Water Flow Calculation

[JPS35]

I need some help calculating water flow and can't find a good calculator/formula to do it. So, hoping some of you might be able to help. Water pressure at spigot is 65psi and 5gpm. Looking to do about 750' of garden hose - 3/8, 1/2, or 5/8 whichever makes the most sense (assuming 5/8 as it is the largest that allows for the most water flow) up a 10 degree angle to the top of a hill. I am assuming with these numbers, it is likely to be a trickle of water that comes out. However, is there a way to calculate gpm with this?

 

[BoomerD]

I need some help calculating water flow and can't find a good calculator/formula to do it. So, hoping some of you might be able to help. Water pressure at spigot is 65psi and 5gpm. Looking to do about 750' of garden hose - 3/8, 1/2, or 5/8 whichever makes the most sense (assuming 5/8 as it is the largest that allows for the most water flow) up a 10 degree angle to the top of a hill. I am assuming with these numbers, it is likely to be a trickle of water that comes out. However, is there a way to calculate gpm with this?

You also need to know the rise...how much elevation between water source and the end.

 

[JPS35]

You also need to know the rise...how much elevation between water source and the end.

Correct. I will have to get this information first. Sorry.

 

[IronWing]

750 feet running up a 10 degree slope yields a ~130ft elevation gain.
130ft hydraulic head = 56.5 psi
This gives you about 20ft (8.5 psi) of useful hydraulic head.

According to this site:

Hoses - Pressure Loss vs. Water Flow

Pressure loss in hoses due to water flow and friction.

www.engineeringtoolbox.com

Allowing an 8.5psi loss in a 750 foot hose (5/8" diameter) chart (first chart) yields that you would get ~0.45 gpm out of the hose.

 

[JPS35]

750 feet running up a 10 degree slope yields a ~130ft elevation gain.
130ft hydraulic head = 56.5 psi
This gives you about 20ft (8.5 psi) of useful hydraulic head.

According to this site:

Hoses - Pressure Loss vs. Water Flow

Pressure loss in hoses due to water flow and friction.

www.engineeringtoolbox.com

Allowing an 8.5psi loss in a 750 foot hose (5/8" diameter) chart (first chart) yields that you would get ~0.45 gpm out of the hose.

Thank you, IronWing. I have the same calculation for height of 130 feet and calculation of pressure loss of about 56.5psi. I am struggling to use the chart or formula to determine the .45gpm out of the hose.

 

[IronWing]

You have 8.5 psi to play with after accounting for the elevation head loss so you can back out the flow rate approximation. On the top chart find ~8.5 psi and move horizontally across the chart until you hit the diagonal 5/8" hose line. Now move vertically down to the x-axis to read the corresponding gpm.

Edit: Hmm. That was per hundred feet of hose length so you might not get any flow with 750 feet of hose. Since the fictional loss drops with flow rate, I think you will still get something since the there is 20tf of hydraulic head acting on the system and that is still pretty good. We have a 400 ft gravity drain hose system with 40 ft of elevation drop and a 1/2" hose which yields about 2.75 gpm.

 

[JPS35]

You have 8.5 psi to play with after accounting for the elevation head loss so you can back out the flow rate approximation. On the top chart find ~8.5 psi and move horizontally across the chart until you hit the diagonal 5/8" hose line. Now move vertically down to the x-axis to read the corresponding gpm.

Edit: Hmm. That was per hundred feet of hose length so you might not get any flow with 750 feet of hose. Since the fictional loss drops with flow rate, I think you will still get something since the there is 20tf of hydraulic head acting on the system and that is still pretty good. We have a 400 ft gravity drain hose system with 40 ft of elevation drop and a 1/2" hose which yields about 2.75 gpm.

Okay, but wouldn't it be closer to 4.8gpm on the bottom for 100 feet, not .48? Something seems off if there is 5gpm at the spigot. 4.8 at the elevation head loss seems high.

 

[deadlyapp]

If you want to do the most accurate calculation, segment the hose into 50 or 100ft segments and calculate the pressure drop through each.

The right thing to do is use Bernoullis and work backwards to get the requisite pressure at the source to get the flow rate you want at the end of the hose. You have the losses from the hose length based on flow you want, you have losses due to elevation, and you can assume pressure at end to be basically zero/atmosphere.

 

[waffleironhead]

Can you use poly tubing for the project? It should have lower friction loss vs garden hose. Its kind of a pita to lay flat and uncoil so you'd need to attach it though.

 

[Charmonium]

The Pythagorean theorem is your friend. Of course if all you have is the length of the slope and an adjacent angle, you might need some trigonometry.

 

[JPS35]

The Pythagorean theorem is your friend. Of course if all you have is the length of the slope and an adjacent angle, you might need some trigonometry.

Already did that which is how I calculated 130 feet high for the hill. It is being used for potable water for a trailer or tiny house. Looking at CPVC or PEX, not sure about HDPE (smooth inside, but has some issues with weathering, cracking, etc.). Have another spigot on the house that does 70psi with 20gpm. That would give it about 13.71psi at the top of the hill (130 feet) accounting for gravity psi loss of .433psi per foot of elevation. Just not sure what the gpm would be at the end of the 750' pipe with 10 degree rise. I would guess this is enough pressure at the terminal end to have some water come out and fill a storage tank. I would think something like a pump, if needed, would be even better to increase the gpm. Then, pipe the water from the tank to the tiny house.

 

[Charmonium]

This might be helpful

Head Pressure Wizard (Advanced) - Everything-Ponds.com

A simple wizard to simplify complex pond head pressure calculations!

www.everything-ponds.com

 

[Paperdoc]

You've looked at starting from two different spigots in the house with different pressure and flow readings. Those alone will illustrate that one real limit on your efforts is where you START from. The pipe diameter and valve size at each of those spigots is limiting you. It would be better to install a new length of pipe (same size as the main water pipes in your house) to the new exterior location with a full-bore shut-off valve (like a ¼-turn ball valve of at least ½" diameter) to maximize the potential flow rate feeding that long hose. And yes, that larger the hose diameter, the less flow restriction it creates.

NOTE you say this is for potable water. I am reminded that I bought a new garden hose recently and it specifically said it is NOT for use in drinking water because it is made with mixed recycled materials. You MUST use some piping that is approved for potable water supply systems.

 

[IronWing]

Also, install a back-flow preventer to keep hose water out of your house.

 

[JPS35]

You've looked at starting from two different spigots in the house with different pressure and flow readings. Those alone will illustrate that one real limit on your efforts is where you START from. The pipe diameter and valve size at each of those spigots is limiting you. It would be better to install a new length of pipe (same size as the main water pipes in your house) to the new exterior location with a full-bore shut-off valve (like a ¼-turn ball valve of at least ½" diameter) to maximize the potential flow rate feeding that long hose. And yes, that larger the hose diameter, the less flow restriction it creates.

NOTE you say this is for potable water. I am reminded that I bought a new garden hose recently and it specifically said it is NOT for use in drinking water because it is made with mixed recycled materials. You MUST use some piping that is approved for potable water supply systems.

Yup. Will be going from the main pipe and lay CPVC to a holding tank. It will use a shut off valve as well. Thanks.

 

[Charmonium]

I don't know about other folks both near and far, but water pressure around here can vary noticeably. So regardless of what 'spot' readings you might be getting for PSI, having an accessible line segment where you could add a pump, should that ever be necessary or desirable, would be worth doing.

It's always worth building with the possibility of future changes and upgrades in mind.