SANDPIPER ST25 - Manual (Page 9)

st1dl5sm-rev0614 Models ST1 & ST25 Page 7
MODELS WITH 1" SUCTION/DISCHARGE OR LARGER, AND
METAL CENTER SECTIONS
The main air valve sleeve and spool set is located in the valve body mounted on the
pump with four hex head capscrews. The valve body assembly is removed from the
pump by removing these four hex head capscrews.
With the valve body assembly off the pump, access to the sleeve and spool set is
made by removing four hex head capscrews (each end) on the end caps of the valve
body assembly. With the end caps removed, slide the spool back and forth in the sleeve.
The spool is closely sized to the sleeve and must move freely to allow for proper pump
operation. An accumulation of oil, dirt or other contaminants from the pump’s air sup-
ply, or from a failed diaphragm, may prevent the spool from moving freely. This can
cause the spool to stick in a position that prevents the pump from operating. If this is
the case, the sleeve and spool set should be removed from the valve body for cleaning
and further inspection.
Remove the spool from the sleeve. Using an arbor press or bench vise (with an
improvised mandrel), press the sleeve from the valve body. Take care not to damage
the sleeve. At this point, inspect the o-rings on the sleeve for nicks, tears or abrasions.
Damage of this sort could happen during assembly or servicing. A sheared or cut o-
ring can allow the pump’s compressed air supply to leak or bypass within the air valve
assembly, causing the pump to leak compressed air from the pump air exhaust or not
cycle properly. This is most noticeable at pump dead head or high discharge pressure
conditions. Replace any of these o-rings as required or set up a routine, preventive
maintenance schedule to do so on a regular basis. This practice should include clean-
ing the spool and sleeve components with a safety solvent or equivalent, inspecting for
signs of wear or damage, and replacing worn components.
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,
gasket and bumper on the valve body. Using the arbor press or bench vise that was used
in disassembly, press the sleeve back into the valve body. You may have to clean the
surfaces of the valve body where the end caps mount. Material may remain from the old
gasket. Old material not cleaned from this area may cause air leakage after reassembly.
Take care that the bumper stays in place allowing the sleeve to press in all the way.
Re-install the spool, keeping the counter-bored end toward you, and install the spring
and the opposite end cap, gasket and bumper 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.
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).