US Patent 7971598 Valve in-line backflow control

A valving assembly, comprises elongated tubular body, a first annular diaphragm in the body, and a first annular seat in the body engaged by the first diaphragm when pressurized fluid flow passes through the body and through the first diaphragm to deflect the first diaphragm, a second annular diaphragm in the body, and a second annular seat in the body engaged by the second diaphragm when said pressurized flow passes through the body and second diaphragm to deflect the second diaphragm, a third seat in the body engaged by the first diaphragm to block reverse flow through the body, an escape port in the body to allow escape of the reverse flow, and a drain port in the body to allow drainage of such fluid in the body upstream of the first diaphragm during such reverse flow.