water pressure test result questons

heatingFun

I am installing a 16' section CI baseboard with a 90 degree turn on my first floor. It is in place and pipes go down to basement and ready to connect to the main line. I did water pressure test yesterday. I have purged all air out. The water pressure was 62psi and then I closed the water loop and separated it from water supply. Then I checked all joints and low points. No leakage was found. This morning the pressure is down to about 43psi. I checked all the connections and low points again. All are dry. I checked several times with my dry figures.

I am wondering why the pressure goes down without air inside? Is this normal? Does this test pass or fail? Is this because there are still some air inside?

icesailor

You can compress a gas but you can't compress a liquid. The difference in hydraulic compression pressure from 0# to 2000# can be one drop of fluid.

Temperature causes fluids ( and air) to expand and contract with rise and fall.

If you started with 62# yesterday, and this AM it is 43#, there is a very good chance that you don't have a leak. If it was filled with air alone and it dropped overnight to 43#, I would think there might be a very small leak in a cast iron section joint. If it was water only and it read 43#, I would say that there is no leak. If it is hydro-air, I would think it doesn't have a leak. There's a difference in how you test.

If a bicycle or car tire tube has a leak so small that you can't find it when submerged in water, it will still go absolutely flat in time.

Larry Weingarten

Hi: Let the ambient temp warm up to the temperature it was when you had 62 psi and see if the pressure increases. If so, you're likely good to go.

Yours, Larry

icesailor

It could be the opposite. The heat of compression of the air is expanded and gives the high set pressure, After time, the air cools to room temperature and contracts, lowering the pressure.

If the pressure stays at the lower pressure (43#?) it should mean that there are no leaks.

I always liked to test with straight air because the gas leak detector soap makes such big bubbles with so little air, you always know if it is leaking. If you get a big pile of mini/micro bubbles, you have a leak. If you have a giant bubble, you have a leak. If you have no bubbles, and the pressure is holding for an hour or more, you almost never have a leak.

j a_2

If your concerned just do a hydrostatic test...

icesailor

He has to be doing a "Hydrostatic test" because you can't pressurize the water without a head of air above it to compress. The more water/less air, the less accurate the test.

j a_2

Agreed….But i like to use a true hydrostatic tester…Used it all the time, on my plumbing and heating systems as well when I was an aircraft mechanic for major airlines testing hydraulic systems at 3000 psi...

j a_2

Funny thing is , there is allowable leakage on airplane hydraulic systems….

icesailor

In that case, the hydraulic tester would be using a by-pass that you can set the test pressure and the pump isn't going to blow the seals. You have to be able to maintain test pressure because if you can't, turning off the pump will cause the pressure to drop. Maybe to zero.

What happens when you get a hydraulic in a cylinder where it fills up with water or any liquid?

It either shatters the piston or bends/breaks the crankshaft. Not so with a air/fuel mixture. It just compresses it.

j a_2

In the plumbing world a hydrostatic pressure tester is normally a hand pump……Pump it up to the pressure you select, shut it of and check for leakage….Ice thats exactly why we had to remove the 6 o’clock spark plug on rotary engines in the cold mornings to prevent piston failure. All the oil would drain down and fill the lower jug, Master Sargent not very happy that morning….

RobG

Why not just test it with nitrogen if it is that important? Nitrogen is pretty inert.

Rob

j a_2

Agree what ever it takes,