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How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.


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Old 11-30-2013, 03:40:08 PM
len k len k is offline
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Default How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.

This question seems to come up often enough, so here's the way I remember the answer.

How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.
This is just another way of saying what is pressure at bottom of a collumn of liquid 1 foot high.

I imagine a box 1 foot on all 3 sides. Force on bottom is weight of liquid inside (for water it's 62.4 #). Surface area of bottom is 12" x 12" = 144 square inchs. So pressure on bottom is 62.4 #/ 144 sq in = 0.433 psi.

If hose is 10 ft, high pressure at bottom is 10 ft x 0.433 psi/ft = 4.33 psi

If liquid is gasoline, use specific gravity of gas (~.73) to ratio the answer.
Presure of 1ft collumn of gasoline is .433 x .73 = .316 psi


water ----- 0.422 psi/ft ---- (~1/2 psi /ft)
gasoline ----0.316 psi/ft ---- (~1/3 psi /ft)

When selecting pump add extra pressure to account for filters and friction losses of hose, when fluid is flowing.

Hope someone finds this usefull.

Last edited by len k; 11-30-2013 at 03:51:53 PM.
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Old 11-30-2013, 04:32:57 PM
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Default Re: How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.

This gauge from a hot water heating system shows the relationship between altitude (height of water column in feet) and pressure.
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Old 11-30-2013, 07:00:51 PM
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Default Re: How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.

Is that a photo of an electric hot water heater set up as a hot water boiler
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Old 11-30-2013, 07:33:29 PM
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Default Re: How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.

Yep. 50 gal electric water heater with a circulator pump feeding 2 heat exchangers hanging from the ceiling. Filled with a 50/50 mix of antifreeze & distilled water.
No gas service (by choice) at the shop. Actually does a pretty good job.


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Old 11-30-2013, 08:27:54 PM
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Default Re: How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.

Did you change out the OEM Temperature & Pressure Relief Valve in the Water Heater to 30lb Boiler Relief Valve?
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Old 12-01-2013, 03:42:23 AM
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Default Re: How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.

T&P valve is original. Has never blown open yet. Highest pressure I have seen is 15psi. Water doesn't go over 140°. I have an expansion tank in the loop that is more than adequate for the size of my system.
I ran seperate 10ga feed lines (on seperate breakers) to both 4500 watt elements and can run both at the same time. Both elements have over temp cut-off protection. At $0.10 / KWH it still costs under $1.00 an hour to run including the pump and fans. I just have to remember to turn the element breakers off an hour before I plan to leave so I don't leave a tank full of hot water behind.
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Old 12-01-2013, 08:32:41 AM
Graycenphil Graycenphil is offline
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Default Re: How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.

Is that cheaper, or better, than just running electric heat?
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Old 12-01-2013, 09:43:55 AM
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Default Re: How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.

Quote:
Originally Posted by John Newman, Jr. View Post
T&P valve is original. Has never blown open
The T&P Valve should be changed to a standard 30lb relief valve.
The O.E.M. T&P valve is not designed for operating a Boiler, which is what you've created. It requires far too high of a pressure to Trip.

My suggestion would be to install a Tee in the relief tapping. Install the correct Pressure relief valve in the side outlet of the Tee, and Bush the top outlet to accept a Taco or equivalent Auto Vent.
This will provide Air elimination from the top of the tank, since you now have a "closed system"

Last edited by BlkBeard; 12-01-2013 at 09:51:58 AM. Reason: clarity
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Old 12-01-2013, 10:19:14 PM
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Default Re: How to calculate ...Pressure it takes to lift a liquid 1 foot, in a hose.

Now, why would there be air at the top of the tank? Hot water outlet is at the same level as the T&P fitting. System has been running since January 2011.
"...Is that cheaper, or better, than just running electric heat?..."
I get more heat faster than anything else I have tried except the kero torpedo heater. Even burning diesel in it, it still cost $4.00 an hour to use that. This is much quieter, doesn't smell and no risk of carbon monoxide death. Does a better job of getting the heat distributed throughout the building (25' X 90'). I do have a few 6' baseboard heaters along the walls and you do not feel their heat once you get more than about 3' away from them. I am running a couple of ceiling fans to stir things up, too.
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