The puncture valve consists of a piston which communicates with the control air system of the engine. In the event of actuation of the shutdown system, and when ‘STOP’ is activated, compressed air causes the piston with pin to be pressed downward and ‘puncture’ the oil flow to the fuel valve.
As long as the puncture valve is activated, the fuel oil is returned through a pipe to the pump housing, and no injection takes place. I have also added a few more comments and attached a file to further explain the function(s) of the puncture valve.
MAN B&W reversing: Reversal of the fuel pump follower only takes place while the engine is rotating. If the engine has been stopped from running ahead and started astern, the fuel pump follower will move across as the engine starts to rotate and before fuel is admitted by venting the fuel pump via the “puncture” valve.
WHAT SHOULD I DO IF AN AIR START VALVE STICKS OPEN WHILE MANOEUVRING:
The fuel pump of the affected unit should be “lifted” (fuel rack zeroed, puncture valve operated or whatever)…
