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View Full Version : What to look for in an air compressor.



Philly
18-04-2013, 09:52 PM
I'm on the lookoput for a cheap air compressor around 25lt. Its only to be used for blasting the CNC when working, air assist on the laser, airbrushing and some larger painting(a4 sized wood, few at a time). Would a standard cheap model do the job or do I need something better?

Thanks, Phil

drumsticksplinter
18-04-2013, 10:33 PM
Hi Phil,

I used to have a very cheap 25ltr compressor, which they used to sell in aldi, power craft or something was the name on it. It was very good for the price and put out around 7cfm, which for its size is excellent. The problem you might face is if you find yourself using more air than you thought and the compressor is kicking in and out to build up pressure, then they can overheat very quickly. Also the direct drive models, which is most of the smaller compressors are very loud, probably over 90DB. After a while the noise becomes an issue. If you can find a smaller belt driven model then this will be quieter.

Hope that helps,

Adam.

Carlb1058
19-04-2013, 12:22 AM
I'm on the lookoput for a cheap air compressor around 25lt. Its only to be used for blasting the CNC when working, air assist on the laser, airbrushing and some larger painting(a4 sized wood, few at a time). Would a standard cheap model do the job or do I need something better?

Thanks, Phil

Phil,

The difference between the 25lt and the 40lt models in physical size is minimal, so IMO I'd be looking at one of them as the price isn't that much different. I bought an el cheapo 40lt as my 15cfm belt drive was losing air and wasn't worth repairing, I'm yet to have my el cheapo over heat and I've painted more cars and bikes with it than I can remember. When it came to airbrushing it was a PITA mainly due to the excessive noise so I bought an el cheapo air brush compresser that put out from memory a max of 60psi but the constant use would knacker one of them.
So in short suss out the 40's before deciding on a 25, the additional expense (if there is any) will pay for itself over time.

birchy
19-04-2013, 12:57 AM
I did a lot of research on air compressors and had a chat with a colleague who used to service them. His basic advice was to get a 50L model with twin piston. More interestingly, he said that Abac make most of the re-branded compressors for the likes of Sealey, SIP, NuAir, Rockworth, Draper, etc. If you look at these, they are all the same motor, pump and tank, just in different colours and with very different price tags!

Sealey 50lt V-Twin Compressor 3hp 11.6CFM SAC5030VE *F.O.C. NEXT DAY DELIVERY!* | eBay (http://www.ebay.co.uk/itm/261189733104)
SIP 06242 AIRMATE TN3.0/50-D 3hp 50 Litre V TWIN AIR COMPRESSOR 50L tool gun | eBay (http://www.ebay.co.uk/itm/180739532939)
Burisch Air Compressor 3HP 50L 50 ltr litre 14CFM V-Twin NEW | eBay (http://www.ebay.co.uk/itm/151025729385)
50L 50 Litre Air Compressor 230V Draper 2.2kW V-Twin Air Compressor 3HP 116PSI | eBay (http://www.ebay.co.uk/itm/151029165798)
Air Compressor 3hp 50lt Twin V Motor 230v SUPER QUALITY | eBay (http://www.ebay.co.uk/itm/290240914024)
SIP (S.I.P) 05287 Airline VDX/50 CM3 Air Compressor 3hp 50Ltr Twin Piston | eBay (http://www.ebay.co.uk/itm/111023823567)

Swarfing
19-04-2013, 01:08 AM
If it was me i would go for a secondhand hydrovane and treat it to a new service kit. Quiet and constant pressure, can't wait to get some dosh to replace my old crappy one. If you do consider it always ask what use time says as it records this on the unit. Not much has change in the design since the sixties, this is for good reason. They will do most jobs without a tank as well.

birchy
19-04-2013, 01:12 AM
If it was me i would go for a secondhand hydrovaneSo would I, but can't justify 1000 for a second hand compressor.

Jonathan
19-04-2013, 01:17 AM
What to look for in an air compressor.

Air.......

Swarfing
19-04-2013, 01:22 AM
They come up much cheaper than that, just don't look for one that looks like you can eat your dinner off. A bottle of sugar soap and a bit of elbow grease is much cheaper than a noisy cheap one take my word for it.

Swarfing
19-04-2013, 01:25 AM
air compressor | eBay (http://www.ebay.co.uk/sch/i.html?_odkw=screw+compressor&_osacat=0&_from=R40&_trksid=m570.l1313&_nkw=air+compressor&_sacat=0)

First one i came to and you can get them cheaper like i say. Don't worry about 3 phase either as you can run it with a VFD

John S
19-04-2013, 01:52 AM
If you go for a Hydrovane go for a 5 series, plenty big enough and many are on single phase.Search on ebay for hydrovane 501

Don't buy the tripod mounted ones, get the tank mounted.

They are different, the tripod mounted ones unload the compressor when pressure is reached so the motor runs all the while.

The tank mounted units have pressure switches.

I run two 5 series side by side but only run one at a time however both tanks are coupled so I have plenty of air.

Iwant1
19-04-2013, 02:09 AM
John could we get a bit more real life usage of the hydrovane 5 series.

I've been looking on ebay for some time now and they do come up often for around 300, which I don't mind paying, but when I read the specs of the 501, it only produces 4.2 cfm FAD. Seems crap against say a 300 secondhand 150ltr Sealey/Abac/Clarke with 14cfm. Would the 501 easily allow for some spray painting, blasting, sanding. Could it even be used for blowing chips away.

Feel like I have to look at a big 3 phase hydorvanes to get any where near descent Ccfm. But then these are a huge step up, with ratings of 20+ cfm.

Are the hydrovane and regular compressor cfm's not comparable?

Cheers Adil

John S
19-04-2013, 02:23 AM
You have basically answerd your own question when you state 4.2cfm FAD which means Free Air delivery. because they don't have a swept volume like a piston compressor they have to state what they put out.

CFM means sod all, CFM is the swept volume x revs in one minute and doesn't take into account valves opening and closing which is when the proper work is done.

Read this.

The "power" of an air compressor (http://www.weldsmith.co.uk/tech/air_compressor/compr_capacity.html)

m_c
20-04-2013, 12:47 AM
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John S
20-04-2013, 12:58 AM
What you have to do with the tankless units is put them on a tank and run them up to see what pressure they spit out before they unload.

Then fit a pressure switch, machine mart are reasonable for these, and set it for 10 pounds less than the test pressure, this way they perform the same as the tank model.

m_c
20-04-2013, 01:31 AM
1234567890

AdCNC
21-04-2013, 12:31 AM
I had a 14cfm twin piston compressor and yes it could kick out 14cfm when the tank was full thats bout it. then i landed on a nearly new Abac 50+cfm jobby and that will do a proper continuous 50 cfm and its alot quieter than the old turd.

John S
21-04-2013, 01:11 AM
and its a lot quieter than the old turd.

Adam,
There is no need to get offensive, I can't help getting old................

martin54
21-04-2013, 02:29 AM
I will have to look for another air compressor now, I have had an el cheapo model for years & it has been great for the things I was using it for, few air tools, bit of spraying, nail gun & blowing up the car tyres was about all it got used for.
Now I have built the blast cabinet it's just to small to handle the flow required at the correct pressure.
Still having read this thread at least I have a better idea what to look out for now.

AdCNC
21-04-2013, 11:39 AM
Lol John how did you know i was talking about you :-p

martin54
25-04-2013, 09:22 PM
Hope this isn't classed as a hijack it is about air compressors lol.

Read what John was saying about compressor outputs & that he had said to look out for hydrovane series 5 units but I'm not sure if something that size would do for the blast cabinet, the 5 series from what I can see chucks out about 5 cfm & the blast cabinet needs a minimum of 7 cfm @ 80 psi, more would be better.
Realise from Johns post that those figures might not mean a lot so needing a bit of help with what might be suitable without having to take out a loan.

m_c
26-04-2013, 12:41 AM
I've got the small clarke blast cabinet, which supposedly requires 10cfm at 80-100psi, however my 3hp cheapo keeps up with it reasonably well.
Constant blasting does mean the compressor never stops, so I do stop occasionally to give it a rest, but it's not caused any issues so far.

I suspect a Hydrovane 5 might be a bit on the small size, however you could always couple it into your existing compressor, and run them side by side.

martin54
26-04-2013, 04:29 PM
I was actually hoping to get away from the cheapo compressors because of the noise they make, even with a pair of ear defenders on it's a bit loud lol. Had thought about running 2 machines together & haven't entirely written the idea off but I'm not in a huge rush to get it going at the moment. Will kind of manage to do my wheels with it even if it does take a lot longer than it should & glass etching will probably need a lot less pressure although I haven't really researched that at the moment.
Pity I don't have a 3 phase supply in the unit as you seem to be able to pick up used screw compressors at a reasonable price although I haven't looked at the running costs of them.

Swarfing
26-04-2013, 06:35 PM
Martin you can hook a compressor up to a vfd so they are not out of the question.

martin54
26-04-2013, 10:26 PM
Martin you can hook a compressor up to a vfd so they are not out of the question.

Did think about a vfd same as the spindle on the router but are you not limited to 3 or 4KW doing it that way? Most of the industrial screw compressors I've seen that sell reasonably cheaply are bigger than that, the smaller ones & single phase compressors seem to sell for a lot more money, I'm guessing because there is far more demand for them from people like ourselves lol.

m_c
26-04-2013, 10:33 PM
Big VFDs are available, but once you go past 2.2/3kw, the price increases quite a bit.

You could run it from a phase converter, however once you get past a few kw you're into quite substantial wiring and current requirements on 240V. Most common screw compressors start around 7kw, which would need 30A from 240V and that's before you consider the startup surge from the motor.
They are alot quieter, but you need to make sure they've been reguarly maintained, as any issues lead to efficiency dropping of quickly, and they're definetly not cheap to fix!

martin54
26-04-2013, 10:47 PM
thanks for the pointers people, definitely need to do a lot more research before making any sort of decision on what's the best way forward.

Swarfing
26-04-2013, 11:50 PM
Also think about the larger the screw compressor (not always the same as a hydrovane) get noisier. Think about the medium to use as well. Checkout soda blasting

martin54
27-04-2013, 11:56 PM
Also think about the larger the screw compressor (not always the same as a hydrovane) get noisier. Think about the medium to use as well. Checkout soda blasting

Still be a lot quieter than the cheap compressor I have at the moment lol.
Soda blasting requires very similar pressures & flow rates although it does work slightly differently. Already got a bag of soda to experiment with along with the glass beads & aluminium oxide. Might be able to borrow a compressor from someone I know to run along side mine for the time being which will at least let me start experimenting. Should help give me a better idea of what I really need to do the job properly.

Swarfing
28-04-2013, 12:02 AM
LOL! I have an old compressor which i very rarely use these days because of the noise. Hope you sort it soon Martin.