US Patent 7857398 Lock-out for empty load device

The present empty/load device includes an inlet to receive a brake signal, an outlet for a brake device, load sensing element, a change over valve responsive to the load sensing element to proportion the pressure at the inlet and the outlet when empty is sensed by the load sensing element, a differential pressure element connecting the load sensing element and the change over valve, and a lock-out mechanism to prevent proportioning of the inlet pressure to the outlet when activated. The lock-out mechanism includes a lock-out valve, in a lock-out position, pneumatically preventing proportioning of the inlet pressure to the outlet. A first spring biases the lock-out valve from the lock-out position. A detent engages the lock-out valve and holding the lock-out valve in the lock-out position. The lock-out valve may be connected in parallel to the change over valve with respect to the inlet and the outlet. Alternatively, the lock-out valve may be connected in parallel to the both sides of the differential pressure element.