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

[frodo]

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?

install a water meter in the piping, then it is not guessing
you will know exactly how much water is being leaked.

 

[Diehard]

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.

I looked at write up using volume. It took me a while to realize what they were doing. It's really kind of a weird way to do it.
Typically to figure the pressure at the bottom of a tank all you have to know is the height in feet to know PSI.
What this formula is doing is assuming you know the Volume in "cu ft"(they completely neglected to say Volume in cu ft and not in gallons) and it's calculating the height in feet. And of course as we said before, in Post #16 above...
1 psi = 2.31 feet of water
1 foot of water = 0.43 psi

Feet x .43 = PSI
Example: 10 feet = 4.3 PSI

I went to that science site where this came from and they have some weird(not practical) examples of calculating things.

So their saying if you know the volume of a cylinder, in cubic feet, but don't know the height, here's how to calculate it.

 

[Jamesplumbing06]

Ahh gotcha.