body. Re-install the spool, keeping the counter-bored
end toward you, and install the spring, opposite end cap and retaining ring on the valve
body. After inspecting and cleaning the gasket surfaces on the valve body and intermediate,
re-install the valve body on the pump using new gaskets. Tighten the four hex head capscrews
evenly and in an alternating cross pattern, at 150 in./lbs. (16.94 Newton meters).
PiloT VAlVe
The pilot valve assembly is accessed by removing the main air distribution valve body from
the pump and lifting the pilot valve body out of the intermediate housing (see Figure 8).
Most problems with the pilot valve can be corrected by replacing the o-rings. Always
grease the spool prior to inserting it into the sleeve. If the sleeve is removed from
the body, reinsertion must be at the chamfered side. Grease the o-rings to slide the
sleeve into the valve body. Securely insert the retaining ring around the sleeve. When
reinserting the pilot valve, push both plungers (located inside the intermediate bracket)
out of the path of the pilot valve spool ends to avoid damage.
PiloT VAlVe AcTUATor
Bushings for the pilot valve actuators are held in the inner chambers wth
retaining rings. An o-ring is behind each bushing. If the plunger has any sideways
motion check o-rings and bushings for deterioration/wear. The plunger may be removed for
inspection or replacement. First remove the air distribution valve body and the pilot valve
body from the pump. The plungers can be located by looking into the intermediate. It may
be necessary to use a fine piece of wire to pull them out. The bushing can be removed
from the inner chamber by removing the outer chamber assembly. Replace the bushings
if pins have bent (see Figure 9 and Figure 10).
fillinG of DriVer cHAMBer WiTH liqUiD
The driver chambers are filled at the factory with distilled water.
If you need to substitute another liquid to prevent system contamination, first consult
the factory for chemical compatibility with pump construction.
Follow the steps listed below to replace the liquid in the pump after disassembly or
liquid loss:
1. Filling is accomplished through the pipe plugs at the top of the liquid chamber.
Drain ports are at the bottom of the liquid chamber.
2. After the driver fluid has been emptied from the pump, the driver diaphragms will
naturally come to center.
3. Remove the entire manifold assembly exposing the ports in the outer diaphragm
chambers.
4. Fill either side with 722 MI. or 24.6 fluid oz. by volume with the driver liquid. It is
imperative that the driver liquid chambers be filled with the correct amount of driver liquid
as too little or too much will cause premature diaphragm failure and erratic pumping.
5. After filling with the proper amount of liquid, if the liquid does not come to the top
of the fill hole, pressure should be applied to the PTFE diaphragm with a blunt tool
through the material flow port in the outer chamber until the liquid comes to the top. If
the main air valve body and pilot valve are removed, the diaphragm rod will be visible in
the intermediate bracket. The hole in the diaphragm rod will assist manual movement.
Use a long taper punch to move the diaphragm rod.
6. When the driver fluid rises to the top of the fill plug hole, apply pipe dope to the pipe
plug, and thread it into the chamber plug hole. (Do not use PTFE tape.) Keep pressure
on the PTFE diaphragm until the pipe plug is tight to prevent air from drawing back into
the chamber.
7. Repeat the filling procedure for opposite side.
TroUBleSHooTinG
1. Pump will not cycle
A. Check to make sure the unit has enough pressure to operate and that the air inlet
valve is open.
B. Check the discharge line to insure that the discharge line is neither closed nor
blocked.