Size of water pipe

[DStyduhar]

Hi guys, sort of a general question here...

I planned to run 1" poly throughout the entire system (150 feet for well and 160 feet from well to house) but we since decided to add two yard hydrants (each 100ft from main line) and am now reconsidering the pipe size. Someone suggested increasing from 1" to 1.25" to keep the pressure drop low and now it got me thinking....

If 1" will suffice, what are the downsides (aside from $$) in increasing EVERYTHING to 1.25" since I have to buy new anyway? Or maybe keep 1" in the well and have larger pipe at the surface? I have seen a bunch of cases like that. We are in the 10-12GPM range.

Also, the pump we are looking at (10GPM 1HP) has a 1.25" outlet yet I see most folks on forums saying that they bushed and ran straight to 1" pipe. If this is so common why didn't just they make the pump with 1" outlet?

thanks,

Drew

 

[ThirdGenPump]

Friction loss is accross distance so if you have longer runs you'd want to use larger pipe to minimize friction loss. As a standard on a 10gpm pump I'd run 1" pipe. It's at 13gpm pumps that I'd typically bump up to 1-1/4".

A 10gpm pipe maxes out at about 18gpm which is where the friction loss on 1" pipe really starts to come into play. There is a significant cost increase from 1" to 1-1/4" pipe and fittings, so if there isn't a need I avoid it.

It's much easier to bushing down off the pump than it is to go up in size, so the discharge on the pumps is typically the maximum size you'd use with that class of pump. Also they want to minimize the number of different casts they make so there isn't a good reason to make 1" casts. I normally reduce from 1-1/4" to 1" by using a 1/1/4male x 1"female check valve. I don't have much faith in manufacturer check valves and prefer FloMatics.

 

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[Reach4]

If 1" will suffice, what are the downsides (aside from $$) in increasing EVERYTHING to 1.25" since I have to buy new anyway? Or maybe keep 1" in the well and have larger pipe at the surface? I have seen a bunch of cases like that. We are in the 10-12GPM range.

Bigger pipe has less pressure drop. The farther you run with the pipe, the better it is to have bigger.

http://www.pressure-drop.com/Online-Calculator/ is not the simplest, but you might find playing with it interesting.

 

[DStyduhar]

Reach, that's sort of what I'm getting at. With lower pressure loss, why NOT go bigger? Aside from cost.

thanks,

Drew

 

[DStyduhar]

ThirdGen,

thanks again for the feedback. Interesting how you draw the line @ 13 gallon pumps. Where would you roughly draw the line with the 10gpm pump with distance included?

thanks,

Drew

 

[Reach4]

Reach, that's sort of what I'm getting at. With lower pressure loss, why NOT go bigger?

It would be slightly advantageous from less pressure to be bigger. A little more work handling the stiffer pipe.

The deal is that at 12 gpm you might have 7 psi drop with 1 inch and 3.5 psi with 1.25 inch... The drops would be less at 10 or 8 gpm. Would a 3 or 4 psi drop difference matter to you? If so, go big.

 

[ThirdGenPump]

Here is a PVC chart, it has pretty similar losses to poly. I didn't see a poly one readily available.

https://i2.wp.com/floridawaterstar....ingfrictionlosschart.gif?resize=575,776&ssl=1

You can see where they start shading which is where you typically jump to the next size rather than operate in and above those ranges. With enough pressure you can force any amount of water through smaller pipe, but fiction loss cubes so you'd need really big pumps to overcome loss at higher rates, pipe being much cheaper than pumps, you go up in size on the pipe long before you consider a larger pump to overcome friction loss. When forcing more water through smaller pipe you also increase the velocity to do so, any given pipe has a maximum acceptable velocity before the water will start eroding it away.

 

[Boycedrilling]

The other thing to consider in sizing pipe is velocity. It is recommended to keep the velocity of water in the pipe at 5 feet per second or less. Many times we will exceed that velocity in drop pipe though. Excessive velocity is one of the things that creates water hammer.

Only two drawbacks to upsizing pipe that I can think of. First is increased cost of materials. Second is only if you are pumping sand in your water. If the velocity isn’t high enough, the sand will not get flushed out of the pipe.

One area you don’t want to oversize your pipe is your hot water line in your house. I have to wait 50-60 seconds in my bathroom from the time I open a faucet until the water gets hot. It seems like forever. That is a function of pipe size.