Plumbing Head Loss Question - Tee or Elbow

[TomU]

I'm doing some plumbing on my pool, and I'm curious if anyone can tell me if there will be a major difference in head loss between the following two configurations (ignore the periods).


1.)................Pump
.....................||
.....................||
Main Drains === Tee === Valve === Yard Drain


2.)................Pump
.....................||
....................Tee === Valve === Yard Drain
.....................||
Main Drains === Elbow

In the first setup, the water to the pump has to make a sharp 90 degree turn while piling into the closed valve. In the second setup, the water makes a smooth 90 degree turn and then travels straight through the tee. Obviously, with the second setup I would never get the last couple of inches of water out of the pipe since the yard drain pipe level is above main drain pipe level by the height of the elbow and the tee. Thanks!

TomU

 

[JohnT]

Are you wanting to be able to drain the pool without the pump? I'm not sure of your goal, but the water in the pipes will always return to the level of the pool water as long as it can get air.

Drawing 1 has one less fitting in the flow of the pumped water, so I'd choose it. I don't believe the area between the T and the valve will have much impact on the flow of water into the pump.

 

[acamato]

Pump to Main Drain:

Setup 1:
Tee-Branch - 8 equivalent feet of 1-1/2" pipe

Setup 2
Tee-Run: 2.7 equivalent feet of 1-1/2" pipe
Elbow: 4 equivalent feet of 1-1/2" pipe

Setup 2 would have 1.3 less equivalent feet of 1-1/2" pipe.

Pump to the yard drain:

Fitting loss is the same for both setups.

For more on fitting friction loss see: http://www.lascofittings.com/supportcen ... ttings.asp

Actual difference in head loss will depend upon pipe size and flow. 1.3' difference is not much. Example head loss @ 40 GPM in 1-1/2" pipe is only 9.54' (4.13 PSI) per 100' of pipe, so 1.3' of pipe is only 0.054 PSI...

To calculate your actual loss here is a online friction loss calculator...

http://www.lascofittings.com/supportcen ... ssCalc.asp

 

[TomU]

Are you wanting to be able to drain the pool without the pump?

Yes, or at least be able to lower the level if I want. I would only ever open that valve with the pump off. I'm thinking it would be handy if I need to lower the water level in the winter and already have the pump and related equipment winterized. This drain line is below the frost line. Here is more of the drawing.

..............................Returns
.................................||
...................Pump === Filter => Waste Port
.....................||.......................||
.....................||.......................||
Main Drains === Tee === Valve ====== Tee === Yard Drain

It doesn't look like there is a big difference in flow restriction, but I wasn't sure since under normal conditions 1/2 of the tee in option 1 will be blocked (by the valve). This means its acting like an elbow, but possibly with much more turbulence. In option 2, there should be virtually no restriction through the Tee. There is no change in direction of the water through it and nothing sticking out that would create turbulence. FWIW, this is all 2" PVC.

I guess the fundamental question is what is the difference in flow restriction between a 90 degree elbow and a tee with one end plugged? (Or how about between a schedule 40 tee [sharp bend] and a DWV tee [larger radius bend]?)

[Edit]
I should have followed that link first, I see some of this info is listed already....
For those that didn't follow the link, here is the difference (for 2" PVC):
- 90 degree direction change through Elbow = 6.0'
- 90 degree direction change through Tee = 12.0'
- Straight through a Tee = 4.3'

So just analyzing the corner where the water is changing direction, option 1 would introduce 12.0' of additional head while option 2 would introduce 10.3' of additional head.

Thanks for providing those links! :-D
[/Edit]

 

[mas985]

The diameter of the pipe has much more of an impact on head loss than the fitting type. For a given plumbing system and flow rate, simply going from 1 1/2" pipe to 2" pipe will reduce the head loss by over 75%!!

Also, as was pointed out a single fitting has very little impact on the over all plumbing head loss so if you really want to reduce head loss, increase the pipe diameter.

 

[TomU]

...simply going from 1 1/2" pipe to 2" pipe will reduce the head loss by over 75%!!

Most people don't appreciate the power of PI R Squared! A 2" pipe is 78% larger than a 1 1/2" pipe. Same idea with pool sizes. A 24' pool will hold 78% more water than an 18' pool (13,500 gallons vs. 7,600 gallons).

 

[acamato]

option 1 would introduce 12.0' of additional head while option 2 would introduce 10.3' of additional head.
[/Edit]

Do not mix up equivlent feet of pipe with head loss. In order to calculate head loss of the pipe & fittings, you need to add up the feet of pipe to the total equivlent feet of pipe of the fittings. The first link gives you the equivalent feet of pipe for the fittings.

option 1 would introduce 12' of pipe to the system not 12' of head.

The 2nd link is where you calculate your head loss. Flow is critical to calculating head loss.

1-1/2" vs 2" @ 40 GPM per 100' of pipe

1-1/2" has 9.54' (4.31 PSI) loss per 100' of pipe
2" has 2.79' (1.21 PSI) loss per 100' of pipe

 

[TomU]

Thanks. I see what you mean.