Brake cylinder maintaining valve

A protection valve comprising:

• a main body having interior chambers with a piston disposed in the interior chambers of the main body and a bushing coupled with the piston in the interior chambers of the main body, the bushing having a venting passageway;
• a first diaphragm coupled with the piston between a brake cylinder chamber of the interior chambers of the main body and the bushing, the brake cylinder chamber configured to be fluidly coupled with a brake cylinder of a brake system, the first diaphragm defining an exhaust chamber of the interior chambers of the main body between the first diaphragm and the bushing, the exhaust chamber fluidly coupled with an exhaust line of the brake system;
• and
• a second diaphragm coupled with the piston between a reservoir chamber of the interior chambers of the main body and the bushing, the second diaphragm defining a brake pipe chamber of the interior chambers of the main body between the bushing and the second diaphragm, the reservoir chamber configured to be fluidly coupled with an emergency reservoir of the brake system, the brake pipe chamber configured to be fluidly coupled with a brake pipe of the brake system,
• wherein the piston and the bushing are configured to move toward a venting position with the venting passageway in the bushing fluidly coupling the brake cylinder of the brake system with the exhaust line of the brake system while a pressure of a fluid in the brake cylinder chamber is at least a threshold pressure,
• wherein the piston and the bushing are configured to move toward a non-venting position with the venting passageway in the bushing not fluidly coupling the brake cylinder of the brake system with the exhaust line of the brake system while the pressure of the fluid in the brake cylinder chamber is smaller than the threshold pressure.