I'm considering re-purposing a 1" line that was originally used for a booster line and a 1.5" skimmer line into a single 2.5" line that will then feed the pump. The question I have is, since the addition of the 1" line is to reduce vacuum losses on the 1.5" line (to get more flow), is it better to use a simple 2.5" Wye Waterway Manifold Wye - 2.5 - 672-8050 or should I use a Jandy never lube 2.5" valve & attempt to mix in the correct proportions. Since the intention is to not have either line exceed the other in feet per second of flow (to reduce vacuum losses) I'd figure a wye makes the most sense.
Combining a 1in and a 1.5" suction line into a Wye manifold?
- Thread starter goku
- Start date
No need to go to 2.5" ... 2" is plenty large and still a larger cross section than the 2 other pipes. If you want to have some control over the suction source, I would use a 3 way valve. There is really no reason to worry about the water velocity.
I read somewhere that 2 1.5" pipes is equivalent to 2.23", what about a single 1.5" and a single 1" pipe? The only reason I want to use a 2.5" in the wye is because my understanding about head loss is that if you have a 3 way valve, and 3 90 degree elbows at 2", if you switch to 2.5", for the same amount of flow it's as if those elbows and valves disappeared entirely.
In the grand scheme of things, a couple 90 turns do not add a significant amount of headloss ... plus it is harder to find 2.5" plumbing (and it is much more expensive) 
The math is simple:
area 1.5" pipe = (1.5"/2)^2 * pi = 0.56 * pi
area 1" pipe = (1"/2)^2 * pi = 0.25 * pi
total = 0.81 * pi
area of 2" pipe = (2"/2)^2 * pi = 1.0 * pi
Your 2 pipes are ~20% smaller than a 2" pipe.
The math is simple:
area 1.5" pipe = (1.5"/2)^2 * pi = 0.56 * pi
area 1" pipe = (1"/2)^2 * pi = 0.25 * pi
total = 0.81 * pi
area of 2" pipe = (2"/2)^2 * pi = 1.0 * pi
Your 2 pipes are ~20% smaller than a 2" pipe.
So my thought was, in order to get maximum head loss reduction without completely re-plumbing , change out a single 1.5" elbow for the skimmer line in the ground near the pad to a 2" elbow and for the 1" line, change the elbow to a 1.5" elbow, after that, merge them into a 2" wye and 2" plumbing and use 2" plumbing after that? There is no check valve before any of this plumbing equipment so I'm thinking of putting one after the wye. Only reason I'm thinking of one is because when I turn off the pump and vent the filter, a lot of the water rushes back down the suction line which may or may not be considered a "feature" since I don't have to drain as much water from the filter when cleaning it.
No, technically two 1.5" would not equal 3" because that is only relating the diameter and not the cross-sectional area.
Yes, you are right the inner diameters are a little different than I used. If you use the 1.61" diameter, then the area is 0.648 for each 1.5" pipe and 0.275 for a 1" pipe
Yes, there is a difference in skin friction.
But, what exactly are you trying to do and hoping to accomplish? This is not designing rocket fuel flow for a rocket
There is absolutely no point in combining a 1" pipe and a 1.5" pipe into a 2.5" wye ... you will NOT notice any flow difference between doing that and just combining them in a 2" 3-way valve and using 2" pipe after that.
The cross section area of the 1.5 + 1 = 0.923 * pi ... which is the equivalent area of a 1.92" pipe .... but a 2" pipe is really 2.067" giving an area of 1.068 * pi.
So you are still only at 86% of the area of the 2" pipe when combining the 2 ... ignoring the skin friction concerns.
Yes, you are right the inner diameters are a little different than I used. If you use the 1.61" diameter, then the area is 0.648 for each 1.5" pipe and 0.275 for a 1" pipe
Yes, there is a difference in skin friction.
But, what exactly are you trying to do and hoping to accomplish? This is not designing rocket fuel flow for a rocket
There is absolutely no point in combining a 1" pipe and a 1.5" pipe into a 2.5" wye ... you will NOT notice any flow difference between doing that and just combining them in a 2" 3-way valve and using 2" pipe after that.
The cross section area of the 1.5 + 1 = 0.923 * pi ... which is the equivalent area of a 1.92" pipe .... but a 2" pipe is really 2.067" giving an area of 1.068 * pi.
So you are still only at 86% of the area of the 2" pipe when combining the 2 ... ignoring the skin friction concerns.