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Using low pressure water flow to generate low flow enhanced pressure.
2

Using low pressure water flow to generate low flow enhanced pressure.

Using low pressure water flow to generate low flow enhanced pressure.

(OP)
I have a project where a water supply of less than 0.1 bar and flow rate 5-10 L/min. I would like to use this water flow to produce a 2 bar stream of water at 0.2 L/min. Effectively intensify pressure using the kinetic energy of the flowing water. I have seen systems like hydraulic ram pumps that use river flow to pump small amount of water well above level or river.

http://en.wikipedia.org/wiki/Hydraulic_ram_pump

However these are large and pulse at low frequency (0.5 or less Hz).

Anybody come across a miniature version that pulses at 10 Hz or higher to produce a smoother flow?

I have the system working with a miniature electric pump the performs well but I would like to eliminate the need for external power source.

Application is domestic water.

Thanks

RE: Using low pressure water flow to generate low flow enhanced pressure.

You need a pump and if you can not (or do not want to) work with electricity, what about compressed air? There are air driven diaphragm pumps available.

RE: Using low pressure water flow to generate low flow enhanced pressure.

Look at the water horsepower available vs required, see if you are trying to create energy or not.

GPM x 8.33 lbs/gallon x specific gravity = lbs/minute of fluid
x head (ft) = ft-lbs/min
33,000 ft-lbs/min = 1 hp

Sorry for the units, but check your available conditions vs what you want to generate. Make sure you factor in efficiency allowance your device(s.) If you have enough margin on efficiency, you might even be able to use a turbine as a generator for low pressure side, then connect to a motor for the high pressure pump. Battery as a buffer, add solar panel for additional energy?

Maybe some sort of direct drive device if you are cutting it close on efficiency.

RE: Using low pressure water flow to generate low flow enhanced pressure.

What about a diffuser? Increase cross section --> slower speed --> increased pressure (according to Bernoulli).

RE: Using low pressure water flow to generate low flow enhanced pressure.

asimpson,

What velocity does the main stream have or can it be made to achieve?

RE: Using low pressure water flow to generate low flow enhanced pressure.

Have you ever seen a water-bed pump? How about a hose-end sprayer? They are called "eductors". They do exactly what you are trying to do.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Using low pressure water flow to generate low flow enhanced pressure.

I was going to suggest the amplifier pumps like Mint suggests...but at 1 psi, you will struggle with seal friction using typical hydraulic cylinder seals. It might still work with a low-friction piston, perhaps using diaphragm seals, but you would have to build it "custom"....and the overhead work for the cylinder valves might reduce your efficiency to zero with such low working head.

The eductors like Dave suggests might also work, but that assumes you have a high flow velocity - not sure that's true here, it's the one piece of information asimpson hasn't given us. If the velocity is high enough for an eductor to generate the required pressure, then even a simple pitot tube would provide the required flow...

RE: Using low pressure water flow to generate low flow enhanced pressure.

He's got 5-10 L/min and wants 0.2 L/min of the combined stream. If you know volume flow rate, velocity is simply a function of pipe diameter. You can get the velocity you want/need by picking the right pipe.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Using low pressure water flow to generate low flow enhanced pressure.

(OP)
Thanks everyone.

I am not sure how diffuser would work.

I'm afraid I don't want to use any other power source other than the motive power of the water.

The velocity through 1/2" pipe would be 129 f/min or 39 m/min. Given the low pressure supply. In this case about 2 m head of 6 ft. for the supply pressure. Using a nozzle to increase velocity may be ineffective and just result in lower flow rate.

I don't see how an eductor could produce a pressure greater than the supply pressure. I understand how they can pump large volumes of liquid using a small flow supply that has high velocity by jetting it through nozzle under pressure.

Mechanical pressure intensifiers seem to be on a much larger power scale than in my situation and friction losses would probably overcome the whole system. That is why the ram pump seemed like a possible solution. It has virtually no moving parts . But I have seen no examples on the scale I require.

RE: Using low pressure water flow to generate low flow enhanced pressure.

Quote:

I am not sure how diffuser would work.

Respectfully, I'm guessing that your schooling was not in ME, or it all would have clicked when you heard "Bernoulli".

For a given stream of constant mass flow, velocity and pressure can be manipulated by changing cross-sectional area.

http://www.learnthermo.com/T1-tutorial/ch05/lesson-C/pg07.php

RE: Using low pressure water flow to generate low flow enhanced pressure.

"But I have seen no examples on the scale I require." ... talk to a manufacturer about scaling

"I don't want to use any other power source other than the motive power of the water" ... i don't know this equipment but i'd've thought you were doing work on the fluid to increase its pressure (so i think you need external power.

RE: Using low pressure water flow to generate low flow enhanced pressure.

2
You're looking for a pertty high efficiency: 40 to 80% depending on the supply flow. I think a hydraulic ram is your only bet. Have you seen this manufacturer's data?

http://www.riferam.com/rams/ramspecs.html

It looks like you'd need a Davey #2

RE: Using low pressure water flow to generate low flow enhanced pressure.

You are right, an eductor must discharge into a lower pressure than the power fluid pressure. I read your original post too quickly.

This sounds like a water wheel driving a centrifugal pump kind of application.

David Simpson, PE
MuleShoe Engineering

"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.

RE: Using low pressure water flow to generate low flow enhanced pressure.

(OP)
I am familiar with the Bernoulli effect , I was just not sure what is meant by a diffuser. If this is an increase in CSA of pipe, how could this increase pressure with respect to pressure driving flow. As I understand the Bernoulli effect generates a pressure difference when velocity is increased by narrowing of CSA dropping pressure at this point with respect to larger CSA before and after narrowing.
Could this be used to pump a small portion of water say 10% to a tank higher than the header tank feeding the main flow? Just like a hydraulic ram pump.

RE: Using low pressure water flow to generate low flow enhanced pressure.

i think bernoulli = "red herring" in this case. 77's link looks to be exactly what you want !?

RE: Using low pressure water flow to generate low flow enhanced pressure.

I think you're right, RB. I've put more thought into this. To get a parcel of water to rise above it's original level, it's total specific energy must increase. Simply trading enthalpy for kinetic energy and incurring losses along the way won't do it.

One of two things must happen:
1.) outside energy input
2.) energy transfered from one portion of the flow to another (e.g. turbine pump).

I thought there might be a way to do this without a pump, but I'm not geting there.

RE: Using low pressure water flow to generate low flow enhanced pressure.

Aw shucks, and just when I thought we were about to invent perpetual motion in this thread.....

rmw

RE: Using low pressure water flow to generate low flow enhanced pressure.

The water ram uses energy from a lot of water to get a little of it up higher. Should be do-able. Use an accumulator tank at the top end to even the flow out?

RE: Using low pressure water flow to generate low flow enhanced pressure.

(OP)
Thanks everyone.

All the ramp pumps on the market seem a bit "agricultural", no offense intended. I need something a bit smaller. Guess I'll have to do some work and try to build one to my specification. Should be interesting.

RE: Using low pressure water flow to generate low flow enhanced pressure.

what's wrong with 77's suggestion of a Davey #2 ? seems to meet the flow and pressure req'd ??

RE: Using low pressure water flow to generate low flow enhanced pressure.

I like zdas04's water wheel driving a pump.

Ted

RE: Using low pressure water flow to generate low flow enhanced pressure.

Have to agree, 77's link is a pretty close match. There are two questions - 1) will there be sufficient head truly available to make the ram pump cycle - it wants a few feet at minimum, and simpson's OP specified a head of only a couple feet; later he says 6 ft. That's about a 2:1 or more difference, which will matter. Same thing matters for any other scheme (turbine driving a pump, boost cylinder pump) - the higher the available supply head pressure, the more energy and higher the energy "quality" in the source flow. The second question will be whether the top pressure and flow delivery will be sufficient. Really it boils down to looking at the flow vs. head curves/tables given for the #2 Davy pump and seeing if it can be made to work. I'm confident that some flow can be made available with some scheme at the source pressure stated, but I'm not at all confident that the specified flow can be achieved; as somebody else noted the system efficiency would need to be about 40 to 50% to get there, which will call for some pretty sharp pencil work. I think the whole system has a better chance for every foot that can be added to the source head (which should be a "duh" statement, right?).

and Dave, I hate to nitpick especially somebody like you who is pretty sharp all around, but this statement is incomplete:

"You can get the velocity you want/need by picking the right pipe. "

- I would add: "but only if you have the source pressure (head) to drive that velocity", which was why I kept bugging asimpson to spec his source pressure. I know you stated you missed the low source pressure in a later post, but that comment just bugged me, seemed like you were saying "duh" to my earlier post.

RE: Using low pressure water flow to generate low flow enhanced pressure.

(OP)
Sorry I cannot be specific on details in terms of pressures and flows. I am investigating the principal and will see how close I can get to desired performance with a product or system I can get off the shelf. It is an R&D project and I do not have a definite application.

I misread data on Davy #2 and I will look back at it. However so far it is the only system available close to what I require

RE: Using low pressure water flow to generate low flow enhanced pressure.

Waterwheel driving a centrifugal pump would probably need some sort of gear drive for speed increase. Then, it would be tricky to size. If flow varies between 5-10 l/min, then the waterwheel speed would vary also. So the pump speed varies, and the pressure varies to the ^2 of the pump speed difference.

I think most feasible is turbine (or waterwheel) driven generator used to charge a battery, which drives an electric motor centrifugal pump.

Low end of supply flow and not enough power? Add another turbine/waterwheel to the system, or other "free" power source (solar.) Or if it is a temporary reduction in flow, just ride it out on battery power.

Don't know how consistent you need the high pressure flow to be, but I think you will have to go electrical here.

RE: Using low pressure water flow to generate low flow enhanced pressure.

Gibson, shame on you! This is the Mechy forum, take your sparky heresy elsewhere! Ram pump and a constant-pressure accumulator(*), no need for messy chemical batteries and dangerous electricity.

(*) A standard hydraulic cylinder with a big honkin' weight on the piston rod.

RE: Using low pressure water flow to generate low flow enhanced pressure.

Quote (1gibson)

Low end of supply flow and not enough power? Add another turbine/waterwheel to the system

Sparkies don't believe in conservation of energy. Strange religion, EE is.

RE: Using low pressure water flow to generate low flow enhanced pressure.

If a turbine/water wheel is deemed appropriate for generating mechanical power from the fluid flow, why limit to only considering rotary pumps?

Pretty sure ways to convert rotary to linear motion are well understood so why not a simple reciprocating positive displacement pump or some such.

Again an accumulator or simple header tank system or similar could be incorporated as required to smooth flow.

Or if you want to stick to rotary motion maybe an archemdies screw or some such but then you'd probably be looking at gearing again.

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RE: Using low pressure water flow to generate low flow enhanced pressure.

There are a number of solutions possible. Water turbine driving a gear pump would work. Using a centrifugal pump would greatly narrow the window of operating conditions. I think the most robust and efficient would be using the piston principle behind the pressure boosters mentioned above.
Friction is almost non-existent with diaphragm sealed pistons.
Combine the principle of an air operated double diaphragm pump (AODD using water pressure rather than air pressure) with pressure booster. Another way to look at it is that a hydraulic piston motor with a large piston area drives a hydraulic piston pump with a smaller piston, and it is double acting so pumping occurs while stroking both ways.

RE: Using low pressure water flow to generate low flow enhanced pressure.

It would be interesting to find a way to do this without moving parts. Wonder if it's possible.

Not talking about "magic", overunity, or perpetual motion. As I mentioned earlier, acquiring energy from part of the stream to deliver smaller part to a higher altidude.

RE: Using low pressure water flow to generate low flow enhanced pressure.

(OP)
A hydraulic ram pump has virtually no moving parts. Apart from flow actuated valves. No magic or over-unity. Problem is they are too big for me in terms of physical size.

RE: Using low pressure water flow to generate low flow enhanced pressure.

Tick,

Maybe, using magneto-fluid-dynamic pumps/turbines? But I coubt there is enough efficiency in current MFD tech to make this particular application work.

RE: Using low pressure water flow to generate low flow enhanced pressure.

A hydraulic ram has one thumping (literally) great moving part.

As a black box you seem to be wanting to convert a large supply of hugh entropy fluid into a small supply of low entropy fluid and the remainder at even higher entropy.

At first sight this is perilously close to a Maxwell's Demon situation, but given that a hydraulic ram, or a generator/pump, actually achieves this, obviously 2LE is not broken. The reason is that you do have reservoirs at different entropies, whereas the demon is more concerned with creating reservoirs from a uniform mush.

Perhaps one way you could do it with no moving parts is with a series of hydraulic jumps and overflows, to build gravitational PE.

Cheers

Greg Locock


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