How to fix sack truck flat tyre?

Drammen

I have a sack truck with pneumatic tyres. 
recently I repaired a puncture in the tube, which I checked in a bucket of water and all looked good, no leaks. 
After I put the tube back in the tyre and pumped it up, it went flat immediately, within 10 seconds. 
 So I took it out and checked it again, no leaks. I even stood on the tube, wiggled the valve, pushed and pulled the tube. No leaks. 
Put it back in the tyre and it goes down working 10 seconds. 
How is this possible?

I even tried the tube with the rim only, no deflation. 
Tried also the tube inside the tyre only (no rim). No deflation. 
I am now very frustrated.

How is it possible that the tube is fine until I put the whole thing back together (tube, tyre, rim), and then it deflates?

Thanks

EricL

Hello @Drammen 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your pneumatic tyre.

Since you've done all the checks for leaks the only possible point where the leak is occurring is the patch itself. When the tube is inflated outside the tyre the patch stretches and settles flat on the surface of the tube. But once inside the tyre the rough interior surface of the tire stretches and pulls the patch open allowing air to go out.

I propose removing the current patch and re-patching it with a new one. Let the patch properly settle and cool off before inflating the tube. Do another water bucket test, but this time do it deliberately in a slow fashion. Examine every millimetre of its surface to make sure you don't miss anything. Once you've secured the tube install it back into the tyre and test again.

Let me call on our experienced members @Dave-1 and @Nailbag for their recommendations.

If you need further assistance, please let us know.

Eric