FORCES AT WORK IN A VALVE – FOR VALVE BUILDERS

THIS IS A DESCRIPTION OF THE FORCES ACTING ON A VALVE.
IT WILL BE HARD TO UNDERSTAND, UNLESS YOU DESIGN VALVES.

HOW A VALVE WORKS:

THE HAMMER STRIKES THE FRONT SIDE OF THE BREACH (OPENING FORCE 1)

FORCE IS TRANSMITTED THROUGH THE BREACH TO THE TOPHAT
PUSHING THE VALVE SEAT OPEN.

FORCE FROM THE HAMMER IS OPPOSED BY THE PRESSURE IN
THE TANK TIMES THE AREA OF THE VALVE ORIFICE (CLOSING FORCE 1)

THE VALVE RETURN SPRING EXERTS A CLOSING FORCE ON THE VALVE (CLOSING FORCE 2)

AIR BEGINS TO FLOW THROUGH THE VALVE STEM

PRESSURE BUILDS UP BETWEEN THE VALVE AND THE PELLET IN THE BREACH

THE PRESSURE IN THE BREACH ACTS ON THE AREA OF THE VALVE STEM
TENDING TO KEEP THE VALVE OPEN (OPENING FORCE 2)

THE PELLET BEGINS TO MOVE DOWN THE BARREL

AIR RUSHING THROUGH THE HOLLOW VALVE STEM CREATES A DIFFERENTIAL PRESSURE
FROM ONE END OF THE STEM TO THE OTHER. THIS DIFFERENTIAL PRESSURE ACTS
ON THE CROSS SECTIONAL AREA OF THE VALVE STEM, CAUSING A CLOSING FORCE (CLOSING FORCE 3).

BEFORE FIREING, OPENING FORCE 2 DOES NOT EXIST
WHILE THE VALVE IS OPEN AND FLOWING AIR, OPENING FORCE 2 IS HIGH
AFTER THE PELLET LEAVES THE BARREL, OPENING FORCE 2 DECREASES BECAUSE THE PELLET NO LONGER HOLDS BACK PRESSURE IN THE BREACH.

BEFORE FIREING, CLOSING FORCE 3 DOES NOT EXIST
WHILE THE VALVE IS OPEN AND FLOWING AIR, CLOSING 3 FORCE IS MODERATE
AFTER THE PELLET LEAVES THE BARREL, CLOSING FORCE 3 IS HIGH

CLOSING FORCE 1 VARIES WITH TANK PRESSURE

CLOSING FORCE 2 (THE RETURN SPRING), VARIES WITH HOW FAR THE VALVE IS OPEN

OPENING FORCE 1 (THE HAMMER FORCE), VARIES WITH THE POWER WHEEL SETTING, THE WEIGHT OF THE HAMMER, THE HAMMER STROKE LENGTH
THE MASS OF THE BREACH, AND THE SPRING CHARACTERISTICS.

OPENING FORCE 2 IS BECAUSE THE VALVE STEM EXTENDS INTO THE BREACH AND FORMS A LITTLE AIR CYLINDER.
THE PRESSURE IN THE BREACH THAT PUSHES THE PELLET DOWN THE BARREL ACTS ON THIS LITTLE AIR CYLINDER TENDING TO PUSH THE
VALVE STEM BACK (THUS OPENING THE VALVE). THE BREACH CAN NOT GO FORWARD BECAUSE OF THE LOCKING KNOB.

I HAVE BUILT VALVES FOR LARGE BORE BARRELS. THIS REQUIRES A LARGE VALVE STEM DIAMETER, MAKING OPENING FORCE 2 DOMINATE,
HOLDING THE VALVE OPEN TILL THE BULLET EXITS THE BARREL.

AS YOU CAN SEE CORRECT VALVE OPERATION IS DEPENDANT ON MANY VARIABLES.

ABOUT THE BEST WAY TO DESIGN A VALVE IS BY TRIAL AND ERROR.

MARK