How is the valve moving about. Is the collar done up tight. Which valves do you have.
Collar was done up as tight as it would go. The pump was causing the valve to move around - at certain positions you could hear the air rushing out.
I think they are wiggle lifeline valves
Sound like there is a rear in the tape that movement in the valve lead to a leak. It probably not the valves fault.
@gillies started
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How is the valve moving about. Is the collar done up tight. Which valves do you have.