plumbing flow question

[DaveS]

Ok, I sold my old thermodynamics book so I'll ask here:

 

I have a pump that pushes water out through a 1" pipe. I take that 1" output and plumb in some 3/4" devices and then have it go back to 1". What happens to the pressure, flow, volume etc at each of the devices? My guess is that pressure (load) on the pump with higher than normal. Will flow rate be impacted (probably)? In the 3/4" devices I am assuming flow rate will be increased more than normal. What about when it goes back to 1"? If someone said something like- "adding that 3/4" restriction will be the equivalent to adding X feet of head for everything after that" that would be a convenient and useful way to picture things.

 

One of the 3/4" devices I am talking about is my UV light. Therefore flow rate is obviously a concern as that would affect kill rate.

 

Thanks all!

[flowerseller]

Makes a big diiference if the pump is a pressure rated pump or not.

 

I'd run 1" or 1 1/4" straight to the item requiring the most flow and then bleed your 3/4 lines from that main line. This should reduce the cause/effect of adjusting one 3/4 line as needed.

Speculation as to the head loss will be just that.

[Brian Ward]

by reduing the size of the pipe, you will be increasing head pressure. take a look over on reef central for their flow rate calculator - it's really good. since you know a little dynamics, try this:

 

Bernoulli's priciple is the guiding principle for this problem. assuming the pump can produce constant, continuous pressure, the total pressure - static + dynamic remains the same. static is the force exerted on the walls of the plumbing, dynamic is the force of the water driving forward. when the water goes from the large diameter to the small diameter, static pressure decreases and dynamic pressure increases - same effect as air over the wing of an aircraft. unless you have a pressure rated pump, your pump probably cannot maintain the constant pressure scenario. in this case, the static pressure will still decrease, dynamic pressure will still increase though not enough to equalize. thus, when you go back to the large diameter plumbing the total pressure will be lower than it was originally.

 

 

 

The original form of Bernoulli's equation[3] is:

 

where:

 

is the fluid velocity at a point on a streamline

is the acceleration due to gravity

is the height of the point above a reference plane

is the pressure at the point

is the density of the fluid at all points in the fluid

 

Everything you ever wanted to know: http://en.wikipedia.org/wiki/Bernoulli%27s_equation

 

I'd recommend the RC calculator unless you do fluid dynamics for fun

Edited March 17, 2008 by Brian Ward

[jakaufman]

i think my brain is melted.

 

now i remember why i went to business school!

[DaveS]

The pump is a pan world 200PS which I believe is a pressure pump.

 

I'd love to run it through all the 1" devices first and then split off to the 3/4" devices but the 1" device is a SCWD and the 3/4" devices are UV and chiller. Plumbing wise it would be very easy to have one of the 2 outputs of the SCWD go to the UV-Chiller line but I don't think that's smart. I'm worried that if my SCWD sticks or stops switching, flow might stop on the UV-Chiller line. That might cause my UV to burn out and Chiller to freeze all at the same time. Yuck. Suggestions?