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Author: Subject: Any air compressor experts in the house?
J666AYP

posted on 29/12/18 at 06:01 PM Reply With Quote
Any air compressor experts in the house?

Hi gents,

Just having a brainfart.... I have a 200L 3hp compressor that I'm using to run my sandblaster. Its draining the air quicker than it can build up (well with the power on high enough for decent results)

Not for the scary part. I have a large propane bottle that I removed the valve from and have washed out several times. If I welded on bungs for a air inlet, outlet, saftey switch and drain plug could I use it to boost my available air? I'm thinking it would put less strain on the compressor and give me less down time?

I'm thinking compressor - regulator - moisture trap- back up tank - moisture trap - sandblaster

Cheers,

Jay

[Edited on 29/12/18 by J666AYP]

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femster87

posted on 29/12/18 at 06:22 PM Reply With Quote
The cylinder would probably take it (vapour pressure of propane at 5oC is going to be around 8.5 bar vs the compressed air pressure at 6/7 bar). The problem is your weld and current condition of the cylinder. If it lets got and depending on the damage/injury you have the consequence might not be worth the savings (home insurance for one).

Cost of getting your weld and cylinder tested might be more than just buying an air receiver. Alternatively, if you are a good welder, complete the weld, dye-pen and some shell thickness test and then test cylinder hydrostatically ( personally I will go up to 2 x required pressure) but 1.5 should be okay

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daviep

posted on 29/12/18 at 06:25 PM Reply With Quote
Additional capacity won't fix your problem it will only change it. You will have longer blasting time but it will take longer to build up the pressure again.

Your compressor is too small for the nozzle you are blasting with, you either need a smaller nozzle or a bigger compressor.

Regards
Davie





A truly great library contains something in it to offend everyone.

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big_wasa

posted on 29/12/18 at 06:33 PM Reply With Quote
I have same problem so I only do small jobs and get bigger stuff done professionally.

Smaller nozles mean its not worth the work and a bigger compressor is a non starter as that would require twin staggered start pumps and a dedicated power suply.

[Edited on 29/12/18 by big_wasa]

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SteveWalker

posted on 29/12/18 at 09:58 PM Reply With Quote
You are overcomplicating it.

Mount the bottle upside-down and simply tee the pipe from the compressor's own reservoir into the existing threaded connection to the bottle. The one connection will act as both inlet and outlet and moisture cannot collect as it is self draining (pipework needs to run downhill all the way).

The regulator and moisture trap need to be connected after the bottle - you want the bottle at the same pressure as the compressor's reservoir, not at the reduced pressure after the regulator, as you are storing more air in the same volume when the pressure is higher. The bottle should be rated well above what the compressor can supply.

No need for a switch, the existing one on the compressor will still do the job.

The extra stored air will allow longer operation before the air is depleted, but will take longer to recharge as well.

I once had to do similar, using an old, but freshly certified, industrial pressure vessel of 10m3 capacity at 300psi (with the diesel driven compressor, that took up the whole of an artic, running continuously) to supply enough air to turn over the "jet engine" part of a gas-turbine driven compressor on its air-starters, for a five-minute purge cycle before starting for factory test purposes.

[Edited on 29/12/18 by SteveWalker]

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indykid

posted on 30/12/18 at 10:20 PM Reply With Quote
Calor propane cylinders are rated for at least 26bar (the pressure relief valve in the tap is set at this) so you should have a fair amount of headroom at 10 bar. If you don't put any valves in line after the T, if you run it inverted as Steve says, you don't need to weld anything on.

Ultimately, you need a bigger/second compressor though.





me? ambivalent? well, yes and no

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clive7883

posted on 30/12/18 at 10:58 PM Reply With Quote
It won't make any difference, the air pump on the compressor will only deliver a given amount C.F.P.M. so regardless of the size of the air tank or tanks , the pump will be working the at the same rate, all it will do is give you a greater amount of air to use before the pump starts up, however the pump will run longer before it cuts out , so longer down time, not really worth all the work, if you have 200ltr tank already.....just my view, others may think differently. If as you say, its 3hp, it can only be delivering around 10 C.F.P.M. that really is not enough for powering a blaster. you may need to think about a larger compressor, but you can.t run much more than 3hp on single phase.


[Edited on 30/12/18 by clive7883]

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907

posted on 31/12/18 at 07:48 AM Reply With Quote
quote:
Originally posted by daviep
Additional capacity won't fix your problem it will only change it. You will have longer blasting time but it will take longer to build up the pressure again.

Your compressor is too small for the nozzle you are blasting with, you either need a smaller nozzle or a bigger compressor.

Regards
Davie






+1

also, once you connect your little compressor to a big tank it will run continuously in its attempt to keep up. It will overheat.

Paul G





Member of the Suttol Owners Club, the MX5 Owners Club and the BMMC

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J666AYP

posted on 31/12/18 at 09:22 AM Reply With Quote
Hi gents,

First of all thanks for the info. I am planning on buying a phase converter and a beast of a compressor after the house move so this will only be a temp fix.

I have reduced the nozzle ID and backed the regulator off abit and this has helped quite abit. im now getting 7-10 mins flat out run time before the compressor kicks back in then about another 4 mins before I drop to 4bar and have to stop.

Im having to stop every 20 mins to re-fill the little blaster anyway so im thinking abit of extra air would be a bonus. I have to drain the pressure in the blaster to do this so thats ample time for the compressor to catch up. So it SHOULD** be easier on the compressor, 1 big charge, 15 to 20 mins blasting then a good 15 min rest while I top up and clean up.

I think my regulator settings had alot to do with the very short run time on first set up. The compressor charges to 10.5 bar (tested and stamped for 16), then running 8 bar through regulator. Then the air valve half open on the blaster. I think I was dumping too much air too quickly on the old setup with the blasters inlet valve being fully open and reg set to 8.5 bar.

Also worth mentioning the propane bottle was brand new when I got it and the internals have been checked with the borescope. If this buys me a exta 5 mins it will work out well as I will have to stop to refill the blaster anyways.

Jay

[Edited on 31/12/18 by J666AYP]

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Barksavon

posted on 31/12/18 at 02:25 PM Reply With Quote
Would a 3hp 14cm compressor be big enough to run a blast cabinet? I'm 'hanging my nose' over one of the vertical one's from machine mart.
Is there a difference between cfm and Free Air Delivery cos I've seen both quoted as an indication of compressor performance???
Thanks
Ian

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rusty nuts

posted on 31/12/18 at 05:27 PM Reply With Quote
I found I had to wait for pressure to build up in a 14CFM compressor when using a small blasting cabinet , now I get stuff done by a pro blaster.
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wetpool

posted on 1/1/19 at 12:27 PM Reply With Quote
I've found it lot more effective to use short bursts of air then a continous stream. Even my 3phase, 3kw comp could not keep up with my (worn out) nozzle in the cabinet. It kept running and pressure would stabilise around 5 bar. With the intermittend operation pressure stays much higher, but I could do with some (arduino?) way of 2/3 hertz puls generation and an electric valve near the pistol......
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