Pipe size

[Denis]

Hello all, I'm new to this forum.

My cottage as a well/pump/tank for drinking water. That cottage is situated on top of a cliff.
Now, I would like to use the cottage's pump/tank to supply another little cottage down the cliff. The cliff is maybe 250 feet high and the little cottage down the cliff is situated approximatively at 450 feet from the cottage. There is no way to dig a well there: it is at sea level!

My question is what pipe size should I use to have a decent pressure down the cliff? I was thinking that since the water is going down, I will not loose to much pressure in the pipe because of the weight of the water in the pipe. I have no idea about the pipe size that I should use between both cottages (remember, they are at 450 feet apart). Should I use one inch pipe or a smaller (3/4 or 1/2) will be ok?

Thanks, Denis

 

[frodo]

450' ? at 60 psi, simple, cottage 1 bath, 1, kitchen, washer, 2 hosebibs use 1'' pvc at 500'
your ok to use 3/4, but i would use 1''

 

[Denis]

450 feet apart at 30/50 psi with a 250 feet slope.

 

[phishfood]

Water develops .453 PSI per foot of height/head pressure. 250' of head pressure X .453 = 113.25 + 50 PSI from your pump = 163.25 PSI at the lower cottage.

Imagine a fire hose in your face when you turn on the shower valve!

You will need a pressure reducing valve, and pipe size will not be a problem.

 

[Denis]

Water develops .453 PSI per foot of height/head pressure. 250' of head pressure X .453 = 113.25 + 50 PSI from your pump = 163.25 PSI at the lower cottage.

Imagine a fire hose in your face when you turn on the shower valve!

You will need a pressure reducing valve, and pipe size will not be a problem.

Thanks for the info. I guess I will be better with a 1/2 inch pipe. If I understand correctly, I should get approx. 106 PSI at the pipe end with a 1/2 inch pipe? Still need a pressure reducing valve.

Is it the same factor for a semi-flexible pipe (pex)?

250 * .453 / 2 + 50 =106.625

 

[frodo]

Thanks for the info. I guess I will be better with a 1/2 inch pipe. If I understand correctly, I should get approx. 106 PSI at the pipe end with a 1/2 inch pipe? Still need a pressure reducing valve.

Is it the same factor for a semi-flexible pipe (pex)?

250 * .453 / 2 + 50 =106.625

I disagree with the use of a 1/2'' pipe.
volume, is what you need to be concerned with

nominal pipe size...........gallons per foot
1/2'' ............................... 0.010
3/4 '' ............................... .023
1'' ............................... .041


pex is even worse, my above calculations are based on nominal pipe size
pex 1/2'' inside diameter is 3/8'' which is .0006 gallons per ft

 

[steventheplumber]

Use 1'' pipe size, and if you thinking about using PEX, a minimum of 1 inch is required to make up for the loss of the inside diameter.

 

[Denis]

Thank you very much to both of you!

I will use 1" pipe with a pressure reducing valve...

 

[frodo]

use 1'' sch 40 pvc, not pex

pex id is 0.863



pvc id is 1.049

 

[speedbump]

If your using poly, get at least 125 psi poly so it can take the pressure. Thin wall PVC is good for around 160 psi, SCH 40 over 400 psi.

 

[Denis]

Hi all,

Lots of infos from you. But a question came to me, could be foolish!

If I put a bigger pipe (lets say 2") will I get less pressure or the pressure will be higher at the bottom of the pipe?

and another one (still more confused!)
Let's say I start for 200' (almost flat) at 3/4 or 1/2 inch and then continue the remaining 250' (slope) with a bigger diameter. What will happen at the bottom end of the pipe?

Usually I can do regular plumbing, but that slope give me lots of headache.

 

[phishfood]

The static (nonflowing) pressure will be the same no matter what size pipe you use. The bigger the pipe, the higher the volume, and therefore the flowing pressure will be. The flat section before you start the large elevation change will need to be bigger than 3/4" or 1/2". As long as you don't have a lot of demand, say more than 2 or 3 standard bathrooms, I would probably use 1" Sch 40 PVC for the whole thing.

 

[speedbump]

Don't get caught up in the mistaken theory that smaller pipe means more pressure. That is only true for the most part where the pipe is large enough to provide the volume then you add a smaller nozzle at the end to increase the distance you can throw the water. The pressure in the pipe and nozzle is still the same. Use smaller pipe and the water won't go as far.