Air Compressor

Realistically the best method for a home built multi stage air compressor would be to start with a small 4 cylinder car engine or the like and make a custom head, cylinder, and valve assy for it where the second third and fourth stage pistons are driven from the original pistons.

As far as sizing your cylinder diameters factor the size for each stage based on what pressure it is going to top out at and balance the loads evenly between the stages.

If cylinder two tops out at 5x the pressure cylinder one tops out at then it needs to be 1/5 the area given an equal stroke length.

You lost me on the math part. Is their a way to figure out the size of the pistons for the 4. If they had the same stroke length.

Been there, done that.

So have you: Air Compressor

I am curious as to how you plan on making an air compressor without the ability to do basic geometric math.

Also pneumatic actuator cylinders typically are not rated for over 250 PSI so using them as compressor cylinders for a 3500 PSI system will not work.

whats a few thousand PSI Between friends?

Worst case: a death sentence!

Ill be making the cyl. on a lathe along with the plunger/piston.and im going to use carboard to make the heads, and put on a little duck tape. If you cant help I dont need your wise/smart mouth.

can you build your own house from start to finish, with out any help? I can.House plumbing and heating,and All the finish work. Can you rebuild a 6 cyl.engine in one day and put it back in the car the 2d day? or you have to Remove it first. Or can you build electronic circuit from a schematic. Sorry i never like to make fun of some one.Oh I also had a plumbing,heating ,remodeling,fire sprinkler Business.Made good money,.

John

This is to....... tcmtech..... no one else.Most people on here are nice and helpfull.

'...Most people on here are nice and helpfull....'

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*snicker snicker snicker....

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Many people on here are helpful, so I understand part of your sentiment.

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But you lost me when you resorted to a slur, calling most people in here 'nice'. There are many people in here who are above being 'nice'. Instead they strive to be 'honest' and 'forthright'. Your mischaracterization of these people as 'nice' is downright mean.

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(Also, many in here have no qualms about responding to a comment that wasn't explicitly made to them, or even a comment that was made explicitly not to them (or anyone else but tcmtech))

I did not interpret his remark as a slur,but rather as a compliment.He did not realize that some people need to have their ego massaged by genuflecting and subjugation to compensate for their low self esteem.

Remember, it is not what you see, it is how you look at it that counts.

truth, im sorry if I offened you. ok so you are NOT a "nice" person. So why don't we lay off the snobby remarks. You always have a few in the mix. So let me put it this way.Most here were helpfull. Please Dont reply, im in a good mood

Conntaxman:

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I'm the one who should apologize.

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My comment was intended to be humorous, yet it apparently fell far short.

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I didn't intend my remarks as snobbish. I was just making light fact that the high value placed on being nice and the high value supposedly placed on being honest are sometimes conflict.

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I do strive to do what is right rather than do what is nice.

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I hope you good mood continues despite my refusal to comply with your request to not reply.

For what it's worth, I assumed #15 was an attempt at humour

Yes I can do and have done all that and a whole lot more as well and I just turned 39 today.

Just ask around the forum. My snarkiness can justifiably hold it's own.

BTW would you like a list and some links to some of my online work?

I certainly hope the carboard (sic.) and duck (sic.) tape comments were sarcastic!

I also hope you have heard what happens when a careless welder or other person knocks over a 2000PSI oxygen tank and breaks the valve. In case you haven't, it becomes a rocket capable of passing through a brick wall! ...and you are talking about twice that pressure!

To produce 4000PSI, you will require extremely tight tolerances machined in heavy, top quality tool steel.

You talk about an 80cc tank. That is roughly 1/3 of a cup, which sounds reasonable for an air pistol or small air rifle. But you talk about a 3/8 or 1/4" pipe to fill it. That is NOT reasonable. Only the very best ($$$) of valves can close off 4000PSI, and the larger the diameter, the more difficult it will be to close. You also talk about a 1 or 2 hp motor. Do you expect to fill this little tank in a fraction of a second?

Be sure to wear heavy eye and body protection and use some form of remote control when you first try this pump!

I was thinking a 2 stroke with reed valves myself

If you insist on trying it with pistons, you need a final compression ratio of roughly 267 to 1.The compression ratio will have as much effect as the piston size.So to make it simple, if you divide the final pressure by 4,you need an average of 67 to one compression.This is higher than most diesel engines.And you will generate a LOT of heat,so you must allow for a lot of cooling.

So let's start with a 2 inch piston,with a 2 inch stroke./that gives 6.82 cubic inches of displacement.Pack all of this air into a head volume of.1.0179 cubic inches.

Your next piston has to have a displacement of 1,0179 cubic inches, with a compression ratio of 67 to one,and so on and so forth for the 3rd and fourth piston.


This will give the desired volume with one stroke,so divide as many times as you wish to get the desired duty cycle for the pistons by changing the stroke.However the final compression ratio must be the same.

These figures are seat-of- the-pants calculations, so I suggest you do you own research and verify with your own calculations.

With the heat involved, you may want to consider water cooling.

For very low volume of filling,remember a manual grease gun produces over 7000 psi,so a grease-over-air cylinder might be practical,messy,but it would probably work.Use compressed air to recycle the piston after each stroke,putting the waste grease into a container for re use.It will still require a lot of pumping to get what you want.If you are really ambitious,you could motorize the grease gun pump.

Good luck with your project.

HiTekRedNek. thank you for you very well explained commet. Like i said, their are many nice people on this fourm,and some, well i wont get into that.I started reading up on compression and the MATH. And know that it can be done and not too hard,they have a pump like a bicycle pump that dose 3800pse for PCP Pellet rifles. and here is a link of a small compressor that a person made Link

http://www.airgunsofarizona.com/shoebox.html

now look at this Link, its just a hand pump

http://www.pyramydair.com/article/using_a_hand_pump_May_2006/30

this one uses an Outside air compressor. for the 1st stage. Why i want to make it 4 stage is to take some pressor off the cyl, and use a smaller motor, and less heat and more practical to use.

I looked around the net for SMALL air cyl, instead of making them but only could find Low psi. Thanks for your help ,I hope you stay around with your very smart comments.

John

Four cylinders at 8:1 compression ratio, each feeding the next, will get you into the ballpark at about 4000 psi. Designing such a thing, however, is not a trivial pursuit; each successive stage will have one-eighth the volume of the previous in order to keep increasing the pressure. I have worked with high-pressure, multi-stage compressors, and I was surprised at how little the piston/cylinder was for the final stage -- roughly one inch in diameter. Four- to six-thousand psi compressors are available commercially, but they aren't cheap.

You will need a large (10 HP minimum) motor -- unless you don't mind waiting a LONG time for 80 cc of air at 4000 psi. You will also need a "custom" crankcase and crankshaft, as well as pistons, rings, rods, bearings, valves, block, heads, and so on. Air at these pressures is not unlike explosives.

Good luck.

hello Ed. i know that the final piston is SMALL., I also though of a v ee type of piston , fat at the top and Small at the bottom. Nice comment John

P2 x V2 / T2 = P1 x V1 / T1.

Apply that to the desired flowrate and the piston sizes just drop out of the mathematics.

Does that look familiar? Or don't Mechanical Engineers do that sort of thing?

Surely you already have a blog on CR4 for this same question?

Why two?

Because he took the advice trom TCMtech to make a multistage compressorjust just to tell him now that he does not need his comments here in this thread.

I am pretty sure that someone that can build a house and whatever and a heating system will also be capable of building a compressor of sorts and I am also sure that one way or the other dead will be the successor of arrogance.

Some have two girlfriends!

(Beware snarky unwanted reply and not a bit meant to be funny!)

Look up the specifications of an existing compressor that is designed for the PSI you require. You will find that the primary cylinders are larger feeding into the secondary cylinders that progressively raise the pressure to desired level. Do not forget the heat factor as you compress you raise the temp and not just a little bit. Most of these compressors are cooled. After you do this go to Ebay and check to see what is available or place a (want it now ) notice. I worked with these compressors in the oil and gas industry for breathing air when working under mask conditions and in SCUBA recharging of cylinders. You will not need super clean air as we needed but basics are the same.

Thank you very much for that great answer.

John

If you think it was a great answer, then rate him a GA, as I did.

May I suggest a few alternate methods to achieve your higher than common pressure requirements:

There are commercially available (and quite a few on the used market) pressure boosters. Some work off of 120/240 volts and others are DC with most in the 12v range. These units take lower pressure non flammable gases and compress it to higher pressures, usually in either the 2,200psi and 4,200psi range. These units are normally used to fill scuba tanks or self contained breathing apparatus (scba). The piping for them varies with the use and preferences of personnel. I would personally suggest that you use high pressure hoses (metal braid enclosing the liner) due to its much higher safety factor and being flexible. Due to the speed of the booster and the need for fast filling of the bottles being filled they usually are used to fill bottles in a cascade system of cylinders and the smaller bottles from these.

If your local fire dept has a "rescue truck" you might stop and look at theirs. It will be larger than you need but you can become familiar with it. I'm sure they would be complemented by your interest in their equipment. You might also ask them who there service company is. You could then use them as a starting point in investigating the system. If they can't help you with used units they might know who can.

For stationary installations it is usually a high pressure compressor filling a cascade of 4 or more cylinders. The smaller bottles are filled from these cascade bottles.

Another alternative would be to forget the compressor and just buy compressed air cylinders and have them refilled when they need to be. A few in a cascade system would be more convenient for you but either set-up works. Your portable bottles could be filled from them. Note- there is usually a rental or demurrage cost while you have them or else you can buy them outright, similar to how welding cylinders are priced..

On a materials/labor/time basis these might be worth a comparison with your proposed system.

Good Luck, Old Salt

When it comes time to do your testing I highly recommend filling the tank almost all the way with water. Since water does not compress very much if something fails, (like the tank), there will be little risk of damage. A tank full of air at 4000 psi. can do a great deal of damage if the air is catastrophically released.

Yes! Yes! Yes!

The untested cylinder is a potential time bomb and you don't know when it will go off! Its damages could be compared to that of a claymore mine or an Improvised Explosive Device!

The fabricator should make an adequate testing device by taking the cylinder and placing it into an appropriately sized steel pipe, Schedule 80 or thicker. If available use Sched 160. Connect all your testing connections. Run at least 100ft of tubing (better if longer) to the tester location which has an impact shield protecting the tester.

Place the pipe in a large metal container (a 30 yard dumpster would be ideal) near the bottom of the container. Always keep the container well vented on the top if it has a cover! Run the tubing (with a pressure gauge or pressure recorder) to your tester position. Have all observers stand at least 250 ft away with proper Personal Protective Equipment on. Important PPE is for shrapnel, eyes and especially ears. Use the ear muff style and not plugs.

When this is all done start the testing. Increase the pressure in steps of about 100 psi. letting it rest for 5 minutes at each step to dissipate heat that has accumulated. Half-way to your desired working pressure stop for at least ½ hour. Resume testing in the same manner. When the desired working pressure is achieve stop for at least ½ hour or more.

Then resume testing in the same manner till a pressure of at least 125% of the working pressure is achieved. It is better to go to 150% of the working pressure. Hold this pressure for 1 hour. If you achieve this you are good to go. Relieve the pressure slowly!

Instead of what I have described, I would suggest that you refer to the National Fire Protection Association (NFPA) standard or the Compressed Gas Association standard for testing cylinders.

Never forget that you are working with a potentially extremely explosive item with shrapnel being shot very far at high speeds.

This is the way that scuba tanks and self contained breathing apparatus (SCBA) are tested when new and at least every 5 years.

OK, why do I go to such a lengthy reply about testing cylinders? I am a volunteer firefighter. In New Jersey, about 12 years ago, there were two accidents where personnel were filling 2,200psi scba cylinders without the now required filling containment cabinets. In the first one a 20 or so year old firefighter was almost killed when a cylinder exploded. He has lost part of his brain, has extreme cognitive deficiencies, lost his eye sight and hearing and one hand to name a few. He has other injuries that I can't recall at this time.

The other one I am more familiar with. As I was driving to our fire station, about 100 yards away I heard a very loud explosion which I didn't know where it came from. When I got to the parking lot there were several people nearly in shock were saying that one of the fire fighters was filling scba cylinders from our cascade bank and the scba cylinder exploded. Upon investigation I found that yes, the cylinder exploded, the firefighter was extremely lucky in that a piece of metal hit his leg and tore off a piece of meat about 2" round down to the bone, and several of the cascade cylinders (approx 5ft tall) had been dented and thrown around the engine room.

Damage to the facility included body damage to one engine. One piece of the cylinder hit the side of an engine, hit the adjacent block concrete wall, hit the ceiling then traveled two engines over and landed on its roof! The cylinder wall thickness of ½" of high strength aluminum had its sides peeled back like you shot an M-80 off in a beer can.

The accident investigation reports for both of these incidents are at the New Jersey Dept of Consumer Affairs, State Fire Marshall web site. Why are these incidents so familiar to me? The second one was at my fire dept!

I have been involved with compressed gasses from lecture bottles to large bulk storage tanks in some sort of responsibility during most of my career in the chemical industry. I cannot caution anyone enough to do only what they are qualified to do and with the appropriate equipment. Not only will CR4 miss you but your family and friends will also. Of course if your wife encourages you to keep doing it perhaps a good divorce lawyer would be best and immediately.

You are fully correct, that is the way steam boilers, amongst many other "vessels" are tested by the authorities both in the UK and Germany for safety at high pressures.....it is the only safe method.

Agree with you. A frequent problem though is getting all the water out of the cylinder after it has been hydro'd. This has been a problem for the semi-conductor field where they use some very exotic gas mixtures that change composition with even the slightest amount of water.

Good Luck, Old Salt

There is a even simpler compressor system that can be built out of a single hydraulic cylinder and a hydraulic pump and valve setup.

You simply use a double acting hydraulic cylinder as a pressure boosting linear actuator of sorts.

Basically the hydraulic pump drives the cylinder from the large end and the port from the rod end is the air pump. Normal 100+ PSI shop air is fed into the rod end through a check valve and the pressure is then boosted by the hydraulic cylinder being extended.

From there a second check valve is used to rout the noe high pressure air to the tank you are filling.

The only detail you need to look at is with the piston to end cap clearances inside the hydraulic cylinder to make sure they have as little volume as possible in order for the cylinder to produce as high of compression ratio as possible. In this application a little basic lathe work could make the piston and cylinder end cap have a near zero dead space volume making conceivable that a large diameter long stroke cylinder could be capable of 500:1 or higher compression ratios on a single stroke.

As far as resetting the hydraulic cylinder the input air from a the shop air source will push the piston back once the hydraulic pressure is released.

With nothing more than basic hydraulic components a high pressure low volume pneumatic booster can be made as well.

Although we have all mentioned at length the dangers of high pressure air, nobody has mentioned the fact that special lubricants are needed in the pump so as to not produce a "one bang Diesel engine"!!!

I have to admit that my infos on this subject are really old and out of date, but I am sure that many/some here can give modern up to date infos on the subject....

The pumps I am familiar with are for breathing air so they use a food grade oil in them but for the most part all others use standard oils.

The "one bang diesel" effect only happens if the air is being heated beyond the point of autoignition of the oil which if proper intercooling stages are used it's not really a problem being the autoignition temperature of most common oils is around 600 - 800+ F where as diesel fuels are around 400 - 450 F.

Most common two stage air compressors in shops have the compression levels high enough in their second stage to be able to ignite oil but due to proper cooling between the stages they do not produce a high enough temperature to get the oil to ignite.

I like the explanation, thanks.

I was simply also remembering when I used air rifles to shoot game in my garden without hitting the neighbors many years ago, after a good clean and re-oil, the first couple of shots would go off like a .22 rimfire.....

But by opening up the transfer port to just below the width of the pellet, the effect was dramatically reduced , probably due to less heating of the air as you mentioned.

I could take out the eye of a partridge or pheasant at around 20 meters, then at least!!! No bits of lead to bite on after cooking as with a shotgun shot bird, nor as loud either.....

'....The pumps I am familiar with are for breathing air so they use a food grade oil....'

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I'm pretty sure even food grade oil in breathing air can cause lipopneumonia.

I have yet to ever taste any oils in my scuba air so I am taking it for granted that that is what the final stage oil and water separators on the compressor systems are there for.