US Patent 7469706 Adjustable pressure double latching valve

Methods and devices for maintaining a minimum pressure of calibration gas, such as in an emission testing system or a similar arrangement, using a double latching valve (DLV). The DLV comprises a body having specific internal passages; a two-way normally closed (blocked) shut-off valve; an enlarged low pressure, sensitive air pilot acting upon the two-way valve; an adjustable sequencing latch valve integrated into the supply latch circuit; and a defined orifice incorporated into the supply latch circuit.