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How Much Compressed Air Can Fill in lpg Tank?

02/27/2016 2:56 AM

i want to do project work on compresed airengine . that's why iam using lpg cylinder as a airtank how much air can i fill in that tank. in psi or bar or kg/cm2

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#1

Re: how much compressed air can fill in lpg tank?

02/27/2016 3:23 AM

Not sure that's legal.... I think I would go with a CO2 tank....

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#11
In reply to #1

Re: how much compressed air can fill in lpg tank?

02/28/2016 4:35 PM

The maximum pressure should be stated on the label/nameplate.

I am not aware of specific regulations that prevent the use of gas cylinders for compressed air. Today's experts in this subject can tell us if there is - ref nos. please.

A gas cylinder is a pressure vessel and providing it meets with the pressure and volume regs it should be acceptable.

You have to watch things like thread sizes, valves and connectors - it is here where you might fall foul of regulations because once you start 'modifying' pressure vessels, you violate their certification approvals - and your insurance company might not like it.

Basic compressed air regulations relate to safe use and protection against violent unintended release of pressure energy - a fault condition. Pressure vessels have construction and test standards and certification procedures to ensure this does not happen.

Similarly regulations exist for gas cylinders where in addition to pressure energy there is also release of fuel energy leading to heat and detonation risk. Likewise regulations exist to protect from release of steam energy leading to burning and scalding.

So if you know what you are doing, you would probably be OK if you stay below the max pressure/volume limits. Typically this is 50 bar-litres.

However, the basic level of your question makes me think you do not have the appropriate knowledge in compressed air engineering to safely juggle the regulations.

This is an engineering site giving good advice saying beware! - but if you can look at 'How to' pages on Google for using gas cylinders as compressed air tanks.

The first time you use the tank for air you will create a serious explosion risk. Although you might have drained all the liquid gas from the tank, the air will mix with the residual gas and form an explosive mixture. The slightest spark - and BANG!

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#13
In reply to #11

Re: how much compressed air can fill in lpg tank?

02/29/2016 1:24 AM

If he's going to use an LPG tank that's never been filled with LPG or any other flammable material - no explosion hazard.

If he's going to use a tank that has contained LPG, he will first have purge the tank with nitrogen or another inert gas, and test to be sure that all traces of LPG have been displaced.

He will also have to change the valving to accept a right handed thread. Title 40 of the Code of Federal Regulations probably has something to say about this.

And as Lyn has noted, this (a car powered by compressed air) has already been manufactured

Having lived in NYC until recently, and worked there most of my life, I've learned that NYC is tough when it comes to LPG.

He should get a copy of the NYC Fire Code, and whatever CGA or NFPA references are cited.

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#14
In reply to #13

Re: how much compressed air can fill in lpg tank?

02/29/2016 9:30 AM

"If he's going to use a tank that has contained LPG, he will first have purge the tank with nitrogen or another inert gas, and test to be sure that all traces of LPG have been displaced."

That brings up a question, why do we purge an 'air/gas' tank with air, then have to make measurements to insure all the 'unwanted air' has been removed?

(All the following assume the tank has been 'emptied' to match local air pressure, and 'fiddly bits' such as valve units have been removed, making the tank the equivalent of an 'empty jug,' largish internal volume, small neck opening.)

Would it not make more sense to purge the tank with a liquid, for example water? If the take is full of water and there are no air pockets/bubbles left, then all the air inside the tank has been expelled. Then you turn the tank over to pour out the water, which fills the tank with 'local air,' wipe the outside dry, add whatever corrosion prevention is needed, and let the inside drip dry, and you're done. All the 'old air' has been purged without the 'flush, test, flush, test again, flush YET AGAIN...' method.

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#2

Re: how much compressed air can fill in lpg tank?

02/27/2016 8:42 AM

200 PSI.

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#3

Re: how much compressed air can fill in lpg tank?

02/27/2016 10:59 AM

Z=PV/RT? perhaps. Find a geeky physics or ME friend, to help you out. Some debri of sand blast hits the face little painful and numb sometimes.

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#4

Re: how much compressed air can fill in lpg tank?

02/27/2016 11:24 AM

The typical safety relief pressure in a 20 - 100 pound tank valve is is usually set between 275 and 350 PSI depending on who made the tank.

That said one time I had a badly dented tank I fixed with my pressure washer and I pumped that up with water to around 800 PSI to get it to smooth out.

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#5

Re: how much compressed air can fill in lpg tank?

02/27/2016 11:26 AM

Air tanks are designed with more corrosion allowance than LPG tanks. Substitutions are not usually allowed.

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#6

Re: how much compressed air can fill in lpg tank?

02/27/2016 12:02 PM

LPG is stored under relatively low pressure. Most tanks about 200 psi. Some to 312 psi.

Get a scuba tank it can be pressurized to 3000 psi.

It is also designed and marked for air.

you will be violating several regulations using a LPG tank for air.

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#7

Re: How Much Compressed Air Can Fill in lpg Tank?

02/28/2016 2:20 AM

As some one already noted, LPG tanks are generally low pressure.

LPG tanks usually have a fixed collar, although some older tanks that have passed required periodic testing may have removable collars.

The maximum permissible pressure allowed for a given type of tank is stamped into the collar or on the shoulder; I have seen some that have the pressure on the footring.

While you may be saving weight using an LPG cylinder, the pressure is going to be low, and not too useful.

A high pressure tank such as the CO2 tank noted by another poster are available to hold pressures up to 6000 psig, and may be specially ordered to hold a higher pressure but there will be a weight increase.

Most of the CO2 tanks that I have seen were rated up to 1800 psig. The pressure rating for a high pressure tank is stamped on the shoulder of the tank.

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#8

Re: How Much Compressed Air Can Fill in lpg Tank?

02/28/2016 1:43 PM

I don't see how this is either safe or complies with local regulations, but for a project (school?) you might get away with it.

You should really get a proper tank and regulator designed for air if possible, or talk with local tank suppliers and ask for their advice on pressure and to obtain the correct regulator to convert your LPG tank.

What type of compressed air engine? Is this a school project?

Also, see numerous threads on CR4 by myself and others on vehicle air-powered engines if you want to know what the end results will be.

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#9

Re: How Much Compressed Air Can Fill in lpg Tank?

02/28/2016 1:53 PM

Tata has already done this.

Have you used the internet to search for air powered cars?

What HAVE you done?

Tata Motors is not to be confused with these:

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#10
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Re: How Much Compressed Air Can Fill in lpg Tank?

02/28/2016 4:07 PM

Interestingly enough both are inefficient means of transport compared to existing internal combustion or battery powered vehicles.

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#12

Re: How Much Compressed Air Can Fill in lpg Tank?

02/28/2016 4:40 PM
  • The thread connections will be wrong on a fuel vessel. FueL vessels use a Left-hand thread. That way it is impossible to fit the wrong connections downstream.
  • SCUBA tanks are designed and insured for air use, and will store more for a given size than an LPG vessel, as they are thicker.
  • If the vessel is within its statutory insurance assessment period, then it may be assumed that it is safe to charge the vessel to the pressure rating at ambient temperature. Of course, charging the vessel raises the temperature of the contents, so the charge must be done slowly enough to allow the heat to dissipate.
  • In terms of energy stored per unit mass, an important criterion for vehicle storage systems, there is nothing much to beat the sodium-sulphur battery at the moment. However, in order for it to be a battery, its internal temperature must be raised above 300degC or so.
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#15

Re: How Much Compressed Air Can Fill in lpg Tank?

03/03/2016 1:16 AM

Sorry to be sending this so late in the discussion, but it was "lost" somewhere on my computer files, and I only found it recently. The markings are explained, and required on all low pressure cylinders transported in the U.S. (and I believe Canada and Mexico also use the these maqrkings.

Hope it helps.

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#16

Re: How Much Compressed Air Can Fill in lpg Tank?

03/08/2016 6:32 AM

I've used propane tanks in the past as air receivers (own use only) & if you look on the tank there is a test pressure stamped on it, there should be a test date as well, when I used mine I took out the valve (first making sure that it's empty)feed an air line in & leave air on for 1/2 hour then turn the cylinder on its head & leave for as long as possible a week would be good but longer will be better at the end of the day the air will still smell of gas for quite some time depending on how many times it is evacuated & refilled, One other thing you need is a drain down valve, where ever you intend to put it you need to weld a collar & drill & tap through both that & the tank wall, You will need a competent welder to do this work this is a pressure vessel & needs to be treated with the utmost care. I used mine for years with no trouble.

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#17
In reply to #16

Re: How Much Compressed Air Can Fill in lpg Tank?

03/08/2016 9:02 AM

I used a gas tank for air, and yes, the smell lingers forever. Mine still smelt of gas even washing out with boiling water and fanning the tank with a hot-air gun, and purging with air for ages.

I am worried when you refer to drilling holes. That might be alright for a qualified expert, but a DIY novice should never drill holes in a gas tank body. Air in and out must be by a suitable adapter screwed into the existing valve hole - complete with gauge and safety valve to relieve excess pressure.

Neither should a DIY novice weld things on the tank - even using a qualified welder - mounting brackets and attachments can easily be made by suitable straps wrapped round and clamped on the outside of the tank.

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#18
In reply to #17

Re: How Much Compressed Air Can Fill in lpg Tank?

03/09/2016 5:42 AM

The one thing I can't see is what pressure he is looking to put in it, somebody mentioned to power a car if that is the case then we're talking thousands of PSI & as an LPG tank could only be used safely at about 200 PSI, anything higher you should look at submarine tanks which when kept in test can be pumped to 5000PSI & BOC can pump them or your local dive shop.

Bazzer

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adreasler (1); Bazzer Englander (2); Casper71 (3); horace40 (2); jack of all trades (2); lyn (2); Mr. small (1); ozzb (1); PWSlack (1); SolarEagle (1); tcmtech (1); Tornado (1)

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