ISOV Failsafe Valves are found on offshore cranes as well as on Oil and Gas installations whereby the valve has to close whenever electric power is lost.This version requires Oil or Air pressure to guarantee its functionality.

The Failsafe version Model F works in the following way:

ISOV has to be opened by rotating the Hexagon as shown. While holding the Hexagon in th eopen position, the pushbutton (2) has to be pressed.

At this stage the rotating Hexagon can be released provided the Push button (2) is pressed.
To hold the open position of the valve the locking switch has to be pressed and release the push button. After this procedure Oil or air pressure will take over the push button function which means that the valve will be latched in open position untill pressure is lost through the 2/3 way solenoid valve.

The 2/3 Valve is a normally closed valve (see diagram) which means that whenever electric power is lost, the 2/3 Way will close the port and starve ISOV of the required pressure to remain in the open position.