STEP GP 3580329 - Caterpillar

INVERSION VALVE CROSS-SECTION (769 Truck 99F3741-UP, 768 Tractor 79S80-UP, 773 Truck 63G6710-UP and 772 Tractor 80S55-UP)Control air, at system pressure, will go around the valve stem to the valve face. Air pressure against the valve face overcomes spring force, moves the valve upward, seats the check valve and blocks the air flow between the supply and delivery ports.The inversion valve spring force will seat the check valve when control port air pressure drops to 45 psi (3.2 kg/cm2). Emergency system pressure reduces with each brake application. Normally, with the third brake application, the system pressure will fall to 45 psi (3.2 kg/cm2) or less, the inversion valve check valve will open and the brakes stay applied.Pressure Protection Valve
Pressure protection valves are used to protect the brake air system against complete pressure loss due to air leaks or component use. The valves will shutoff the supply to a part of the system at some pre-set value and will not re-open until the supply pressure rises to a level above the shutoff pressure.Supply air pressure at a predescribed level against the partially exposed valve face overcomes the spring force and unseats the valve. Air flows past the valve and out the delivery port to charge the circuit. Unseating the valve exposes more valve face and the valve will stay open until the system air pressure is below the pressure required to open the valve. The valve will stay closed until supply pressure builds up to the original opening pressure.
PRESSURE PROTECTION VALVE CROSS-SECTIONAll pressure protection valves in the brake air system, except the valve between the front emergency tank and the hand control valve supply port, open at an ascending supply pressure of 80 psi (5.6 kg/cm2) and close at a descending air pressure of 65 psi (4.6 kg/cm2). The pressure protection valve between the front emergency tank and the hand control valve supply port, opens at 75 psi (5.3 kg/cm2) and closes at 60 psi (4.2 kg/cm2).The opening and closing pressures are adjusted at the factory and need not be readjusted.Relay Valve
The relay valve supply port is connected to the emergency or standard air supply tanks. The valve spring holds the valve seated and blocks air flow to the delivery ports.Modulated control port air pressure forces the diaphragm down against its spring pressure. The depressed diaphragm assembly unseats the valve and supply air flows to the delivery ports. When delivery air pressure plus spring force exceeds the modulated control air pressure, the diaphragm is forced up closing the valve and blocking supply air from the delivery ports. Delivery air pressure is held at approximately the level of the modulated control air pressure.When the control air pressure is released by the foot valve, the diaphragm spring opens the exhaust port (hollow center of the valve) and delivery air exhausts to the atmosphere.
RELAY VALVE CROSS-SECTIONIn the standard brake system on earlier machines, each delivery port is connected directly to a rear brake cylinder air chamber. On earlier machines with the emergency brake