| 摘要 |
A dual capacity empty/load changeover valve for a railway freight car in which a piston-operated check valve controls the supply of compressed air delivered from the auxilary reservoir to the brake cylinder via the car control valve. The check valve is connected to a balance piston having equal opposing pressure areas, one of which is subject to the air supplied to the brake cylinder under all conditions of car loading. The opposing pressure area of the balance piston is pressurized in a load condition and depressurized in an empty condition, thereby establishing a proportional mode of brake control during empty car braking. A proportioning spring acts on the balance piston to establish the brake cylinder pressure at which the check valve becomes operative to proportion the air supplied to the brake cylinder. In one embodiment of the invention, the proportional spring exerts a fixed force and in another embodiment, the proportioning spring exerts a variable force on the balance piston according to the empty car load weight, so as to vary the ratio at which the brake cylinder pressure is proportioned.
|
