Pressure flow pipe size question

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icatchlarge

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Complicated question here but I’ll start:

we have a well that feeds our Main house, (over 1 inch line, unsure) then goes to 3/4 in the basement, two filters and a neutralizer, then out running 3/4 line 225 ft winding uphill to a cottage. Pressure issue is up there.

a guy dug the whole thing and mistakenly replace the original 1 inch galvanized steel (which connected down from the cottage to the 3/4 filter area in the main) with 3/4 PEX. So he went smaller accidentally.

a plumber told me he put the wrong one in, should have been 1 or even 1 1/4 inch all that way. But, I don’t know if the plumber is taking into account the 3/4 reduced diameter area.

He has agreed to replace the line for free. Remember, the line would pass the filters etc through 3/4 and then go to 1 1/4 inch, replacing the current 3/4 connection to the 3/4 filter area.

So, big to small to big, vs the current big to small to remaining small for 225 feet.

However now I’m wonder:

1) would the size diameter increase after the filter 3/4 area in the main house to 1 1/4 (currently it is 3/4 the whole way remember) area matter at all, due to the reduced size after the well in the filter area? Could it potentially be worse? Or is it still an improvement since there is 200+ feet of bigger pipe? Hard to find this on the net.

remember it’s:
Current: big pipe to small to 225ft small
Vs: big pipe to small to 225ft big

Thank you!!!
 
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wwhitney

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What's the elevation difference between the main house and the cottage, and is the only source of pressure in the system the well pump? What are the settings on the pump pressure switch and the pressure tank?

You lose pressure due to elevation gain, 1 psi for every 2.3 ft of elevation, just from the weight of water. Say the only source of pressure is the well pump, and you have it controlled by a 40/60 pressure switch, so at the house you'll see 40 to 60 psi. So if the pressure sensor is in the basement, and you look at pressure at a shower head on the first floor 11 ft higher up, you'll see 35 to 55 psi. And if a shower head on the second floor is another 11 ft up, it will see pressure of 30 to 50 psi.

So now if your cottage is say, 45 ft higher than your pressure switch, it will see at best pressure of 20 to 40 psi, regardless of the size of the pipe leading to the cottage. Where the pipe size comes in is how much that pressure drops further when you try to draw water at a a significant rate. Larger pipe is always better in that regard, but the frictional pressure losses from flow add up, so you will still see pressure loss from the earlier smaller diameter segment. At a certain point, that pressure loss dominates and there's no point to upsizing further.

For example, if you only ever draw 2 gpm at the cottage, that 225' of 3/4" PEX (ID of 0.68") is only going to cause 2.3 psi of pressure loss. But if you were able to draw 10 gpm, it would cause 44.4 psi of pressure loss. And that's just that length of pipe, the pressure loss from the filters and everything earlier is on top of that.

So the upshot is that upsizing the cottage lateral will reduce one component of pressure loss, but you need to look at all the components of pressure loss to be sure that's the correct place to focus your efforts.

Cheers, Wayne
 

icatchlarge

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What's the elevation difference between the main house and the cottage, and is the only source of pressure in the system the well pump? What are the settings on the pump pressure switch and the pressure tank?

You lose pressure due to elevation gain, 1 psi for every 2.3 ft of elevation, just from the weight of water. Say the only source of pressure is the well pump, and you have it controlled by a 40/60 pressure switch, so at the house you'll see 40 to 60 psi. So if the pressure sensor is in the basement, and you look at pressure at a shower head on the first floor 11 ft higher up, you'll see 35 to 55 psi. And if a shower head on the second floor is another 11 ft up, it will see pressure of 30 to 50 psi.

So now if your cottage is say, 45 ft higher than your pressure switch, it will see at best pressure of 20 to 40 psi, regardless of the size of the pipe leading to the cottage. Where the pipe size comes in is how much that pressure drops further when you try to draw water at a a significant rate. Larger pipe is always better in that regard, but the frictional pressure losses from flow add up, so you will still see pressure loss from the earlier smaller diameter segment. At a certain point, that pressure loss dominates and there's no point to upsizing further.

For example, if you only ever draw 2 gpm at the cottage, that 225' of 3/4" PEX (ID of 0.68") is only going to cause 2.3 psi of pressure loss. But if you were able to draw 10 gpm, it would cause 44.4 psi of pressure loss. And that's just that length of pipe, the pressure loss from the filters and everything earlier is on top of that.

So the upshot is that upsizing the cottage lateral will reduce one component of pressure loss, but you need to look at all the components of pressure loss to be sure that's the correct place to focus your efforts.

Cheers, Wayne

thank you Wayne! I had a feeling more info may be needed. So:

- yes significantly higher. I don’t know how much, but uphill, and I would estimate just by the naked eye 3rd or 4th story higher then well...

- info you mentioned, don’t know well setting, but I have observed 40psi on the gauge in well and also I have observed 40psi in the basement, after filters, before cottage run.

-I have observed 30 psi in cottage after that run, on new line 3/4.

-after line in cottage was run into a diaphragmatic tank up there (119 gallon Dayton, old, psi of 38 but previous owner said he reduced it for some reason) psi was improved to 40. Water pressure is good to livable initially up there when using, but when using water it can get poor I suspect as the tank empties and it calls/competes with us down hill.

so with that info- primary question is, will a new 1 1/4 pipe be “better” then the 3/4 existing pipe main house, with all those variables? Plumber here says yes, but at this point I want to know it’s worth their effort to fix their “mistake”.

Plumber here says “flow” will still be better with a bigger pipe over that distance. Is he correct? If it is improved is a little, that might make all the difference because we are close. But scientifically I don’t fully understand the “disruption” in flow at the 3/4 filter area. Thanks again!
 

Reach4

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So a short comment: pressure drops from flow (dynamic) add. So just because you use 3/4 to a point, that doesn't mean that using 1-1/4 after is useless. For an analogy, if you have to walk through 300 ft of sand (hard walking) doesn't mean that having a concrete walk the rest of the way (easy walking) is a waste. OK that's a bit of an exaggeration to make a point.

The pressure drops from altitude (static) are what they are-- almost 1/2 psi lost per foot of altitude rise.

There are pipe pressure drop calculators available if you want to add up the drops.
 

wwhitney

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So, you have a well pump, a pressure tank in your main house basement, and a pressure tank in the cottage? No booster pump at the cottage? Then the well pump is the only source of pressure, but the two tanks can store it. [I would think you'd have a chcek valve on the supply side of the cottage pressure tank, so that its storage capacity is just for the cottage, rather than shared with the main house.]

What usage at the cottage is it for which you find the pressure anemic?

With time and a pressure gauge you could do the following tests to characterize what you currently have: (or failing that, hopefully you can consider the tests as a thought experiment to help understand the difference sources of pressure loss):

1) For a baseline, put a pressure gauge on a hose bibb in the main house, preferably just after the filters. Turn on a lavatory faucet to about 0.5 gpm and observe the behavior of the pressure gauge. It will probably do something like start off at say 50 psi, slowly fall to 40 psi, then start rapidly rising up to 60 psi, then start slowly falling again. That would be the behavior with a 40/60 setting on the pressure switch controlling your pump, and the hose bibb at the same elevation as the pressure switch.

2) Then repeat the test with a higher draw to determine the effect of your filters, assuming the filters are the only thing between the pressure switch and the hose bibb. E.g. start filling a tub and measure the flow rate, say it's 5 gpm. You might find the pressure behavior is now that it falls to 37 psi and then rises to only 57 psi. The 3 psi difference from the behavior before is the pressure drop imposed by your filters at 5 gpm flow (I just made up those numbers).

3) Now repeat test 1 but up at the cottage. Say you find the behavior is that instead of 40/60, you see 25/45. That 15 psi shift is entirely due to elevation (assuming that frictional losses at 0.5 gpm are negligible.) That would mean your cottage hose bibb is about 35 ft higher than your main house hose bibb (15 psi * 2.31 ft/psi).

4) Lastly, repeat test (2) at the cottage. If you are able to get the same flow rate (5 gpm in my example), then if the pipe between your two measuring points were huge and caused no frictional pressure loss, you'd see exactly the sum of the two effects already measured, so 22/42 in this example. To the extent that you see lower pressure, like say 15/35, that lower pressure is attributable to the frictional losses in the piping between the two measuring points, which would be dominated by the 225' cottage lateral. So that's the only pressure loss that could be reduced by upsizing your cottage lateral.

Now in step 4 it seems likely you won't be able to get the same flow as in step 2 because of the additional piping distance. So to properly do the comparison you'd need to redo step 2 but throttle the flow rate to match the flow rate you measured in step 4. Which would be an argument for doing step 4 before step 2, unless you are interested in better characterizing the pressure loss of your filters.

And of course, this is a somewhat idealized version of your setup, you may have some other components or piping that causes some pressure loss, the hose bibbs may not be in the optimal place for pressure measurements, etc.

Cheers, Wayne
 

icatchlarge

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So, you have a well pump, a pressure tank in your main house basement, and a pressure tank in the cottage? No booster pump at the cottage? Then the well pump is the only source of pressure, but the two tanks can store it. [I would think you'd have a chcek valve on the supply side of the cottage pressure tank, so that its storage capacity is just for the cottage, rather than shared with the main house.]

What usage at the cottage is it for which you find the pressure anemic?

With time and a pressure gauge you could do the following tests to characterize what you currently have: (or failing that, hopefully you can consider the tests as a thought experiment to help understand the difference sources of pressure loss):

1) For a baseline, put a pressure gauge on a hose bibb in the main house, preferably just after the filters. Turn on a lavatory faucet to about 0.5 gpm and observe the behavior of the pressure gauge. It will probably do something like start off at say 50 psi, slowly fall to 40 psi, then start rapidly rising up to 60 psi, then start slowly falling again. That would be the behavior with a 40/60 setting on the pressure switch controlling your pump, and the hose bibb at the same elevation as the pressure switch.

2) Then repeat the test with a higher draw to determine the effect of your filters, assuming the filters are the only thing between the pressure switch and the hose bibb. E.g. start filling a tub and measure the flow rate, say it's 5 gpm. You might find the pressure behavior is now that it falls to 37 psi and then rises to only 57 psi. The 3 psi difference from the behavior before is the pressure drop imposed by your filters at 5 gpm flow (I just made up those numbers).

3) Now repeat test 1 but up at the cottage. Say you find the behavior is that instead of 40/60, you see 25/45. That 15 psi shift is entirely due to elevation (assuming that frictional losses at 0.5 gpm are negligible.) That would mean your cottage hose bibb is about 35 ft higher than your main house hose bibb (15 psi * 2.31 ft/psi).

4) Lastly, repeat test (2) at the cottage. If you are able to get the same flow rate (5 gpm in my example), then if the pipe between your two measuring points were huge and caused no frictional pressure loss, you'd see exactly the sum of the two effects already measured, so 22/42 in this example. To the extent that you see lower pressure, like say 15/35, that lower pressure is attributable to the frictional losses in the piping between the two measuring points, which would be dominated by the 225' cottage lateral. So that's the only pressure loss that could be reduced by upsizing your cottage lateral.

Now in step 4 it seems likely you won't be able to get the same flow as in step 2 because of the additional piping distance. So to properly do the comparison you'd need to redo step 2 but throttle the flow rate to match the flow rate you measured in step 4. Which would be an argument for doing step 4 before step 2, unless you are interested in better characterizing the pressure loss of your filters.

And of course, this is a somewhat idealized version of your setup, you may have some other components or piping that causes some pressure loss, the hose bibbs may not be in the optimal place for pressure measurements, etc.

Cheers, Wayne
Thanks Wayne, sounds like an exciting experiment!

I guess where Im at though is the guy is coming back Monday to change the 225ft 3/4 line to a 1 1/4 line. Elevation is the same, as is track of the line etc. My simple question is, after being interrupted by a 3/4 section of filters, does physics say that changing to a 1 1/4 bigger line be X better? I don't really need to know at the moment how much better (because I assume a bigger pipe going up there is a good idea, even if I have to do more work like tap into the well line directly (which would unfortunately avoid filters and neutralizers.)

If the answer is yes then I'll be confident to go forward and know this is an improvement. Remember, the original line of this section was 1 inch (before the current 3/4) , so he mistakenly downsized to 3/4.
 

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Thanks all, another question: I was advised by a plummer to use a "Poly" pipe instead of Pex for the 1 1/4inch new line, with fittings and clamps. Is this a better idea in your opinion then the Pex? The 3/4 installed is currently a Pex.

Is "Poly" Polyethylene?
Guy is coming Monday and I need to watch everything that happens here. Any advice appreciated as to what to watch out for in connections, types of fittings, etc.

And indeed, at 6 gpm from our basement, (which I checked with a bucket) and running 225 ft in a 3/4, (excluding elevation factor) friction chart says 8.91 psi loss! At 1 1/4inch, it is below 1.0- incredible. this needs to be done. And, it jumps to 12 psi loss and beyond if I ever add 7 or more gpm in the basement and left the current 3/4 line. Psi loss is negligible friction-wise at 1 1/4 line.
 

icatchlarge

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Oh, and I believe his point probably had to do with the fact that you need to upsize a Pex even more then the original galvanized steel. So maybe Poly is a better material vs. Pex in terms of flow and psi loss? If so, is it a material that will last the test of time? Thanks again.
 

Reach4

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Poly should be polyethylene. SIDR sized pipe fits barbs, and you secure the barbs with two worm-gear stainless steel clamps, with the worms on opposite sides.

SIDR poly is cheaper than pex in the bigger sizes, and is bigger ID for a given nominal size. ASTM D2239 is the applicable size spec, and you may see that term.

For reasons I don't understand, I think HD calls this pipe IPS polyethylene pipe, but I would search further to make sure of that.
 

icatchlarge

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Poly should be polyethylene. SIDR sized pipe fits barbs, and you secure the barbs with two worm-gear stainless steel clamps, with the worms on opposite sides.

SIDR poly is cheaper than pex in the bigger sizes, and is bigger ID for a given nominal size. ASTM D2239 is the applicable size spec, and you may see that term.

For reasons I don't understand, I think HD calls this pipe IPS polyethylene pipe, but I would search further to make sure of that.


Thank you very much very helpful, since I will be the lookout tomorrow on this guy. Also, how does this connect to copper? Looks like I'll have to make sure he heats every connection also. I'd like him to cut out a leaky valve and re-do the shutoff valve and the water drain valve, but I don't know how much more complicated it is going to copper from Poly vs from Pex (which he did last time.)
 

Reach4

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Thank you very much very helpful, since I will be the lookout tomorrow on this guy. Also, how does this connect to copper? Looks like I'll have to make sure he heats every connection also. I'd like him to cut out a leaky valve and re-do the shutoff valve and the water drain valve, but I don't know how much more complicated it is going to copper from Poly vs from Pex (which he did last time.)
Usually with MIP thread adapters. The word used for the adapter part that goes into the poly pipe is "insert" fitting.
bma-125nl-2.jpg


Let me say that there are other polyethelene pipes which are good that are not SIDR. They use some adapters that are not barbs. If that is what your plumber is used to, that is good too.
 

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OP, I did not make it through all the replies but I wanted to provide some helpful info. I am in the engineering field and run stuff like this daily. One thing you must realize is pressure drop through a pipe is relative to the flowrate you try to flow through it. If you only need .1GPM through a 3/4 line at that distance, that is no problem, but under normal house flowrates, that will be a problem.

I actually just ran some calcs on a very similar job and recommended 1.25" HDPE pipe. I think once you swap out that very long run with the bigger pipe, you will get the performance you are looking for. If not, report back. Another simple test procedure is to install cheap pressure gauges in various places so you can observe the pressure drop.

There are some variables in determining pumped head needs, but lets just see what the new line does first. I suspect that will fix ya.
 
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