I am building in a shower as part of a remodel. Supply lines are PEX. Does a shower valve exist where the supply hooks up below, like straight shots upward to the valve, rather than coming in from the sides, hot and cold? I am coming up through the floor below, and am wondering how much having an elbow 3" from the valve will affect water flow? Do elbows change pressure/flow noticeably? I probably wouldn't think about it, except the house is one of the earliest built here, and the water pressure has been brought up at city council meetings many times in our years here. Thank you.
Need some help with water flow physics and all that
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Jadnashua
Retired Defense Industry Engineer xxx
Pressure can be broken down to a couple of factors:
- static pressure: this will be the same, regardless of how it is plumbed. It is based on the supply +/- and gravity effects which amount to 0.43#/foot of elevation change- drops as you go up, rises when you go down.
- dynamic pressure: this will be affected by several things including, the type of pipe used, the ID, the number of fittings (which includes straight, and any angles, the length of the run, and the volume as the higher the volume, the more friction becomes an issue
Pex is better than say copper for friction effects, but can be severely affected because its ID is smaller than copper in the same nominal size (the nominal OD is the same on both, but the ID differs to compensate for the strength of the material).
How much a single elbow will affect the dynamic pressure can be looked up in tables for the specified materials. I don't remember that off the top of my head. One elbow won't change the dynamic pressure all that much.
The dynamic pressure could contribute to your satisfaction overall. If volume is an issue, using a larger pipe is called for verses coper.
One of the major advantages of pex is that because it bends easily (just don't exceed the maximum bend radius - you can use a bend support bracket to ensure that) which often allows you to eliminate any fitting where one would be required with copper. IOW, while it may not look 'neat', it often can work by just bending the pipe so it is in the proper orientation.
- static pressure: this will be the same, regardless of how it is plumbed. It is based on the supply +/- and gravity effects which amount to 0.43#/foot of elevation change- drops as you go up, rises when you go down.
- dynamic pressure: this will be affected by several things including, the type of pipe used, the ID, the number of fittings (which includes straight, and any angles, the length of the run, and the volume as the higher the volume, the more friction becomes an issue
Pex is better than say copper for friction effects, but can be severely affected because its ID is smaller than copper in the same nominal size (the nominal OD is the same on both, but the ID differs to compensate for the strength of the material).
How much a single elbow will affect the dynamic pressure can be looked up in tables for the specified materials. I don't remember that off the top of my head. One elbow won't change the dynamic pressure all that much.
The dynamic pressure could contribute to your satisfaction overall. If volume is an issue, using a larger pipe is called for verses coper.
One of the major advantages of pex is that because it bends easily (just don't exceed the maximum bend radius - you can use a bend support bracket to ensure that) which often allows you to eliminate any fitting where one would be required with copper. IOW, while it may not look 'neat', it often can work by just bending the pipe so it is in the proper orientation.
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https://www.uponorpro.com/~/media/e...ntlengthcharts_0816.ashx?version=020820170938 has numbers comparing their F1960 type vs others. Their system come out better, of course.
In reality, the article exaggerates for purposes of your shower. Their table is at 8 ft per second (a little over 4 gpm), and shower flows are less. The effect is not linear. The differences at lower flows would be lower.
I don't think that an extra elbow will be noticeable.
In reality, the article exaggerates for purposes of your shower. Their table is at 8 ft per second (a little over 4 gpm), and shower flows are less. The effect is not linear. The differences at lower flows would be lower.
I don't think that an extra elbow will be noticeable.
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Thank you for information, I would just bend the PEX, as I have through most of truss joists I'm running through, with some bend supports in strategic locations, but the joist space I'll be in with the shower valve leaves very little space (5") to bend the tubing, so I though maybe a shower valve exists to just hook into coming up from the bottom, though I haven't located one yet.
Thank you for the table link. Am I understanding this data correctly as the values in the table represent the equivalent length (in feet), so if a value was stated for a fitting as 10.00 then that is the equivalent of the same pressure drop as 10 additional feet of straight piping?
Jadnashua
Retired Defense Industry Engineer xxx
Yes, if the fitting factor is 10, it is equivalent to 10' of straight pipe.
Each brand/type/size of pex will have a minimum bend radius which you can find when looking through their specs. Generically, pex-A has the smallest bend radius, and usually, with that type, the preferred fitting is an expansion type verses a crimp. The expansion fittings have less of an impact on the dynamic pressure because the ID of the fitting is larger (which is why the corresponding OD is bigger, and requires the expansion tool to make the fitting actually fit inside of the tubing). That results in the less friction, because of that larger ID.
Each brand/type/size of pex will have a minimum bend radius which you can find when looking through their specs. Generically, pex-A has the smallest bend radius, and usually, with that type, the preferred fitting is an expansion type verses a crimp. The expansion fittings have less of an impact on the dynamic pressure because the ID of the fitting is larger (which is why the corresponding OD is bigger, and requires the expansion tool to make the fitting actually fit inside of the tubing). That results in the less friction, because of that larger ID.
The cartridge in the valve is the biggest limiting factor.
And then you have a flow restricted shower head on top of that. There is way more water to the valve than the valve will ever put out.
And then you have a flow restricted shower head on top of that. There is way more water to the valve than the valve will ever put out.
Jadnashua
Retired Defense Industry Engineer xxx
It depends on if you're trying to support multiple shower heads or to fill a tub. 1/2" pex is fine for a single showerhead...with more, or for the quickest filling of a big tub, it could be an issue. If you have a tall building, the loss due to trying to push things up that far mean you may want to minimize any other losses that you can account for.
