Thread: Fixing an air compressor! Is it worth it!

Originally Posted by KBs PensNmore

I got an elcheapo also, takes 20 mins to get to 100 psi, touch spray gun 1 Min wait 20 mins etc...
Anybody want it.
Kryn

It has taken me about 2-1/2 yrs to get rid of my elcheapo......

my bro took it last week....and I havent given him my new ph no.....lol

Originally Posted by Ben Dono

Are belt drives really that much quieter?

Yes. In a direct drive with 2 pole motor the compressor runs at 2800rpm. Belt drive units have the compressor geared down to about 1:2 or 1:3 (1400 to 900 rpm). To pump the same air volume in a given time, the latter needs a compressor with bigger displacement. The lower rpm increases compressor life. The reduction and the flex in the belt drive makes motor starting much easier, increasing motor life too.

Direct drive is cheapest entry level.

Next up is either belt drive single stage pump, or direct drive double stage pump. Belt drive is quieter and lasts longer. Double stage is more efficient. Which to choose depend on application.

Next up is belt drive and double or triple stage pump.

Next up are scroll and screw compressors, definitely overkill for home use.


Then there are also oil free compressors, consider one of those if you want to use it for painting. These either use multistage rubber vane pumps, or dry lubed piston pumps (teflon or carbon lined).

I might look at a 3phase then if they are even quieter.... I can't say I have noticed 3phase motors being any quieter that a single phase induction motor though.. Maybe I have not been paying any attention to that!

Originally Posted by eskimo

It has taken me about 2-1/2 yrs to get rid of my elcheapo......

my bro took it last week....and I havent given him my new ph no.....lol

If mine doesn't die by the end of this year my son might be getting mine as part of his Xmas present.

The amount of noise they make also depends upon the efficiency of the intake muffler/filter.

Most are pretty rudimentary.

My belt drive Binks Bullows is noisy in the shed, but not enough to give you a headache. Bearable.

Rob

Originally Posted by cba_melbourne

Next up are scroll and screw compressors, definitely overkill for home use.

Not if you want to do any serious sand blasting....

I have a Bunnings direct drive POS compressor. Had it over 10 years now, it's copped a flogging.

PDW

I'm glad I posted up the question! I'm surprised at so many responses.

Thanks PDW, sandblasting was one of the other things I wanted to have a crack at!
Would a 13cfm handle blasting medium sized jobs.....say a motorbike frame or cast iron garden furniture. (Not that I have plans to do either, they were the first type of sandblasting jobs that popped into my head!)

I'm looking at the toolex/airmac t20 with a 120L tank.....maybe the 70L as a lot of the time it's used as a duster! I can always rig up an auxiliary tank for the bigger jobs. I don't think airmac is Aussie...I might keep looking!

Originally Posted by Ben Dono

I can't say I have noticed 3phase motors being any quieter that a single phase induction motor though..

Ben...you are right

take two units, same compressor...equal output ie cfm, one single phase the other three phase..no noticable difference in sound levels

what is trying to be advised here is that direct drive elcheapos are running at 2800 rpm compared to say 600-900 or so and hence are noisier...but take a larger compressor requiring say 6hp 3 phase unit running say a 1400 rpm motor with compressor running at say 700rpm...the elcheapo would most likely be quieter

in general, bigger means more noise, faster may or mean more noise

however even a single ph 3 hp air compressor can be quite noisey...just ask our cat...it gets out of the shed real fast..... and hence if nearby for long times use ear protection

Originally Posted by BobL

If mine doesn't die by the end of this year my son might be getting mine as part of his Xmas present.

lol...why wait till then...give him an early Xmas present...you wont be sorry

Originally Posted by simonl

I see better TV's on peoples natures strips!

hmm hmm
you not running around the neighborhood picking them up are you?...lol

Originally Posted by Ben Dono

I'm glad I posted up the question! I'm surprised at so many responses.

Thanks PDW, sandblasting was one of the other things I wanted to have a crack at!
Would a 13cfm handle blasting medium sized jobs.....say a motorbike frame or cast iron garden furniture. (Not that I have plans to do either, they were the first type of sandblasting jobs that popped into my head!)

16 to 20 cfm is the sweet spot IMO - a compromise on the small side for people without 3 phase power. Air tools use a huge amount of air too - die grinder comes to mind.

I'm not a good person to ask as I have 4 compressors ranging from the POS Bunnings unit that's good for nothing but running a nail gun and a small spray gun up to the 120 cfm Hydrovane unit.

If I could only have 2 and I didn't need to toss one in the back of the truck every so often I'd have a 16 to 20 cfm heavy duty unit with as big a tank as I could get, and at least a 250 cfm diesel powered unit for blasting. 95% of the time the smaller unit would do me, but I wouldn't go much under 16 cfm as they all lie anyway.

FWIW.....

PDW

Watch out for grossly "inflated" cfm or L/min or HP figures being advertised with most diy type compressors. It is the same advertiser tricks like with household vacuum cleaners.

To me, a diy compressor is single phase and hooked up to a 10A powerpoint. 10A x 24V=2400W input power. Assuming a motor efficiency of 70% (and that is generous for a chinese motor), that is 2400x0.7=1,680W shaft power. 1,680W/746=2.25HP. Any claim of a single phase compressor with an ordinary 10A power cord having more than 2.25HP is therefore rubbish.

And there is a physical limit, how much free air flow a 2.25HP motor can generate. A typical diy direct drive 10A power cord compressor has a 2HP motor and a single stage pump of about 7CF. But 7CFM displacement at 2700rpm is only barely 5SCFM at 100psi. The most common sales trick it to specify displacement (CFM) and describe it as free air delivery (SCFM).

But then I see these even worse eBay offers, where a brand new 12CFM compressor with 3HP motor and single phase cord with 10A plug is offered. Makes me think of Godfreys selling a 2000W vacuum cleaner for 49.95 (where a 10A universal motor has at best a 50% efficiency)...

I thought they were all supposed to quote FAD (free air displacement) now, so that you can at least compare apples with apples?

Simon

Originally Posted by eskimo

lol...why wait till then...give him an early Xmas present...you wont be sorry

Yes I will - he will want a whole mother Xmas Present!