Brake cylinder maintaining valve
A brake cylinder maintaining valve may include spool valves or poppet valves. When the pressure in the brake cylinder drops below its original set pressure, such a maintaining valve may feed brake pipe (BP) pressure through a choke to replenish and maintain brake cylinder (BC) pressure up to a certain point. If the leak is too great, such as when it exceeds the capacity of the choke, the brake cylinder pressure will not be maintained. Such a maintaining valve may be either integrated into the control valve, or it may be mounted remotely to the brake system. If mounted remotely, it may be connected by multiple ways, including through a conventional 4-port access plate.
1. A brake cylinder maintaining valve for maintaining brake cylinder pressure in freight car brake equipment, comprising:
a first valve including a diaphragm with a brake pipe pressure on an upper surface thereof and an auxiliary reservoir pressure on a lower surface thereof;
a first check valve coupled to said first valve and having auxiliary reserve and atmospheric pressures on opposing surfaces thereof;
a second valve including a diaphragm with a first brake cylinder pressure on an upper surface thereof and a second brake cylinder pressure on a lower surface thereof;
a second check valve coupled to said second valve and having the second brake cylinder pressure and the brake pipe pressure on opposing surfaces thereof; and
wherein the second check valve provides the brake pipe pressure through a choke to replenish the second brake cylinder pressure if the second brake cylinder pressure is below an original set pressure represented by the first brake cylinder pressure.
2. The brake cylinder maintaining valve according to claim 1 , wherein in a service lap position the first brake cylinder pressure is substantially equal to the second brake cylinder pressure.
3. The brake cylinder maintaining valve according to claim 2 , wherein said diaphragm of said second valve is adapted to move when the first brake cylinder pressure is less than the second brake cylinder pressure by a predetermined amount, thereby opening said first check valve and allowing the brake pipe pressure to replenish the second brake cylinder pressure to said original set pressure.
4. The brake cylinder maintaining valve according to claim 3 , wherein said predetermined amount comprises about 8 to 12 pounds per square inch (PSI).
5. The brake cylinder maintaining valve according to claim 4 , wherein said predetermined amount comprises about 8 pounds per square inch (PSI).
6. The brake cylinder maintaining valve according to claim 1 , wherein said original set pressure is charged from the second brake pipe pressure.
7. The brake cylinder maintaining valve according to claim 1 , wherein said original set pressure is charged through a supply valve.
8. The brake cylinder maintaining valve according to claim 1 , wherein said original set pressure is exhausted through an exhaust valve.
9. The brake cylinder maintaining valve according to claim 1 , wherein said diaphragm of said first valve is adapted to move when the brake pipe pressure is greater than the auxiliary reserve pressure, thereby opening said first check valve, exhausting the first brake cylinder pressure to atmosphere, and returning the brake cylinder maintaining valve to its charging lap position.