Quick Question! Trenching water line to barn

kmdigital · Jun 23, 2008

honeycutt said:
If your pressure switch is at the pump do not put anything between the pump and the tank. This will give you problems in the long run. The pump will tend to keep cycling while using the part that is installed between the 2 and the service life of the pump will be shortened.

Not if the line between the pump and the tank are adequately sized. I've had it setup this way for almost 20 years, and absolutely no problems.

barnfield · Jun 24, 2008

kmdigital said:
Not if the line between the pump and the tank are adequately sized. I've had it setup this way for almost 20 years, and absolutely no problems.

Right, because I'm pretty sure that if the check valve is located at the pump (and not closer to the tank) then this isn't a problem.

cddva · Jun 24, 2008

I would listen to what DavidPerry is saying regarding sizing your line. A smaller line will produce a greater pressure drop per unit length. I think the 1" line is the way to go for the pipe run length you mentioned. Good luck!

ampsucker · Jun 24, 2008

don't forget to include changes in elevation or number of bends in your pressure drop equation. the straight pipe alone will drop your pressure 20-25 psi in the 3/4" size. any other increase in static head or right angles in the run (usually expressed as equivalent straight pipe feet) will only lower the pressure at the end even more.

on the other hand, water flows faster through a smaller pipe which is handy if there's, say, a hot water heater on one end and you don't want to wait forever for the water to get hot. though i don't see how that would benefit you much in this situation.... maybe if you want good, cold well water out of the ground as quickly as possible in the barn. otherwise, i would go with the bigger pipe.

amp

LarryD · Jun 25, 2008

I've got a 1" line from the pressure tank to a manifold of valves controlling my house, pastures, and another hosebib near the pumphouse.

The pasture line is almost 700' feet long and even the last hosebib fills the water trough pretty fast, even with a 25'-30' rise in elevation. I used 1" to reduce friction loss and I think it was the right way to go.

I will advise that if I'm in the shower and the wife goes to fill a trough, well I know it immediatly.

Highbeam · Jun 27, 2008

770'. This is a no-brainer, go for the larger size of 1". Water lines do not work on the weakest link principle but the head loss of each element adds up to take flow away.

To tell you the truth, I would go even bigger for that long of a run. 1.5" is not out of line here.

gemini5362 · Jun 27, 2008

J_J said:
Crossing the electric line should not be a problem. Check with the utility company and verify the depth. That electric line should be down about 36 in , and the water pipe should be below the frost line. I would still use 1 in, and put a bladder tank at the barn.

Crossing the electric line might be a big problem I would recommend not doing that if possible. When I ran the electric line underground to my house the electric company said the ditch had to be 36 inches deep. I had it dug that deep. The electric company ran plastic pvc with the line in it. The pvc did not sit on the bottom of the ditch right and in some places it was only about 18 inches deep. I would not trust how deep that line is and when you have it marked it wont be marked how deep. If you dont have to cross it dont.

RedDirt · Jun 28, 2008

DavidPerry, cddva, ampsucker and Highbeam have it right. The issue of pipe diameter vs length of run is friction loss.

Head loss (or gain) is a factor too if there is a change in elevation. I vaguely recall head loss/gain to be .42 pounds per foot difference in elevation. I'd need to check a reference that is not handy right now.

If you need to keep fitting losses to a minimum with poly pipe typical hose clamped internal fittings, bevel the inside diameter of the fittings, both ends. I just use my trusty sharp pocket knife.

Rockin' G Ranch · Jun 28, 2008

RedDirt said:
DavidPerry, cddva, ampsucker and Highbeam have it right. The issue of pipe diameter vs length of run is friction loss.

Head loss (or gain) is a factor too if there is a change in elevation. I vaguely recall head loss/gain to be .42 pounds per foot difference in elevation. I'd need to check a reference that is not handy right now.

If you need to keep fitting losses to a minimum with poly pipe typical hose clamped internal fittings, bevel the inside diameter of the fittings, both ends. I just use my trusty sharp pocket knife.

Water weighs 8.33 pounds per gallon which equates to 0.433 psi/ft.
To calculate proper line size it is ALL about friction. The available pump rate is dictated by back pressure - unless the pump is a positive displacement pump in which case you could burst the line becasue that type of pump can put up pressure until something burst. I'm sure you have a centrifugal pump which is rate dependent on back presure. It will actually "pump through itself" when the maximum pressure/rate of the impellar is reached. All waterwell pumps are centrifugal pumps (or should be).
Therfore, to calculate the proper line size the friction drop of the entire system must be calculated. This is calculated by knowing the length of straight line, number of elbows and head difference.
If you don't want someone to calculate the hydraulic engineering involved (by the way I am a registered engineer) just use the largest line possible. For the length of line you suggested I would personally not use anything less than 1.5" line (I normally use large safety factors to ensure I don't go too small).