Diaphragm controlled air relief valve

Claim 1

An air relief valve for a pumping system, comprising: a valve casing having inlet and outlet ports connected by a through chamber; a valve seat on the walls of the through chamber and intermediate the inlet and outlet ports; a valve stem slidably received in a first bore in the valve casing on the upstream side of the valve seat, the valve stem extending through the region of the valve seat; a valve head on the end of the valve stem extending through the region of the valve seat, the valve head being adapted to have sealing engagement with the valve seat to close the through chamber; biasing means for urging the valve stem and valve head in the downstream direction to normally hold the valve head away from the valve seat; a flexible diaphragm secured to the valve casing and to the valve stem at a point intermediate the first bore and the valve head, the diaphragm dividing the through chamber into a first region communicating with the first bore only and a second region communicating with the inlet and outlet ports and extending across the valve seat; and the casing being provided with a second bore axially aligned with and communicating with the first bore but of greater diameter than the first bore, the end of the second bore opposite the first bore being closed, the valve stem extending into the second bore, and a piston being connected to the end of the valve stem within the second bore, the first region of the casing chamber and the bores being substantially filled with oil, sufficient clearance being provided between the valve stem and first bore and between the piston and the second bore to permit oil flow at a controlled rate.