Hi Simon, thanks for the post. I'm familiar with the Zodiac valves and have changed them before - no issues there - as you say the inner valves generally leak a small amount and the outer cap is the main seal - these were all fitted 100% properly and not leaking.
Obviously I double checked this after the first time out yesterday but as per post above the same thing happened second time out.
I've got an accurate guage, details here:
Adapting a pressure gauge for a SIB...
I've had my ear all round it in a silent garage yesterday to listen for hissing and absolutely nothing.
As a comparison the keel has a small leak (always has - you can hear it and see it bubbling) but even with the obvious leaking if I pump that up to say 3.5 psi it will still be 3 psi two days later.
This morning (having left it for 12 hours with just under 4 psi all round the three chambers are still showing a little less (3.75 psi or so) but all consistently including the port tube so I put that down to changes in atmospheric pressure or just the slight loss through the valves. After 30 mins at sea the starboard tube yesterday would have been down to 1.5 psi...