I have an 8" (20cm) irrigation pipe. The lid is secured with a threaded bolt through the center that screws into a bracket in the pipe. I need to detect leaks when the cap is not securely closed. The cap will be underwater and the water pressure can be upwards of 2 psi (25MPa).
I'm thinking a flow meter on the outside of the lid, but I need to detect leaks at any point on the seal.
Any ideas?
A flowmeter in the irrigation pipe comes to mind.
What about sound - a leak might make a sound ?
agrimes:
the water pressure can be upwards of 2 psi (25MPa).
25MPa = 250 bar is around 3600 psi
I use a paper napkin. touch it to the pipe, if it comes back dry, no leaks.
dave-in-nj:
I use a paper napkin. touch it to the pipe, if it comes back dry, no leaks.
You missed the part where he said the lid will be under water. 
Water inside and outside the pipe? Sounds like all you need is a better gasket.
You could use TWO flow meters, one either side of the valve, somewhere along the run - and the flow should balance if there are no leaks.
The pipe is an agricultural irrigation valve. It flood irrigates crops and is underwater for sometime after the water stops flowing.
The 2 psi pressure is correct, sorry about the math error. It should convert to approx 14kPa.
I've looked at flow meters, but I can't figure out how to detect flows on any part of the seal (over the whole circumference).
Perhaps a sleeve that surrounds the lid and the flow meter can see if water leaves the sleeve?
Thank you all for your suggestions.
I meant for the flow meters to be installed in the pipework not around the seal. This way you are monitoring the flow in the pipe out to the fields, both before and after the valve. If they don't match then the valve must be leaking.
DangerToMyself:
You missed the part where he said the lid will be under water.
I didn't say it would work for him, just that is what I use.
but, we are all just guessing. he has not given proper information.
a cap on a water pipe that is submerged.
what is the problem if it leaks ?
WHICH way is it leaking ?
what is the pressure ? 2 PSI or 3,500 PSI ? not that there is much difference.
how much of a leak.
how large is the surrounding tank ? say the lid is inside of a 10 gallon bucket and the water is leaking out of the seal. the water level in the bucket will rise. done deal.
what is the history of the leak ? if this has happened, once, in 1967, then who cares. if it happens hourly, then you need a new lid.
Ralph_S_Bacon:
I meant for the flow meters to be installed in the pipework not around the seal. This way you are monitoring the flow in the pipe out to the fields, both before and after the valve. If they don't match then the valve must be leaking.
got any sense of a flow meter for an 8 inch pipe that can resolve the difference of flows for a leak of a few GPH ?
