Calculating Water Pressure Without a Gague

"20in of water" is in itself a pressure of 4980N/m².

"I have heard the water goes down in to a lower abandoned mine and then comes back up"

Yes - The cavity will fill up and the abandoned mine will eventually overflow as well if the water does not find a weaker spot which can breached or find an opening to escape.

Pressure inside the mine will be determined from the depth below the surface of the water. If there is any known weak spot(s) in the abandoned mine that can pass water through to an adjacent working mine the level must be reduced by pumping or diverting the inlet flow into a watercourse.

Also remember that water from a mine may (will) contain pollutants.

Hi,

What is the relevance of the abandoned mine? I presume its a case if the water went down and didn't come up again You would be a happy bunny. You know your flow rate it seems and the ditch is 30'' deep,so what? Are you trying to lead the flow away from your property or do something useful with it? More info would help!

I wasn't sure if the water going down and back up would impact the pressure. The water starts out on top of the mountain soaks down into one mine and flooded it so they drilled bore holes and put it thirty feet down into another mine so they could work the upper mine then it comes back up the thirty feet and several hundred feet later into the creek. There is a tremendous amount of force to the water. I wanted to know if there was enough pressure to generate electricity with a water turbine. I know the pressure can be converted to feet head and that with the flow determines how much electricity you can generate

Hi humor08.

If I get the picture correctly you are saying that the water issues under pressure into your ditch but that you have no way of getting back to the source in the abandonned mine to dam it up or create a pressure tight bulkhead. If this is so then all you have availble in trrms of pressure head is the 30'' depth in the ditch.; only by leading this in a closed pipe (which remains full ) will you be able to develop a 'head' of water flowing at your declared volume. The lower you can go the higher the pressure and the more energy for your turbine. For every 30feet you will gain approximately 1 atmosphere of pressure head.

Low head turbines are typically of the bucket type impeller or 'pelton wheel' design.

27" water column = 1 psi on the gauge

27" water column = 1 psi on the gauge

I think this should be 32 feet =~15 PSI

look here

http://hyperphysics.phy-astr.gsu.edu/Hbase/pman.html

27" = 2'-3" = 1 psi .

15 psi = 34.5 feet or 32 ft = 14.22 psi as has been taught last 40 years.

What the heck round it around.

Pressure in a static liquid is proportional to the depth alone and is not influenced by the size or shape of the containing vessel.

If, for example, a tube one inch square, or having a cross-section area of one square inch, is filled to a vertical height of 2.31 feet (27.7 inches) with water having a specific gravity of 1.0, the water will weigh one pound and the pressure at the bottom of the tube will be one pound per square inch.

A 2.31 foot-high column of mercury, which has a specific gravity of 13.55 would weigh 13.55 pounds and the pressure would be 13.55 pounds per square inch.

Likewise, a petroleum oil having a specific gravity of less than water, will exert correspondingly less pressure. The general formula for pressure is :

Pressure in lb. per sq. inch = Head in feet x Sp. Gr. / 2.31

Since it's an open ditch, pressure isn't really the issue. At 14 cfs that's 873.824 pounds of water passing a given point in that ditch every second.

Assuming the ditch is pretty level as it crosses your property, the best way to harness the energy might be the way the Romans used their aqueducts for hydropower- put a series of undershot wheels in the ditch, gear them together with bicycle or motorcycle chain, then use their combined output to power to a generator.

If you have a significant change in elevation as the ditch crosses your property, consider building a dam in the ditch at the high end, then running a pipe to the low end of the property, by which time you will have enough head pressure to run a small water turbine. Not enough pressure? Go old-school and use a flume and a breast or overshot wheel.

If your interested in electricity production you'll want the head from point of collection to a suitable turbine site. The water as it comes out of the mine is not applicable because it is not in an integral penstock. 1 psi per 2.2 vertical feet. 14 cfs has a great potential for small hydroelectric production.

I understand everything you are saying eventhough I am not a mathematician. I am 63 years old so cut me a little slack on trying to recall my high school math. What I am trying to deal with is a very unique situation. It is not my property it isn't anyones property it runs under a state highway. The water is visible a few places through steel grating. That is how I calculated the flow. I dropped a stick in and it took it 21 seconds to go 90 feet, working the time out I calculated it to be 257 feet it would travel in one minute then calculated the cubic feet and divided by 60 seconds thus giving me the 14 cfs. I am confident that is right. You can go no farther than the portal. This water has ran like this since the 1940's so it can't be stopped or damned up. We were in a severe drought situation last year and had entered the extreme category in November. The water depth ran 13 inches all through the drought but dropped to 10 inches in November. Then has been 18 to 20 inches ever since early December. Discounting the drought I would say the average water depth for the year would be at least 15 inches. Now is where I get lost. I know the feet head is a vital aspect of power generation along with the flow. I know that 1 psi equals 2.31 feet head of pressure. I will pull up the calculator and do some math and you let me know if I am right or wrong. I may only be able to get 10 ft vertical drop maybe 15 to twenty but will work with 10. If I could put a 12 inch pipe and maybe also an 8 inch pipe back into the ditch far enough to get that much of a vertical drop before it enters the turbine would all the square inches in the pipe count? I will only work with the 12 inch pipe now. I know the area of a circle is pi times the radius squared so the area of a 12 inch pipe would be 113 square inches. In a 10 ft vertical drop divided by 2.2 would give 4.54 psi would you then multiply the area 113 square inches by 4.54 giving 513 psi and multiplying that by 2.31 would give 1185 feet head of pressure. I know anyone could probably use a bigger pipe but I am just figuring to see if my match is correct. Thanks for your expertise

1 cfs = 449 gallons per minute. So, 14 cfs = 6284 gpm. Static psi on a pipe doesn't change with pipe size. So, a simple equation for potential hydro electricity is volume in gpm X head in feet / by 10. So at 6248 gpm and 10 feet of head you have a potential of 6.284 kVA. Contact canyon industries with your specs and they can give an idea of the cost for a turbine... usually around $1 per watt or so. I install micro-hydro for a living; your volume steps up your potential to small-hydro and I don't have all the data readily available for your specs, but what I can say is a 10" pvc pipe can pass around 1000 gpm with nominal friction, 12" may not be big enough for 6000+ gpm depending on penstock length. Due to flow dynamics, it is required to set up a wier or other method to get an accurate flow calculation. I'm not clear on the details of your situation with regards to access, both physical and legal, but I hope this info helps a little. Good luck.

Humor08,

I am not sure I understand if you are trying to use the water before or after it leaves your (your company's) property.

But if it is after and it runs under a State Highway then it is the State's Property and you are probably going to have a very difficult time making any use of the water unless you can do it before it leaves YOUR (or your company's) property. The State is not very likely to want to make changes to an established watercourse particularly if it has the potential to impact a highway, no matter how remote. Adding a power generating apparatus of any kind will increase the head upstream of the structure and cause potential flooding during wet weather events.

Good Luck

After the water passes under the highway it exits and falls about 15 feet into a creek. About 50 feet from where the water exits there is an old building that straddles the creek from one side to the other. The building is very well built and will outlast me by at least 100 years. The idea was to catch the water in a plume line run it down underneath the building and run it through a turbine. There would be overflows built into the plume line to pass off the excess water so no back up and flooding could occur. There would be a hole cut in the floor and the turbine put down through it. So no state property has to be bothered. I conceived the idea as being a small commercial operation but if everyone is correct there can not be enough pressure generated to generate a substantial amount of electricity. This water travels for miles coming out of the old mine. I think the mine went for about 11 miles. There is a tremendous push behind it but it would only be confined in a pipe coming out of the plume for a distance of about 5 feet. I would think the tremendous push behind the water would generate a lot of pressure. I guess you can't overcome the laws of physics.

The pressure at the water surface, once it exits into the open atmosphere, is going to be 1 atm. as others have stated.

hello,

if you want to stay fairly legal with the highway dept. put a catch at the end of their pipe outlet. you say it drops there 15 to the bottom of the creek. well, that is 15 feet of head. the catch would never run out of water. also the creek has a slope to it. just run your pipe down the creek. the farther you run it, the higher the head. double the head and you double the pressure. the water turbine doesn't care where it is situated. also, the turbin is going to have a fairly small inlet compared to your supply pipe. when you neck down to match the turbin you will get a velocity increase in the flow rate thru the necked down portion. i think you have excellent potential for running a pelton wheel.

there are many manufacturers of turbins for turning water flow/pressure into electricity. talk to them. try to figure out the difference in height (head) from the output of the state pipe to as low as you can put the turbine. you might really be surprised what your head really is.

joe

"1 psi per 2.2 vertical feet."

oops, my error.... 1psi = 2.31 feet

You might understand better if you realise that the water surface in the ditch is at atmospheric pressure throughout the length of the ditch.

If you want to use the water to drive (say) an overshot water wheel (the simplest for this sort of situation), or put into a pipe and run through any other type of turbine (a pump run backwards works well), then the available pressure is as per the Bernoulli equation:

head (rho*g*h) + velocity head (0.5 rho v*v).

Hi humor08,

The reply from 'sceptic' is very appropriate, as the overshot wheel will work quite well provided you can arrange for the ''lade'' or approaching water channel to be adequately supported above ground. The overshot type only really derives its useful energy from the top to slightly below the shaft centre line so although your water hill be presented to a 10ft diameter wheel your power will be generated over the first 5ft or so(roughly 50% of the potential energy). It will still be a big brute as with the flow indicated you will need a wide wheel or else you design the whole thing to utilise say only part of the available flow.

Your idea of running a pipe in the stream bed is difficult to achieve in practice as with only 2feet or so of water depth there is a tendency to 'suck' air into the inlet and this, depending on the gradient, can be difficult to eliminate. Therefore if the point is reached when the turbine demand exceeds flow the whole line can become affected by air causing the process to come to a standstill as more and more enters the pipe destroying the continuous column you need to produce your full head; then you have to try and persuade the trapped air to leave...not easy and if it happens frequently you'll wish you had never done it! To avoid this situation occurring you really need to excavate a 'fore bay' of sufficient depth to keep the inlet submerged at all times. I'm sure you don't want to get involved in a lot of expensive civils,so back to the simple wheel.

I once designed a conversion to electricity generation for an existing corn mill, the speed increase drive using vee-belts was an interesting exercise. No point in trying to go for AC with synchronising as you will never do it; stick with a DC generator and think of ways of using that.

Hope this helps

what if we apply Bernoulli's equation for that case with the following assumption

1) Consider abandoned mine as a closed tank with pressure P1

2) water velocity inside tank is V1 =0

3) Consider tank center as a datum line , Z1 =0

4) water pass through a closed channel for vertical hight Z2 from datum line and with velocity V2 and pressure P2 = 0 ( open ditch)

apply Bernoulli's equation between point 1 with ( P1,V1.Z1) and point 2 with ( p2,v2,Z2)

Now P₁/ω + V₁²/2g + Z₁ = P₂/ω + V₂²/2g + Z₂ + friction losses bet points(1,2)

refer to up mention assumptions then

P₁/ω + 0 + 0 = 0 + V₂²/2g + Z₂ + friction losses bet points

If V₂ is known 257 feet /min ( according to your calculations )

Z₂ vertical hight from mine center to outlet ditch ( can be approximately calculated)

for simplification consider friction loss =0

ω water density

finally P₁/ω = V₂²/2g + Z₂

if Z₂ is known , tank or your mine pressure can be calculated

Humor08,

At an existing 10-year-old hydro plant, I can get 970 kW with a vertical drop of 29 feet and a flow of 400 cfs from an open-ditch canal. If the relationship were linear, at 1/2 the head and 3.5% of the flow, you'd probably get no more than 15-20 kW from your flow. The losses will be proportionally higher on a smaller system, so the actual output will be somewhat less.

Bottom Line: If there is a use for that power nearby, it might be worthwhile (with a VERY long payback). Otherwise, the losses to get the power to the utility might exceed your generation.

It is a shame there isn't more drop I could tie to the grid within 30 feet

If it's that close, and the jurisdiction permits it, connect to the building service and backfeed to the grid. In many locations, the utility is required to buy the power, although what they have to pay varies wildly from state to state.

You'll have to front all the money to buy the turbine-generator and build the associated infrastructure (piping, building rehab, breakers & synchronizing equipment, etc.) before you see any return. I strongly recommend you do a detailed cost-benefit analysis to see if the investment is worth the return.

It isn't worth it I would have to live to be 1000 years old of course I would like to. I may try to block the ditch for 15 to 20 seconds to see what kind of pressure reading I can get. Since this line is about water I may start another one and pick all of your brains on wind energy. In the late 70's I worked in a tunnell that came off the mountain a big belt line went through it. I am going to guess the measurments of the tunnell to be 1500 feet in length. 20 ft height, and 40 feet wide and the wind speed to be 20 to 25 mph. It is a natural updraft and is constant at this speed 24 hours a day 365 days a year. I guess this will end this thread I appreciate everyones input. I will title the next thread " Wind Energy IN Tunnels " Look for it and everyone who wants to contribute I thank you in Advance

Who says we have to play by mother natures laws. Everone agrees that you can't beat the laws of mathematics If you have a lot of head and a lot of flow fantastic, or if you have a lot of head and a small flow you can do ok, or if you have a little head and a lot of flow you can do ok. I guess I am thinking outside the box, way outside the box. The gentleman who has a turbo plant with a 29 ft drop amd a flow of 400 cfs should pay attention to this. It will work I just don't know how well it will work. If that gentleman cold achieve another 20 psi it would more than double his output. Using mechanical energy from some of the water get a good pump. Place it where it will not cavitate. Instead of an electric motor use the water flow to turn the shaft and impeller there would have to be vanes on the shaft. Cut a hole in the pipe going to the turbine and weld a four inch pipe into it. Connect the outlet from the pump to the pipe and see how many more psi can be gotten. It would take a good pump the kind maybe that we used in the coal mines. Maybe you can fool mother nature.

Humor08,

You can't significantly increase the pressure on the inlet to a hydro turbine unless the entire inlet system is enclosed. 20 PSI is equivalent to 8.8' of head. The water will simply flow back up the normal intake, equalizing like a manometer.

Also, a properly designed hydro turbine is already taking nearly all the energy out of the water. Driving a pump with another turbine in the same flow stream is a losing proposition. The losses in the pump/turbine unit simply take away from the energy available to the main turbine. The Francis turbines in my plant already operate at ~95% efficiency. Any modification would be difficult to justify on a cost-benefit basis.

Due to the low head, a Francis unit would not work well at your site. I suspect a bulb unit, or a modified Kaplan, would work best for you.

A pump can be run in reverse as a turbine.

Get a pump suitable to supply the measured head and flow you have available, build a sump and use it to pipe the water you have, then run the pump in reverse as a turbine driving whatever you want to drive. The reverse efficiency is very roughly that of the same performance point in the forward direction. (Usually a bit lower)

Of course, as the pump now runs in reverse, loctite all your threaded connections so they don't unscrew. It is no fun having an impeller come loose and fly into the casing at full speed!

From the flow and head you have available, I would guess one of the mixed flow pumps would be your best bet.

You can extract extra energy by running a draft tube from the exhaust to lowest discharge point. The tube should diverge at between 7 and 9 degrees to slow the flow and enable the maximum energy extraction.

With no more head and flow that I have I am not sure I could generate enough additional psi to do much good but the gentleman with the high flow and little head could benefit greatly with some additional psi

I know there are a lot of variables but approximately how much more pressure static pressure could be generated at the turbine head by installing a mechanical pump and pumping into the line feeding the turbine

Converting 14cfs gives 398l/s, 29' gives 8.8m.

The hydraulic power (ie at 100% efficiency) is 34.3kW.

A mixed flow pump run as a turbine with a generator attached, should better 50% overall efficiency giving a projected yield of around 17kW (roughly 23hp).

Whether this is worth the cost of the works to capture the flow, then pipe it far enough to get sufficient drop and the required machinery and electrics is something only you can decide, but you could get 408kWHr per day, which may or may not be worthwhile.

hello:

could you please give a simple sketch without bothering about scale and all that.

water flow in a open ditch is called gravity flow; water flows due to difference in levels at two points and if you manage to insert a pressure guage any where in the stream, it will show zero or almost zero.

unless you make the water flow through a pipe, you cannot harness power except through devices which work on low head/ large flow like water wheel, archimedian spiral etc.(get help from wiki)

if the water is flowing into one more mine and coming out, this second mine with its exit must be at a still lower level.

the whole picture may be clearer with a sketch.

shankar mallipatna, bangalore india

If you don't mind I will call you by name, Shankar I tried making a sketch in paint I don't have the talent or the room but I will do my very best to describe this so you can get a good picture. I have a friend from India who is a mechanical engineer he teaches one graduate class at the University of Maryland. I think he is considerd to be one of the best in the world in the field of energy. His name is Ashwani Gupta I know he has won many awards maybe you have heard of him or some of his work. He stays gone a lot doing consultations. So I haven't ran this by him.

I will try to be very descriptive. I have an open ditch coming out of an old abandoned mine. The flow is 14 cfs where it dumps into a creek. I know there is no pressure in the open ditch. I plan on catching the water in a plume and channelling it down underneath a building that straddles the creek. The plume will have a dip in it like so _____________ now take your pencil and close the bottom to the top line

\___/

That will be the dip in the plume. I will refer back to this in a little bit. The plume line will continue and go underneath the building where a pipe will come out of the plume line and go to the turbine when the water enters the pipe at that time I can start to build pressure. The trouble is there will be no more than 5 to 7 ft of pipe before it enters the turbine so very little head pressure, with no more pressure than that and without a tremendous flow it isn't worth the time and effort or expense to do it. Refering back to the dip in the plume in an effort to boost the head pressure. If anyone could mount a pump that would be turned by water pressure it may boost the head pressure, mount the pump on top of the plume with only the suction line extending into the water in the dip in the plume line, run the shaft from the pump back to where the water enters the plume line out of the ditch, the ditch is covered so it limits what can be done, the pump shaft will have to have vanes on it so the water can turn it. There can be about a 40 ft length of 4 inch pipe ran up into the ditch to feed the pump shaft. It takes a little bit of the flow but if the pressure can be increased it is worth it enclose the end of the pump shaft where the water will go into it to turn the shaft and set it on an angle that will get the optimum rpm's on the shaft of course you will have to leave an opening for the water to exit after it has turned the shaft. Have a hole cut into the pipe that is feeding the turbine with a four inch pipe welded into it on an angle. Have the discharge from the pump feed into the pipe feeding the turbine. That way you will have water under pressure feeding into the pipe that feeds the turbine without interfering with the flow. I am not sure how much more pressure anyone could get. I hope I have been descriptive enough so that you can follow my logic.

I am not even sure where to begin other than to say this, running the flow through a the vanes of pump that is only being powered by said flow WILL NOT PRESSURIZE THE FLOW. In fact it will draw energy from the flow to push the blades of the pump. The additional head created upstream of the pump will be equal to the the losses through the pump, so if anything you will have less energy available downstream of the pump due to minor losses through the pump. Essentially, there is no point in putting the pump inline with the turbine.

Either it is me or everyone is failing to grasp what I mean. There is more than ample flow for the turbine you take a small part of the flow to turn the pump. This occurs prior to the water entering the pipe that feeds the turbine. The discharge end of the pump then feeds into the pipe line feeding the turbine. You haven't lost any water you haven't lost any flow. The water coming out of the pump will be under pressure therefore it should boost the pressure inside the pipe feeding the turbine.

Hi Humor08

I am sorry to be the one to 'pour cold water' all over your ideas but what you are proposing runs contrary to all known scientific principles and the laws of nature. Put quite simply if what you are proposing was to work then all of mankinds' energy worries would be at an end. Check out the Second Law of Thermodynamics

Basically you are suggesting a way on enhancing the available energy presented to the turbine by taking some of that flow and making it do some work by turning a pump and reintroducing all the water back into the inlet of the turbine. Sorry, nothing will happen ;some water will pass through system but the pump part will not do any work, it cannot!

As explained by other contributors you have a finite amount of energy due entirely to the quantity flowing and the height through which it can fall. If that amounts to say 35kW that is it! End of story. Cut it any way you like , over a wheel or down a pipe to the 'kaplan' turbine, one turns slowly the other faster but the total energy remains the same.

The economics of this scheme look extremely weak and therefore the investment must reflect the potential yield or else your successors will be picking up the tab.