Pressure-actuated normally open fluid valve

A method of converting a normally closed electric solenoid valve to a non-electrically operated normally open valve, comprising providing said solenoid valve including a flow path through a valve seat, a housing extending from said valve seat, and a plunger normally spring-biased into valve-closing contact with said valve seat but retractable into a cavity in said housing by energizing a solenoid coil to open said valve, and comprising the steps of:

• a) removing said spring-biased plunger;
• b) modifying said housing to allow the selective introduction of a pressure medium into said cavity;
• c) sealing closing off said cavity from said flow path with a diaphragm sufficiently flexible to normally be pushed off said valve seat by the pressure of a fluid flowing in said flow path;
• and
• d) selectively introducing a pressure medium into said cavity so as to bias said diaphragm into contact with said valve seat when it is desired to close the valve.