Patent GB-1028034-A (GB)
Title: Fluid pressure relay valve assembly
Inventor: DOBRIKIN HAROLD LAURENCE
IPC: B60T15/20
Filed: 1962-10-23
Abstract: 1,028,034. Fluid pressure brakes. BERG AIRLECTRO PRODUCTS CO. Oct. 23, 1962, No. 40141/62. Heading F2F. In a fluid pressure relay valve assembly suitable for the purpose of communicating the brake operating cylinders of a road vehicle (for example a tractor-trailer combination) with a fluid pressure source or with the external atmosphere, a first piston and valve assembly 31, 34, 40 is adapted to control the flow of braking fluid from a suitable source to an outlet passage 53 to the chambers of the brake actuating cylinders and a second piston and valve assembly 7, 18 which admits the supply pressure to the first piston and valve assembly and to the connections of the reservoir only when the value of the supply pressure exceeds the reservoir pressure, there being a spring-loaded check valve 11 provided for this purpose. In the condition shown in Fig. 2 emergency pressure fluid is supplied through the connection 5 and if this pressure is below a certain predetermined amount, such as 55 p.s.i., only the ball valve 11 is opened to allow pressure fluid to enter the trailer tank or reservoir via connection 21. At the same time the pressure fluid flowing past the open ball valve 11 flows into the chamber C between pistons 31 and 34 to urge the piston 34 against the lower piston 40 and open a connection to the brake chambers via connection 53 so as to set the brakes whilst the charging operation is in progress. When the emergency pressure increases above the predetermined pressure level, the piston 7 is moved downwardly to the position shown in Fig. 3 wherein fluid from the emergency line continues to pass to the trailer tank or reservoir but ceases to pass to the brake chambers since opening of lower piston 18 of the second piston and valve assembly allows the lower piston 40 of the first valve assembly to rise and seal off the connection between chambers B and G thereby permitting fluid to flow from the brake chambers through transfer passage 30 to the exhaust connection 17. When the reservoir pressure has reached an adequate level the ball valve 11 will be closed and since the brake chambers are vented to atmosphere movement of the vehicle is permitted, the pressure in the reservoir now having reached a predetermined safe level. If the pressure in the emergency line falls below a predetermined level compressed air flows from the trailer reservoir via the central hole in the lower piston 18 of the second piston and valve assembly along transfer passage 30 to move the pistons 31 and 34 of the first piston and valve assembly apart to open the lower piston 40 and permit fluid under pressure from the reservoir to pass from the connection 20 past the open piston 40 to the brake chambers. Fig. 6 shows the position assumed when the brakes of the vehicle are operated through the application of normal service pressure. In this condition emergency fluid pressure above the predetermined level is effective to retain the piston 7 in the lowered position and passes the ball check valve 11 to bring the chamber B in communication through passages 10a and 20 with the emergency pressure entering through inlet 5 and, through passage 21, with the tank pressure of the vehicle. Upon application of service pressure entering through inlet 32, the piston 31 is caused to move downwardly so that the piston 34 is also moved downwardly mechanically to lower the piston 40 and unseat the valve annulus 49 from its valve seat 45 to place the chamber B in communication with chamber G and thus with the outlets 53 to the brake chambers of the vehicle to apply the brakes. Release of the service pressure above the piston 31 causes the lower piston 40 to be closed by the spring 54 and fluid from the brake chambers escapes via the central aperture 35 in the piston 34 and through the transfer passage 30 to exhaust to release the brakes.