Inflatable deflation.

I have a 9ft inflatable that partly deflates overnight,then inflates somewhat in the morning.It is obviously due to the temparature change.The boat has always done this,but recently it does not re-inflate to the same degree.
I have carefully gone over it with washing up liquid and water searching for leaks,but found none.I have replaced the valves and checked them also.
Is this a normal thing that is to be expected?I use the boat on the canals,and after 15mins of putting it in the water[which is very cold]I need to top the pressure up.It stays up at that pressure all day.
The boat has a detachable transom.i.e.tubular stainless and timber.
Anybody have a similar problem?

 

Yes, everybody with an inflatable that has reinforced tube material is familiar with that. Only the cheap PVC boats where the tube can expand freely do not suffer from it.

The pressure increases/decreases with 0.36% for each degree C.

 

Thanks CDK,thats nice to know.Having a problem that I cant suss out really bugs me.

Have you any idea why it doesn't re-inflate to the same pressure the next day?Even though the temparature has gone up.Both tubes are effected equally.It has a blow up deck,which is not re-enforced,this stays inflated.I have fitted a removable ply deck over it.The air pressure and temperature here in the UK has been up and down drastically recently,and it has rained on it quite a lot.
Thanks for your reply.V

 

If it has the same sort of valves I have on my tender the valve design is such that some air is allowed to escape if the pressure exceeds the limit. It is not very accurate, but the manufacturer doesn't like a lot of ruptured returns within the warranty period.

You could look into that and see if adjustment is possible. Or you could make some sort of expansion chamber that you keep connected to the valve, something like a rubber appendix. Looks weird of course, but I'm sure it will work.
A perfect and invisible solution would be to pour some liquid in the tubes that has approximately the same vapor pressure as the air pressure you want to have in your boat. If the pressure rises, some of the vapor returns to its liquid state, reducing the volume. I never found the time to experiment, but probably the hydrocarbons in a contact cleaner or antistatic spray could have the right properties.

Repackaged as an "inflatable pressure equalizer" this surely is a business opportunity. As far as I know no such product is on the market at this time.

 

My understanding is that both the air and the fabric expand. If it doesn't come back, then it must have some type of leak.

 

The valves I bought were the same type that came with the boat,they do seem a bit frail looking.They were not expensive.
Great business idea,but not really my forte'
Bit worried about hanging appendages out of the boat,the wrong one might get tangled round the prop.
Thanks for your advice,it's much appreciated.V

 

Hi,I think another check with washing up liquid and water might be in order.
Maybe a thicker solution will bubble more.
Many thanks for your advice. V