Pool builder from H**L!

[msm859]

Just for the record "decreasing" pipe size will NOT increase water pressure -- if anything it will decrease the water pressure. Decreasing the pipe may increase "velocity" but you can do that at the end of the pipe.

[JohnT]

Just for the record "decreasing" pipe size will NOT increase water pressure -- if anything it will decrease the water pressure. Decreasing the pipe may increase "velocity" but you can do that at the end of the pipe.

In a pool plumbing system, decreasing pipe size most certainly will increase pressure. You are restricting flow with the same size pump. Unless your pipe has the capacity to carry much more water than the pump can deliver (not the case with pools), any change in pipe size will result in increased pressure at the pump.

[waterbear]

In a pool plumbing system, decreasing pipe size most certainly will increase pressure. You are restricting flow with the same size pump. Unless your pipe has the capacity to carry much more water than the pump can deliver (not the case with pools), any change in pipe size will result in increased pressure at the pump.

EXACTLY! The water features were supposed to be plumbed with 3/4 inch pipe so the flow rate is much too high causing them to overflow yet there is not enough pressure (or velocity) to allow them to work properly. I have been in contact with the manufacturer to find a remedy for this short of tearing up the deck and repluming although I did have to replace some of the exposed plumbing due to faulty pcv joints and leaks already.

[ehorn]

Just a little water flow dynamics for you, there is a standard equation we use to calculate water flow which is:

PV = nRT

Where P = Pressure V = Volume, n = number of moles R = universal constant T = Temperature. Usually the nRT side is constant so in a pipe we look at:

P1V1 = P2V2

So in a case with a pool where a pump is pumping at a constant volume rate the pressure would change. So here if a pipe diameter decreases the pressure would have to increase. Depending on the size difference you can calculate what the exact pressure change will be.

Eric