Theoben Rapid Forum

I have a Mk1 fitted with a 400cc bottle. I recently had to change the old ball bearing style bottle valve for a best fittings one. The problem I have now is the bottle valve does not appear to open properly and is restricting the flow of air to the gun. If the bottle is empty I can screw the bottle down until the valve butts up to the bottle adapter but if the bottle is filled to 180 bar it will not screw all the way down to the bottle adapter. Has anyone experienced this before or have the guru's on here got a solution.

Sometimes you can back off the internal grub screw that the spring sits on.

IMO there's something not quite right with the dimensions of the pips, as if they cant over in the bore and stick under pressure.

One possible reason-  I think the spring is too short and stiff in comparison to older valves and alternatives.
OE/BSA/RAW/DrBob all have softer springs with more travel.

Maybe the spring and the seat grub position is  optimized for the slightly shorter travel of the BSA pushpin?

And .....even though the BF valve screw all the way in without air-pressure; that extra 0.5mm plus any difference in the bottle holder is enough to throw it all out.

The valve should not be screwed in tight under the spring,
Most of the force holding the valve shut is the air pressure inside the bottle, the spring is only to initially hold the valve closed when empty or seat it at the end of filling when the air pressure both sides of the valve are equal.

Rule of thumb, count the number of turns from when you first feel the grub-screw on the spring until it's tight & then back it off halfway.
a short heavy valve spring needs less 'preload' than a longer softer one.

Thanks for the replies guys.