View Full Version : 45 vs 90 degree elbows

11/28/2005, 12:55 PM
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.


11/28/2005, 01:18 PM
degrees is degrees, same restirction through 2 45's as 1 90. At least in the venting world thats true.

11/28/2005, 01:48 PM
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.

11/28/2005, 02:20 PM
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.

11/28/2005, 02:30 PM
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.

11/28/2005, 03:49 PM
good stuff, just tagging along to see result... any updates?

11/28/2005, 04:02 PM
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.

11/28/2005, 04:13 PM
But a 90 gives you more turbulence in the real world.............

11/28/2005, 06:25 PM
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.

11/28/2005, 06:32 PM
Spaflex makes the whole argument kinda mute.

11/28/2005, 06:56 PM
what's spaflex?

11/29/2005, 12:44 AM
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.

11/29/2005, 01:04 AM
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.

11/29/2005, 06:07 AM
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.

11/29/2005, 09:36 AM
C-mon someone has to set the record strait!

11/29/2005, 09:45 AM
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.

11/29/2005, 10:50 AM
Try using sweepers instead of elbows.


11/29/2005, 11:50 AM
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,

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.

11/29/2005, 11:52 AM
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"?


11/29/2005, 12:00 PM
I would go with two 45's.

11/29/2005, 12:15 PM
I dont know either, but when I was doing my plumbing, I used 2 45's when possible.

11/29/2005, 08:00 PM
is there a easy way to calculate head loss? lets say you have a 1000 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?

11/29/2005, 09:29 PM
sweepers can be found on www.savko.com

11/30/2005, 01:14 AM
They are also called 90* long turn elbows. Old Yeller Tang gave me this link.


11/30/2005, 07:55 AM
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?

11/30/2005, 08:12 AM
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.....:)