Air Components Used On Air-Over-Hydraulic Panels
Emergency Valve
EE Relay Emergency Valve A71891
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This valve controls pressure to the service brake pressure cluster on
type A/HM-HRC and A/HM-ERC systems supplied after September, 1978. It
applies pressure from the right half of the horizontal reservoir.
Whenever emergency port is pressurized above 50 psi, reservoir port R
is poised for application to delivery port D at whatever pressure is
applied to service port S. Without pressure at the service port
*, no pressure is applied to the
delivery port. Whenever emergency port pressure drops below 40 psi, pressure at the reservoir port is applied to the delivery port. Hence the valve applies pressure to the service brake pressure cluster in "emergencies". |
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| * Service port is not used on A/HM-HRC systems and must always be open to atmosphere. | |
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SYSTEM IDLE In the idle condition, emergency port pressure is off, reservoir port is open to delivery port. Service brake pressure cluster is applied if reservoir pressure is available. The check valve has no function and is closed permanently. With no emergency pressure, the emergency piston and valve cartridge is held in by spring force and the exhaust poppet closes service port while the inlet poppet opens a passage to the relay piston. Pressure on the relay piston forces it down against spring force, sealing the inlet-exhaust poppet and opening reservoir port to delivery port. SYSTEM NORMAL When emergency port is pressurized, 65-80 psi compressor pressure forces the emergency piston and valve out against spring force, pulling the exhaust poppet open and the inlet poppet closed. With no pressure at the service port, the return spring forces the relay piston up, allowing relay inlet-exhaust poppet to seal reservoir port and open delivery port to exhaust port. Service pressure cluster is released. SERVICE STOP (AHM-ERC Systems only) When service port is pressurized, pressure strokes the relay piston against spring force. The piston picks up the relay inlet-exhaust poppet valve, first closing the exhaust passage and then unseating the poppet to open reservoir port to delivery port. When the force on the relay piston balances opposing spring forces, the piston is forced to lap, permitting the spring loaded relay inlet-exhaust poppet to close while holding the exhaust passage sealed. The valve remains poised in this "hold" position, relaying delivery port pressure equal to service port pressure. EMERGENCY STOP Reduction of emergency port pressure below 40 psi triggers the valve to apply reservoir pressure, as described in SYSTEM IDLE section above. |
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SERVICING THE EE RELAY EMERGENCY VALVE
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The valve should be replaced or overhauled using both seal and maintenance kit
should any abnormal symptoms occur. |
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During the overhaul the unit should be cleaned to remove any accumulation of
foreign matter in the valve passage. Coat all seats and bearing surfaces with
a thin coat of Dow Corning 33 medium consistency grease. |
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SERVICE PARTS INFORMATION
EMERGENCY VALVE SECTION
RELAY VALVE SECTION
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