Compressor puzzle

Post by **chimpboy** » Thu Oct 12, 2006 11:43 am

Help me out. I have a decent compressor with a 40 litre tank. By decent I mean that it fills the tank to 120psi or so no problems, and fast.

I just got a sander to use with compressed air, which likes 90 psi. No problems setting the regulator to this.

The problem I have is that it runs for a matter of literally seconds, like five seconds, before the pressure has dropped way too much and it stops. Then I pull the trigger again and it goes a bit... repeat... then wait for the compressor to fill up again.

I've used compressors of similar tank size before and I am sure I've gotten a bit more time out of them...

Is my problem that I simply have a tank that's too small or is there something I can check?

Post by **pongo** » Thu Oct 12, 2006 12:10 pm

id say your compressor is too small

Post by **chimpboy** » Thu Oct 12, 2006 12:19 pm

pongo wrote:id say your compressor is too small

Hrmm, fair enough... what do I need?

Post by **Shadow** » Thu Oct 12, 2006 12:36 pm

chimpboy wrote:
pongo wrote:id say your compressor is too small
Hrmm, fair enough... what do I need?

A Bigger compressor

See if your sander has any CFM rating, Youl need to have a compressor with a higher CFM rating than your sander, otherwise the compressor will run 100% duty cycle. The bigger the tank the better of course.

Could also try turning the regulator at a lower pressure, about 70? if it still woks at this pressure, that way you will get more time between pump-up's. Air usage will be exponential with respect to regulator pressure.

Post by **chimpboy** » Thu Oct 12, 2006 12:58 pm

Hmm. Well the sander claims to be 4cfm, the compressor claims to be 10cfm.

Something doesn't quite feel right about this, the compressor is showing 110+ psi, and the sander just stops the second it hits any significant load. Is there any way it could be a component of the sander or can I be pretty definite that I need a bigger compressor?

I don't mind having an excuse to get a bigger compressor, btw, but it will have to wait a bit.

Post by **noelb1** » Thu Oct 12, 2006 1:23 pm

we sell an onboard air kit which uses 2 x Bushranger max airs into a 20ltr tank set at 150psi cutoff and you can run a 1/2 inch rattle gun nonstop ,

Post by **Damo** » Thu Oct 12, 2006 3:47 pm

I know this isn't answering your question but I would run an electric sander instead of an air sander. Effeciency wise you will be a lot better off.

Post by **chimpboy** » Thu Oct 12, 2006 4:45 pm

Damo wrote:I know this isn't answering your question but I would run an electric sander instead of an air sander. Effeciency wise you will be a lot better off.

Seems that way! I went looking for one today. Does anyone know what sort I should go for to prepare body panels for painting? I can do the fine parts by hand but when I am getting the body filler flat I could use mechanical help

Something like this? http://cgi.ebay.com.au/ws/eBayISAPI.dll ... 0035001313

?

I am after something that has a decent sized flat surface so that I can sand the flat surfaces without gouging them.

Post by **Shadow** » Thu Oct 12, 2006 5:18 pm

Sounds like your sander is either shit, or needs some mainenance. a 10cfm compressor should be good to drive pretty much any hand-airtool.

Post by **-Scott-** » Thu Oct 12, 2006 5:33 pm

Unless they're dodgy brothers ratings - 10cfm may be a free-air flow, but you won't get 10cfm at 90psi - more like 1.5 to 2 cfm of 90psi air.

I'd expect your sander's rating to be 4cfm at 90psi.

What's 40 litres? 1.5 cubic feet? Time your compressor to "top up" your tank from 80 psi to 100 psi. The figure needs to be in the order of 20 seconds or less, or you're kidding yourself.

Post by **460cixy** » Thu Oct 12, 2006 5:44 pm

yup you need a bigger tank 40ltr is nothing

Post by **-Scott-** » Thu Oct 12, 2006 6:35 pm

460cixy wrote:yup you need a bigger tank 40ltr is nothing

A bigger tank will only extend the time he can sand before he has to stop and wait, and will then take longer to fill again. It doesn't affect the compressor's flow. If his compressor can't supply 4cfm@90psi a larger tank isn't a solution for continous operation.

What does the compressor flow at 90psi?

Post by **bazzle** » Fri Oct 13, 2006 12:01 pm

Also drip some oil down the inlet to sander.

Bazzle

Post by **BowTieGQ** » Fri Oct 13, 2006 9:19 pm

What is the purpose of your sanding exactly anyway? It may be best done by hand. Failing that, get a 17cfm for the shed and you'll use it for everything. If you're after something 9"ish, get a Makita or Hitachi. I have 2, one for grindind and one for buffing. Air tools are very inefficient whan compared to electric.

Post by **me3@neuralfibre.com** » Sat Oct 14, 2006 2:40 pm

Sounds like you are sanding bog. Air sanders need huge compressor flow. Cheap air sanders need more - they suck.
3 Options.
1. Electric Random Orbital (Hitachi for me) - easy $200
2. Large CFM compressor - $800
3. 2 x GMC cheapies from bunnings - $99 ea piped together = same flow as (2).

Paul

Post by **chimpboy** » Sat Oct 14, 2006 2:55 pm

me3@neuralfibre.com wrote:Sounds like you are sanding bog. Air sanders need huge compressor flow. Cheap air sanders need more - they suck.
3 Options.
1. Electric Random Orbital (Hitachi for me) - easy $200
2. Large CFM compressor - $800
3. 2 x GMC cheapies from bunnings - $99 ea piped together = same flow as (2).

Paul

Heh, option three crossed my mind as well. But I am now leaning towards getting a good new compressor for my workshop, while keeping the cheapie (it was a gift) for more portable use. Come to think of it I can always plumb that one in with the new one as well.

It looks like $700 plus gets a pretty good compressor. Pity I'll only have single phase...

Post by **droopypete** » Sat Oct 14, 2006 3:04 pm

http://www.festool.com.au/mediandoweb/i ... KTIVPROD=1

This is my favorite sander, from super fast material removal to the finest of finish sanding.
Peter.

Post by **Shadow** » Sat Oct 14, 2006 5:37 pm

me3@neuralfibre.com wrote:Sounds like you are sanding bog. Air sanders need huge compressor flow. Cheap air sanders need more - they suck.
3 Options.
1. Electric Random Orbital (Hitachi for me) - easy $200
2. Large CFM compressor - $800
3. 2 x GMC cheapies from bunnings - $99 ea piped together = same flow as (2).

Paul

Tthe GMC's are 5.4CF/M with a 30litre tank for $99.

For $800 you get a 3 piston 3.5HP Renegade from tradetools with i think an 80 litre tank, 310L/m ~ 11CF/M. My brother (carpenter) has a 13CFM renegade, but i dont see it on tradetools website anymore.

So for the same price you could get 8 GMC's, tap em all together, get 40CFM and 240Litre tank capacity LOL

Sure youd be running 16HP of motors though.

Post by **Reddo** » Sat Oct 14, 2006 7:30 pm

air sanders have no torque that's why they stop so easy and no amount of air can overcome this inherent failing. Cheaper units are worse, and I and others have been caught out by this failing. Seems like a good idea, but they just don't cut it in the workshop unless the work is very light on.

Use electric orbital if any on body filler, but you'll probably find hand jobs are best, working from courser grades to finer , feeling your way as you go.

Post by **Reddo** » Sat Oct 14, 2006 7:34 pm

oh...and note the current draw on the compressor at max load. Three cylinder units may draw close to 10 amps which in some areas is too much for the local domestics supply, particularly at night when power is at a premium and often voltages drop below 240V. This may cause the unit/motor to stumble, overheat and shut down contuinuously - a real pain if you're trying to work with the air.

Post by **Shadow** » Sat Oct 14, 2006 7:53 pm

Reddo wrote:oh...and note the current draw on the compressor at max load. Three cylinder units may draw close to 10 amps which in some areas is too much for the local domestics supply, particularly at night when power is at a premium and often voltages drop below 240V. This may cause the unit/motor to stumble, overheat and shut down contuinuously - a real pain if you're trying to work with the air.

o_O

10amp is more than your socket is rated at, but all power circuits in houses are 16amp and I have quite often taken it to this limit with no significant voltage drop.

A guy I know runs nearly 40amp's worth of cold rooms off a typical house supply (runs business from home) and has no problems.

If you were that worried you could have a 25AMP GPO installed by a sparky. Which AFAIK uses the same size cable as all other house GPO circuits(2.5mm), but has a dedicated line instead of daisy chaining all over the house.

Unless you have a very poor power grid drawing 10 amps is no problem at all.

Ive run my brothers 13CFM compressor off a 30 metre lead and it didnt have any problems running either.

Post by **Reddo** » Sat Oct 14, 2006 8:50 pm

yeah, point taken, could be just another Tassie failing! Problem here arises at night only when demand causes voltage drop which causes current drop off etc etc.

As you say, one way around it is to run larger cabling from the mains supply to the required power point, eg., use stove wire which should fix the problem allowing more current flow, lower resistance etc.

40 amps is a huge amount to draw from a domestic supply line! I have drawn 30 from a heavy supply line to an outlet dedicated for a welder and it gets quite hot at max amperage!

Post by **chimpboy** » Sat Oct 14, 2006 11:10 pm

Reddo wrote:yeah, point taken, could be just another Tassie failing! Problem here arises at night only when demand causes voltage drop which causes current drop off etc etc.

Better dam something for more hydroelectricity!

Post by **chimpboy** » Wed Nov 01, 2006 3:00 pm

Okely dokely, I've been doing my research and there are some decent 240V (single phase) compressors out there.

Also in my digging... there's a recent Australian standard for air compressor performance, using a defined methodology from the CAAA (Compressed Air Association of Australia).

Now using this methodology, most of the compressors out there end up with lower ratings (in litres per minute) than they are usually claiming. But it's consistent and it seems to me like you would be silly to buy a compressor that doesn't have a CAAA rating now.

My compressor from Supercheap is a 2.5 hp, 40 litre model. It's actually been pretty good but using the CAAA rating system it scores a pretty pissweak 112 litres/minute. That's 4 cfm. Bear in mind that pre-CAAA, the compressor was claiming 10 cfm, which was a crock.

Anyway, using the CAAA ratings, there are compressors around that deliver 270 l/min (a genuine 9.5 cfm) for under $750. Bear in mind these are claiming more like 400 (14cfm) or 350 (12 cfm) overseas without the standard measuring system.

Well, I thought it was pretty cool that it's becoming possible to compare the farkers more easily. I know it's probably old hat to some people but to me it was useful new info.

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