45 vs 90 degree elbows [Archive]

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longhorn_reef

I am designing my plumbing layout (1" and 1.5" PVC). Does anyone know if there a significant reduction in head loss achieved by using 2 45s vs. a 90 degree elbow? I am wondering if the extra space & effort required to use 45s would pay off in the long run.

Thanks

BrokeColoReefer

degrees is degrees, same restirction through 2 45's as 1 90. At least in the venting world thats true.

Reeforbust

What would be easier to do.......Make a sharp 90 degree turn in your car or make two 45 degree turns. You would have to slow down on the 90 degree.
From my experience, 45's flow better than 90's because the water doesn't hit a "wall" and then have to change direction instantly. They will all get the job done and if you don't need every ounce of flow out of your plumbing, I would go with what is easiest for you.

areze

I believe the 45s are better, the dynamics of the water passing through will be smoother and thus less restrictive in the 45degree bend. it wont be an OMG difference, but it may be worth while if you have the room.

joedirt

I'm gonna say opposite you guys on this one. For some reason I want to say the flow coeffient of a 45 is slightly more than 1/2 of the coefficent of a 90. Thus if you have 2 45's you are exceeding that of a single 90.

I don't have any data to back this up, but maybe I'll look later.

dannieboiz

good stuff, just tagging along to see result... any updates?

thrlride

When doing the headloss calculator using 45's takes away more flow than 90's. Not much difference though. For instance, using 2 45's vs 1 90 made you lose 1 gph. Using 6 45's vs 3 90's made you lose 3 gph.

Reeforbust

But a 90 gives you more turbulence in the real world.............

BrokeColoReefer

simple math IMO, when figuring gas plubling, gas venting, wood chimneys, you calculate 2 45 = 1 90 for restriction purposes. I have no idea how water reacts. Just makes logical sense to me that it would be the same. I woud think the curve surface area are the same in both instances, who cares if it goes throug a 45, then runs a while then another 45, same curve, same surface area. IMO. The differance is so little i wouldnt think it would matter. At least im not all alone on this line of thought.
Ryan

bvoss

Spaflex makes the whole argument kinda mute.

Kinetic

what's spaflex?

Neo-Fight

I don't think you can simply add the angles of the 2 (or more) elbows and say that 1 90 elbow is equivalent to 2 45s, in terms of head loss. Consider that if you use flexible tubing to go from a horizontal outlet to a vertical outlet, you just made a 90 degree turn - it just had a very large radius.
Popular opinion (not that it is always right, mind you) says that a large radius (less turbulence, backpressure) 90 degree turn using flexible tubing would create less headloss than a 90 degree pvc elbow. I would then conclude that 2 45s would create less turbulence and backpressure than a single 90.

theatrus

Fluid mechanics is complex stuff ;)

And I seriously don't feel like digging out the textbook and figuring this one out. In the short end, 2 45s is probably not going to give you much advantage over a single 90.

bvoss

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Spaflex is flexible PVC. I used it on my last tank and it made it big difference in flow. You glue it like PVC using conventional fittings, but it bends to a pretty reasonable radius. You end up with a fes sweeping curves instead of lots of little turns and jogs.

You can get it a most pool stores.

BrokeColoReefer

C-mon someone has to set the record strait!
BUMP

tokitay

Originally posted by BrokeColoReefer
degrees is degrees, same restirction through 2 45's as 1 90. At least in the venting world thats true.

Here's a little plumber input: Two 45's will definitely have less restriction than one 90 (except in venting, it does not matter). Having said this, the difference is not really that big (when pumping water).

If you have the room, use two 45's. If it is really tight, stick with 90's.

tacocat

Try using sweepers instead of elbows.

Sweepers
http://i3.photobucket.com/albums/y58/ZevinLauren/flow.jpg

joedirt

OK here it is. The flow coefficient or minor loss of a 90 is .25, while a 45 is .42

Using the formula to calculate equivelent straight length pipe vs. a bend,

KD/f=L
K = Coefficient
D = Diameter
f = friction loss using a generic .02

traveling through a 45 is equivelent to 21" a 90 is equivelent t0 12.5" so if you use 2 45's cut that by 1/2 and you have 10.5" which is less than the single 90.

basicly to push water through 2 45's is the same as pushing it through 10.5" of pipe, you can get 2" more pipe passing through a single 90, making the 90 more efficient.

now there are alot of other factors that can effect this but for all intensive purposes 90's are better.

longhorn_reef

Sweepers...now that looks like a good idea, looks like a long-radius elbow that would flow much better than standard 90, but I've never seen those before. Any idea where they are sold and if they're available in 1" and 1.5"?

Thanks

ol'reefer

I would go with two 45's.

tygger

I dont know either, but when I was doing my plumbing, I used 2 45's when possible.

BrokeColoReefer

is there a easy way to calculate head loss? lets say you have a gph pump and you have 4 90's hooked rite to it, any idea what the output would be? is there a typical GPH deduction (percentage wise)per elbow?
Ryan

Kinetic

sweepers can be found on www.savko.com

tacocat

They are also called 90* long turn elbows. Old Yeller Tang gave me this link.

http://acmehardware.com/pd--1-12-90deg-Pvc-Lsw-El.aspx

longhorn_reef

Thanks for the links on the sweeper fittings! I noticed that these appear to be drain fittings rather than schedule 40, so I wonder if they are safe to use on the return (high pressure) side of the system. Tacocat's pic above looks like a good application but I wonder about using say between the pump discharge and say a partially closed ball valve where the fitting might see some pressure?

Reeforbust

I wonder if they are safe to use on the return (high pressure) side of the system

Anything will work.....You don't have that much pressure.....:)

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) , I second the one comment about sweep 90s. If you have room, seems like a sweep 90 should beat out a regular 90 or two 45s... You might see if you can find some hydraulic data on those...

I used them for my solar installation, which, when engaged, significantly increases the number of 90s in the water path (like by 10 or so!). And when they re-did my pad to integrate the solar, I asked them to swap out as many of the old 90s for sweeps that space would allow. I now only have a couple left (not counting what's underground).

I also added a flow meter which helps me determine variable pump speed for pool water turn-over rate, as well as figuring out the pump speed for providing the solar panels with what they require, without having to do all the math (if I could even figure that out that way). I'm also watching flow rate, along with filter pressure, to get an idea of system performance vs filter condition. The Pool Math app tracks that data for me, which I can then check up on periodically.

With no foundation in fact or expertise (but that's never stopped me before!) , I second the one comment about sweep 90s. If you have room, seems like a sweep 90 should beat out a regular 90 or two 45s... You might see if you can find some hydraulic data on those...I used them for my solar installation, which, when engaged, significantly increases the number of 90s in the water path (like by 10 or so!). And when they re-did my pad to integrate the solar, I asked them to swap out as many of the old 90s for sweeps that space would allow. I now only have a couple left (not counting what's underground).I also added a flow meter which helps me determine variable pump speed for pool water turn-over rate, as well as figuring out the pump speed for providing the solar panels with what they require, without having to do all the math (if I could even figure that out that way). I'm also watching flow rate, along with filter pressure, to get an idea of system performance vs filter condition. The Pool Math app tracks that data for me, which I can then check up on periodically.

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