The present invention is related to improved railroad car brake control valves and particularly to such improvements as relate to the adverse effects of vibration on piston valves and the like.
Railroad car brake control valves, such as ABD, ABDW and ABDX valves, presently employ piston operated valves comprising a piston member that operates in a bushed bore and a slide valve member that is carried by the piston member for controlling the pneumatic porting between the slide valve face and the mating face of a slide valve seat formed in the bushing. The slide valve/seat interface requires a very close, lapped-fit. A special lubricant is provided to assure controlled, low friction movement of the slide valve and piston. Diaphragm operated pistons are employed, and a close fit is also provided between the piston member guides and the generally cylindrical piston bush in order to support and guide the piston member in the bushing bore.
With the trend toward light-weight railroad cars, such as aluminum coal hopper cars, for example, relatively severe vibration can occur when such light-weight cars are operated under less than ideal dynamic conditions. Wheel surface irregularities including out-of-roundness, worn truck components, and rail conditions are believed to contribute to such dynamic operating conditions that result in severe vibration of the brake control valve on the car.
Under conditions in which severe vibration is encountered, vibration can be transmitted to the piston member. Presently, the piston member employed in the industry standard ABD, ABDW, and ABDX type brake control valves is made of die cast aluminum, while the bushing in which the piston member operates is brass. Such high levels of vibration as are sufficient to induce vibration of the piston member can cause excessive wear of the piston member guide due to progressive abrasion. Such abrasive wear of the aluminum piston member has been found to cause general contamination of the piston and slide valve with a fine, oxidized aluminum powder resulting from the accumulation of particulates of aluminum formed by the abrasion of the piston guides. This residue tends to absorb the slide valve lubricant which also increases slide valve friction and causes high piston operating pressure differentials and consequent erratic and unacceptable behavior of the aforementioned control valves.