TM 55-203
Check passages for cleanliness and blow out if
8-15.
Shop Maintenance of AB Control Valve
necessary. Replace chokes in the same location from
which removed. The choke fittings for each portion are
a. General
described under the heading for that particular portion.
(1) The purpose of these instructions is to avoid
(11)
Replace all springs which show rust pits
unnecessary expense due to careless handling of the
or distortion, or which have a permanent set. A list of
parts. It is possible to dismantle or assemble all parts of
springs and a table of identification are presented under
the valve readily. If excessive force is required, make
the heading of that particular portion.
an investigation immediately as to the cause of the
(12)
When reassembling valve portions,
difficulty.
tighten cap screws and nuts sufficiently to prevent
(2) When dismantling the operating portions,
gasket leakage but not excessively to cause distortion of
exercise care to avoid distortion of belts, studs, nuts,
covers and gaskets.
and like items by using tools especially adapted for this
type of work. Similar care must be taken to avoid
b. Service Portion
mutilation or damage when dismantling the valves with
(1) Choke fittings. The service portion contains
respect to pistons, springs, gaskets, slide valves,
five choke fittings. Three of the five choke fittings are
graduating valves, and like items.
shown in figure 8-20. They govern the flow of air
(3) Completely dismantle the operating portions
through the ports in which they are located as follows:
and lay out the parts as illustrated in figures 8-20
(a) The choke located in the body under the
through 8-25. Wash all metal parts in approved solvent
cover controls the flow of air from the quickservice
that will dissolve oil and grease without abrasion.
portion to the atmosphere.
(4) Dip all gaskets and rubber seated valves in
(b) The choke located under the limiting
approved solvent to assist in the removal of greasy dirt
valve cover controls the flow of air in the quickservice
and immediately wipe dry after cleaning. Do not soak
passage between the slide valve and the limiting valve.
the parts in the cleaning fluid.
(c) The choke located in the cover controls
(5) Replace all gaskets which have broken or
the flow of air in the passage between the release
flattened beads or any that reveal cracks or cuts on
insuring valve and the slide valve exhaust in service lap
diaphragms or sealing surfaces. Remove and replace
position.
all "0" rings.
(d) The correct orifice size of each of the
(6) Brush serviceable gaskets with a soft bristle
above three chokes is 1/32-inch drill.
brush (such as a shoe brush) to remove any remaining
(e) Two chokes (not illustrated) which are
dirt and to give them a polish.
located in the service portion body, control the charging
(7) Check all piston bushings for shoulders,
of the auxiliary reservoir. The correct orifice size is No.
grooving, cracks, pitting, hollow ring bearing surfaces,
57 drill (.043 inch).
and for taper and out-of-round with a dial indicator gage.
(2) Springs. The service portion has a total of
If necessary, true up the bushings on a precision
ten springs (nine coil and one leaf) which are identified
grinder, boring machine, or hand grinder before being
as follows:
gaged for ring size. After bushings are reconditioned,
(a) Release insuring valve spring ((8), fig 8-
wipe with an oily cloth and then wipe clean with a clean,
21) holds the valve on its seat until brake valve pressure
lint-free cloth. Finally, clean with an approved solvent to
rises 1 1/2 pounds above auxiliary reservoir pressure.
remove all traces of powdered bushing material before
(b) Diaphragm spring ((5), fig. 8-22) acts
reassembling the piston.
on the diaphragm of the quick-service limiting valve to
(8) When necessary to remove or replace the
hold the valve open until the force of the spring is
piston ring, use suitable tools to avoid damage to the
balanced by a brake cylinder pressure of 10 pounds.
groove.
(9) Splined socket choke plugs are now
(c) Piston spring
((12), fig 8-22)
supplied in place of the screwdriver slotted type. The
mounted in the stem resists movement of the piston and
splined socket type can be readily removed or applied
graduating valve after the feed grooves or charging
without damage to the choke plug or to the thread in the
ports are closed and just previous to opening of the
tapped hole.
preliminary quick-service port.
(10)
The size of chokes is important. The
choke fittings must be removed, cleaned, and inspected,
to insure that they are not restricted. Do not use
metallic tools for cleaning chokes, as their size and
shape must not be changed.
8-22
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