View Full Version : Gravity fountain, water reservoir


GodLied
08-11-03, 01:28 PM
A general rule of thumb is that water seeks comparable levels. That is why there is no such thing as an infinite siphon or a reverse siphon. So, is it a rule of thumb that a gravity fed fountain will not achieve a height higher than the reservoir that feeds it?

JMG.

spoilsport
08-11-03, 02:25 PM
No, it isn't a rule at all. Make the fountain spicket extremely small in diameter and the reservoir really large (in width and length, low in height). The Venturri effect will easily give the water enough velocity to clear the reservoir.

Pete
08-11-03, 09:28 PM
What's the Venturri effect?

Intuitively, I don't think a gravity fed fountain could exceed the height of the reservoir (unless the reservoir is under extra pressure, of course)... Let me do some maths...

Pete
08-11-03, 11:03 PM
Is the Venturi effect related to the momentum of water in the reservoir as the level falls?

GodLied
08-12-03, 02:16 PM
Originally posted by spoilsport
No, it isn't a rule at all. Make the fountain spicket extremely small in diameter and the reservoir really large (in width and length, low in height). The Venturri effect will easily give the water enough velocity to clear the reservoir.

Spoilsport, I will look into the Venturri effect. However, water pressure depends on depth, not shape. So, water pressure feeding the nozzle depends on depth of water in the reservoir: more depth, more feed pressure. Temperature of the reservoir water changes the density of the water and that changes the depth the reservoir water has to be to operate the nozzle. Water pressure exiting the nozzle depends on the nozzle design. Some low pressure fire hose nozzles operate at a feed pressure of 50 psi. A reservoir has to be pretty deep to feed 50 psi to that low pressure nozzle.

Are you fairly certain a gravity fed fountain can, by the Venturri effect, achieve a height exceeding the height of the reservoir that feeds it?

There must be losses in the transfer of water from the nozzle to the reservoir to prevent the system from being impossible by my prior proof that all perpetual motion devices cannot produce more energy than they contain. Surely the edges of the stream of water might marginally evaporate so that the transfer is not 100% and the transfer is not a perpetual motion mechanism. Losses from evaporation would be the fuel of the system that would need to be added to the reservoir to keep the system functioning: the nozzle has an operating feed pressure that will not be met if the reservoir water level is below a particular value.

Hmm. I will look into the Venturri effect. Marks Standard Handbook for Mechanical Engineers shows Venturi meters but not "Venturri effect." What text did you find "Venturri effect"?

JMG.

spoilsport
08-12-03, 02:40 PM
Venturri effect is the effect that happens when fluid is pushed through an increasingly smaller pipe. To keep the flux equal on each end the fluid must accelerate as it pass through.

In other words, the pipe starts out wide and goes towards an increasingly smaller size until it reaches the nozel.


Hmm. I will look into the Venturri effect. Marks Standard Handbook for Mechanical Engineers shows Venturi meters but not "Venturri effect." What text did you find "Venturri effect"?

I think it was a high school physics textbook actually, but I could be wrong. I could also be wrong about the name or even the effect could not exist. Who knows, memories get mixed up sometimes. Obviously flux has to be equal on both ends of the pipe when it is full of water and the only way I can think that this would happen is by the effect I described, which is exactly the way I remember it from the textbook.

I just found this link too: http://itll.colorado.edu/modules/templates/dsp_body.cfm?action=indphenomenon&phenomenon=118

spoilsport
08-12-03, 02:43 PM
One last thing. I think I am wrong about this now that I consider it could create a perpetual motion machine, but who knows?

GodLied
08-12-03, 02:43 PM
Originally posted by spoilsport
No, it isn't a rule at all. Make the fountain spicket extremely small in diameter and the reservoir really large (in width and length, low in height). The Venturri effect will easily give the water enough velocity to clear the reservoir.

You must have meant Venturi effect. Venturi effect is used to increase velocity and decrease pressure of fluid flow. The height of the reservoir has to be higher than the height of the nozzle to have any flow at all. How low of a height are you forecasting will work with a Venturi nozzle to achieve circular fluid flow by a gravity fed fountain that feeds the reservoir powering the fountain?

JMG.

spoilsport
08-12-03, 02:52 PM
You must have meant Venturi effect. Venturi effect is used to increase velocity and decrease pressure of fluid flow. The height of the reservoir has to be higher than the height of the nozzle to have any flow at all. How low of a height are you forecasting will work with a Venturi nozzle to achieve circular fluid flow by a gravity fed fountain that feeds the reservoir powering the fountain?

I guess you hadn't read my new comments yet, but it occurred to me that the it would allow a circular flow, which is clearly impossible.

GodLied
08-12-03, 11:42 PM
Originally posted by spoilsport
I guess you hadn't read my new comments yet, but it occurred to me that the it would allow a circular flow, which is clearly impossible.

Water hammer devices allow for pumping water up stream but there are losses of water which prevents the water hammer device from being a perpetual motion device.

A fountain squirts water upstream but not likely higher than is necessary to provide constant operating pressure for the fountain. There are nozzles that adjust to variable pressure to maintain a stream of water at various input pressures. Hmmm, I still doubt the potential for a venturi effect to allow water to flow out of a basin's bottom into a basin's top.

JMG.

GodLied
08-13-03, 12:01 AM
Originally posted by Pete
What's the Venturri effect?

Intuitively, I don't think a gravity fed fountain could exceed the height of the reservoir (unless the reservoir is under extra pressure, of course)... Let me do some maths...

The Venturi effect is why some brass/plastic twist hose nozzles can squirt over a house and others of different designs cannot at the same input water pressure. However, a house is not as high as the column of water to produce the input pressure of county water.

Suppose you want to have an input pressure of 50 psi, the column of source water has to be over 90' high. Is there a 50 psi nozzle that can shoot a stream of water 100' high at an angle to refill the column of water? Probably not.

JMG.

Pete
08-13-03, 01:06 AM
If a perfect liquid under constant pressure P is forced out an opening of area A, is there a formula for the velocity of the ejected liquid?

GodLied
08-13-03, 02:06 PM
Originally posted by Pete
If a perfect liquid under constant pressure P is forced out an opening of area A, is there a formula for the velocity of the ejected liquid?

There should be, ask Spoilsport.

However, if a low pressure 50psi fire hose nozzle can shoot water to a point on a building 116 feet above the height of the nozzle, then the Venturi effect allows circular motion of fluid minus evaporation losses.

JMG.

spoilsport
08-13-03, 08:56 PM
A fountain squirts water upstream but not likely higher than is necessary to provide constant operating pressure for the fountain. There are nozzles that adjust to variable pressure to maintain a stream of water at various input pressures. Hmmm, I still doubt the potential for a venturi effect to allow water to flow out of a basin's bottom into a basin's top.

Yeah, I definitely doubt it too, although it would be pretty freaking awesome. I really want to try and expirement with this. Maybe once work slows down I'll find the time mess around with physical items.

GodLied
08-14-03, 08:06 PM
Originally posted by spoilsport
Yeah, I definitely doubt it too, although it would be pretty freaking awesome. I really want to try and expirement with this. Maybe once work slows down I'll find the time mess around with physical items.


The worlds highest gravity fountain does not squirt higher than the source of its feedwater.

All of the world's lesser gravity fountains do not squirt higher than the source of their feedwater.

Using firehose nozzles as a basis, data does not give answers to prove or disprove my corrollary that a nozzle does not exist which will allow water to fountain into the basin that feeds the fountain.

Nozzle design matters: some nozzles reach farther than others with the same psi and gallons per minute (gpm). Data from Elkhart Brass shows some 50psi nozzles that can, at a height of 4 feet and an angle of 32 degrees in still air conditions, reach a point on the ground that is 200 feet from the nozzle. That does not answer the question if the nozzle can shoot a target 116 feet above the nozzle. That angle might have to be steeper than 45 degrees. Wind can stop the system altogether by preventing the water from entering the basin.

JMG.

Pete
08-14-03, 08:13 PM
I think a fire hose might be a different case... Do fire hose pumps produce constant flow, constant pressure, or something else?

GodLied
08-18-03, 03:22 AM
Originally posted by Pete
I think a fire hose might be a different case... Do fire hose pumps produce constant flow, constant pressure, or something else?

Usually a fire hose is connected to a fire hydrant. Without a fire hydrant, water is pumped from a reservoir such as a water tank. In the case of a fire hydrant, pressure depends on the number of hoses and the number of hydrants in use at one time. In the case of pumped water from a reservoir, pressure can be constant while supply drops with use.

If there is a fire department whose 50psi nozzle can eject water to reach a target 116 feet above the nozzle, then one can make a perpetual motion machine that violates my general rule that no such machine can exist. If there is a 50psi nozzle that can eject water significantly higher than 116 feet, water can be made to flow uphill.

JMG.

Pete
08-19-03, 08:57 AM
What precisely does "50psi nozzle" mean? (with references, if possible)

GodLied
08-21-03, 01:50 PM
Originally posted by Pete
What precisely does "50psi nozzle" mean? (with references, if possible)

Nozzles from Elkhart Brass perform based on the water pressure entering the nozzle. To measure that pressure, a gauge is placed between the nozzle and the hose. When I refer to a 50 psi nozzle, I mean a nozzle fed with 50 pounds-per-square-inch water pressure. Some nozzles designed to operate at a higher water pressure will not reach very far at 50 psi.

The effective reach, farthest distance water touches ground, depends on water pressure and the flowrate. Pressure and flowrate are directly proportional to effective reach. An increase in pressure increases effective reach. Also, an increase in flowrate increases effective reach.

To see the effect of pressure on effective reach, get a paper or plastic jug. Fill it with water. Leave the lid off. Puncture the sides at different heigts. The lowest punctures have the highest effective reach because water pressure increases with depth. This example may be found on the internet as a lesson plan for school children.

To see the effect of flowrate and effective reach, buy a cheap spray bottle from a garden supply store. Those multipurpose bottles can either emit a steady stream or a mist. Mist does not go as far as a steady stream. Mist permits less flow than steady stream. A hairstylist might mist a persons hair while another person might use the steady stream setting to squirt a cat off a couch from across the room.

JMG

GodLied
08-21-03, 02:01 PM
Originally posted by GodLied
.... Mist permits less flow than steady stream. ...


Oh, because mist evaporates, a misting nozzle can put water higher than a reservoir but the mist will not do work unless it is condensed. That is why micro nozzles cannot make perpetual fountains.

JMG.

Pete
08-21-03, 06:11 PM
Nozzles from Elkhart Brass perform based on the water pressure entering the nozzle. To measure that pressure, a gauge is placed between the nozzle and the hose. When I refer to a 50 psi nozzle, I mean a nozzle fed with 50 pounds-per-square-inch water pressure.

Is there a pressure gradient along the nozzle? Is the exit pressure higher than the entry pressure? Would such a gradient exist in a gravity-fed system?

GodLied
08-22-03, 01:01 PM
Originally posted by Pete
Is there a pressure gradient along the nozzle? Is the exit pressure higher than the entry pressure? Would such a gradient exist in a gravity-fed system?

Nozzle design can consider the Bernoulli equation. Using the Bernoulli equation and having the center of the nozzle the same height as the center of the inlet pipe, the equation simplifies. If the mouth of the nozzle is smaller than the butt of the nozzle, water flows faster out of the nozzle than it did flowing into the nozzle. With that understanding and the Bernoulli equation, a nozzle reduces pressure and increases velocity; or, increases pressure and reduces velocity. Such facts of construction work no matter what supplies the water pressure.

Am off to town.

JMG.

GodLied
08-23-03, 05:08 AM
Let me provide some equations. Consider a symmetrical conical nozzle. Let its diameter that connects to the hose be D. Let its diameter that does not connect to the hose be d. Let V_1 be the velocity of water entering the nozzle and let V_2 be the velocity of water exiting the nozzle.

V_2 = ((D/d)^2)V_1

Let P_1 be the pressure entering the nozzle and P_2 be the pressure exiting the nozzle. Let p be the density of the water flowing through the nozzle.

P_2 = P_1 + p((V_1)^2)(1 - (D/d)^4)

With those pressure and velocity relations one can state the Venturi effect. However, I have previously considered it is impossible for there to be a nozzle such that the ejected water will exceed the height of a column of water providing pressure P_1 to feed the nozzle. If you can find such a nozzle, you can make water flow uphill. Once up a high hill, water can fall and generate power. Such a system generates more power than is necessary to replace water lost to evaporation. Such a system, although not perfect, produces more energy than is put into it. Such a nozzle cannot exist.

Oh, the higher one goes, the less water weighs, the higher the column of water to produce the desired P_1. In addition, water density varies with temperature. Any change in density changes the height of a column of water to produce the desired P_1.

JMG.

WaterGuy
05-10-10, 02:30 PM
Well all you people are being mislead. It can be done and has been done. Raising water up a tube /PVC pipe to a height higher than the source using air pressure had been done by the Greeks some 1700 years ago. Look up Heron of Alexandria and you will find this has all been done.


email me if would like a graphic of the process.

michael.mulvey@roadrunner.com

Pete
05-10-10, 05:02 PM
Thanks Water guy, but the original post specified "gravity fed fountain".

We know that you can raise water higher than the source if you use a pump driven by another source of energy.