How much do PEX crimp fittings reduce water flow?

[James23912]

My “plumber” used PEX , which is fine but I got the plastic 90 turns and he promptly broke two of the first three and instead used the insert type 90 degree plastic fittings, I later finished the job and was able to use the bending type with a little patience, I have covered most of the walls but some are still accessible, so I am wondering if I should try to change the few 90s that are left, for example, the line to washer has two 90s just in the 8 feet or so between the machine and the manifold, all half inch. I see that it is more common now to use an expansion tool which I assume is done to keep the inside dimension the same, how much of a problem will this be, if any?

 

[Reach4]

I see that it is more common now to use an expansion tool which I assume is done to keep the inside dimension the same, how much of a problem will this be, if any?

You cannot use expansion (F1960) fittings with most PEX that is not PEX-A. https://www.pexuniverse.com/types-of-pex-fittings tells types.

How much the difference matters depends on the flow. For a bathroom with even 1/2 inch pex using brass elbows, probably not noticeable. It would not be noticeable for a shower, and only noticeable for a bath fill if timing the fill.

https://www.esmagazine.com/ext/resources/ES/White_Papers/Files/PDF/Worm-White-Paper.pdf is interesting. They get most of their data from Uponor, I think.

When specifying fittings, one must design with the same system intended to be used in the application. If an engineer specifies a PEX system with F1960 fittings, but the contractor installs any of the alternatives, system velocity — and therefore performance — will be significantly impacted. ASTM F1960 fittings are, in many cases, preferred over alternate fitting connections. In an F1960 connection, the installer simply uses an expansion tool to expand the PEX-a pipe and PEX-reinforcing ring before inserting a fitting. As the ring and pipe shrink back down to their original size, it creates a strong, durable connection that holds tight with up to 1,500 psi of radial force. A 1-in F1960 engineered polymer (EP) fitting has a 67% greater flow rate, at 8-ft per second, than a F2159 plastic fitting and 22% greater flow rate than an F1807 brass fitting.
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Notice your elbows will have less pressure drop if they are brass than if they are plastic.

 

[Sponsor]

 

[wwhitney]

Every fitting has an "equivalent length". For example, an F1807 (brass for crimp connection) 1/2" 90 degree elbow has an equivalent length of ~9' , while an F2159 (plastic for crimp connection) 1/2" 90 degree elbow has an equivalent length of ~13.5'.

So if you have a 9' 1/2" PEX run that could be done with 2 bend supports, and you instead do it with 2 F2159 elbows, you've effectively quadrupled the length of the run, for pressure drop purposes. That's not necessarily a problem, as even if the run was 36' with no elbows to begin with, you might have used 1/2" pex.

To properly answer the question of whether it's worth replacing those elbows, you'd need to know the complete graph of your distribution piping, along with the pressure available at the source (water lateral or well) and the demands (gpm) of each usage point.

But if replacing the elbows means using couplings, the benefits are reduced. An F1807 1/2" coupling has an equivalent length of ~2', while a F2159 coupling has an equivalent length of ~6.5'. So replacing one F2159 1/2" elbow with with two F2159 couplings is basically a wash; if you replace it with two F1807 couplings, it would be a reduction in 9.5' of equivalent length.

Cheers, Wayne

 

[Reach4]

From https://www.etnasupply.com/ASSETS/DOCUMENTS/ITEMS/EN/Uponor_LF2935050_Manual.pdf
Appendix C Fitting Equivalent Length

Note that drops for pex are usually published for 100 ft lengths.
This seems to to say "don't worry about it."

 

[Jadnashua]

When a fluid goes through a restriction, the Bernoulli principle says the fluid speeds up through that restriction, then slows down on the other side. It does create friction, which is why the equivalent length increases, but the flow may not change much. The equivalent length is what determines the pressure drop across the network. IN a shower, unless it's multiple heads, 1/2" pex should be fine. If it's a tub/shower, 1/2" pex versus say copper of the same size, the volume would decrease when filling a tub.