3/4 pex water pressure

[gani]

my main broke at my house and i'm switching from quest 3/4 pipe to 3/4 pex pipe. I'm using the crimp connections and they turn my 3/4 pex joints/connectors to roughly a 1/2 inch. I have 5 sinks, 3 toilets, 2 bathtubs and 2 spouts outside also ice maker, washing machine, and dishwasher are all branched from my main water pipe T. Will I have enough pressure to run 2 showers, dishwasher, washing machine and a sink or 2

with 3/4 pex?

[Scottpat]

my main broke at my house and i'm switching from quest 3/4 pipe to 3/4 pex pipe. I'm using the crimp connections and they turn my 3/4 pex joints/connectors to roughly a 1/2 inch. I have 5 sinks, 3 toilets, 2 bathtubs and 2 spouts outside also ice maker, washing machine, and dishwasher are all branched from my main water pipe T. Will I have enough pressure to run 2 showers, dishwasher, washing machine and a sink or 2

with 3/4 pex?

Going to PEX I would seriously consider 1". You also must take into consideration how high the water needs to go to reach all of the fixtures. The higher it must travel the more pressure and volume you need.

Pressure is not really a concern if you had good pressure before, a concern is volume!

[Jim Katen]

Upsize to 1" and use full bore fittings.

[John Dirks Jr]

Like Scott said, volume is the important factor, not pressure. It's why both he and Jim recommend the 1" line.

[rjbrown2]

When you do the math for pressure drop in a circular pipe in the kind of situation you find in residential plumbing, you note that the drop is directly proportional to the volume flow rate (gallons/minute) but inversely proportional to the fourth power of the diameter of the pipe. This is so overwhelming that whenever there is the slightest question about sufficient supply based on pressure, go bigger even if costs a little more. Saying it in other words, for the same pressure drop you will be able to deliver a lot more water to the point that something else will be the limiting factor.

[Marc]

When you do the math for pressure drop in a circular pipe in the kind of situation you find in residential plumbing, you note that the drop is directly proportional to the volume flow rate (gallons/minute) but inversely proportional to the fourth power of the diameter of the pipe. This is so overwhelming that whenever there is the slightest question about sufficient supply based on pressure, go bigger even if costs a little more. Saying it in other words, for the same pressure drop you will be able to deliver a lot more water to the point that something else will be the limiting factor.

More like the square of the radius of the pipe which is to say the doubling the diameter reduces pressure drop by a factor of 4, which is the square of 2.

Marc

[rjbrown2]

Marc: I was putting into words the classic Hagen-Poiseuille (perhaps one of your relates?) equation for laminar flow of an incompressible Newtonian fluid in a long constant cross section pipe.

To wit, the pressure drop is expressed as:

Delta P = (128*Mu*L*Q)/(Pi* D^4)

or in terms of R

Delta P = (8*Mu*L*Q)/(Pi*R^4)

Where Delta P = pressure loss, L = pipe length, Q = volume flow rate, Mu = dynamic viscosity, D = diameter, R = radius, and Pi is our constant 3.14159...etc

[Marc]

Marc: I was putting into words the classic Hagen-Poiseuille (perhaps one of your relates?) equation for laminar flow of an incompressible Newtonian fluid in a long constant cross section pipe.

To wit, the pressure drop is expressed as:

Delta P = (128*Mu*L*Q)/(Pi* D^4)

or in terms of R

Delta P = (8*Mu*L*Q)/(Pi*R^4)

Where Delta P = pressure loss, L = pipe length, Q = volume flow rate, Mu = dynamic viscosity, D = diameter, R = radius, and Pi is our constant 3.14159...etc

Ok. But isn't that equation intended for higher viscosities than water? Water at 20C has a viscosity of only 0.001

Marc

[rjbrown2]

Marc:

Poiseuille conducted his original experiments in the 1840s using distilled water and eventually extended his work to other fluids. The H-P equation is very much applicable to water.

I think I know the root of our difference here (as if anyone cares now except you and me) The form of H-P changes when Velocity is included in the Delta P equation instead of Q

Delta P = (32*Mu*L*V)/D^2

The reason I discussed the form that I did was because the variables that were relevant in the discussion were: pressure and flow rate

[Jim Katen]

A slightly bigger pipe gives a whole lot more flow.

[Marc]

Marc:

Poiseuille conducted his original experiments in the 1840s using distilled water and eventually extended his work to other fluids. The H-P equation is very much applicable to water.

I think I know the root of our difference here (as if anyone cares now except you and me) The form of H-P changes when Velocity is included in the Delta P equation instead of Q

Delta P = (32*Mu*L*V)/D^2

The reason I discussed the form that I did was because the variables that were relevant in the discussion were: pressure and flow rate

Alright. Thanks. I was looking at it from strictly as a function of circular area vs radius but I see the other factors in that now.

Marc

[Ben H]

A slightly bigger pipe gives a whole lot more flow.

Best answer.

[rjbrown2]

That's where I started, but a gave just a little more than that in words, because the question revolved around the relative importance of pressure vs. flow. It only got mathematical when I was questioned on it.

?It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience.? Albert Einstein

Happy T Day!

[Marc]

That's where I started, but a gave just a little more than that in words, because the question revolved around the relative importance of pressure vs. flow. It only got mathematical when I was questioned on it.

?It can scarcely be denied that the supreme goal of all theory is to make the irreducible basic elements as simple and as few as possible without having to surrender the adequate representation of a single datum of experience.? Albert Einstein

Happy T Day!

Not to worry. All's fine.

Marc