There are few moving parts in the motor and pump.
CAUTION
(See figures 9-7 and 9-8.) They include the piston, the
Ensure that recharging and servicing connections
two relief valves, and the spool. Of these components,
are free of dirt and other contaminants.
the relief valves seldom fail. The most frequent failures
occur in the O-rings. There are several O-rings in the
pump and motor, and that means there are lots of places
where leaks can occur. Disassembly and repair of the
5. Firmly attach the recharging hose to the
pump and motor is covered in depth in
recharge connection (12), and open the recharge
AG-750AO-OMM-000, and you should consult that
valve (9).
publication for detailed repair procedures. Our
NOTE: The pressure regulator on the recharging
discussion here will focus on replacing O-rings.
unit should be set to 3,500 psi.
When removing O-rings, use proper O-ring
6. Open the servicing valve of the recharging unit.
removal tools and techniques. If you fail to do so, you
When all cylinder pressure gauges (3) indicate
may cause more damage than the original problem. If
3,500 psi, close the recharge valve (9), the
you use improper techniques to remove O-rings, it
can cause scrapes and gouges where O-rings come
manifold by-pass valve (6), and all six lever
into contact with metal surfaces. These blemishes
control valves (4 and 5).
may then cause cuts, nicks, or scrapes in the O-rings
7. Close the servicing valve of the recharging unit,
themselves. Any such damage to the O-rings or the
metal surfaces they contact can cause incomplete
and slowly disconnect the recharging hose to
seals. NAVAIR 01-1A-17 gives detailed instructions
b l e e d o ff p r e s s u r e b e f o r e r e m ov i n g t h e
o n h ow t o m a ke p r o p e r O - r i n g r e m ova l a n d
connection completely.
installation tools.
Maintenance
During installation, identify each O-ring by part
number. Do not rely on physical appearance because
Some of the more common repair procedures for
many O-rings look alike; however, they differ in size
the A/M26U-4 nitrogen servicing unit are covered
and the material used in construction. While installing
here. This discussion is for training and familiarization
O-rings, make sure they are not twisted, installed
purposes only. For actual maintenance of this unit, use
inside out, or nicked. Backup rings are just as
AG-750AO-OMM-000, Operation and Maintenance
important as O-rings, as they support and hold the
I n s t r u c t i o n s w i t h I l l u s t ra t e d Pa r t s B re a k d o w n
O-rings in place. Make sure they are installed
(Intermediate and Depot), Nitrogen Servicing Unit,
correctly. (See NAVAIR 01-1A 17 for more details on
A/M26U-4, and AG-750AO-MRC-010, Periodic
backup rings.)
M a i n t e n a n c e R e q u i re m e n t s M a n u a l , N i t ro g e n
While the pump and motor assembly is
Servicing Unit, A/M26U-4.
disassembled, you should make a complete inspection
NOTE: When installing pipe-threaded fittings,
of all surfaces, not only for scrapes and gouges but for
antiseize tape (polytetrafluoroethylene) is used to
cracks that could cause leaking. After repairs are made,
prevent seizure of tapered threads. Do not however, use
take care in reassembling the pump and motor
antiseize tape on fittings with flared or cone-shaped
assembly. Be alert for visible signs of shaved or cut
ends. When used, antiseize tape must not extend
O-ring pieces. If you see such signs, remove the
beyond the first three threads.
component and reinstall a new O-ring. After the pump
and motor assembly is reassembled and reinstalled on
M OT O R A N D P U M P . -- A s p r ev i o u s l y
the nitrogen servicing unit, pressure-check the unit for
mentioned, two different motor and pump assemblies
leaks and proper pressure output of 3,500 psi.
are used on the A/M26U-4. Different repair kits are
available for both types of motor and pump assemblies.
PRESSURE REGULATOR.--The pressure
Five kits are available for repairing one of the
regulator is one of the few components on the nitrogen
assemblies. You can also order individual O-rings and
servicing unit that is considered repairable. As
other parts, but you will normally use one of the repair
previously mentioned, two types of regulators are
kits. Before you order a kit or other parts, check the part
available for use with the A/M26U-4. The most
number of the motor and pump assembly you are
common problem with the older type pressure
working on.
regulator is a stripped adjusting knob due to improper
9-14
