Compressed Air Through 1/4" Tubing With 1/8" Holes 3" Apart

Any productive ideas for what? to do what? Are you having a problem? If so, what is the problem?

I am having a problem finding an economically priced and capable air compressor for maintaining 200 psi in the described tubing with holes in it. Getting 200 psi to the end of the tubing is difficult. I cannot describe the project I am working on but, it does require that I achieve getting 150 psi to 200 psi built up in the tubing so as to have an equal amount of air blowing out of all the holes. Thank you! Rosario Imbese at: resdiaser@sbcglobal.net.

I'm not an expert and I'll have to dig up my compressed air manual (it's here somewhere) but before I do that I'll make a few comments.

You've got a 20 ft long tube with 1/8" holes 3 inches apart. That's about 80 holes. You're going to need a huge compressor to get 200psi in it. 1/8" is a rather large hole. In the factory where I work, a hole that size will make a very loud noise and will probably be reason enough to shutdown the process until we could fix it. The pressure drop caused by that one hole can affect the whole control system.

If I may hazard a guess, you intend to submerge this thing (an aeration tube for a wastewater treatment plant?). If the depth of the tube is deep enough, you're problem may be solved since the resistance offered by the water depth will raise the pressure in the tube. By how much, I can't say.

Also, to get an equal amount of air out of all the holes, you may need to do one of two things: 1.) your pipe or tube needs to be reduced in diameter the farther it is from the compressor or, 2.) your hole diameters need to gradually change, from larger to smaller as it gets further away from the source.

Well somebody brought their brain!

Actually did some mental engineering.

Fair dinkum!

milo

I AGREE! GOOD JOB! 2 Kudos for you.

The water pressure on the holes will be a function of the depth or the head pressure which is about 0.47 PSI per foot of depth.

so at 400 feet..problem solved.

Correct, assuming that the tube will be submerged in water.

What about Salt water, Milk or or oil?

What is the process that this manifold? will be used in?

What is the intended goal?

Greetings,

The Total Flow area of the 1/8" holes, is greater than the flow area of the 1/4" tube.

In effect you are trying to make 200PSI at the end of a megaphone.

If you want to make a bubbler and have a 20 foot line with 200 psi in it, you need 1/100" pinholes to let through the bubbles every 3 inches.

Try that on a short length and increase the hole size slightly for more volume. a doubling of the diameter quadruples the air flow. If you want a low pressure bubbler, all you need is about 3 psi for 6 feet deep and you can then use 1/8" holes, but will need 1/2" level pipe. If pipe not level the low end can fill with water on a low pressure system.

This is commonly used to stop ice from forming around a boat in winter

If you have 80, 1/8' holes that would be equivelant to a single hole of 10" in diameter.

What a load of rubbish!!!

You work out the area of a 1/8th" hole and multiply it by eighty and then work that area back to find the diameter.

It will be no where near 10". I estimate about 1"

You're right. The area of a 1/8" hole is 0.01227in². Multiply that by 80 and you get 0.98in².

However, a series of 80 holes with diameter of 1/8" drilled next to each other will produce a series of closely spaced holes, 10 inches long.

Any way you look at it, it's still a great big hole for a compressed air system.

10 inches long but not 10 inches in diameter

10" diameter = 78.54 sq inches which is 80x the area that we're dealing with.

A little too quick with this answer. The equivalent of a 10 inch long 1/8th inch wide slot and even that is not quite equivalent to 80 holes due to the fluid dynamics of a hole versus a slot.

You will have a pressure drop each time you pass one of the smaller holes. If you wish to have about 150psi at the end of the 80 hole tube, you will have to increase the diameter of your main pipe. I would suggest you try at least a 1" pipe although my feeling is that it requires closer to a 2" pipe if the pressure is to be reasonably maintained right to the end.

It is not a simple matter of cross sectional areas but rather of volume flow and frictional losses over the length of the pipe (we will skip the temperature changes due to the compression/expansion of the air for the sake of simplicity).

However, if we take the whole thing very simply as just volume flow:

Area(80 x 1/8 holes) = 80 x (pi/4 x 1/8^2) = 80 x 0.0123 = 0.984 in2

Say we take 4 times this area so that the ratio of small holes to the main tube is about 1:4

Area(main tube) > 0.984 x 4 = 3.936 in2

Equivalent diameter = sqr(4x3.936/pi) = 2.24 in

A second way is to use several smaller tubes each with 20 holes

A but out of my field but would this work any better if the pipe was a loop allowing it to be pressurised from both ends?

...I would guess that as a compressor, you will need something like the main engine of a 747 working at about 80% of its normal load!!!

Seriously, I think that if you really need help, you will have to disclose a little more info for the very helpful CR4 people, or fix the problem on your own.....you have certainly been give some good info from them already.....

In nominal atmospheric conditions of 0 psi gauge (14.7 absolute) and 60F at a sharp edged hole open to normal atmosphere, the air supply pressure will cause a flow of free air in accordance with the approximate formula:

Q = F x d² x P_s

Where Q=cfm, d=diameter of hole in inches.

Ps is the supply pressure in psi absolute, and F is the flow factor.

F= 9.4 when the supply gauge pressure is above 14.7 psi

F= 9.05 when the supply gauge pressure is below 14.7 psi

Thus at 200 psig your first 1/8th hole will deliver: 9.4 x 0.125² x (200 + 14.7) = 32.3 cfm. Assuming no pressure loss along the pipe the 80 holes will require 2,583 cfm.

In reality you will never get this amount of air into a 1/4" pipe (leave alone out the other end) unless you have a compressor pushing out 4,382 psi. circa 2,366 hp.

Greetings-How long do you want to hold this pressure? Reading these other posts-sounds like you will need a big compressor. You might need to put a large surge tank on the line to hold pressure. All depends how long you want to hold pressure! James

I only want to hold the pressure for 7 seconds at a time once daily. Also, it will not be submerged under water. I apreciate all of your suggestions. Keep it going. Thank you!

Connect both ends of the tube to the compressor

Someone else mentioned a loop. You mean hook up both ends of the tubing to the same compressor. Thanks!

I have to agree with the other posts on the tubing diameter being too small. If your only trying to hold it for a few seconds several times a day then why not use something along the principal of an air cannon. You can store up a large volume of air at 200 psi in a baffle tank that can blast a hig volume of air for a very limited time.

Does this sound feasible to the rest in here??

Love your David Russel Quote:

"We live in a Newtonian world of Einsteinian physics ruled by Frankenstein logic" David Russell

I would suggest that it is incomplete- should be "We live in a Newtonian world of Einsteinian physics ruled by Frankenstein logic subordinated to a Reptilian brain."

milo

Not my quote but like the addition :)

Many of these posts are providing potential solutions but they are also raising questions or making assumptions that part of the suggested solution is feasible. Apparently the application is top secret or part of a new device yet to be patented or something like that so if you expose too much, well then you would have to kill all of us after the fact we figured out a solution. I personally don't have time for that and it would be a terrible inconvience. In an effort to help you help us help you (reference Jerry McGuire) what follows is a list of the provided REQUIREMENT, the SUGGESTED SOLUTION and the QUESTION(S) I see that has/have been raised.

Economically priced and capable compressor - solution suggested a large, i.e. expensive and large; Question: define economically priced and are there any restrictions like weight, size, noise level, heat dissipation, environmental exposure?

1/4" tubing - solutions suggested to increase diameter or install multiple 1/4" tubes with subsets of holes in each; Question: What is the actual diameter/size restriction and what is the cause of it, i.e. is it at the insertion point (assuming it is in some closed container) or is it in the process area (meaning where the air will be discharged)? Whatever the restriction is, is it a radial restriction or is it in one plane only? For example, if there is only enough room for a 1/4 I.D. tube in the y dimension but there is a much less stringent restriction in the x dimension then a rectangular tube could be used to provide the necessary volume, increased structural strength, increased area to disperse holes over thereby reducing structural degradation, increased area to place more, smaller holes, if that is an option, etc.

Solution suggested to provide supply connections at both ends; Question: Are both ends accessible? Which brings some follow-on questions: In what plane will the tubing be installed? How will the tubing be supported? Will the holes be on one side only? If so that will impose a significant reaction force. Can smaller holes be used on opposing sides (staggered slightly to minimize structural weakness) to offset the reaction force?

The previous paragraph mentions a structural consideration. The application description states that the tubing material is unknown. Is it unknown because you can't tell us or because you don't know? Structurally, a 1/8" diameter hole in a 1/4" tube removes a significant amount of tube wall material and will cause a significant degradation in overall strength. 200 PSI being discharged for 7 seconds is going to cause quite a physical shock at each exit point. Please clarify whether the 1/4" is I.D. or O.D. Whichever it is, the other dimension may be determined by the material and wall thickness used. An example, would be 1/4 inch copper pipe versus 1/4 inch annealed copper tubing.

There may be some more questions but I hear the yard and the lawnmower calling so enough fun with showing how much I don't know. I seem to do that on regular basis though.

Dincon, This one problem is one of many (not that many) but, all the ones will fit together and work. By economically I mean the lowest price compressor that will solve the problem. I dont want to put a price on it becuase that will limit everyones interest. They will say thats not possible and not get involved. If we are capable of doing it is the question, then we will work on pricing. There are no weight restrictions though, the lighter the better. Size is somewhat of a problem in that we could use nothing larger than 1 3/4 inches outer diameter tube (maybe slightly larger if we benefit from it). Noise is a slight problem. You would not want to wake people up in the middle of the night. Heat is not a problem though you wouldnt want it to start a fire. There is a slight exposure to the elements indirectly. It will be outdoors, not submerged in water. There is no diameter/size restrictions (see above). Air will be discharged to a section of level tubing (could be as long as 40 ft.-20 ft. if we had to) and try to maintain 150 psi to 200 psi for no longer than 7 to 8 seconds out of each hole. I dont know what you mean by "radial restriction or plane only" and I may have already answered your question. The tubing does not have to be 1/4 I.D., it could be larger and could taper or be a rectangular tube. Both ends are accessible though, we were closing one end to be able to build up air pressure enough to achieve 150 psi to 200 psi. The tubing will be installed level. There might possibly be some bends, vertical sections (without 1/8 inch holes-only used to connect to level sections with 1/8 inch holes), and angled sections. The tubing will be supported by brackets. Keeping it stable should not be a problem because the apposing side of the tubing with holes will be backed up against a solid surface. There will be holes on only one side of the tubing (see previous sentence). I guess holes could be used on apposing side but, that will make building pressure in the tubing even that much more difficult. The material is unknown only because we will use whatever is required (least expensive the better). Thank you for taking the time to share in our fustration!

You've defined the solution, now try to enlighten us as to the problem!

http://www.google.com/search?sourceid=navclient&aq=t&ie=UTF-8&rls=GGIH,GGIH:2007-02,GGIH:en&q=exair+air+knife

another possible solution above

The "radial or plane" question was directed at if it was possible to increase the size of the tubing beyond 1/4" by using a flat tube that was several inches wide thereby allowing the tubing volume to be expanded. Sounds like it could be although the larger size moving away from tubing will make the routing you've described more difficult.

The heat issue was more to go with how the heat generated by the compression of air would be able to be dissapated. The noise was sort of along the same lines in that it is helpful to know something about the environment and the proximity to other things/neighbors that could be affected.

The material restriction question was focused on the environment it is to be installed in and how strong did need to be, i.e. self-supportin, minimumal support, etc.

Noise - Well, discharging air at that pressure through that many holes is not going to be very quiet so hopefully it will be inside something to significantly attenuate that noise. The compressor(s) can be shielded with noise abatement panels or housed in a building with sound absorbing walls as long there is a way to dissapate the heat.

The discharge being from one side only would cause a tremendous torque to be imposed that with no or minimal support would quickly result in a reshaped tube. If the holes were on each side but alternating so each hole was six inches from the next one on the same side then the torque would be negated. If the air would still be discharged every 3 inches just not in the same direction every 3 inches.

Both ends being accessible would allow air to enter from both ends or allow the option of having two independent tubes entering from both ends and that are supported in the middle.

What I'm thinking of now has been suggested previously, at least in part, of using a large holding tank to store the volume of air at a minimum pressure of 300 psi +/-. The 200 psi pressure will acheived by a pressure regulator in the discharge line. The higher the pressure the smaller the volume necessary to store but the more expensive the compressors. The lower the stored pressure the larger the volume required but the compressors are cheaper. If this is done one a day then there will be 23 hours 59 minutes and 52 seconds to recharge the tank although I would initially aim for around six hours just to see where the calculations and costs wind up. I would investigate using several small compressors instead of a single large one. You could also use less expensive low (relative) pressure high volume unit(s) to get a "base pressure" built up quickly then take over with high (again, relative) pressure low volume units to boost the pressure to the required limit. Compressors such as are used to recharge scuba tanks can take the pressure plenty high enough and if the holding tank is large enough then the tank heating may not be significant.

Good luck and I hope I've provided some ideas that will be of benefit.

I can understand the need for secrecy but it's giving me fits since there are things I might need to know in order to give a good suggestion.

You just want a low cost compressor that will provide you with the required pressure in a pipe full of large holes. If you said that you want to push so many cubic feet of air through the holes in so many seconds then you'd get much better answers and we wouldn't be saying that you'd need an enormous compressor to do it.

The problem with specifying pressure is that, with the size and quantity of holes, you won't get 200psi in the pipe in 8 seconds. It will take time to pressurize the pipe because of the pipe volume as well as the air bleeding out of the holes. Your 8 seconds might be up before you get up to 200psi.

I heard the lawn mower calling yesterday but I had the will power to resist it.