Self-lapping type control valve device

摘要

In a self-lapping type control valve device, a check valve is provided by means of a seal at the interface of the control piston diaphragm and a recess in which the diaphragm is connected to the valve body, the seal being effective to isolate a control chamber on one side of the control piston from a constant pressure chamber on the opposite side when the control piston is actuated in response to a reduction in the control chamber fluid pressure to initiate a brake application. This seal is displaced from a ridge at the opening of the recess with which the diaphragm is also engageable when actuation of the control piston occurs in response to a relatively large reduction of the control chamber pressure. The point of engagement of the diaphragm with the ridge defines a pressure area of the diaphragm subject to the control chamber/constant pressure chamber differential that is less than the pressure area of the diaphragm when the diaphragm is disengaged from the ridge due to a lesser pressure differential being effective to actuate the control piston. In so varying the effective pressure area of the diaphragm, the integrity of the seal effect of the check valve is assured at low as well as high brake levels.