How To Choose A Water Pump

[Dr. Burrito]

On the subject of making sure the pipes can handle it, is there rated information printed on the pipes themselves or how else is this determined, as I am determined to have a shower with far more velocity and force than what I have at present.

Thanks,

Dr. B

[Boksida]

The information at Grundfos does however say that it is a centrifugal pump and not a jet pump.

Thanks,

Chownah

Every household jet pump I have seen has been centrifugal. The alternatives are progressive cavity or reciprocating and these are rare.

[CGW]

On the subject of making sure the pipes can handle it, is there rated information printed on the pipes themselves or how else is this determined, as I am determined to have a shower with far more velocity and force than what I have at present.

Thanks,

Dr. B

The plastic pipe I have used in Thailand has no Psi rating on it, there is different quality, the more expensive having a larger wall thickness (the price difference is next to nothing) I run 50 - 55 psi on my house and have had no problems in the last three years.

One other comment on this thread, if you have a pressure tank after the pump, - advisable - the pressure switch should be on it, not the pump.

Final comment, Thai's are still learning about plumbing, for some reason they are happy to sell you the smallest pump, the & the cheapest - small inside diameter pipe, the UPVC pipe they use is long outdated with superior product, but not locally available, (they like to use 3/8" run 3/4" if you can then s wedge down to taps etc.)

The bigger the pipework and pump you have = more Pressure

Cheers

[Boksida]

On the subject of making sure the pipes can handle it, is there rated information printed on the pipes themselves or how else is this determined, as I am determined to have a shower with far more velocity and force than what I have at present.

Thanks,

Dr. B

The blue PVC pipes made by Thai Pipe are marked Class 5, 8.5 an 13.5. The number refers to the rated working pressure in kg/sq.cm.

[chownah]

The information at Grundfos does however say that it is a centrifugal pump and not a jet pump.

Thanks,

Chownah

Every household jet pump I have seen has been centrifugal. The alternatives are progressive cavity or reciprocating and these are rare.

The difference between a jet pump and a centrifugal pump is that a centrifugal pump's action is to spin the water in a housing creating "cetrifugal force" which creates the pumping pressure....while a jet pump's action is to force a small stream of high pressure high velocity water from an orifice and into a venturi sort of a setup (I don't know if it is properly called a venturi or not) which converts the energy in the high velocity stream into a stream of lower velocity but greater volume. This is sort of a brief and sketchy explanation but I hope it is clear that I am trying to indicate that the pumping mechanism which pumps the usable water is quite different between these two types of pumps....a better explanation could be found on the internet I'm sure.

chownah

[lopburi3]

On the subject of making sure the pipes can handle it, is there rated information printed on the pipes themselves or how else is this determined, as I am determined to have a shower with far more velocity and force than what I have at present.

Thanks,

Dr. B

Do not believe there is a problem with even the basic plastic pipe and normal water pressure but the issue is installation. Many will cut pipe short at junctions and not obtain a proper seal and they also use burning the pipe to make bends rather than go out to buy the proper angles. Our original house contained a short section of flexible clear hose to join two sections around a wall beam (slip fit over the plastic pipe). That was done 30 plus years ago but such things still take place today. The burning to make a bend was two years ago.

[Boksida]

The information at Grundfos does however say that it is a centrifugal pump and not a jet pump.

Thanks,

Chownah

Every household jet pump I have seen has been centrifugal. The alternatives are progressive cavity or reciprocating and these are rare.

The difference between a jet pump and a centrifugal pump is that a centrifugal pump's action is to spin the water in a housing creating "cetrifugal force" which creates the pumping pressure....while a jet pump's action is to force a small stream of high pressure high velocity water from an orifice and into a venturi sort of a setup (I don't know if it is properly called a venturi or not) which converts the energy in the high velocity stream into a stream of lower velocity but greater volume. This is sort of a brief and sketchy explanation but I hope it is clear that I am trying to indicate that the pumping mechanism which pumps the usable water is quite different between these two types of pumps....a better explanation could be found on the internet I'm sure.

chownah

A jet pump is a centrifugal pump with the device you mentioned to give greater suction lift. On a "shallow well jet", the venturi is on the surface and on a "deep well jet", down hole. The attached file may help.

Jet_pumps.pdf

[chownah]

The information at Grundfos does however say that it is a centrifugal pump and not a jet pump.

Thanks,

Chownah

Every household jet pump I have seen has been centrifugal. The alternatives are progressive cavity or reciprocating and these are rare.

The difference between a jet pump and a centrifugal pump is that a centrifugal pump's action is to spin the water in a housing creating "cetrifugal force" which creates the pumping pressure....while a jet pump's action is to force a small stream of high pressure high velocity water from an orifice and into a venturi sort of a setup (I don't know if it is properly called a venturi or not) which converts the energy in the high velocity stream into a stream of lower velocity but greater volume. This is sort of a brief and sketchy explanation but I hope it is clear that I am trying to indicate that the pumping mechanism which pumps the usable water is quite different between these two types of pumps....a better explanation could be found on the internet I'm sure.

chownah

A jet pump is a centrifugal pump with the device you mentioned to give greater suction lift. On a "shallow well jet", the venturi is on the surface and on a "deep well jet", down hole. The attached file may help.

Jet_pumps.pdf

Indeed, that is one way to describe it....but usually I have heard it described as a venturi type device with a centrifugal pump providing the high velocity stream. I guess the point is that jet pumps are usually used (I would say "always used" but then I'm sure that someone could come up with an exception) for pumping water from depths greater than a centrifugal pump can SUCK. The reason a jet pump is used is because the venturi part of it will fit inside a well casing quite easily while designing a centrifugal pump to fit inside a well casing is problematic and implementing this design is more expensive than the jet pump hardware. The downside of the jet pump is that it takes more energy to pump the same amount of water.

One more note: A jet pump does not have appreciably more suction lift than a centrifugal pump...both are limited to being able to suck to the height equivalent to atmospheric pressure....the jet pump's big advantage is that when the venturi is place down the well it does not have to suck...it can push the water up and pushing the water up does not have the same atmospheric pressure limitation.

Chownah

Edited September 27, 2007 by chownah

[Boksida]

One more note: A jet pump does not have appreciably more suction lift than a centrifugal pump...both are limited to being able to suck to the height equivalent to atmospheric pressure....the jet pump's big advantage is that when the venturi is place down the well it does not have to suck...it can push the water up and pushing the water up does not have the same atmospheric pressure limitation.

Chownah

Apparently you were unable to download the attachment explaining how suction lift is increased. Would you like me to pm it to you?

[chownah]

One more note: A jet pump does not have appreciably more suction lift than a centrifugal pump...both are limited to being able to suck to the height equivalent to atmospheric pressure....the jet pump's big advantage is that when the venturi is place down the well it does not have to suck...it can push the water up and pushing the water up does not have the same atmospheric pressure limitation.

Chownah

Apparently you were unable to download the attachment explaining how suction lift is increased. Would you like me to pm it to you?

I read it and I think that they were vague in their description of what was actually being done. They said that if a jet pump venturi was placed at the inlet of a centrifugal suction pump that its suction lift would be increased.....they don't say, for instance if the jet is installed right next to the centrifugal pump which they are boosting or if the jet gets installed at the inlet of the suction pipe at the bottom of the well which is what I expect they are talking about. I think they are trying to say that water can be brought up from a deeper level with this arrangement but I'm not convinced that the way they describe it is entirely accurate as far as saying that the suction lift of the centrifugal pump is increased.

Fact is that any kind of suction pumping hardware can not lift water more than the equivalent of atmospheric pressure...it is physically impossible regardless of the kind of apparatus being used to create the suction. It may be that a jet pump can suck water a tiny bit higher than a centrifugal pump because its smoother operation brings on cavitation at a slightly higher lift but I'm reasonably sure that the difference between what a jet pump and a centrifugal pump can do in this regard is minimal....but I could be wrong and I'd be interested in seeing some specs for different pumps that show me wrong....I'm always wanting to learn more.

Chownah

Edited September 27, 2007 by chownah

[Boksida]

I read it and I think that they were vague in their description of what was actually being done. They said that if a jet pump venturi was placed at the inlet of a centrifugal suction pump that its suction lift would be increased.....they don't say, for instance if the jet is installed right next to the centrifugal pump which they are boosting or if the jet gets installed at the inlet of the suction pipe at the bottom of the well which is what I expect they are talking about. I think they are trying to say that water can be brought up from a deeper level with this arrangement but I'm not convinced that the way they describe it is entirely accurate as far as saying that the suction lift of the centrifugal pump is increased.

Chownah

The only reason I know for using a jet pump is to increase suction lift. The textbook from which the attachment was scanned is kind of a Bible in my industry and you are the first person I have come across in 40 years who has the technical expertise to dispute the basics. Jet pumps have always behaved exactly as described in the book for me. The suction lift is increased by the amount of pressure reduction at the venturi less friction losses etc.

[chownah]

I read it and I think that they were vague in their description of what was actually being done. They said that if a jet pump venturi was placed at the inlet of a centrifugal suction pump that its suction lift would be increased.....they don't say, for instance if the jet is installed right next to the centrifugal pump which they are boosting or if the jet gets installed at the inlet of the suction pipe at the bottom of the well which is what I expect they are talking about. I think they are trying to say that water can be brought up from a deeper level with this arrangement but I'm not convinced that the way they describe it is entirely accurate as far as saying that the suction lift of the centrifugal pump is increased.

Chownah

The only reason I know for using a jet pump is to increase suction lift. The textbook from which the attachment was scanned is kind of a Bible in my industry and you are the first person I have come across in 40 years who has the technical expertise to dispute the basics. Jet pumps have always behaved exactly as described in the book for me. The suction lift is increased by the amount of pressure reduction at the venturi less friction losses etc.

Maybe we are using different definitions of "suction lift". My thinking is that on planet earth no single stage pump can lift water more than 10 metres through suction alone...it is possible to build a series of pumps with each lifting (theoretically) up to about 10 metres but each pumping stage could only lift up to about 10 metres and no more....it is physically impossible....is this contrary to your thinking? In the example in your text file is it your understanding that the venturi is placed at the bottom of the well or at the top near the centrifugal pump?

Just to compare our points of view, the only reason I have ever heard of to use a jet pump (other than the text you provided) is to cheaply pump from greater depths than a topside pump installation is capable of...namely about 10 metres. Are the applications you have dealt with agricultural...or what?

Chownah

Chownah

[chownah]

I googled around and found this concerning the suction lift limit for shallow well jet pumps:

"Shallow well jet pump: The jet assembly is located on the suction side of the impeller. Water is supplied to the nozzle under pressure from the pump. As the drive water moves through the nozzle and venturi a partial vacuum is created drawing more water from the well up the suction pipe. A portion of the water is directed to the discharge outlet for the distribution system, the rest is recirculated to the ejector.

In driven wells (sand point wells) the check valve can be installed in-line near the well head or pump and the well casing can be used as the suction pipe.

The shallow well jet pump's suction lift limit is 25 feet at sea level. "

I found that at:

http://www.aquacosm.com/articles_detail.asp?ArticleID=14

This is consistent with my approximately 10 metre limit for suction lift as a theoretic limit....25 feet being about 7 1/2 metres and definitely less than the 10 metres I mentioned. It seems like the centrifugal pumps I have bought for my domestic water supply all seem to call out a max suction lift of 8 metres but I could be mistaken....if this is correct then this would put them roughly on a par with the shallow well jet pump installations for suction lift....I guess. I'm certainly willing to hear other information on this.

Chownah

[Boksida]

I googled around and found this concerning the suction lift limit for shallow well jet pumps:

"Shallow well jet pump: The jet assembly is located on the suction side of the impeller. Water is supplied to the nozzle under pressure from the pump. As the drive water moves through the nozzle and venturi a partial vacuum is created drawing more water from the well up the suction pipe. A portion of the water is directed to the discharge outlet for the distribution system, the rest is recirculated to the ejector.

In driven wells (sand point wells) the check valve can be installed in-line near the well head or pump and the well casing can be used as the suction pipe.

The shallow well jet pump's suction lift limit is 25 feet at sea level. "

I found that at:

http://www.aquacosm.com/articles_detail.asp?ArticleID=14

This is consistent with my approximately 10 metre limit for suction lift as a theoretic limit....25 feet being about 7 1/2 metres and definitely less than the 10 metres I mentioned. It seems like the centrifugal pumps I have bought for my domestic water supply all seem to call out a max suction lift of 8 metres but I could be mistaken....if this is correct then this would put them roughly on a par with the shallow well jet pump installations for suction lift....I guess. I'm certainly willing to hear other information on this.

Chownah

You are quite correct that the theoretical unassisted suction lift for any pump is 1 atmosphere (1 bar = 10 metres). This is not practically possible and is more likely to be closer to 6-8 metres. The jet gives some assistance to closer approach the theoretical possible. Even 2 metres at these depths is 20% improvement which is quite worthwhile. The other advantage is that it is easier to recover "prime" if the suction has drained.

The deepwell jet is more efficient but, in my opinion, not very practical in these days of cheaper submersibles. Running the eductor with two pipes down the well is a pain in the butt.

Oilfield jet pumps, where a couple of thousand psi pressure loss across the jet can be achieved, are impressive but are also losing out to submersibles because of the low efficiency.