Air Components Used On Air-Over-Hydraulic Panels
Air Treadle Valve
Type FG Air Application Valves
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This valve meters application pressure from reservoir port to delivery port, in
proportion to operating force. Operating force for the treadle valve is applied
by foot. Operating force for the HRC hydraulic remote controlled valve is
applied by an integral hydraulic slave cylinder. The hydraulic slave cylinder
is operated from a remote industrial control cylinder in the cab. |
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How The Application Valve Works
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Controlling force applied against the spring retainer is transferred to the
metering spring which, in turn, strokes the reaction piston against its return
spring. During this stroke, the piston picks up a spring loaded inlet-exhaust
valve poppet. The exhaust port chamber is sealed off as the piston meets the
poppet, and the continuing stroke then depresses the poppet, permitting
compressed air to flow into the delivery port chamber. Braking pressure beneath
the reaction piston forces it to lap. The reaction piston, compressing the
metering spring to balance between forces, thus assumes a position which
permits its spring loaded poppet valve to seat and seal the inlet while holding
the exhaust closed. The unit now remains poised in holding position until a
change in controlling force unbalances it, either to admit increased air
pressure or to exhaust the system. |
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Normal operating sequences test the type FG application valve. Should an internal leak develop, it can be detected at the exhaust port and it must ont be confused with normal exhaust. A leak, while released, indicates the valve poppet is not sealing its inlet; while applied, the poppet is not sealing the exhaust. Nominal leakage (slow bubbling when covered with suds) has little consequence. Should pedal feel seem erratically light, then suddenly heavy and severe acting, the large O-ring on the reaction piston may be leaking. Air leaks around the mounting, while applied, also refer to the piston O-ring. The inlet-exhaust poppet valve can be inspected by removing the retaining ring and shield located in the exhaust port at the bottom of the valve. Guide seal friction tends to hold the parts assembled; however, the spring will gradually force the parts out. The reaction piston can be inspected by removing the spring retainer from the top of the valve body. On the treadle model, separate the body from the mounting flange by removing the three screws (3/8"-16x1" Flat Hd.). Pull the treadle fulcrum pin and lift off the treadle in order to reach one mounting screw. Should the operation of the valve become slow or hesitant after prolonged service, disassemble and clean the unit. A seal kit and maintenance kit includes all parts needed for complete overhaul. When re-assembling the valve, cover all bearing surfaces with a thin film of grease (Mobilplex No. 47, or equal). After re-assembly of the treadle valve, set screw (24) should be adjusted for minimum lash of the plunger (22) between roller (20) and retainer washer (4). No adjustment of the HRV valve is necessary. |
Parts Description
Service Replacement
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