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View Full Version : gravity flow vs pipe size vs draw down looking for chart or math

boggen
02-05-2006, 01:18 AM
i been searching for math / formula, or a chart to go by. for sizing pipe for gravity feed situations.

looking for formula that makes scince to me. were i can either plug in the numbers and come up with the chart. a chart would be nice but it seems a chart be limited in amount of info that could be put into it.

i get 2" pipe is around 2000 max per 1" or :confused: draw down inches
i get 4" pipe is around 3000gph max per 1" or :confused: draw down inches
and many other variations of the above

from reading over at http://www.engineeringtoolbox.com/ i gathered some links from the site that might help someone. :confused: i have tried other sites but all the online calculators to other. just don't seem geared for what is wanted for a gravity flow gph for ponding.:mad:

the following pages come to mind in trying to figure out gravity flow. but what numbers and from what charts and from were.... concept and applying is just not there yet for me. :(

--------------------------------

formulas

gravity flow calculation
http://www.engineeringtoolbox.com/mannings-formula-gravity-flow-d_800.html

static pressure and head pressure (seems to deal with gravity)

--------------------------------

charts and other misc info.

friction loss pipe chart for sch 40 pipe
http://www.engineeringtoolbox.com/pvc-pipes-friction-loss-d_802.html

friction loss pipe chart for fittings
http://www.engineeringtoolbox.com/pvc-pipes-equivalent-length-fittings-d_801.html

for ID (inner diameter) of pvc sch 40
http://www.engineeringtoolbox.com/pvc-cpvc-pipes-dimensions-d_795.html

for ID (inner diameter) for hoses (gauge)
http://www.engineeringtoolbox.com/BWG-wire-gage-d_508.html

amount of flow (velocity) to have in pipe to keep stuff from setteling out.
http://www.engineeringtoolbox.com/slurry-transport-velocity-d_236.html

Geometric relationships like area, wetted perimeter and hydraulic diameter
http://www.engineeringtoolbox.com/flow-section-channels-d_965.html

density and weight of water
http://www.engineeringtoolbox.com/water-density-specific-weight-d_595.html

Air Pressure and Altitude above Sea Level
http://www.engineeringtoolbox.com/air-altitude-pressure-d_462.html

Ryan S.
02-05-2006, 09:54 AM
http://www.efunda.com/formulae/fluids/draining_tank.cfm#calc

This is what I use for my calculations, Bernoulli equation

hacnp
02-05-2006, 10:53 AM
Roarks web site has an excellent calc. for gravity flow into which you put in your choice of flow rates. I used it to calculate my yet to be built Q system and to check my calculations on the main pond.

"B"
02-05-2006, 11:29 AM
Roarks web site has an excellent calc. for gravity flow into which you put in your choice of flow rates. I used it to calculate my yet to be built Q system and to check my calculations on the main pond.

L5Vegan
02-05-2006, 12:09 PM
http://www.click2roark.com
Look for the Flow velocity calculator.
A velocity of 1.1 -1.2 FPS is about the ballpark for around 1inch of drawdown per transfer.

hacnp
02-05-2006, 12:11 PM
Roark's puddle (http://www.click2roark.com/cgi-win/weborder.exe?operation=getdoc&document=index2)
You must register and then look in the index on the left side about 1 quater of the way down the page

L5Vegan
02-05-2006, 01:46 PM
For a rule of thumb use the following
2 inch pipe 750GPH
3 inch 1500GPH
4 inch 3000 GPH

These flows will give you around 1 inch of drop at each transfer with some fudge factor to acount for differing pipe length and number of bends. :yes:

If you are just trying to get the concept clear in your head think of the calculator that Ryan gave a link to as showing the available power (volume) provided by the difference in elevation. Then this volume is lowered by the friction of the pipework connecting the two containers (Friction loss chart (http://www.mdminc.com/Friction_Loss_Chart.htm) ). Just remember that friction is not linear. I don't remember the formula , but it's a function of the square of the velocity.

Dan

schildkoi
02-05-2006, 01:55 PM
Does not include friction loss in piping.

Steve

jinx
02-05-2006, 03:18 PM
Hi Steve, thanks for the chart. I,ve waited 2 years to see this. Hope you dont mind if i share it with others when they ask. Thanks for sharing.

boggen
02-05-2006, 04:24 PM
awe thank ye :D::cool: :yes: :eek: schildkoi

so if someone has
100ft of pipe from bottom drain to setteling chamber
using a 4" pipe
and has 7536gph getting pull through the 4" pipe for a 2" draw down

http://www.engineeringtoolbox.com/p...loss-d_802.html (http://www.engineeringtoolbox.com/pvc-pipes-friction-loss-d_802.html)
they would have an additional 10.8" draw down ((100 feet of 4" pipe at 7500gph = 10.8" head))

10.8" friction loss
+2" draw down
--------------
= 12.8" total draw down? :confused: :confused:

ak764
02-05-2006, 04:35 PM
Hi all, I am just wondering if I am understanding the concept. According to the chart above, if you have a 4" pipe supplying the barrel/filter/SC or whatever, if the water level in the filter is the same as the pond level, approximately 7500 GPH is supplied to the barrel but at this rate, the water level in the barrel will go down about 2". So your exit pipe needs to be below this to keep a constant supply of water going. Am I completely way off on this? I am quite new to all of this. :confused:

Andrew

boggen
02-05-2006, 04:39 PM
http://www.efunda.com/formulae/fluids/draining_tank.cfm#calc

This is what I use for my calculations, Bernoulli equation
after looking at schildkoi and the page you gave Ryan S. looks like about the same info....i ran over this page once before and i think i was following the picture and not thinking out the depth out correctly.

""depth of spout, Az"" for above website should say for us pond folks, ""draw down inches""

boggen
02-05-2006, 04:49 PM
you got the right idea ak764

to add to what you stated ak764.
at 7500gph useing 4" piping = 2" draw down ((from info above.))

pond to 1st filter water level in 1st filter will be 2" below pond water level.
1st filter to 2nd filter water level in 2nd filter will be 4" below pond water level.
---scince 2nd filter is pulling from 1st filter. an extra 2" drop is needed to get the flow needed through the 4" pipe.
2nd filter to 3rd filter water level in 3rd filter will be 6" below pond water level.
---scince 3rd filter is pulling from 2nd filter. an extra 2" drop is needed to get the flow needed through the 4" pipe.

and to put the last twister on it. all the filter chambers in above example. the top rim needs to be above the water level of the pond. so if the pump does get shut off. the chambers do not overflow and leak every were.

ak764
02-05-2006, 04:58 PM
Thanks for the explanations. I am finally getting this stuff. I built my pond last year. I have a 4000 gallon pond, 300 gallon Skippy/waterfall with a bunch of scrubbing pads and bags of strapping material. worked great last year (water was crystal clear). I have a Sequence pump which I think pulls at about 5000-6000 gph. I wanted to add a sc/barrel with static media and was afraid that gravity feeding would not keep up with the pump rate. But I think I can do this now. :cool:

Thanks again.

Andrew

L5Vegan
02-05-2006, 05:27 PM
Steve C.
I'm going to take the the devils advocate (or maybe the other D.A.) position for a moment.

While I agree with the basic flows for 1 inch of drop for all three sizes of pipe I think that the chart is wrong on most everything else. :eek:

1. It looks like one flow was solved for and the rest of the chart was made using simple multiplication and division.

2. I can't find any flows shown on the chart that match your velocity formula.

3. You have said in the past that gravity flow from 2" at 5 feet of head will produce 230 gph, but now at only 1 foot will produce 11,304 GPH. :eek: :confused:

4. The fraction of an inch section for 2" doesn't match the rest of the chart.
I changed it to match (shown below).

(Ducking) :)
Dan

schildkoi
02-05-2006, 07:51 PM
One was for gravity flow at the rim of a tank and the other is through piping and the draw done from one tank to the next.

Steve

L5Vegan
02-06-2006, 01:02 AM
Steve,
Technically, the previous discussion was about the return from a barrel filter
through two, two inch pipes with a 2.5 feet differrence in water level in the filter and the pond. The rim of the tank was not part of the equation. What was assumed was a pipe full of water not a mixture of water and air so some means to accomplish this is in place. The example did seem to morph into one 2 inch pipe and a 5 foot difference in elevation, which is fine with me to simplify the math.

If I have two containers and pump water from container one into container two and gravity feed back from container two to container one, I don't think it makes a difference which one I label pond and which I call filter.

Dan

luke-gr
02-06-2006, 12:21 PM
EDIT: Deleted post. Im over my head. :D:

schildkoi
02-06-2006, 02:40 PM
I thought I responded once and its not showing, so here goes again.

The previous discussion had to do with the gravity flow out of a barrel through a 2" line (or multiples, I can't remember). The 2" line was at the TOP of the barrel leaving little to no room for elevation head to "push" water through the 2" opening(s). This is very different than the elevation head nescessary to push a given volume through a given sized pipe since the elevation is "fixed" (semi) in the pond and the draw down is at the flow equal to that of the pump pulling from the chamber for the given transfer pipe diameter.

Without going back and doing the math from the previous example, let's say that the 2" pipe will flow the 230 gph through the opening WITHOUT any given elevation head when using the 2" orafice at the top of the container.

Apples and oranges comparisons actually. The chart is simply for transfer lines between pond and chambers (and subsequent chambers as pointed out as well). Your other example Dan is a totally different application. If memory serves some indicated that a syphoning action would keep the chamber from over flowing up to the 5' elevation flow factor. That in and of itself presumes that the water level exceeds the pipe and will never suck air as well (which it would). If you go back and relook at that thread, I eventually dropped out of that discussion (knowing other arguments were not exactly well thought out but yet unable to explain thoroughly enough so that the light bulbs came on).

Steve

L5Vegan
02-06-2006, 09:21 PM
Lets take a look at a couple of pictures.
Assuming same diameter pipes and ignoring friction loss which of the six pipes will flow the most water.
http://img.photobucket.com/albums/v376/l5vegan/Grav01.jpghttp://img.photobucket.com/albums/v376/l5vegan/Grav02.jpg
To see the extremes lets focus on pipes D and F. It seem that pipe D would flow more water than F. This is incorrect. ALL THE PIPES WILL PRODUCE THE SAME FLOWS. :yes:
I think the hang up is the mental picture of needing water above the inlet to the pipe that is transferring the water to push the water through the pipe.
Seems logical, but it is false. THE ONLY THING THAT MATTERS IS THE DIFFERENCE IN WATER LEVELS. Yes, a siphon would produce the same flows with the same difference in water levels.

Dan

L5Vegan
02-06-2006, 10:04 PM
Without going back and doing the math from the previous example, let's say that the 2" pipe will flow the 230 gph through the opening WITHOUT any given elevation head when using the 2" orafice at the top of the container.

When I actually set it up and tested it, it flowed over 7,400 GPH. :eek: :yes:
That was with the water level even with the inside top of the pipe or up to an inch below. Never over the pipe. :)
Equivalent pipe length of 28.5 feet.
Dan

schildkoi
02-06-2006, 10:43 PM
But that wasn't the example I was citing. It was the flow through a given size orafice...without the syphoning (still think it would overflow at a gievn rate though )).

An both yours and Mine (below) are still not the same as from chamber to chamber at the same elevation (although Mine is close if the adjoining barrels are connected straight across at the same hieghts.

Steve

L5Vegan
02-06-2006, 11:31 PM
Steve,
http://img.photobucket.com/albums/v376/l5vegan/Grav03.jpghttp://img.photobucket.com/albums/v376/l5vegan/Grav04.jpg

You can pick direction of flow right to left or left to right.

But that wasn't the example I was citing. It was the flow through a given size orafice...without the syphoning (still think it would overflow at a gievn rate though )).

So either I'm that incompetent, or a liar? :confused: :(

Dan

Ryan S.
02-07-2006, 09:03 AM
Dan,

Steve's chart is generally correct, he stating that drag was ignored. If you look at the link I posted, it allows you to adjust for varables. It is correct. The chart is a good quick reference.

Alot of jumping around in this topic:

In your last set of pics (post #23) the answer is very easy. All the 3 pipes will flow exactly the same amount at given water height. (Pipe D would be capable of flowing a hair more b/c of one less turn).

Ryan

Ryan S.
02-07-2006, 09:16 AM
Post 20:

Lets assume the barrell is filled to the line you have and all lines are closed with valves. Lets see what happens if you open each valve separetly at the same water level:

http://img.photobucket.com/albums/v376/l5vegan/Grav01.jpg

Assume line C is down 1" from water line, B is 12" and C is 24"
Assume Discharge coefficent is .90 and water is freshwater at 1 kg/l

Line C: 1224gph
Line B: 4242gph
Line A: 6000gph

Ryan S.
02-07-2006, 09:20 AM
In the above example that is what they would flow exacly when opened. Take the barrell with line A. When you open the valve A would start flowing at 6000gph with 24" of water in the tank. It would be constantly slowing as the water level droped. When water level on was down half way to 12" line A would be flowing at 4242gph, when water level droped to 1" it would be flowing at 1224gph. So it would start at 6000gph untill it stoped at no flow as the tank emptied (since the tank was above the water level of the pond).

Ryan S.
02-07-2006, 09:26 AM
If you were using the same barrell and wanted to know how much water you could pump through it on a continous basis at that water line these numbers would apply:

Line C: 1224gph
Line B: 4242gph
Line A: 6000gph

However Line B and C are kinda risky, since anything stuck over the inlet or in the pipe would drastically change the flow capablities and may cause the barrell to overflow if they did. Since C is moving a slower velocity any partical blocks would be less signifcant. So say if you needed 4000gph of flow, although B and A would certianly work, it would be much better to just put a 4" pipe in C's location.

schildkoi
02-07-2006, 09:53 AM
I "think" what Dan is trying to say at what rate could the tank's water be replaced and not overflow. Which is where the difference lies.

This is also an apples to oranges comparison (totally different application) than draw down from one tank to the next at initially the same elevation (verses 2 tanks at differing elevations). The quick reference chart is for the former, not the latter.

Steve

Ryan S.
02-07-2006, 10:02 AM
Ok then, the same max numbers apply to keep water level at given level in picture. Amount over this would be determined by the amount of available space between the water line in the pics and the rim of the tank, which was not given. If this was known, distance between lowest part of rim and exit pipe this would the spout depth in formula to give max flow rate without overflowing barrell.

schildkoi
02-07-2006, 10:22 AM
Both you and Dan are very "sharp".

I guess one of my issues with Dan's example is "why"? I don't understand why someone would pump water up 5' and then "pipe it" back down? I can see where pumping it up 5' to a waterfall or such would have an application (would thus fall into my example). Why spend the added energy (larger pump for same flow) of going up 5' without any payback or purpose? I know, I get "anal" from time to time. :)

Steve

luke-gr
02-07-2006, 12:17 PM
This is also an apples to oranges comparison (totally different application) than draw down from one tank to the next at initially the same elevation (verses 2 tanks at differing elevations). The quick reference chart is for the former, not the latter.

Steve

That is what I posted in my earlier response that I erased. I figured I was just behind the learning curve. Im doing my best to follow this. Interesting stuff. Steve makes a pretty good point in that most folks wont pipe water up very high to pipe back, but I had thought about it as a way to hide my filters.

So much to learn,
Luke

schildkoi
02-07-2006, 12:23 PM
If you aren't piping up for a waterfall, then why not bury them in the ground and save the added expense of a bigger pump (more \$) and higher running costs (add'l more \$)?

Steve

luke-gr
02-07-2006, 02:14 PM
WHen I said I thought about it, I meant I HAD thought about it and decided against it. I was thinking about the EZR type filter and I think those would be a pain to bury (I could be wrong) with all the asssociated valves, plumbing, etc. Ive since moved away from that idea.

EDIT: Oh yeah, I was going to pipe them to the waterfall

L5Vegan
02-07-2006, 06:39 PM
I agree that this discussion has limited application to most of us, and yes it is expanded from the original question. If you look at posts # 7 and 8 Steve and I agree on the answer to that for most filters. the reason that I'm not giving up is that I used to not get it, but the light bulb did come on. Now I'm just trying to share the concept.

The real apples to oranges is using a discharge into free air calculator and applying it to submerged discharge. Of course it works well enough for our purposes. :yes:

Ryan,
You did an excellent job of illustrating Steves position.
I just want to say that you are looking at it 100% wrong. :D:
If you set your discharge height to the difference in the water levels in the two tanks it will give you the flow rate for ANY of the six pipes. The depth of water over the intakes and outlets doesn't matter.

My only real objection to Steve's chart is that I don't think that the flows would increase in a linear manner. I honestly have no idea if its right or not because I haven't tried it (Yet). As i already said the line for one inch of drop is all 99% of us should care about, and it looks right on.
Dan

hacnp
02-07-2006, 07:02 PM
Both you and Dan are very "sharp".

I guess one of my issues with Dan's example is "why"? I don't understand why someone would pump water up 5' and then "pipe it" back down? I can see where pumping it up 5' to a waterfall or such would have an application (would thus fall into my example). Why spend the added energy (larger pump for same flow) of going up 5' without any payback or purpose? I know, I get "anal" from time to time. :)

Steve
Purpose 1, gravity tpr from submerged biofilter.

Purpose 2, winter bypass that keeps submerged filter running during winter

I use both, My gravity tpr runs about 7000 GPH during the summer and the same as a bypass for the filter during winter. Excess flow is run thru a second bypass during winter.

L5Vegan
02-07-2006, 07:12 PM
Dan,

Steve's chart is generally correct, he stating that drag was ignored. If you look at the link I posted, it allows you to adjust for varables. It is correct. The chart is a good quick reference.

Alot of jumping around in this topic:

In your last set of pics (post #23) the answer is very easy. All the 3 pipes will flow exactly the same amount at given water height. (Pipe D would be capable of flowing a hair more b/c of one less turn).

Ryan
I'm running out of different ways to explain this, but lets try another approach.
http://img.photobucket.com/albums/v376/l5vegan/Grav05.jpg
It sounds like we all agree that if we pump water from the right tank in the pic to the left tank we will get equal flows through the pipes (Ignoring friction of course.) :yes: :cool:
Now visualize slowly increasing the flow until the draw down looks like this.( No I don't care where all the extra water went, maybe there's an overflow on the pond :rofl: )
http://img.photobucket.com/albums/v376/l5vegan/Grav06.jpg
At what point does our apple suddenly become an orange. :)
Dan

schildkoi
02-07-2006, 07:17 PM
Gravity is a constant and the volume of water (creating the elevation head) would be linear. The formula is what the formula is:
Q (water quantity)= Pipe cross sectional area * Velocity head

A given "drop" yields a given velocity head.

The numerical term which is used for the velocity energy is V2/2g where g is the gravitational constant 32 ft/sec . Algebraically the units work out nicely; V is velocity which is measured in ft/sec; g is gravity which is measured in ft2 /sec. Multiplying V by itself (V x V = V2 ) results in units of ft2 /sec2. Dividing one by the other the measuring unit of the term, V2/2g, comes out to be, once again, feet (of head).

So, in our example, the drop of an inch (converted to ft) is our velocity head. The cross sectional area for a given pipe size is constant and thus all other variables in the equation are linear, proportionally.

Steve

schildkoi
02-07-2006, 07:32 PM
OK Dan, I thinkj I see where you are going, but still not "real life". The top line is for a skimmer, the middle for a midlevel pick-up and the bottom as a bottom drain (as an example). But, please keep in mind that all three lines would connect to the filtration chamber at the same elevation, typically at the 1/3 hieght and the chamber would not be deeper than the pond...typically. In that example, providing that all 3 pipes remained fully flooded, they would in fact all have the same flow as you describe in your very first post. Like I said, I can get "anal" and require realistic examples to unclog my brain.

Now, its still all horse pucky as it relates to my quick reference chart since we are not attempting to say at which discharge hieght from the pond anyway. We are looking at any transfer that can remain fully flooded and the total drop in elevation from one tank to the next in water level. So although your original premise is true that the discharge hieght may not matter (but can in varying scenerios), it still has nothing to do with level of drop in the second chamber for a given flow rate. Follow?

Steve

Ryan S.
02-07-2006, 07:45 PM
Ryan,
You did an excellent job of illustrating Steves position.
I just want to say that you are looking at it 100% wrong. :D:
If you set your discharge height to the difference in the water levels in the two tanks it will give you the flow rate for ANY of the six pipes. The depth of water over the intakes and outlets doesn't matter.Dan

I'm sure you mean well, but YOU are completely wrong.

The same forumla/link I posted can calculate every topic discussed here.

My kids are driving me crazy wright now but I will to explain it again when I get a chance.

Ryan S.
02-07-2006, 08:13 PM
I'm running out of different ways to explain this, but lets try another approach.
http://img.photobucket.com/albums/v376/l5vegan/Grav05.jpg
It sounds like we all agree that if we pump water from the right tank in the pic to the left tank we will get equal flows through the pipes (Ignoring friction of course.) :yes: :cool:
Now visualize slowly increasing the flow until the draw down looks like this.( No I don't care where all the extra water went, maybe there's an overflow on the pond :rofl: )
http://img.photobucket.com/albums/v376/l5vegan/Grav06.jpg
At what point does our apple suddenly become an orange. :)
Dan

So all three lines are completely open? I previously thought you were compairing 3 different locations for a pipe, not that each would flow back, but anyways. It makes no practical since in a a real world filtration example to this? In both examples, NO, the flow rate between all pipes will not be equal. The lower pipes have more pressure from the weight of water and will flow with greater velocity than volume. This is a really simple concept, take a paper cup and pop 3 holes in the side. The bottom will flow the most, the middle next, and the uppermost the least. ON the first pic, it depends if the water line is exactly equal, if water lines are equal they should flow the same.

schildkoi
02-07-2006, 10:22 PM
Your example of the paper cups was exactly how I originally envisioned it.....but it is not the same as Dan's example. connecting the pipes to another chamber with water level above the upper most pipe and all pipe lengths being equal equalizes the pressure and become the same working elevation head thus the same flow. All three pipes have the same elevation head ( difference in chamber water levels) and thus the same flows.

That being said, its still not the same apples to apples comparison for the elevation drop or my quick reference. :)

Steve

Ryan S.
02-07-2006, 11:07 PM
We are moving through topics quick...

Steve, in picture #2 I respectfully disagree, I think the bottom outlets will be flowing more. Pipes exiting into the water should make no difference than if all pipes when strait horizontal. Spout depth in calculation would be lesser of outlet location or water level in other tank. Picture #1 its more difficult. If water levels are exactly equal there should be ablsolutely no difference in flow rates give equal fiction loss between outlets. So to answer Dan's question, apples become oranges when there is difference between outlet depth AND water level.

Now if you can find me 2 2" low resistance flow meters to borrow, I would happy to put togher 2 barrells, pump, and all the fittings to document. I've been wrong before (don't tell my wife), but I think right on this one.

schildkoi
02-08-2006, 12:25 AM
If all 3 discharge pipes were above water level in the second chamber you would be correct. But the back pressure at each level when all are below water level counteracts the added elevation of these on the 1st chamber thus making the flows equal (its only the elevation head difference in water level from one chamber to the next that matters in Dan's example. I don't have to join 2 pipes together, I can use my 4" bottom drain to Nexus, verses my 4" gravity skimmer to Nitritech. At the same flow rates, the drop in both is equal (or very close...slight differences in friction loss of the piping).

I hate it when I am wrong and then proving their point to boot! Grrrrrrrrrrrr :)

BUT Ryan, We are still correct on the quick reference chart :)

Steve

Cowiche Ponder
02-08-2006, 01:53 AM
uh.... I think I got about 1/90th of what has been discussed on this thread.... but it was good!!

L5Vegan
02-08-2006, 02:47 AM
Steve,
Welcome aboard. :yes: :D:
I had to go out for the evening, but I spent it thinking about gravity. :)
I have a long rambling explanation, but instead I went to the efunda calculator and left all the default settings except the depth.
here's what it said for velocity at different depths.
1cm=.443m/sec
10cm=1.4m/sec
100cm=4.43m/sec
1000cm=14m/sec
So for each 10 times increase of depth the output would increase ~3.16 times, or the square root of ten.
Dan

boggen
02-08-2006, 02:58 AM
nice little debate ya all having :yes: and i think i am comprehending what is being said.

i know what i want. but hhhmm ya lol.
--gravity
--tempature ((60 F))
----type of fluid ((water))
------Absolute Pressure = 0.59 (ft H2O)
------Density = 1.938 (slugs/ft3)
------Kinematic Viscosity = 0.0000121 (ft2/s)
------Dynamic Viscosity = 0.00002344 (lb.s/ft2)
------Specific Weight = 8.3378 (lb/gallon)
--pipe material ((pvc sch40))
------roughness
------inner diameter
------length
--------actual length of pipe
--------fittings

----pump
--------pipe length and fittings on IN let side of pump
--------pipe lenngth and fittings on OUT let side of pump
--------highest point pump most push water up to.
---------were the end of the pipe that connects to OUT let side of pump meets air (postive number), or water level in given chamber (can be neg or postive number)
--------were the end of the pipe that connects to the IN let side of the pump meets air (ugh you don't want that), or water level in given chamber (can be neg or postive number)
------pump chart head to gallons per hour.

given scenario

Chamber A has unlimited volumn of water and never drops or raises in water level ((thought as pond for this purpose))
Chamber B is 4 foot diameter 4 foot tall
chamber C is 4 foot diameter 4 foot tall
chamber D is a unlimited void, and can never get filled. ((thought as pond for this purpose))

Chamber A outlet gravity feeds through a fully flooded pipe to chamber B inlet
chamber B outlet gravity feeds through a fully flooded pipe to chamber C inlet
chamber C outlet flows through a folly flooded pipe to pumps inlet.
pumps outlet flows to chamber D.

problem 1.
how much water height is needed in chamber C, to keep the pump from running dry

problem 2.
how many gph are needed to replenish the water in chamber C in order to keep above or equal to problem 1 water height?

problem 3.
if we know we are taking 3000gph from chamber C, we know we must supply 3000gph to chamber C. which solves problem 2....

if we use one inch pipe.
what is the distance between chamber B water level height and chamber C water level height. needed to get 3000gph flow, through a once inch pipe?

this number in all intense purpose could be thought of as static head.

problem 4.
if we look at the following.

--pipe material ((pvc sch40))
------roughness
------inner diameter
------length
--------actual length of pipe
--------fittings

we can look at charts, and figured out how much resistence, or dynamic head that will be placed on the flow of water flowing through a 1" pipe.

this number in all intense purpose can be thought of as Dynamic head.

problem 5.
if we know the number from problem 3, and problem 4. can we state that the total distence between, water level in chamber B, and water level chamber C is total head. or rather total gravity head needed to supply 3000gph through a 1" pipe? or should we stick with draw down?:confused:

------------------
next set of problems are wonderings in how to determining the answers to above problems.

problem 6
does the negitive pressure on the pumps inlet side. create problems when figuring water height needed in chamber C?

problem 7.
if we replaced chambers B and C. with chambers A and B. were both inlets and outlets are gravity feed. we now have a new set of problems. that deal with calculating.... if graivty flow and water height, vs pump flow and water height. can the numbers be easly swapped?

problem 8.
order of calculation.....
what comes first chicken or the egg http://www.koiphen.com/forums/images/smilies/To%20funny.gif

boggen
02-08-2006, 04:03 AM
the picture is there, for idea,

inlet and outlet. for both chambers. need to be taken into consideration. IMHO which pipe will flow more. with thought to water current. and resistance of what water meets within its flow.

the paper cup and 3 holes placed in it. is a good example when. we under size a gravity feed pipe. :mad: and the pump starts sucking air. ""raises hand not me""

coming in low or from the bottom. has its advanatages. for a diy, when they mis figured draw down. but. does coming through the bottom or coming in low. like the C pipes. in the given pictures cause more flow?

i will say yes.
i realize there is more force / weight / pressure at the bottom. of left chamber, but we must subtract the same amount of force / weight / pressure from the right chamber. if we raised the pipe to say pipe B.

but in the yes is in thoughts to currents, debree in the water, other gases / liquied within the water. it may be hardly messureable of the other things. but overall. id say it would count up in long run.

i will also say no also. again reasons given above.

on a more theoretical type of idea....
if all pipes are equal resistence.
and the currents within the chambers. were made to draw from each pipe equally. ya sure. but not real world.

Ryan S.
02-08-2006, 09:25 AM
If all 3 discharge pipes were above water level in the second chamber you would be correct. But the back pressure at each level when all are below water level counteracts the added elevation of these on the 1st chamber thus making the flows equal (its only the elevation head difference in water level from one chamber to the next that matters in Dan's example. I don't have to join 2 pipes together, I can use my 4" bottom drain to Nexus, verses my 4" gravity skimmer to Nitritech. At the same flow rates, the drop in both is equal (or very close...slight differences in friction loss of the piping).

I hate it when I am wrong and then proving their point to boot! Grrrrrrrrrrrr :)

BUT Ryan, We are still correct on the quick reference chart :)

Steve

I still do not agree. The water level in the second tank is irrelavant for Lines C and B. It is significant for A. The spout depth in the calculation is the lesser of the difference of water line OR spout depth. Its outright silly to think the backpressures in both ends of the pipes is equal b/c they are both underwater given the significant difference in water level between the tanks. If the pump was cut off the water in the first chamber would quickly rush to second untill both are level, this proves my point. This is what happends in an open system.

http://img.photobucket.com/albums/v376/l5vegan/Grav06.jpg

Lets make some assumptions on the depths posted and an assumption on discharge coefficient. We can not only see that flow between lines is different, but also we can caculate the extact flow of the pump.

Depth from current water line in tankA
C 1"
B 12"
A 24"
Waterline in Tank B Compaired to tank A 18"
Assume discharge coefficent of .90

Flow Rate on each line by Bernoulli equation. Roughtly 39" of freshwater = 1psi, in the following we will define pressure by inches of water

Line C: Total pressure 1" from tank A
C= 1224gph

Line B: Total pressure 12" from tank A
B= 4242gph

Line A: Total pressure 18" from tank A (That is 24" from tank A minus 6" from tank B
C= 5196gph

Total flow of pump need to replicate this system 10,662gph.

Ryan S.
02-08-2006, 11:45 AM
I don't have to join 2 pipes together, I can use my 4" bottom drain to Nexus, verses my 4" gravity skimmer to Nitritech. At the same flow rates, the drop in both is equal (or very close...slight differences in friction loss of the piping).

Not really, if are running say 3600gph through them, both have ~1" drop, both are operating on the same pressure. Not the same as in example

Ryan S.
02-08-2006, 12:03 PM
In first one, same as above, there is 1" of pressure on both lines. Where they enter the tank under the water level is not significant. Both lines if friction was equal would flow equal. In this case, for 2 4" lines to feed the tank with 1" water line loss the flow will be ~7200-8000gph.

In the second picture the variables have changed. Say there is now a 18" difference in water line between the tanks. The Skimmer line has 1" of pressure. This is limited by the highest point of the outlet line. That implies it will flow at ~3600-4000gph. The bottom drain line now has 18" of pressure however. For this situation to exsist the bottom drain is now flowing whatever a 4" line at 18" drop would, I imagine 25kgph or so. This is also what applies to Dan's example, you can drop the skimmer line down to the bottom also, as long as the highest point is still at the top, 1" down the same pressure applies and the same results apply.

schildkoi
02-08-2006, 12:56 PM
Ryan first, Keep in mind, I believe in Dan's example, only one line is open at a time, not all 3 at once.

Dan,
You can teach an old dog new tricks....or at least refresh their memory!
I did find an error in my charts! This is why constructive debate is soooooo good! Somewhere in my original calcs I got sidetracked. I went back, refreshed my mind with the formulas and double check my calculations. The process isn't that hard if you follow the formulas (I don't like hydrolic calculators and much prefer the old methods of doing the calculations myself.

There is a simple formula for my chart and its application (it was in a previous post but perhaps got lost with all of the backup):

Q (water quantity) = pipe cross sectional area * Velocity

Velocity head (V Sqrd* 64) = the draw down in elevation between vessels. Thus V = Sqrt(Drop(in ft)/64).

So, for a 2" line with a 1" drop the following calculation is performed:
V = sqrt(.0833/64) = .03607 ft/sec

Q = (3.14"/12) (pipe cross sectional area) * .03607 (velocity) = .009 Cu ft /sec. Converting cu ft per sec to hour = .009 * 3600 = 32.4 cu ft per hour

Now, convert Cu ft to gallons 1 cu ft = 7.48 US gallons

32.4 * 7.48 = 242.35 gph not the 942 in my charts.....I'll need to take a harder look at those previous calculations and update the charts.

Doing the calculations above replacing the 1" (.0833 ft) with 2" (.1666) We yield the following gallonage for a 2" line with 2" drop:

V = .0510 ft/sec

Q = .013 cu ft/sec = 46.8 cu ft/hour = 350 US gallons per hour

Now, if we relook at that 5' example of Dan's, it yields:

V = .2795ft/sec

Q = .073 cu ft/sec = 262 cu ft/hr = 1965 US gallons per hour

Ok Ryan and Dan...double check me...again :)

Going back to that old thread Dan and I refferred to then, the max to be pumped up 5' and plumbed back down (not spilled over) would be 1965 gallons per hour (before the tank overflowed). Right Dan? It was my original 242 for simply spilling out that that 5' level.

Well, enough of this for now....I have some charts to redo. :)

Steve

And after all of that, those calculations are all wrong too! GRRRR

Ryan S.
02-08-2006, 01:48 PM
I have no idea what he is talking about now. My first replies were based on one line open at a time, since that is a logical installion method (compairing where to place a return). But after that it moved to gravity-flow TPRs and they are all truely open in his example, and I thought he was trying to say you can have 3 returns off the barrell at different heights with the same flow rate, which in one given example (not difference in water line between the two containers) was true but was false in the other chart posted.

Rich L
02-08-2006, 04:16 PM
Too much to follow. If the lines are below the surface and have equal entries and exits, the flow will be equal for any difference in height.

If an entry or exit point are close enought to the surface for the resistance caused by oriface vortenes to show the flow will not be the same on that pipe.

So much for theory, now try to measure the difference in flow. What I'm saying, is Steve's on track. It's worth trying to understand the concepts he presents. He doesn't give answers, he teaches.

L5Vegan
02-08-2006, 08:05 PM
Steve,
these are the velocities that I keep getting :confused:
.1"= .7303 feet per second
1"= 2.31 FPS
10"=7.303 FPS
1'= 8FPS

If that is correct then friction is already playing a big part at 1" of draw down.

Dan

L5Vegan
02-08-2006, 08:28 PM
Ryan,
I agree with your description for your pics. When the outlet of one pipe is above the surface of the water then everything changes. How do you apply this to my pics where the inlets and outlets are all submerged?

It really doesn't matter to me if you want to consider the pipes all open at once or one at a time. They are just meant to represent various inlet and outlet depths, not a recommendation on filter design.
Dan

L5Vegan
02-08-2006, 08:45 PM
[font=Arial]if we know the number from problem 3, and problem 4. can we state that the total distence between, water level in chamber B, and water level chamber C is total head. or rather total gravity head needed to supply 3000gph through a 1" pipe? or should we stick with draw down?:confused:
In my mind draw down is below pond level and before pump while gravity head pressure is after the pump and above the pond level. Not definitions, just how I think of it.

the answer for 1" pipe is that you are going to have a lot of wasted space in your filter chambers and a lot less flow through the returns than you could have. :To funny:

IMHO the next big change in pond construction will be up sizing the return piping from the filters. :)

Seriously, it sounds like you have a better grasp of this whole thing than i do. :yes: Thanks for letting me hijack your thread. :yes: :)
Dan

Ryan S.
02-08-2006, 08:54 PM
Ryan,
I agree with your description for your pics. When the outlet of one pipe is above the surface of the water then everything changes. How do you apply this to my pics where the inlets and outlets are all submerged?

It really doesn't matter to me if you want to consider the pipes all open at once or one at a time. They are just meant to represent various inlet and outlet depths, not a recommendation on filter design.
Dan

In an open system it would make no difference in any example posted in this thread.

L5Vegan
02-08-2006, 09:22 PM
In an open system it would make no difference in any example posted in this thread.
What do you mean by open? Non pressurized? Flow through?

boggen
02-08-2006, 10:05 PM
In my mind draw down is below pond level and before pump while gravity head pressure is after the pump and above the pond level. Not definitions, just how I think of it.

the answer for 1" pipe is that you are going to have a lot of wasted space in your filter chambers and a lot less flow through the returns than you could have. :To funny:

IMHO the next big change in pond construction will be up sizing the return piping from the filters. :)

Seriously, it sounds like you have a better grasp of this whole thing than i do. :yes: Thanks for letting me hijack your thread. :yes: :)
Dan:rofl: no worries, keep it going. someone is bound to search for something and this thread will come up, and may provide a intresting read for someone. :yes:

i can comprehend most of what is being said. but to put A to B will take time.

this is about 100th write up... of below. in attempt to stay half way to the thread.... i hope....

---------------------------------

problem A.
if we know we are taking 300gph from chamber B, we know we must supply 300gph to chamber A.
if we use one inch pipe.

what is the distance between chamber A water level height and chamber B water level height. needed to get 300gph flow, through a once inch pipe?

this number in all intense purpose could be thought of as static head.
-----------------------------------
all numbers below are completly fake DO NOT USE numbers.
going to call this ""boggen's 900z gravity pump""
specs for pump.
type of pump: gravity flow, (not centrifuge, or volumn displacement pumps)
it has a 1" inlet and 1" outlet
it is made out of 1" schedual 40 sewage pipe
can produce up to 900,000,000 millons gallons per hour at 500,000 inchs of negative head. ((negitve head = distance between water level height of 2 chambers))
it can do wonders for those waterfalls you should see it in action!!!.

((plot points are faked / made up))
---------------------------------------
negitive|
---------------------------------------
---6"---| -----------------------x ----
--------------------------------------
---5"---| --------------------x--------
--------------------------------------
---4"---| ---------------x------------
--------------------------------------
---3"---| ------------x---------------
--------------------------------------
---2"---| ---------x------------------
--------------------------------------
---1"---| -------x--------------------
--------------------------------------
---0"---| --x--------------------------
---------------------------------------
--------| 100 | 200 | 300 | 400 | 500 |
--------|-----Gallons per hour--------|
we don't need to know what the friction loss is. we are just messureing how much gph of water this pump will produce.
the only main thing we would need to determind what this pump produce is.
---inside diameter of a 1" pipe ((being schedual 40, you can find charts with the info))
---what formula / equations / math to use. i will leave that to the pro's

-------------------------------------------
problem B.
if we look at the following.
--pipe material ((pvc sch40))
------roughness
------inner diameter
------length
--------actual length of pipe
--------fittings
we can look at charts, and figured out how much resistence, or dynamic head that will be placed on the flow of water flowing through a 1" pipe.

this number in all intense purpose can be thought of as Dynamic head.
-----------------------------------------------
we already know we will be using schedual 40 1" pipe.
and we will be drawing out 300gph out of the last chamber.
---we can then look up a standard pump chart. for 1" schedual 40 pipe and figure out friction head loss in length of pie runs. and also figure out 90's, tee's, wye's using the same charts.
but this is were the kicker is....
---we need to calculated the head loss into gallons per hour.
---then add that ""head loss gallons per hour"" to 300 gallons per hour we will be removing from the last chamber.
---this new number we can re look at ""boggen's 900z gravity pump"" pump chart noted above. and take this new number as GPH and see how much negitive head we will need. to produce 300gph with friction loss / head loss figured in.

----------------------------------------------
to further the discusion....
the charts that everyone is racking there brains over in the post. are the plot points that would go into pump chart. something like the above ploted out chart.

i hope i understanding it all correctly..:rolleyes: :confused:

Ryan S.
02-09-2006, 09:06 AM
What do you mean by open? Non pressurized? Flow through?

Tank and pond are open, not in enclosed air tight containers. As pictured in examples

Ryan S.
02-09-2006, 09:24 AM
No difference in pressure That is ignoring friction loss. Given the drop in the examples, water will be moving through the pipes at a high velocity, so friction loss will be magnified somewhat between lines that have more turns and pipe length.