Gravity Water Pressure

[johnk]

I was wondering with all the knowledgeble people on here who would know how to figure out the amount of water pressure corresponding to the height of the holding tank. I have a natural spring that I get my water from roughly 60 to 70 ft higher elevation from my cabin that goes into a 250 gallon holding tank. It runs to my cabin through 1" well tubing. My outside hose with nozzle will shoot water roughly 60 feet with no pump. Does anyone know how this is calculated without a gauge??


John

http://users.adelphia.net/~gizmo/

 

[CurlyDave]

For static water, the pressure due to gravity is 1 atmosphere for every 32 feet of water, or 14.7 psi/32 = 0.46 psi per foot.

There will be some pressure drop due to flow through the hose and pipe but this is usually small, if the pipe is sized properly.

In your instance, the height that matters is the difference between the top of the water level in the holding tank, and the outlet you have attached your hose to.

 

[brad_oatley]

1 lb of pressure for every 2.3 feet of water height (head)

 

[EddieWalker]

Water preasure also increases as you downsize pipe. In the gold rush days of California, the miners woudl strip mine using the water preasure from gravity and downsizing pipe.

For example. At the highest point you start with a 4 inch pipe. A quarter of the way down you step it down to a 3 inch pipe. Then next quarte is a 2 inch pipe and the last quarter of the distance is a 1 inch pipe. If you attach a standar 1/2 inch gargen hose to the end of that pipe you will have considerable preasure.

If you ran the whole distance with any sized pipe, but stayed the same size the full distance, than you wold only have the preasure of gravity.

The difference can be HUGE the longer the distance.

Those old time miners had enough preasure to wash away mounain side looking for gold!!!!

You can buy a cheap guage at Lowes or Home depot in the lawn sprinkler section that screws onto a spicket to measure the preasure. I had a house at the bottom of a hill. The water line was 1,200 feet of 1 inch pipe. Preasure at the meter was 80 pounds, but it was 120 at the house!!!

Eddie

 

[Highbeam]

Eddie, for once, I will have to disagree with you.

Pressure will never be higher than the static pressure unless you slam valves shut to create a water hammer effect. The static pressure has nothing to do with pipe size but is based entirely on elevation head.

Things change with flow but the pressure in a pipe can only go down as the flow goes up.

You still get conservation of energy. The miners had incredible flow and not so much pressure that did the work of blasting those hillsides away, the bullet had left the gun. If you stuck a pressure gauge in the line just before their open nozzle you would have found nearly no pressure. High velocity in a pipe means low pressure and is why you can work those liquid fertilizer siphons without a pump.

 

[EddieWalker]

Highbeam,

Thanks for the correction. I defer to your expertise as I was passing on what I was told many years ago at a mining museum.

I've never actually tried the larger pipe to smaller pipe technique to increase preasure, but thought it made sense when it was explained to me.

If I understand it correctly, it was the amount of head on the line that gave them the preasure to wash away the hills. The greater the verticle distance, the more preasure they had for their nozzles.

Thanks, I do have first hand experience whith increased preasure from long runs going down hill, but none at mining. /forums/images/graemlins/grin.gif

Eddie

 

[Egon]

Whatever: Static water pressure is dependant on atmosperic pressure and hight differential. Kinetic water pressure is still dependant on the same principals minus friction/turbulence losses.

Egon

 

[Highbeam]

"If I understand it correctly, it was the amount of head on the line that gave them the preasure to wash away the hills. The greater the verticle distance, the more preasure they had for their nozzles."

That sounds good. Head is the source of energy, the only source without a pump, so more head is more better. High head above their nozzles gave them lots of potential energy which they converted to lots of kinetic energy for the blasting. Maybe it's just terminology like cement vs. concrete, but won't you agree that once that water left the nozzle it is not pressurized at all? The velocity of the water did the work.

I propose that the reduction in pipe size as they neared the nozzle only reduced the effectiveness of the water cannon by creating more loss due to friction. It was likely cheaper to use smaller pipe and easier to move around. The nozzle itself is where the high flow/low velocity is switched to low flow/high velocity. Would have been great fun to run a cannon like that.

Egon: What's the whatever about?

 

[johnk]

When I get up there in a week or so I'm going to take my GPS and get an accurate read on the elevation difference. It may even be higher than I thought.

 

[johnk]

Would putting another holding tank just below the main one help or hinder the pressure or make no difference if I plug the vent on the top of the holding tank installed 10 feet BELOW the top one. I thought it would kind of step up the pressure... The more water in reserve the better. Thanks for all the replies.

John