Device for sensing pressure and governing the operation of safety valves

Claim 1

A safety valve system for a pressure vessel comprising in combination: a safety valve mounted on said vessel and including: a valve member engageable with a seat to close said vessel and openable to relieve pressure therein, a piston rod connected to said valve member, a valve piston connected with said piston rod, and a main cylinder receiving said valve piston and pressurizable to bias said valve piston in a direction maintaining said vessel closed; a pressure-sensing and valve controlling device spaced from said safety valve and from said vessel, said device comprising: a control-valve body spaced from said vessel and from said safety valve, a first chamber formed in said body and connectible to said vessel and to said main cylinder, said first chamber being provided with a first control valve adapted to close communication between said first chamber and said main cylinder, a second chamber formed in said body, connected to the atmosphere and to both said first chamber and said main cylinder at a connection in said body, said second chamber being provided with a second control valve adapted to close communication between said first chamber and main cylinder on the one hand and the atmosphere on the other hand, respective control rods positioned to act upon said control valves, respective control pistons operatively connected to said control valves, respective control cylinders receiving said control pistons and connectible to said vessel for pressurization thereby to bias said control piston in directions in which said control pistons maintain said first control valve closed and open said second control valve, and respective springs acting upon said control rods so that below a given pressure value in said vessel said first control valve is open to connect said first chamber to said main cylinder while said second control valve is closed and above a given pressure value in said vessel said first control valve is closed while said control valve is opened to vent said main cylinder to the atmosphere through said second chamber; and respective conduits connecting: said main cylinder to said chambers at said connection, said control cylinders to said vessel, and said vessel to said first chamber.