SANDPIPER MP04D - Manual (Page 2)

Model MP04D Design Level 3 Page 2 520-136-000 10/02
AIR SUPPLY
Air supply pressures cannot exceed 125 psi (8.61 bar). Connect the pump air inlet
(see Figure 1) to an air supply of sufficient capacity and pressure required for desired
performance. When the air line is solid piping, use a short length of flexible hose (not
less than 3/4" [19mm] in diameter) between pump and piping to eliminate strain to pipes.
AIR INLET & PRIMING
For start-up, open an air valve approximately 1/2" to 3/4" turn. After the unit primes,
an air valve can be opened to increase flow as desired. If opening the valve increases
cycling rate, but does not increase flow rate, cavitation has occurred, and the valve
should be closed slightly.
For the most efficient use of compressed air and the longest diaphragm life, throttle
the air inlet to the lowest cycling rate that does not reduce flow.
A NOTE ABOUT AIR VALVE LUBRICATION
The MARATHON pump’s pilot valve and main air valve assemblies are designed to
operate WITHOUT lubrication. This is the preferred mode of operation. There may be
instances of personal preference, or poor quality air supplies when lubrication of the
compressed air supply is required. The pump air system will operate with properly
lubricated compressed air supplies. Proper lubrication of the compressed air supply
would entail the use of an air line lubricator (available from MARATHON) set to deliver
one drop of 10 wt., non-detergent oil for every 20 SCFM of air the pump consumed at its
point of operation. Consult the pump’s published Performance Curve to determine this.
It is important to remember to inspect the sleeve and spool set routinely. It should
move back and forth freely. This is most important when the air supply is lubricated. If a
lubricator is used, oil accumulation will, over time, collect any debris from the compressed
air. This can prevent the pump from operating properly.
Water in the compressed air supply can create problems such as icing or freezing of
the exhaust air causing the pump to cycle erratically, or stop operating. This can be
addressed by using a point of use air dryer (available from MARATHON) to supplement
a plant’s air drying equipment. This device will remove excess water from the
compressed air supply and alleviate the icing or freezing problem.
EXTERNALLY SERVICEABLE AIR
DISTRIBUTION SYSTEM
Please refer to the exploded view drawing and parts list in the Service Manual
supplied with your pump. If you need replacement or additional copies, contact your local
MARATHON Distributor, or the MARATHON factory Literature Department at the
number shown on page 1. To receive the correct manual, you must specify the MODEL
and TYPE information found on the name plate of the pump.
MODELS WITH 1" SUCTION/DISCHARGE OR LARGER,
AND NON-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 a retaining ring (each end) securing the end cap on 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 supply,
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
WARNING
The weight of the air supply line end
of the filter must be supported by
some means other than the air valve
cap. Failure to provide support may
result in damage to the pump.
Fig. 2 Exhaust muffler
Fig. 3 Filling the driver chamber
Fig. 4 Purge air in pump by moving
diaphragm rod.
DANGER
Before doing any maintenance on
the pump, be certain all pressure is
completely vented from the pump,
suction, discharge, piping, and all
other openings and connections.
Be certain the air supply is locked
out or made non-operational, so
that it cannot be started while work
is being done on the pump. Be
certain that approved eye protec-
tion and protective clothing are
worn at all times in the vicinity of
the pump. Failure to follow these
recommendations may result in
serious injury or death.