Hey, smart people. I've been having a discussion with a firefighter that's gone something like this (heavily paraphrased): He: You know you can only lift water about 28ft with a pump? It's physically impossible to pump it higher than that if the pump is at the top of the lift. (e.g., a pump at the top of a well, something like that) Me: I think that's only a limit for a vacuum pump. Doesn't it work if you prime the pump from the top? He: I repeat, it's physically impossible to pump water higher than 30ft with an elevated pump. I made this diagram to try to describe what I was thinking, since he wasn't understanding my explanation: http://www.ericjacobsen.org/pics/Pumpsnstuff.jpg The pertinent stuff is Example 3, where Case A is the limit imposed by trying to lift water with a vacuum pump. The pressure differential between 1 Atm and a complete vacuum created behind the pump is the limitation, so I suggested Case B and Case C, where a prime tank with enough volume to fill the pipe and the pump is used to prime the system, so that the pressure differential is no longer limiting the ability to lift the water. So far the response is simply, "That won't work." Apparently common firefighter training conveys that this is impossible, but I'm failing to see why. I've found little on the internet with the searches I've tried, with the exception of how trees pump water as high as, apparently, 450m under tension (which is pretty cool, btw). Does anybody know of an example of this sort of thing working or a reason why it wouldn't? Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
TOTALLY OT: Pumping water with an elevated pump.
Started by ●November 20, 2007
Reply by ●November 20, 20072007-11-20
Eric Jacobsen wrote:> Hey, smart people. > > I've been having a discussion with a firefighter that's gone something > like this (heavily paraphrased): > > He: You know you can only lift water about 28ft with a pump? It's > physically impossible to pump it higher than that if the pump is at > the top of the lift. > > (e.g., a pump at the top of a well, something like that) > > Me: I think that's only a limit for a vacuum pump. Doesn't it work > if you prime the pump from the top? > > He: I repeat, it's physically impossible to pump water higher than > 30ft with an elevated pump.Elevated above what?> I made this diagram to try to describe what I was thinking, since he > wasn't understanding my explanation: > > http://www.ericjacobsen.org/pics/Pumpsnstuff.jpg > > The pertinent stuff is Example 3, where Case A is the limit imposed by > trying to lift water with a vacuum pump.The proper terminology is "suction pump". A vacuum pump is used to create a vacuum, as in semiconductor fabrication.> The pressure differential > between 1 Atm and a complete vacuum created behind the pump is the > limitation, so I suggested Case B and Case C, where a prime tank with > enough volume to fill the pipe and the pump is used to prime the > system, so that the pressure differential is no longer limiting the > ability to lift the water. > > So far the response is simply, "That won't work."He's right. The pressure at the free surface of the sump (and in the pipe at the same elevation) is atmospheric, say 15 psia. It drops linearly with elevation to zero at 34 feet, (ignoring that it will boil at much over 32 feet), and becomes negative after that. A column of water sustains very little tension.> Apparently common firefighter training conveys that this is > impossible, but I'm failing to see why. I've found little on the > internet with the searches I've tried, with the exception of how trees > pump water as high as, apparently, 450m under tension (which is pretty > cool, btw).Under capillary conditions, yes. in a pipe, no.> Does anybody know of an example of this sort of thing working or a > reason why it wouldn't?Go back to Case C of example 3. Mark off the 32 feet as in Case A and continue the scale up to the pump. What is the inlet pressure at the pump? Is that physically realizable? What is the vapor pressure of water at room temperature? (Water boils when its vapor pressure exceeds the external pressure.) Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 20, 20072007-11-20
On Tue, 20 Nov 2007 17:32:31 -0500, Jerry Avins <jya@ieee.org> wrote:>Eric Jacobsen wrote: >> Hey, smart people. >> >> I've been having a discussion with a firefighter that's gone something >> like this (heavily paraphrased): >> >> He: You know you can only lift water about 28ft with a pump? It's >> physically impossible to pump it higher than that if the pump is at >> the top of the lift. >> >> (e.g., a pump at the top of a well, something like that) >> >> Me: I think that's only a limit for a vacuum pump. Doesn't it work >> if you prime the pump from the top? >> >> He: I repeat, it's physically impossible to pump water higher than >> 30ft with an elevated pump. > >Elevated above what? > >> I made this diagram to try to describe what I was thinking, since he >> wasn't understanding my explanation: >> >> http://www.ericjacobsen.org/pics/Pumpsnstuff.jpg >> >> The pertinent stuff is Example 3, where Case A is the limit imposed by >> trying to lift water with a vacuum pump. > >The proper terminology is "suction pump". A vacuum pump is used to >create a vacuum, as in semiconductor fabrication. > >> The pressure differential >> between 1 Atm and a complete vacuum created behind the pump is the >> limitation, so I suggested Case B and Case C, where a prime tank with >> enough volume to fill the pipe and the pump is used to prime the >> system, so that the pressure differential is no longer limiting the >> ability to lift the water. >> >> So far the response is simply, "That won't work." > >He's right. The pressure at the free surface of the sump (and in the >pipe at the same elevation) is atmospheric, say 15 psia. It drops >linearly with elevation to zero at 34 feet, (ignoring that it will boil >at much over 32 feet), and becomes negative after that. A column of >water sustains very little tension. > >> Apparently common firefighter training conveys that this is >> impossible, but I'm failing to see why. I've found little on the >> internet with the searches I've tried, with the exception of how trees >> pump water as high as, apparently, 450m under tension (which is pretty >> cool, btw). > >Under capillary conditions, yes. in a pipe, no. > >> Does anybody know of an example of this sort of thing working or a >> reason why it wouldn't? > >Go back to Case C of example 3. Mark off the 32 feet as in Case A and >continue the scale up to the pump. What is the inlet pressure at the >pump? Is that physically realizable? What is the vapor pressure of water >at room temperature? (Water boils when its vapor pressure exceeds the >external pressure.) > >JerryJerry, thanks. I came to the same conclusion with a little more searching, and although I couldn't find a reference that said 'it boils', I'd concluded that that was basically what would happen. I'm glad you've confirmed that for me. FWIW, I did, in my searching, find a reference from 1969 where a guy in the UK sorted out that if you eliminate cavitation nuclei and do a few other things, like de-aerate the prime water, you can 'suction' water to 17m. This was a paper in Nature in 1970, so the credibility is pretty high. He claimed to be working on improvements, but I didn't find anything subsequent. I also found some other confusing things: As you mention there are claims that one 'can't pull water, only push it' because water has no tensile strength, and other sources that claim liquids in certain conditions have very high tensile strengths...which is what the guy who did the 17m lift was exploiting. Regardless, for the majority of applications the ~30 ft limit appears to be real enough. At least now I understand why. Eric Jacobsen Minister of Algorithms Abineau Communications http://www.ericjacobsen.org
Reply by ●November 20, 20072007-11-20
Hi Eric, A 'vacuum' is the lowest pressure that you can create in a pipe if you are pumping air, but with a liquid the position is entirely different as a column of liquid has a tensile strength. A suitable pump can actually 'pull' the liquid, creating a negative pressure. The 28 ft. limitation comes in with water because water will boil at room temperature when a near-vacuum is applied. This means that the column of water breaks up into bubbles and the liquid component collapses to the bottom of the pipe. In theory it should be possible to pull an oil column much higher, even allowing for its lower density relative to water. Because of its lower vapuur-pressure, oil will not boil under a vacuum at room temperature. In photos of oil-wells they often seem to be pumping from the top, but that is as close as I have ever been so I can't say for sure. The case you mention of tree transpiration is an interesting one, as the water is actually pulled up by the leaves. I am not sure that this has been completely analysed. The fact that the water is in very fine tubes in the tissue of the tree must have something to do with it, together with the adhesion of the water to the tube wall. Regards, John Eric Jacobsen wrote:> Hey, smart people. > > I've been having a discussion with a firefighter that's gone something > like this (heavily paraphrased): > > He: You know you can only lift water about 28ft with a pump? It's > physically impossible to pump it higher than that if the pump is at > the top of the lift. > > (e.g., a pump at the top of a well, something like that) > > Me: I think that's only a limit for a vacuum pump. Doesn't it work > if you prime the pump from the top? > > He: I repeat, it's physically impossible to pump water higher than > 30ft with an elevated pump. > > I made this diagram to try to describe what I was thinking, since he > wasn't understanding my explanation: > > http://www.ericjacobsen.org/pics/Pumpsnstuff.jpg > > The pertinent stuff is Example 3, where Case A is the limit imposed by > trying to lift water with a vacuum pump. The pressure differential > between 1 Atm and a complete vacuum created behind the pump is the > limitation, so I suggested Case B and Case C, where a prime tank with > enough volume to fill the pipe and the pump is used to prime the > system, so that the pressure differential is no longer limiting the > ability to lift the water. > > So far the response is simply, "That won't work." > > Apparently common firefighter training conveys that this is > impossible, but I'm failing to see why. I've found little on the > internet with the searches I've tried, with the exception of how trees > pump water as high as, apparently, 450m under tension (which is pretty > cool, btw). > > Does anybody know of an example of this sort of thing working or a > reason why it wouldn't? > > > > Eric Jacobsen > Minister of Algorithms > Abineau Communications > http://www.ericjacobsen.org
Reply by ●November 20, 20072007-11-20
John Monro wrote:> A 'vacuum' is the lowest pressure that you can create in a pipe if you > are pumping air, but with a liquid the position is entirely different as > a column of liquid has a tensile strength. A suitable pump can actually > 'pull' the liquid, creating a negative pressure.> The 28 ft. limitation comes in with water because water will boil at > room temperature when a near-vacuum is applied. This means that the > column of water breaks up into bubbles and the liquid component > collapses to the bottom of the pipe.> In theory it should be possible to pull an oil column much higher, even > allowing for its lower density relative to water. Because of its lower > vapuur-pressure, oil will not boil under a vacuum at room temperature. > In photos of oil-wells they often seem to be pumping from the top, but > that is as close as I have ever been so I can't say for sure.That is if there are no low boiling point (high vapor pressure) hydrocarbons (or others) in the oil. I always thought the oil well pumps pulled a cable that went down to the bottom of the well where the actual pump was. -- glen
Reply by ●November 20, 20072007-11-20
Jerry Avins wrote:> Eric Jacobsen wrote: >> Hey, smart people. >> >> I've been having a discussion with a firefighter that's gone something >> like this (heavily paraphrased): >> >> He: You know you can only lift water about 28ft with a pump? It's >> physically impossible to pump it higher than that if the pump is at >> the top of the lift. >> >> (e.g., a pump at the top of a well, something like that) >> >> Me: I think that's only a limit for a vacuum pump. Doesn't it work >> if you prime the pump from the top? >> >> He: I repeat, it's physically impossible to pump water higher than >> 30ft with an elevated pump. > > Elevated above what? > >> I made this diagram to try to describe what I was thinking, since he >> wasn't understanding my explanation: >> >> http://www.ericjacobsen.org/pics/Pumpsnstuff.jpg >> >> The pertinent stuff is Example 3, where Case A is the limit imposed by >> trying to lift water with a vacuum pump. > > The proper terminology is "suction pump". A vacuum pump is used to > create a vacuum, as in semiconductor fabrication. > >> The pressure differential >> between 1 Atm and a complete vacuum created behind the pump is the >> limitation, so I suggested Case B and Case C, where a prime tank with >> enough volume to fill the pipe and the pump is used to prime the >> system, so that the pressure differential is no longer limiting the >> ability to lift the water. >> >> So far the response is simply, "That won't work." > > He's right. The pressure at the free surface of the sump (and in the > pipe at the same elevation) is atmospheric, say 15 psia. It drops > linearly with elevation to zero at 34 feet, (ignoring that it will boil > at much over 32 feet), and becomes negative after that. A column of > water sustains very little tension. > >> Apparently common firefighter training conveys that this is >> impossible, but I'm failing to see why. I've found little on the >> internet with the searches I've tried, with the exception of how trees >> pump water as high as, apparently, 450m under tension (which is pretty >> cool, btw). > > Under capillary conditions, yes. in a pipe, no.There is no difference. The capillary condition is not sucking from the top. It is sucking in a distributed manner the whole way up. If a localised condition occurred in the capillary system that equated to 10m of sucking, things would behave like any other sucking up a pipe.> >> Does anybody know of an example of this sort of thing working or a >> reason why it wouldn't? > > Go back to Case C of example 3. Mark off the 32 feet as in Case A and > continue the scale up to the pump. What is the inlet pressure at the > pump? Is that physically realizable? What is the vapor pressure of water > at room temperature? (Water boils when its vapor pressure exceeds the > external pressure.)Jerry loves quoting sewerage treatment works. There is a good reason why those works build very expensive large holes in the ground, and put their huge inlet water pumps at the bottom. People think politicians are a bit bit wet, but there is a difference. The suckage of water has its limits. :-) Steve
Reply by ●November 20, 20072007-11-20
I think the system my parents had while I were a kid was using something called injection pump. Most of the water were send back into the drill hole in a second pipe, and only part of the lifted water were used at once. Our well was 12m (40feet), and I cannot remember anything about any pump in the bottom. There were 2 pipes in the drill hole, one for water going down. We had to prime the system with water, if it lost water. I guess the drill hole were air tight, but not sure (to raise pressure in the hole). It has been some years ago. And me getting older, I cannot remember all that well ;-) How does this sound anyway? -- Christen Fihl
Reply by ●November 20, 20072007-11-20
Eric Jacobsen <eric.jacobsen@ieee.org> writes:> On Tue, 20 Nov 2007 17:32:31 -0500, Jerry Avins <jya@ieee.org> wrote: > >>Eric Jacobsen wrote: >>> ...... >>> I've found little on the >>> internet with the searches I've tried, with the exception of how trees >>> pump water as high as, apparently, 450m under tension (which is pretty >>> cool, btw).If this refers to newer work on the subject, I would be very interested to find it too. As this is not related to my regular work and I am German, I have no idea of good terms to search for. Please could you help me?>> ... >>> Does anybody know of an example of this sort of thing working or a >>> reason why it wouldn't?An example is the traditional device for measuring preasure of air: close a tube of glass at one end (by melting), fill it with mercury, submerge the open end into mercury in a container, bring the tube into vertical position. Provided the tube is long enough, the level of the mercury in the tube will be about 760mm above the one in the container. In the upper end of the tube is vacuum.> > FWIW, I did, in my searching, find a reference from 1969 where a guy > in the UK sorted out that if you eliminate cavitation nuclei and do a > few other things, like de-aerate the prime water, you can 'suction' > water to 17m. This was a paper in Nature in 1970, so the credibility > is pretty high. He claimed to be working on improvements, but I > didn't find anything subsequent.Yes, I once also read about this.> > I also found some other confusing things: As you mention there are > claims that one 'can't pull water, only push it' because water has no > tensile strength, and other sources that claim liquids in certain > conditions have very high tensile strengths...which is what the guy > who did the 17m lift was exploiting. >The problem here is, what you understand under tensile strength. Its a macroscopic quantity which is rather easily measured for a rod of metal. At a microscopic (atomic) scale we see that the strength is produced by intermolecular forces and those we also have in water as can be seen from a drop of water on e.g. a greasy surface. So water also has tensile strength though it can not be measured the way it is done for metals. I just did a simple experiment in my kitchen which, I think, clearly demonstrates the tensile strength of water. I filled a class of _cold_ water up next to the rim. (Temperature was about eight Celsius.) Then I looked for the next thing that might be appropriate and got hold of an eating-knive, where the end of the handle is of metal, a little rounded, and about 8x12 millimeters in crossection. I emerged the end of the handle a little into the water and pulled it slowly upwards, holding the knive in vertical position. The water kept connected to the handle until it's end was 2 or 3 millimeters above the surface. So I ``pulled'' water, which, I claim, requires ``tensile strength''. But I won't say this is ``very high tensile strength''. When pulling up water by 10m, a column of one square-centimeter crossection weighs 1kg. Hardly anybody would call a rope of half an inch diameter strong, when it breaks under a load of a few kilograms. -- hw
Reply by ●November 20, 20072007-11-20
Heinrich Wolf wrote:> Eric Jacobsen <eric.jacobsen@ieee.org> writes: > >> On Tue, 20 Nov 2007 17:32:31 -0500, Jerry Avins <jya@ieee.org> wrote: >> >>> Eric Jacobsen wrote: >>>> ...... >>>> I've found little on the >>>> internet with the searches I've tried, with the exception of how trees >>>> pump water as high as, apparently, 450m under tension (which is pretty >>>> cool, btw). > > If this refers to newer work on the subject, I would be very > interested to find it too. As this is not related to my regular work > and I am German, I have no idea of good terms to search for. Please > could you help me? > >>> ... >>>> Does anybody know of an example of this sort of thing working or a >>>> reason why it wouldn't? > > An example is the traditional device for measuring preasure of air: > close a tube of glass at one end (by melting), fill it with mercury, > submerge the open end into mercury in a container, bring the tube into > vertical position. Provided the tube is long enough, the level of the > mercury in the tube will be about 760mm above the one in the container. > In the upper end of the tube is vacuum. > >> FWIW, I did, in my searching, find a reference from 1969 where a guy >> in the UK sorted out that if you eliminate cavitation nuclei and do a >> few other things, like de-aerate the prime water, you can 'suction' >> water to 17m. This was a paper in Nature in 1970, so the credibility >> is pretty high. He claimed to be working on improvements, but I >> didn't find anything subsequent. > > Yes, I once also read about this. > >> I also found some other confusing things: As you mention there are >> claims that one 'can't pull water, only push it' because water has no >> tensile strength, and other sources that claim liquids in certain >> conditions have very high tensile strengths...which is what the guy >> who did the 17m lift was exploiting. >> > > The problem here is, what you understand under tensile strength. Its > a macroscopic quantity which is rather easily measured for a rod of > metal. At a microscopic (atomic) scale we see that the strength is > produced by intermolecular forces and those we also have in water as > can be seen from a drop of water on e.g. a greasy surface. So water > also has tensile strength though it can not be measured the way it is > done for metals. > > I just did a simple experiment in my kitchen which, I think, > clearly demonstrates the tensile strength of water. > > I filled a class of _cold_ water up next to the rim. > (Temperature was about eight Celsius.) Then I looked for the next > thing that might be appropriate and got hold of an eating-knive, where > the end of the handle is of metal, a little rounded, and about 8x12 > millimeters in crossection. I emerged the end of the handle a little > into the water and pulled it slowly upwards, holding the knive in > vertical position. The water kept connected to the handle until it's > end was 2 or 3 millimeters above the surface. So I ``pulled'' water, > which, I claim, requires ``tensile strength''.You demonstrated surface tension. Search for a way to measure surface tension with a wire frame one centimeter wide and an analytical balance. The general topic id physical chemistry.> But I won't say this is ``very high tensile strength''. When pulling > up water by 10m, a column of one square-centimeter crossection weighs > 1kg. Hardly anybody would call a rope of half an inch diameter strong, > when it breaks under a load of a few kilograms.It is what keeps the water in a soap bubble from flowing to the bottom. See http://tinyurl.com/2h3fbl for a wonderful treatise on the subject. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●November 20, 20072007-11-20
John Monro wrote:> In theory it should be possible to pull an oil column much higher, even > allowing for its lower density relative to water. Because of its lower > vapour-pressure, oil will not boil under a vacuum at room temperature. > In photos of oil-wells they often seem to be pumping from the top, but > that is as close as I have ever been so I can't say for sure.Have you ever noticed those nodding things in pictures of Texas? They are reaching deep down to pump up the oil from below. Deep wells use more sophisticated pumps popped down the holes, when natural pressure no longer pushes the oil out. Steve
