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#524870 08/18/20 03:13 PM
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Hi,
I was wondering if you could help me? I have a 20 year old rectangular pond that is 1.4 acres, 7 feet deep, 60% covered in lillies that has never been aerated. From the sizing charts it looks like I could go with a Fujimac 150 linear diaphragm pump. The normal operating psi of the pump is 2.9 psi with 5.3 cfm. Since my pond depth is 7 feet I know that my psi will be around 3 psi and the pump is rated for a normal operating range of (2.2 - 3.4 psi) so I know the depth should be ok.

Where I am confused is I need to run 50 feet of 1/2 tubing from the pump to the water. Then I need to split the line and run two 100 foot 1/2 inch weighted hoses with a diffuser on each end. This would be a total of 250 feet of 1/2 tubing. How much would that add to my psi?
Also I am not sure how much the diffusers will add to my psi?

The sizing chart for this pump says it is good for 1.5 acres 8-10 feet deep. But by the time I add on the extra psi for the 250ft of 1/2 inch tubing and 2 diffusers, I will be well over the suggested operating range of (2.2 - 3.4 psi). Is it ok to go above this psi operating range? If so how much can I go above the operating range?

Thank you for any help it is much appreciated!
Craig

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If you put the deepest diffuser on the bottom at 7 foot...that's 3.5 psi.

One diffuser will add about 1/2 psi.

That totals 4 psi without the pressure drop from the line. Use the following calculator to do the math for you (about 1/4 of the way down the page {Online Compressed Air Pipeline Pressure Drop Calculator - Imperial Units} using 4 psi, 50 foot of 1/2" line, putting out 3.5 CFM which is about right for your pump at 4 psi)...

https://www.engineeringtoolbox.com/pressure-drop-compressed-air-pipes-d_852.html

You get an added 2.4 psi that totals 6.4 psi working back pressure. That takes it off the pump chart and that is only using the 50 foot to the pond. That pump is too small for what your wanting to do.

Even if you were to use 5/8" line...it puts the back pressure at it is still off the curve...

[Linked Image from forums.pondboss.com]

One 9" diffuser is too few for a 1.4 acre pond, anyhow.

Check out this thread that I participated in today. The OP has very similar questions. It has a bunch of links in it that will give you a lot of direction...

https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=524869#Post524869

My off-the-cuff guess is that you need a 1/2 hp (maybe a 1/4hp) rotary vane pump or an equivalent piston pump (or a half a dozen of the Fujimac 150's). Read through some the post links in that thread and get back to us with more questions. Be glad to help.

Welcome to the club BTW!

Last edited by Quarter Acre; 08/18/20 04:28 PM.

Fish on!,
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I will do more homework, thank you so much!

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Not to disagree with the recommendation above but... I disagree. Completely.
The answer is not always a bigger pump, (or a half a dozen of the Fujimac 150's). Geeze.
Good intentions, bad math, and a little biased.

Purdue,
Welcome to the forum. You put together a fairly solid plan, and it will work.
The diaphragm pumps are an excellent choice.

I only make a couple recommendations to consider.
* Run a 3/4" pex tubing on the 50ft run to the water.
* Go with low back pressure diffusers. The Matala 12" would be perfect for you.
* Consider up-sizing your hose. It's a one time cost.

Report back on your success.

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Journeyman always chimes in with good posts (seriously). I do have the best of intentions and can be biased too. But, if my math is off, please correct me...I would hate to lead someone astray. And, the "half dozen comment" was overzealous...my bad.

Some more math...I will spell it out for good scutiny's sake...

Using the above calculator and the following estimates. I get 0.32 psi of added back-pressure for the 50 foot run...

- 3.5 CFM (an estimate of the air flow that I figured would represent the pump's ability from the chart and my experiences with compressed air flow in lines)
- 50 foot of 3/4" line (per journeyman's recommendation, bigger line does mean less back-pressure)
- & 4 psi which closely corresponds to the 3.5 CFM from the chart.

Doing the same for the added 100' lengths of 5/8" line, I get 0.44 psi with the following inputs...

1.75 CFM (half of the overall flow per line)
100 foot of 5/8" line ,
& 4 psi which corresponds to the overall 3.5 CFM from the chart.

That's 3.5 psi for the deepest diffuser depth plus, let's say for argument's sake , zero from the diffuser (which is highly unlikely), plus the combined back-pressures of 0.76 psi..equals 4.26 psi.

That puts the operating point of the pump outside the manufacturer's suggested pressure range . It will pump enough air for 2 Matalas at this pressure, but it won't be as efficient and will likely wear the pump faster.

I tend to error on the safer side with any estimations and those estimations, now, need to be adjusted due to the calculated back-pressures. It's kind of moving target if you know what I mean. But, I believe this exercise yields a close approximation of what will happen given the system parameters. This is shown by the closeness of my original guess of 4 psi and the resulting 4.26 psi. I would, ultimately, want to figure in some losses for valves and fittings which would make the pump even less appropriate. Note: using 1/2" line instead of 5/8" line would take the back-pressure to 5.18...that's off the chart.

If this system was all that I had to work with and was confident that it would turn the pond over...I would be inclined to move the diffusers up 2 feet in the water column to lesson the pressure associated with the depth of the deepest diffuser. This would put the pump in the suggested operating range. The next step would be to estimate the total gallons of pond water, the lift rates of the diffusers to see what kind of turnover cold be expected.

I also have done no calculations regarding pond size and would be concerned that 2 diffusers would not meet Purdue's expectations in the 1.4 acre pond, especially if the system would not be run 24/7. Hence my recommendation for a larger pump...meaning a few more diffusers too.

I would love to learn more than I think I know, so please...if anyone can find error in my thinking...I won't take offence, but rather appreciate the lesson.


Fish on!,
Noel
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QA,
I see too often, you're giving advice similar to above, where the answer is, they need a pump like yours, and it's just not correct. The diaphragm pumps are great, for many reasons. They are easy to maintain, reliable, quieter, draw a lot less power, and most important of all - they work, great. Been thinking of making a separate post to this point, for a while.

Even though intentions are good, when you use math to support your predetermined notion, well that's not good either, opens the door for mistakes that you might otherwise catch.

Originally Posted by Quarter Acre
If you put the deepest diffuser on the bottom at 7 foot...that's 3.5 psi.
This is wrong. This is the foundation of your math mistake. While 3.5psi at 7 feet is correct, the (1/2" hose) is not one square inch. It is actually, 0.196 square inches. So 3.5psi x 0.196si = .686psi.

Pressure loss of the 12" Matala diffuser is 0.144psi.
Total 0.686psi + 0.144psi = 0.83psi to overcome, before aeration starts.

If pump pressure is 4psi, subtract 0.83psi = 3.17psi left to do some aeration.
The 3.17psi remaining, after traveling 150ft of 1/2" hose, has a theoretical - 5.98cfm potential.

https://www.rapidairproducts.com/technical-faq/flow-rate-calculator

The diffusers only require 1cfm to work well.

Bottom line, it will work, and quite well, with the diaphragm pump he asked about. I know this, because I did the research too, a long time ago. Then installed it, which I know I have reported on as working quite well.

And by the way, my Pump (Hiblow 120LL), only draws 90 watts of power, to make what looks like, pitchers mounds of aeration.

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Originally Posted by Journeyman
And by the way, my Pump (Hiblow 120LL), only draws 90 watts of power, to make what looks like, pitchers mounds of aeration.

I'm still looking for a cost-effective aeration solution, and 90 watts of power seemed really low, so I did some number crunching, using the power usage rates for my area, and it would be $6.30 per month to run a 90 watt system, 24/7. If I don't run it from 2:00pm to 6:00pm (their designated "peak hours") from April 15 through October 15th, where the rate is quadrupled, it would only cost $3.00 per month. Now you got me interested...


"In the age of information, ignorance is a choice." - Donny Miller
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Journey,

This calculation of yours..."3.5psi x 0.196si = .686psi." is the force of the air in pounds not the pressure in pounds per square inch.

3.5 psi (Pounds/ Square Inch) TIMES 0.196 si (the cross sectional area of the line [Pi X radius^2] in Square Inches). The square inches cancel and you are left with pounds which is a unit of force. The pressure (psi) at any given depth is the same regardless of the line size. In other words...the pressure a pump will see while trying to pump air down to 7 feet deep will be 3.5 psi regardless of the line size (neglecting frictional losses). Pressure drop due to frictional loses are calculated using the size of line, length, and material surface.

At this point, I believe "This is the foundation of your math mistake".

This is the first time I have heard of any pressure loss for the Matala's. Is this something you derived from testing, or otherwise? I am not doubting the 0.144 psi number you state, just curious where it came from. I have heard and tested the Vertex ones to be around 1/2 psi. Knowing a good number for the Matala would be a good addition to pond aeration calcs.

I, too, believe that the diffusers work best around 1 CFM. Vertex's lift charts were developed at 1 CFM and I have read somewhere that the Matala's are rated for 1.5 CFM.

My approach for determining the actual CFM is to calculate the pressure caused by the depth of the deepest water (estimated at 0.5 psi per foot), let the above link calculate the back-pressure caused by the lengths & sizes of lines, throw in 0.5 to 1 psi for plumbing losses and add them together. This results in a theoretical pressure that a gage at the pump would indicate. Then go to the chart and back into the CFM's.

I am have difficulty understating how the Hiblow 120LL only pulls 90 watts under a loaded situation...that's incredible!


Fish on!,
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Originally Posted by Steve_
Originally Posted by Journeyman
And by the way, my Pump (Hiblow 120LL), only draws 90 watts of power, to make what looks like, pitchers mounds of aeration.

I'm still looking for a cost-effective aeration solution, and 90 watts of power seemed really low, so I did some number crunching, using the power usage rates for my area, and it would be $6.30 per month to run a 90 watt system, 24/7. If I don't run it from 2:00pm to 6:00pm (their designated "peak hours") from April 15 through October 15th, where the rate is quadrupled, it would only cost $3.00 per month. Now you got me interested...


Steve,
Rest assured, it's only 90 watts power draw and it does the job.

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Originally Posted by Quarter Acre
Journey,

This calculation of yours..."3.5psi x 0.196si = .686psi." is the force of the air in pounds not the pressure in pounds per square inch.

3.5 psi (Pounds/ Square Inch) TIMES 0.196 si (the cross sectional area of the line [Pi X radius^2] in Square Inches). The square inches cancel and you are left with pounds which is a unit of force. The pressure (psi) at any given depth is the same regardless of the line size. In other words...the pressure a pump will see while trying to pump air down to 7 feet deep will be 3.5 psi regardless of the line size (neglecting frictional losses). Pressure drop due to frictional loses are calculated using the size of line, length, and material surface.

At this point, I believe "This is the foundation of your math mistake".

This is the first time I have heard of any pressure loss for the Matala's. Is this something you derived from testing, or otherwise? I am not doubting the 0.144 psi number you state, just curious where it came from. I have heard and tested the Vertex ones to be around 1/2 psi. Knowing a good number for the Matala would be a good addition to pond aeration calcs.

I, too, believe that the diffusers work best around 1 CFM. Vertex's lift charts were developed at 1 CFM and I have read somewhere that the Matala's are rated for 1.5 CFM.

My approach for determining the actual CFM is to calculate the pressure caused by the depth of the deepest water (estimated at 0.5 psi per foot), let the above link calculate the back-pressure caused by the lengths & sizes of lines, throw in 0.5 to 1 psi for plumbing losses and add them together. This results in a theoretical pressure that a gage at the pump would indicate. Then go to the chart and back into the CFM's.

I am have difficulty understating how the Hiblow 120LL only pulls 90 watts under a loaded situation...that's incredible!


QA,
Rest assured, it's only 90 watts power draw, and it does the job. I have confirmed the wattage to be exactly what the manufacturer claims. Which by the way, is actually less than half of the power draw of the pump you have, to do the same job.

I believe you when you say you want to learn, so here goes, and keep in mind, according to your math, my good working system, don't work.

On the 3.5psi pressure thing at the 7 foot depth. Try and visualize this, That is pounds per square inch, every square inch. It's kind of pressure that would crush a submarine, because that's a lot of square inches. The thing with the hose is, the pressure has no effect on the walls, or anything, but the opening of the hose. The opening of a 1/2" hose is a lot smaller than a square inch. The 3.5psi is only acting on the opening. So the multiplier applies. Bigger opening, more square inches, bigger multiplier.

Think it through.

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Originally Posted by Journeyman
Originally Posted by Steve_
Originally Posted by Journeyman
And by the way, my Pump (Hiblow 120LL), only draws 90 watts of power, to make what looks like, pitchers mounds of aeration.

I'm still looking for a cost-effective aeration solution, and 90 watts of power seemed really low, so I did some number crunching, using the power usage rates for my area, and it would be $6.30 per month to run a 90 watt system, 24/7. If I don't run it from 2:00pm to 6:00pm (their designated "peak hours") from April 15 through October 15th, where the rate is quadrupled, it would only cost $3.00 per month. Now you got me interested...


Steve,
Rest assured, it's only 90 watts power draw and it does the job.

I looked into it. It says 100 watts, if its the right one. Either way, that's some amazing energy consumption. Is this the correct one? https://www.amazon.com/Hiblow-120LL-Long-Life-Pump/dp/B00JGUMUGC


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Originally Posted by Journeyman
Originally Posted by Quarter Acre
Journey,

This calculation of yours..."3.5psi x 0.196si = .686psi." is the force of the air in pounds not the pressure in pounds per square inch.

3.5 psi (Pounds/ Square Inch) TIMES 0.196 si (the cross sectional area of the line [Pi X radius^2] in Square Inches). The square inches cancel and you are left with pounds which is a unit of force. The pressure (psi) at any given depth is the same regardless of the line size. In other words...the pressure a pump will see while trying to pump air down to 7 feet deep will be 3.5 psi regardless of the line size (neglecting frictional losses). Pressure drop due to frictional loses are calculated using the size of line, length, and material surface.

At this point, I believe "This is the foundation of your math mistake".

This is the first time I have heard of any pressure loss for the Matala's. Is this something you derived from testing, or otherwise? I am not doubting the 0.144 psi number you state, just curious where it came from. I have heard and tested the Vertex ones to be around 1/2 psi. Knowing a good number for the Matala would be a good addition to pond aeration calcs.

I, too, believe that the diffusers work best around 1 CFM. Vertex's lift charts were developed at 1 CFM and I have read somewhere that the Matala's are rated for 1.5 CFM.

My approach for determining the actual CFM is to calculate the pressure caused by the depth of the deepest water (estimated at 0.5 psi per foot), let the above link calculate the back-pressure caused by the lengths & sizes of lines, throw in 0.5 to 1 psi for plumbing losses and add them together. This results in a theoretical pressure that a gage at the pump would indicate. Then go to the chart and back into the CFM's.

I am have difficulty understating how the Hiblow 120LL only pulls 90 watts under a loaded situation...that's incredible!


QA,
Rest assured, it's only 90 watts power draw, and it does the job. I have confirmed the wattage to be exactly what the manufacturer claims. Which by the way, is actually less than half of the power draw of the pump you have, to do the same job.

I believe you when you say you want to learn, so here goes, and keep in mind, according to your math, my good working system, don't work.

On the 3.5psi pressure thing at the 7 foot depth. Try and visualize this, That is pounds per square inch, every square inch. It's kind of pressure that would crush a submarine, because that's a lot of square inches. The thing with the hose is, the pressure has no effect on the walls, or anything, but the opening of the hose. The opening of a 1/2" hose is a lot smaller than a square inch. The 3.5psi is only acting on the opening. So the multiplier applies. Bigger opening, more square inches, bigger multiplier.

Think it through.

Uh...something's up here. I'm glad your system works.

But submarine crush PSI is more like 400+ PSI, not 3.5. Also your interpretation of how pressure works on the system isn't right. There's 3.5 PSI pushing on everything at that stated depth. Width of tube and tube opening affects resistance to flow, not the interaction with water pressure. It's much harder to blow through a skinny straw than a fat one at any depth.

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Point taken, enough on the confusion, a little more on the aeration portion.

The system that has been working well on my 1.2 acre pond, 11 feet deep;

HiBlow 120LL pump. One pump, not half dozen.
3 diffuser heads, Vertex XL2 (double 9"), Matala 12", and homemade one.
85ft run from barn to pond gate-valve station, 3/4" pex tubing underground.
92ft run from valve station to Vertex diffuser, 3/4" pex tubing.
240ft run from valve station to Matala diffuser, 3/4" pex tubing.
60ft run from valve station to homemade diffuser, 3/4" pex tubing.
Diffuser depth was 11ft for the first year on all diffusers, now 9ft, for thermocline reasons.
3rd summer of almost nonstop running, timer off for 8hrs maybe 14 hot days a years.
Maintenance, cleaning the inlet air filter with warm soapy water, once a year.
Power draw is 90 watts on cool days, up to 101 watts on hot days, (snap shot of last 24 hrs attached).
Noise level is a whisper.

The Matala diffuser, even though has the longest run (325ft), it has the best flow and must be throttled back, to divert more flow to Vertex. Thus Matala - very low back pressure by comparison. Back pressure = 4" of water (.144psi) as advertised by Matala. Good value.

Vertex diffuser, puts out slightly finer bubbles. Good quality.

Homemade diffuser is 3/4" pex tubing, in a hula hoop, with #80 drill bit holes inside and out. Probably will be replaced with another Matala.

All the diffusers are mounted to a milk crate, to keep off the bottom.

Pump is controlled by a WiFi outlet, that I can enable timer function, or turn off anytime. The power meter chart attached, is from that app. But, I believe leaving it running almost 24-7-365 is easier on the pump and the diffusers, so hot days that last only a day or two, it stays running.

All and all, I recommend this type system.

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Nice description of your system Journey. The key to it doing as well as it is, is the fact that it has no lines less than 3/4" even though they are rather lengthy. Do you have a pressure gage in the system at the pump? With that reading, you could determine the total CFM output from the pump curve.


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Noel
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Thanks QA,
I knew I forgot something.

It runs very close to 4psi (gauge at pump), according to HiBlow specs = 90lpm (3.17cfm).

http://www.hiblow-usa.com/wp-content/uploads/2017/06/HP-100LL-120LL_170308.pdf

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Im more confused than ever now after reading all that. I can tell you guys are on a different level of smartness than me.


The people who say I can't do it can just sit the @^#% down and watch me. Friends call me Rusto I also subscribe to pond boss mag. http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=504716#Post504716
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Originally Posted by RStringer
Im more confused than ever now after reading all that. I can tell you guys are on a different level of smartness than me.


Stringer, this is the key part:

The system obviously works well...and...

"It's much harder to blow through a skinny straw than a fat one at any depth." = "The key to it doing as well as it is, is the fact that it has no lines less than 3/4" even though they are rather lengthy."

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I wish I was more electrically inclined. 90 watts at 4 psi is pretty amazing! I had assumed that the manufacturer's spec of 90 watts was at zero back pressure (running the pump without any lines hooked to it).

I have amp tested my pump throughout it's pressure range (and beyond) with the following results...

0 psi = 3.6 amps
3 psi = 3.9 amps
5 psi = 4.1 amps
6 psi = 4.2 amps
7 psi = 4.4 amps
8 psi = 4.6 amps
9 psi = 4.8 amps
10 psi = 5.0 amps
11 psi = 5.2 amps
12 psi = 5.4 amps
13 psi = 5.7 amps
14 psi = 5.8 amps
15 psi = 6.2 amps

My pump typically runs at 6 psi which equates to 483 watts (if I did the math right...4.2 amps x 115 volts). The difference between my pump (Gast 0523) and Journey's HiBlow is that the Hiblow has much less mass in the moving parts. This allows it to use less energy, but it is not capable of the higher CFM's and higher pressures and a vane pump has a fair amount of spinning steel components. My pump is certainly overkill for my 1/4 acre pond, but it is not working far from or outside the manufacturer's suggested range. Hence my recommendations for a large pump. Purdue's pump would be working outside the suggested range at 3.5 psi. It would put out 3 CFM at 4 psi and that could run 2-3 diffusers. The lines would have to be like Journey's at 3/4" all the way through, however to get that.

What confuses me is the relationship between watts and horse power. The 0523 is a 1/4 hp pump. According to common web calculators...that's 186 watts. At my lowest amp tests (no lines hooked to it) the pump uses 3.6 amps...3.6 amps X 115 volts equals 414 watts OR 1/2 hp. Not sure how to explain that??? Anybody? If you look at the specs on the 0523 pump, it states 0.18 KW (equal to 180 watts) which is equal to 1/4 hp. It never operates at this wattage....Hmmm? Given the HiBlow's wattage of 99 ...that's about 1/8 hp.


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I have no doubt Journey's system is working because he says it is. However, there is significant confusion between force and hydrostatic pressure. The compressor has to overcome hydrostatic pressure - not force. QA is correct on his unit analysis. Hydrostatic pressure is 0.052 X density of fluid X depth. The 0.052 is just a unit conversion factor to get to psi. The hydrostatic pressure is purely a function of depth given a fixed density. Water can only apply force when there is a surface area to which the pressure is applied. If you are talking about a hose opening, since it is an opening there is no force only hydrostatic pressure. The opening of the hose size has nothing to do with hydrostatic pressure and again, since it is an opening there is no force. There is force on the hose itself but it a few psi isn't much pressure so it is strong enough. When the compressor is running, the internal pressure on the hose is actually greater then the external pressure - it is more likely to burst than collapse.

The friction loss is going to be pretty small in all cases because these compressors just aren't generating very many cfm so the velocity isn't a big issue unless you get a really tiny hose. Friction loss curves are not an exact science. I have found that my Keeton areation system has almost zero pressure loss through about 250' of 5/8" hose.

The density of water is 8.33 lb/gal so the gradient for water is 0.433 psi/ft. You might add a few hundredths of psi for pond water due to suspended solids but I would be surprised if you get to 0.5 psi/ft. It would take a water density of 9.61 lb/gal to get to 0.5 psi/ft. The gist is you can take your water depth times around 0.433 - 0.45 psi/ft and unless you are using really small hose or moving really high cfm's you are going to be really close. It doesn't sound like much but rounding up to 0.5 psi per foot of water depth is actually a pretty big overestimation.

No offense to anyone.....................

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Originally Posted by RStringer
Im more confused than ever now after reading all that. I can tell you guys are on a different level of smartness than me.

I wouldn't be too sure of that!


Kris

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Originally Posted by MisterA
It doesn't sound like much but rounding up to 0.5 psi per foot of water depth is actually a pretty big overestimation..

Very true! Thanks for the reminder. So, at 7 foot of water depth the error would be in the neighbor hood of 1/2 psi and getting into the nitty gritty, that's a 1/2 psi the pump is getting back.

Originally Posted by Kris B
...The friction loss is going to be pretty small in all cases because these compressors just aren't generating very many cfm so the velocity isn't a big issue unless you get a really tiny hose. Friction loss curves are not an exact science. I have found that my Keeton areation system has almost zero pressure loss through about 250' of 5/8" hose.

I am having trouble with this statement. Help me out please. I don't know your system's parameters so I used 4 CFM & 6 psi as guesses, 5/8" id hose, & 250' long. I plug them into the calculator below...

https://www.engineeringtoolbox.com/pressure-drop-compressed-air-pipes-d_852.html

...And get 3.4 psi. Maybe that is a line going to a single diffuser and only has 1 CFM...that still yields 0.26 psi. I believe the line sizes and lengths can add up to an amount that should be considered when scrutinizing a system's design. Jouney's example using all 3/4" line makes the line losses almost negligible, but compared to the OP's original thoughts of using 1/2" line...that would be a mistake.

Originally Posted by Kris B
Originally Posted by RStringer
Im more confused than ever now after reading all that. I can tell you guys are on a different level of smartness than me.

I wouldn't be too sure of that!

That's funny right there!


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Noel
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I'm pretty sure. I'm next level bull$hitter 4 sure. But talking all those numbers and ratios I'm out. In my town we have a pond with a fountain in it tht looks really good and want to add one. Are they beneficial to the water quality?


The people who say I can't do it can just sit the @^#% down and watch me. Friends call me Rusto I also subscribe to pond boss mag. http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=504716#Post504716
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QA - I may have been too hasty saying the line loss is entirely negligible. Although my system shows almost no pressure loss that is probably due to the gauge. It would take an electronic gauge measuring in the .0 and .00 range to get an accurate assessment and I have a 30 psi liquid filled gauge. There will be some line loss but unless the velocity gets to turbulent flow it is going to be fairly small. I will say this, and not to be argumentative but to help PurduePond with his problem, if the assumption is made that the head - hydrostatic pressure - is 0.5 psi/ft as seems to be a common assumption on this forum, then when sizing a system a person can in all likelihood neglect the friction loss unless it is a really complex system.

For example, let's assume the water density is 8.5 lb/gal instead of 8.33 lb/gal due to suspended solids. Then the head is 0.052 X 8.5 = 0.44 psi/ft. For a 12' pond the difference between 0.44 psi/ft and 0.5 psi/ft is 0.72 psi. Based on your calculation the pressure loss is 0.26 psi - much smaller than 0.72 psi. To me at least, it doesn't make sense to make an assumption of 0.5 psi and then try to calculate the pressure loss in great detail. The base assumption makes the detail calculation negligible.

I am not that familiar with these compressors cost as I just bought an off the shelf system ready to go. I did install it myself but I did my research and went with convenience over cost. However at these low discharge pressures and volumes, if a person sizes assuming 0.5 psi/ft of head then they should be covered for any pressure drop and they can simplify their lives by taking it out of the equation. If you are going to calculate the head then yes, you should pay attention to the pressure drop as it will matter and 3/4" hose is better than 5/8".

Again, I am not trying to be argumentative and you certainly seem to understand fluid flow and mechanical systems, I am just trying to make a hard decision easier. For my system I just over sized on discharge pressure but I know not everyone has that luxury.

Thanks for the pressure drop calculator link.

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Let me add the caveat - as the pond gets shallower then the system pressure drop becomes much more critical. However, at the point a pond starts getting that shallow then surface aeration is a better solution than bottom aeration and head gets taken out of the equation entirely. If a person wants to go with bottom aeration in a shallow pond of much areal extent things do get more complicated which might seem counter intuitive.

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Mister, You are absolutely right about neglecting any line losses when the over assumption of 0.5 psi is used for our small BOW aeration systems. That is a mistake I have been making.

I looked into the Keeton aeration systems and the smallest electric system they offer can pump air down to 50 foot below the surface. They must be using a positive displacement pump. When using such a pump...a lot of weak design parameters can be over come with shear power. I am sure the Keeton's are very good systems, but what I am saying is that when someone tries to put together a DIY system with a tight budget in mind...attention to the details becomes very important. Diaphragm pumps do not supply a lot of pressure and just 1 psi can mean the difference between working well and not working so well. Whereas, an over-sized pump can compensate for some oversight when it comes to the details such as plumbing restrictions & line loss. I think this is why you see alot of canned units coming with 1/2" hose. It's one of the reasons I went with a rotatory vane pump for my system. I was not experienced with aeration and wanted that extra safety factor of the additional 5 psi to save me if I messed up my thinking. Which I did to some degree with respect to the individual lines that run from the pump to the water's edge. I used three 25 foot long - 3/8" Pex lines that I had left over from something and I believe that added some back pressure to my system. My pump sees around 6 psi back pressure. That would have made the above diaphragm pumps inadequate for my cobbled system.

I hope we have not run off Craig by getting SOOOO deep. Come back Craig...we'll get something figured out for you.

I have certainly learned a lot and enjoyed the conversations! One of the best aeration detail threads we've had lately!

Last edited by Quarter Acre; 08/21/20 10:55 AM.

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Noel
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