Estimating rate of pipe leakage by measuring rate of pressure drop?

[fixitron]

I have a client with a drilled well, pumping to a pressure tank in the house. Coming off of the pressure tank is a separate line that supplies water to the barn (roughly 150 ft. away), using 1" black plastic water pipe. There is a water leak in the buried line somewhere between the house and barn. The line has ball valve shutoffs in the house, just before the line goes into the ground, and in the barn, shortly after it comes out of the ground. I have attached a 0-100 psi pressure gauge to the hose bibb located between the shutoff in the barn and another ball valve shutoff on the downstream side of the hose bibb, allowing me to isolate just the line between the house and barn and measure the pressure. With the pressure tank in the house at 50 psi, and the line open up to the second isolation valve in the barn (the one downstream of the hose bibb), I shut the isolation valve in the house and go to the barn and watch the pressure gauge. In about 5-6 minutes the pressure slowly drops to about 10 psi (and I stop watching it). The leak is not at the gauge or hose bibb. or the isolation valves.
What I would like to do is to estimate the rate of leakage. Knowing the diameter of the piping and length of piping, I can calculate the enclosed volume. I would think that there would be a way to correlate rate of pressure drop to rate of leakage, which would allow us to determine whether the leak is large enough to spend thousands of dollars to run a new line. Any thoughts?

 

[Jamesplumbing06]

Just because you asked for thoughts. Your wasting time. It can be figured out. Frodo , diehard or voleti might have access to the charts. But realistically it’s just a bunch of water and will run electric bill up for running pump, wear out pump, cause a bigger middle of night emergency, and finally but not likely a small depression in yard collecting water. You can get a mechanics probe and listen down ditch you think is the path. 150’ thru me would be a minimum machine job charge of $1300. Might take 4 hours start to finish.

 

[fixitron]

It is not a huge leak, and your estimate for ditching is good, but doesn't take into account having to go through the foundation and slab in both the house and the barn. We could tee off at the well, but we would still have to go through foundation of the barn and would also have to go underneath the driveway.
I know from experience that you cannot estimate the path that was taken for the line between house and barn. A mechanic's probe would be useless for a pipe buried in the ground, particularly for such a relatively small leak. I have had some success with a dowser, but not always (yes, I do believe in dowsing).

 

[wood4d]

150' 4 feet deep $1300 wow Did they bury a wire with the poly? That would help find it.

 

[Jamesplumbing06]

Yeah dowser works great. And here water lines are 18”. Most of the time they bubble. And yeah 2 foundations and a barn. U might get a $1500 if you buy me a Iowa hydrant for bard. 18” not real deep.

 

[Jamesplumbing06]

150' 4 feet deep $1300 wow Did they bury a wire with the poly? That would help find it.

Not 4’ deep. No. That’s a day and half at least. We 18” -22” depending on soil but try to stay at 20

 

[Jamesplumbing06]

When we go thru foundation slab it’s important to have the correct expensive tools. A 28” x 1.25” sds bit set at little angle 2” inside wall will come out house around 24”. Takes 5 minutes to drill. Release bit and push bit out with pipe. Tip keeps the pipe from catching and centers in hole while keeping pipe covered.

 

[fixitron]

The pipe must be 4 ft. deep here in Central Vermont, because the frost line goes at least that deep. The house sits on a knoll above the barn, which makes trenching a bit challenging on the steep bank to the house. The barn had a hydrant located several feet from an outside wall. I could hear the water running at the base of the hydrant, so we recently cut into the concrete slab, dug down and removed the very corroded hydrant. That area of the barn is now heated so we did not replace the hydrant but continued with straight pipe (wrapped with heat tape in case it is needed in the future). Having to remove and replace part of a wall to do that, along with other impediments, resulted in a cost of over $7,000. Since the buried pipe is plastic, we took the chance that there would not be another leak, but now we find that there is one. I can only guess at two scenarios. The first is that they used 100 ft. rolls of pipe and joined them with a galvanized fitting that is now corroded and starting to leak. The second is that frost heaving over the years has pushed a rock into the pipe which has started to cut into the pipe (the earth does move).
Again, the leak appears to be a slow one, , certainly not enough to cause problems such as a sink hole or over-exerting the well pump, especially if the water to the barn is turned off when not needed (which is not that often).
I have used SDS bits to get piping through foundations. I never thought about extensions and drilling at an angle (which I have often done through wood framing members).
Still looking for a way to estimate the leakage rate, but thanks for the thoughts.

 

[chiraldude]

To estimate the leak rate try the following:
Shut off the barn pipe.
Let the pump run up the pressure tank to full pressure.
Open a valve somewhere in the house and catch the water in a bucket.
Shut off the water when the pressure has dropped about 5psi then measure how much water is in the bucket.
Pump the pressure tank back up and open the barn valve.
Use a stopwatch to track how much time it takes to drop 5psi.
Now divide gallons/minute and you have your leak rate.

Not an exact measurement but should be close enough for your purpose.

 

[Jamesplumbing06]

The pipe must be 4 ft. deep here in Central Vermont, because the frost line goes at least that deep. The house sits on a knoll above the barn, which makes trenching a bit challenging on the steep bank to the house. The barn had a hydrant located several feet from an outside wall. I could hear the water running at the base of the hydrant, so we recently cut into the concrete slab, dug down and removed the very corroded hydrant. That area of the barn is now heated so we did not replace the hydrant but continued with straight pipe (wrapped with heat tape in case it is needed in the future). Having to remove and replace part of a wall to do that, along with other impediments, resulted in a cost of over $7,000. Since the buried pipe is plastic, we took the chance that there would not be another leak, but now we find that there is one. I can only guess at two scenarios. The first is that they used 100 ft. rolls of pipe and joined them with a galvanized fitting that is now corroded and starting to leak. The second is that frost heaving over the years has pushed a rock into the pipe which has started to cut into the pipe (the earth does move).
Again, the leak appears to be a slow one, , certainly not enough to cause problems such as a sink hole or over-exerting the well pump, especially if the water to the barn is turned off when not needed (which is not that often).
I have used SDS bits to get piping through foundations. I never thought about extensions and drilling at an angle (which I have often done through wood framing members).
Still looking for a way to estimate the leakage rate, but thanks for the thoughts.

Yeah up north is a new ball game for me. I am in Tn. Going back to when you mentioned about hydrant. You did remove the old hydrant? Before continuing on

 

[Diehard]

To estimate the leak rate try the following:
Shut off the barn pipe.
Let the pump run up the pressure tank to full pressure.
Open a valve somewhere in the house and catch the water in a bucket.
Shut off the water when the pressure has dropped about 5psi then measure how much water is in the bucket.
Pump the pressure tank back up and open the barn valve.
Use a stopwatch to track how much time it takes to drop 5psi.
Now divide gallons/minute and you have your leak rate.

Not an exact measurement but should be close enough for your purpose.

I believe the section of pipe containing the leak was isolated from the pressure tank, if I understood it correctly.
If that's the case, and we know that water is almost incompressible. (takes about 5800 psi to compress water 1.8% in volume.)
The factor that causing it not to immediately drop to zero pressure with just a loss of less than a drop of water, is the fact that it's in 150 feet of 1" black plastic water pipe, which has expansion capabilities under pressure.
I just wonder why it only goes to 10 psi, unless it slopes up 23 foot above the gauge location.

 

[argile]

useless, you could have dug up the pipe in the time you took to post the question

 

[argile]

yes. plant flowers along the path. you won't have to water them!

 

[Jamesplumbing06]

Thx captain obvious. If you laugh I like ya if your not laughing then don’t bother getting mad. I won’t care. Just poking.

 

[Jamesplumbing06]

I believe the section of pipe containing the leak was isolated from the pressure tank, if I understood it correctly.
If that's the case, and we know that water is almost incompressible. (takes about 5800 psi to compress water 1.8% in volume.)
The factor that causing it not to immediately drop to zero pressure with just a loss of less than a drop of water, is the fact that it's in 150 feet of 1" black plastic water pipe, which has expansion capabilities under pressure.
I just wonder why it only goes to 10 psi, unless it slopes up 23 foot above the gauge location.

Why does it have a pressure tank on gravity system? O and hey diehard. I been meaning to ask (In lack of reasearch) what is the formula for figuring pressure? I had just always been verbally told to multiply by .76 for every foot in height. But do realize that 1” carries more than 3/4 therefore each pipe contains different physical weight but does that dramatically change the pressure since water takes so much to compress. My teacher was a father who thumped me and said everything happens because he says so. Lol I love every day to prove him wrong and thump his head now. Lol kidding about last sentence

 

[Diehard]

Why does it have a pressure tank on gravity system? O and hey diehard. I been meaning to ask (In lack of reasearch) what is the formula for figuring pressure? I had just always been verbally told to multiply by .76 for every foot in height. But do realize that 1” carries more than 3/4 therefore each pipe contains different physical weight but does that dramatically change the pressure since water takes so much to compress. My teacher was a father who thumped me and said everything happens because he says so. Lol I love every day to prove him wrong and thump his head now. Lol kidding about last sentence

1 psi = 2.31 feet of water
1 foot of water = 0.43 psi
It doesn't matter how big the pipe is because the weight is for pressure per square inch. So if you have a pipe with say one square inch cross section, 1 foot high, filled with water, the pressure at the bottom would be 0.43 psi.
If the pipe was say 12" in diameter with 1 foot high,filled with water the pressure at the bottom is still 0.43 psi.
The total weight across the entire 113 sq.in.(cross sectional area of a 12" pipe.) 113 x .43 = 48.6 lbs

What was that about a gravity system?

 

[Diehard]

useless, you could have dug up the pipe in the time you took to post the question

Sounds like you must live in a southern state. Unlike Vermont where frost goes down 4 to 5 ft.
I think a backhoe digging a 150 foot trench 4 feet deep in a few minutes would be a task.

 

[Jamesplumbing06]

yeah Tn. 8” frost line 24” dig depth here. Set the trencher to walking and follow it with pipe in ground and good hand rake to push dirt back in hole. OSHA would come unglued but I get it done. Mini ex take a little longer but not enough to fuss about.
Thanks for the formula. He was almost correct. Lol. Just wrong number to multiply.

 

[Jamesplumbing06]

Tank? I thought we were on the thread about the gravity pressure from a holding tank in the valley. My bad. Disregard

 

[Jamesplumbing06]

Hey diehard. Check this formula that just popped in front me today. This formula takes volume into account. I don’t believe everything I see on internet. So seeing if you can understand the language better. I just a plumber.