# For you engineers...

digitalbeachbum
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For you engineers...

My wife and I recently got a rain barrel. It was one of the ones converted from a food safe container, 55 gallons. We painted it and found a location where we wanted it. My wife said she wanted a stand for it, but I decided to make one out of used lumber. I figured I would save us \$55.

Today she said, "It needs to be a certain height to increase the psi"

I looked at her inquisitively, "huh? really? where did you get that information from?"

"The web. It's all over all these DYI websites. They all said that raising the rain barrel increases the psi"

I should have taken the high road on this, but I goofed.

So she sends me the links and I started to read their information on how "you increase head pressure by increasing the height"

Well, basic hydraulics doesn't say this, what it says is that for every foot column you increase your psi. So a 1 foot container has 1 foot column or .43 psi.

A 10 foot container has 10 foot columns and 4.3 psi.

Our container is about 4.5 feet tall so it has 1.94 psi.

Raising a 4.5 foot tall container 20 feet in the air still has a 1.94 psi, but...

If you have a 45 foot tall container 3 inches off the ground you have 19.35 psi.

So I get in to it with one of these "masters of rain barrels" who tells me that municipalities have these giant towers which are 100's of feet up in the air. I correct him and say, "no, they are 100's of feet tall, the top of the towers are usually 165 to 200 feet up off the ground but the towers actually have 100's of feet of "foot columns" which gives the high psi.

"It isn't the height of the barrel, it's the height of the top of the water as compare to the water main".

I don't get it. I'm not a scientist. I'm not super smart, but common sense tells me differently.

Beyond Saving
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I hate to break it to you,

I hate to break it to you, but your wife is right. The pressure is created by the potential energy of gravity, so the higher the container is the more potential energy and therefore the more pressure at a given point in the system. The hydraulic head is calculated by adding energy from movement of the fluid, energy from pressure in the fluid and energy from the height of the fluid relative to the water main. In a gravity fed system like a rain barrel, height is by far the most influential variable.

http://en.wikipedia.org/wiki/Bernoulli's_principle

The end result is that the maximum possible psi can be calculated by multiplying the distance of the top of the water compared to the water main which will be roughly .43 * x feet. Your actual psi will probably be a little less because of other variables such as temperature, friction etc.

If, if a white man puts his arm around me voluntarily, that's brotherhood. But if you - if you hold a gun on him and make him embrace me and pretend to be friendly or brotherly toward me, then that's not brotherhood, that's hypocrisy.- Malcolm X

Jeffrick
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I am an engineer who believes in the KIS*S principle, [Keep it Simple * stupid] . Don't over think the project, don't get all jumbled up with ratios and formulae that even engineers find confusing (I'm mechanical  not  hydrolic type engineer). Beyond Saving is right, IT'S GRAVITY, and don't think beyond that simple point.

A ten foot tower will give you more psi then a nine foot tower, it's that simple. 12 foot will give you more then 10 foot, simple, eh? To increase your psi beyond any formula you read, use a 6" dia. drain pipe straight down [180 degree] jointed to a 1" horizontal feed to the house.

One caveat to consider is the smog in your area,  I live in the GTA [pop. 5+ million, + their cars  trucks and factorys] I wouldn't drink or shower in the rain water here.  In Guyana where I own  a  house I do. Guyana has very little smog, high winds and it rains every 2nd or 3rd day during the dry season. Every house has a rain barrel, [mine has two] they are  400 gal. size and reach ten to twenty feet above ground. The water pressure is not quit the same as the GTA,  but it is more then adiquit.

Hope this helps. And you owe me \$200 for the engineering consultation.

"Very funny Scotty; now beam down our clothes."

VEGETARIAN: Ancient Hindu word for "lousy hunter"

If man was formed from dirt, why is there still dirt?

digitalbeachbum
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Beyond Saving wrote: I hate

Beyond Saving wrote:

I hate to break it to you, but your wife is right. The pressure is created by the potential energy of gravity, so the higher the container is the more potential energy and therefore the more pressure at a given point in the system. The hydraulic head is calculated by adding energy from movement of the fluid, energy from pressure in the fluid and energy from the height of the fluid relative to the water main. In a gravity fed system like a rain barrel, height is by far the most influential variable.

http://en.wikipedia.org/wiki/Bernoulli's_principle

The end result is that the maximum possible psi can be calculated by multiplying the distance of the top of the water compared to the water main which will be roughly .43 * x feet. Your actual psi will probably be a little less because of other variables such as temperature, friction etc.

Thanks for posting but you have missed several issues.

To clarify, I am stating that:

A 3 foot, 55 gallon rain barrel is at sea level. The psi at the bottom of the rain barrel is 1.29 psi

A 3 foot, 55 gallon rain barrel is at 30 feet above sea level. The psi at the bottom of the rain barrel is 1.29 psi

Bernoulli's Principle is a fine attempt, but I think it is incorrectly applied to this issue.

In fluid dynamics, Bernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

I would like to point out Pascal's barrel experiment:

and also

I concede that a 3/8th hose will have increase psi over a 5/8th hose, but it will lose volume (and vice verse) a 5/8th hose will lose psi but increase volume.

I also concede that the psi at the end of any hose will instantly decrease as the amount of fluid is released from the rain barrel.

I also concede that the hose bib on this rain barrel is improperly placed (not on the bottom, dead center), but rather to the side and slightly higher than the bottom. No I didn't create this rain barrel.

And one other thing, only if you increase the amount of water while using a taller rain barrel can you increase the psi of the output.

If you took a 30 foot hose and stretched it straight up 90 degrees, filled it with water, you would have more psi than a 3 foot, 55 gallon barrel raised 100 feet off the ground.

digitalbeachbum
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Jeffrick

Jeffrick wrote:

I am an engineer who believes in the KIS*S principle, [Keep it Simple * stupid] . Don't over think the project, don't get all jumbled up with ratios and formulae that even engineers find confusing (I'm mechanical  not  hydrolic type engineer). Beyond Saving is right, IT'S GRAVITY, and don't think beyond that simple point.

A ten foot tower will give you more psi then a nine foot tower, it's that simple. 12 foot will give you more then 10 foot, simple, eh? To increase your psi beyond any formula you read, use a 6" dia. drain pipe straight down [180 degree] jointed to a 1" horizontal feed to the house.

One caveat to consider is the smog in your area,  I live in the GTA [pop. 5+ million, + their cars  trucks and factorys] I wouldn't drink or shower in the rain water here.  In Guyana where I own  a  house I do. Guyana has very little smog, high winds and it rains every 2nd or 3rd day during the dry season. Every house has a rain barrel, [mine has two] they are  400 gal. size and reach ten to twenty feet above ground. The water pressure is not quit the same as the GTA,  but it is more then adiquit.

Hope this helps. And you owe me \$200 for the engineering consultation.

Jeffrick

Thanks for posting, but like Beyond I think my argument has been missed.

Yes, a 10 foot tower will give you more psi than a 9 foot tower, but we aren't working with a tower here. We have a 3 foot, 55 gallon rain barrel which hasn't increased in size. We have only raised it up in the air.

Since the psi at the bottom of the barrel is created directly to the weight of the water, the gallons per cu in (foot column) determines the psi at the bottom of the barrel.

When a hose is hooked up to the hose bib, you haven't increased the amount of water in the barrel either. In fact, you now need to deal with friction and I'm betting that the psi in the hose will actually cause the psi at the end of the hose to drop when you open the nozzle.

I'd also like to say that in my research I found out that the hose bib you use will make a difference in initial psi.

Beyond Saving
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digitalbeachbum wrote:Thanks

digitalbeachbum wrote:

Thanks for posting but you have missed several issues.

To clarify, I am stating that:

A 3 foot, 55 gallon rain barrel is at sea level. The psi at the bottom of the rain barrel is 1.29 psi

A 3 foot, 55 gallon rain barrel is at 30 feet above sea level. The psi at the bottom of the rain barrel is 1.29 psi

In fluid dynamicsBernoulli's principle states that for an inviscid flow, an increase in the speed of the fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid's potential energy.

I would like to point out Pascal's barrel experiment:

and also

I concede that a 3/8th hose will have increase psi over a 5/8th hose, but it will lose volume (and vice verse) a 5/8th hose will lose psi but increase volume.

I also concede that the psi at the end of any hose will instantly decrease as the amount of fluid is released from the rain barrel.

I also concede that the hose bib on this rain barrel is improperly placed (not on the bottom, dead center), but rather to the side and slightly higher than the bottom. No I didn't create this rain barrel.

And one other thing, only if you increase the amount of water while using a taller rain barrel can you increase the psi of the output.

If you took a 30 foot hose and stretched it straight up 90 degrees, filled it with water, you would have more psi than a 3 foot, 55 gallon barrel raised 100 feet off the ground.

I don't see what sea level has anything to do with it. You don't put a rain barrel on a stand because you want it a certain height above sea level. You put it on a stand to increase its relative height from the spigot, whether you are 1000 feet above sea level or 1000 feet below it is irrelevant. You aren't taking the water directly from the bottom of the barrel. You presumably have a line attached to deliver the water to wherever you want it. If you put your rain barrel 100 feet off the ground you are going to have a hose attached to it. Making the distance from the water to your output 153ft and get roughly 65.79 psi when the barrel is full.

Yeah, if you put the barrel up 150 feet and just open it up at the bottom you are going to have water coming down with very little pressure but that would be ridiculously pointless and that isn't what people are recommending you do when they suggest putting the barrel on a stand. They are assuming that you are smart enough to realize you will have a hose going from the barrel to the ground. The psi at a particular point in the system is dependent upon its height relative to where the barrel is. The lower it is than the barrel, the more psi you will have. Your link to Pascal's barrel test just supports the reason why you would want to put a rain barrel on a stand. Gravity creates pressure, so having water come down a long height will create more pressure than water traveling horizontally.

If, if a white man puts his arm around me voluntarily, that's brotherhood. But if you - if you hold a gun on him and make him embrace me and pretend to be friendly or brotherly toward me, then that's not brotherhood, that's hypocrisy.- Malcolm X

digitalbeachbum
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Beyond Saving wrote:I don't

Beyond Saving wrote:
I don't see what sea level has anything to do with it. You don't put a rain barrel on a stand because you want it a certain height above sea level. You put it on a stand to increase its relative height from the spigot, whether you are 1000 feet above sea level or 1000 feet below it is irrelevant. You aren't taking the water directly from the bottom of the barrel. You presumably have a line attached to deliver the water to wherever you want it. If you put your rain barrel 100 feet off the ground you are going to have a hose attached to it. Making the distance from the water to your output 153ft and get roughly 65.79 psi when the barrel is full.

Yeah, if you put the barrel up 150 feet and just open it up at the bottom you are going to have water coming down with very little pressure but that would be ridiculously pointless and that isn't what people are recommending you do when they suggest putting the barrel on a stand. They are assuming that you are smart enough to realize you will have a hose going from the barrel to the ground. The psi at a particular point in the system is dependent upon its height relative to where the barrel is. The lower it is than the barrel, the more psi you will have. Your link to Pascal's barrel test just supports the reason why you would want to put a rain barrel on a stand. Gravity creates pressure, so having water come down a long height will create more pressure than water traveling horizontally.

Using sea level is used for practical purposes of providing a universal constant in reference to the location of the barrel. It is just easier for the sake of argument.

I'm sorry to see you have missed the discussion. Thanks for the post.

Ktulu
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Let me try the kiss

Let me try the kiss principle...

Suppose you have two plastic cups half full with water ( I said half full, that's right ).  You connect the bottoms with a hose sort of like you did in grade 5 science class.  If the cups are at the same level, they're both half full, if you raise one of them, the water, aided by gravity, will flow to the point of least resistance and go into the lower cup.  So far I'm assuming we agree, now imagine that you have a membrane over the top of the lower cup, as as the water level level rises (from you raising your other cup) the air compacts against the membrane and increase the PSI in the lower cup.

Now think of that setup only you're raising the rain barrel and you're measuring PSI at the tap...  the higher you go, the more water will try to rush out, aided by gravity, and the more air will compact... I hope this is clear.

I think where you are being confused is where you measure the PSI.  If you have a 1 gallon container, the PSI at it's tap will be x regardless of the height.  If you attach a hose to it, however, the PSI is directly proportional to the distance increase from the other end of the hose.  In other words, the higher you raise the barrel relative to the end of the hose, the more pressure you get.

"Don't seek these laws to understand. Only the mad can comprehend..." -- George Cosbuc

digitalbeachbum
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@Ktulu1)Take two cups, 1

@Ktulu

1)

Take two cups, 1 foot tall, filled with the same amount of water.

Raise one 30 feet in the air. The other is kept at ground level.

The psi has not changed in the cup raised 30 feet. They both have .43 psi.

2)

Same experiment but this time, put a faucet on the bottom of the cup 30 feet in the air and attach a 30 foot hose to it. The hose is capped at the end.

Now, depending on the amount of water in the cups, the diameter of the hose will determine the psi.

If the hose is a 5/8th garden hose and the cups hold one cup of water, when you release the water down the hose you could lose psi.

If the hose is a 5/8th garden hose and the cups hold 40 gallons of water, when you release the water down the hose you will most certainly increase psi.

3)

Same experiment but this time, put a faucet on the bottom of both cups an connect the two cups with a hose.

Raise the one cup up 30 feet in the air and release the water.

The water will rush down, per Pascal's Laws for fluid mechanics and flood the lower cup.

If that cup is sealed tight, it could possibly cause the lower cup to rupture.

What every one seems to keep missing is that two equal containers, filled equally with water, is of equal psi at 30 feet as it is at ground level.

The location of the faucet is a factor is maximizing psi as the water exits the container.

The diameter of the hose is a factor in maximizing psi and the flow of the water as it exits the container.

The height of the container only makes a difference 1) for accessibility of the faucet 2) allowing Bernoulli's pricinple and 3) Pascal's Law to be observed.

Jeffrick
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KIS*S!

digitalbeachbum wrote:

@Ktulu

1)

Take two cups, 1 foot tall, filled with the same amount of water.

Raise one 30 feet in the air. The other is kept at ground level.

The psi has not changed in the cup raised 30 feet. They both have .43 psi.

2)

Same experiment but this time, put a faucet on the bottom of the cup 30 feet in the air and attach a 30 foot hose to it. The hose is capped at the end.

Now, depending on the amount of water in the cups, the diameter of the hose will determine the psi.

If the hose is a 5/8th garden hose and the cups hold one cup of water, when you release the water down the hose you could lose psi.

If the hose is a 5/8th garden hose and the cups hold 40 gallons of water, when you release the water down the hose you will most certainly increase psi.

3)

Same experiment but this time, put a faucet on the bottom of both cups an connect the two cups with a hose.

Raise the one cup up 30 feet in the air and release the water.

The water will rush down, per Pascal's Laws for fluid mechanics and flood the lower cup.

If that cup is sealed tight, it could possibly cause the lower cup to rupture.

What every one seems to keep missing is that two equal containers, filled equally with water, is of equal psi at 30 feet as it is at ground level.

The location of the faucet is a factor is maximizing psi as the water exits the container.

The diameter of the hose is a factor in maximizing psi and the flow of the water as it exits the container.

The height of the container only makes a difference 1) for accessibility of the faucet 2) allowing Bernoulli's pricinple and 3) Pascal's Law to be observed.

Refer to post #2;  the first paragraph.   Keep it Simple,  and don't over think the equations and veriables. It's a waste of time.   Yes 2 equal containers will have   equal psi at   30 ft. & ground level.  the psi  difference comes at 8000 ft.  [eight thousand feet above sea level]. YOU  ARE NOT doing a rain barrol at 8000 ft.  so Bernoulli &  Pascal can walk off in the sunset in what ever heaven hell or Valhalla they ended up in.

Refer to post # 1   & post # 2  the key here is GRAVITY. Kiss it!!!!!  A dead drop of thirty feet will give you higher psi:   Is that what you want? Dead drop with a wide pipe [6"] at 180 degrees;  make the horizontal joint at 90 degrees to a 5/8 " spout for a max psi at exit point.  For more psi;  widen the dead drop  pipe and narrow the the horizontal;  plus narrow the spiggot at the exit point.        There are machines;  useing this simple principle, that use water to cut through granite!!!!   Compressed air in the water tank creates the 1000's of  psi needed for the job, yet it is the same principle; GRAVITY>

"Very funny Scotty; now beam down our clothes."

VEGETARIAN: Ancient Hindu word for "lousy hunter"

If man was formed from dirt, why is there still dirt?

digitalbeachbum
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Jeffrick wrote:

Jeffrick wrote:

Refer to post #2;  the first paragraph.   Keep it Simple,  and don't over think the equations and veriables. It's a waste of time.   Yes 2 equal containers will have   equal psi at   30 ft. & ground level.  the psi  difference comes at 8000 ft.  [eight thousand feet above sea level]. YOU  ARE NOT doing a rain barrol at 8000 ft.  so Bernoulli &  Pascal can walk off in the sunset in what ever heaven hell or Valhalla they ended up in.

This is my original point and why I originally balked at the claims. The psi in the barrel stays the same at either elevation, but yes, as you go up and away from the Earth the difference would be greater.

One thing I did not know, which I learned during this research, is that the astronauts which go up in to "space" don't experience true weightlessness. They are in a continue free fall even at 250 miles.

Jeffrick wrote:

Refer to post # 1   & post # 2  the key here is GRAVITY. Kiss it!!!!!  A dead drop of thirty feet will give you higher psi:   Is that what you want? Dead drop with a wide pipe [6"] at 180 degrees;  make the horizontal joint at 90 degrees to a 5/8 " spout for a max psi at exit point.  For more psi;  widen the dead drop  pipe and narrow the the horizontal;  plus narrow the spiggot at the exit point.        There are machines;  useing this simple principle, that use water to cut through granite!!!!   Compressed air in the water tank creates the 1000's of  psi needed for the job, yet it is the same principle; GRAVITY>

Yes, a dead drop of 30 feet will have a dramatic effect on the water, but as I previously stated the location of the faucets is not a dead drop (on the bottom of the barrel). The faucets are to the side and are several inches up.

I've seen those machines that use pressurized water to cut stone, which is how they rescued the kid who fell down the well hole back in the 80's.

EXC
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digitalbeachbum wrote: Now,

digitalbeachbum wrote:

Now, depending on the amount of water in the cups, the diameter of the hose will determine the psi.

The hose pipe diameter does not affect PSI, it affects the flow rate.

Pressure is a measurement taken when water is not flowing. When people say they have low pressure, they should really say the have poor flow. Flow rate is a function of both pleasure and pipe/faucet size.

The thing with a rain barrel is you need to decide do need a low flow at high velocity like for a sprinkler or shower spay or low velocity at high flow like to fill up a bucket/tub/sink.

Once you know what you want the water to do, you can determine height of the tank and size of the pipes and faucets. What all do you want the water to do?

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