Benchtop air compressors

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8th May 2018, 06:10 PM
John G

Benchtop air compressors

Does anyone have any experience with the small benchtop air compressors?

Such as https://sydneytools.com.au/lincoln-l...air-compressor

Are they next to useless for anything except pumping up the tires on a kids bike?
The reason I ask is the only spray gun I own is a crappy electric airless unit which tends to spit rather than spray.
I don't have the room, nor do I spray enough to justify a big or expensive compressor.

Would this be hopeless for trying to spray smaller items like furniture? (as opposed to trying to repaint a house)
I would be keen to experiment spraying varnish/poly etc instead of brushing.
8th May 2018, 06:26 PM
Lappa

Common range of CFM requirements for spray guns is 5 to 15 CFM.

https://www.dcjinc.com/wp-content/up...uns-Catlog.pdf

220 litres/min is approx. 7.8 CFM.
So it should suit the range of smaller spray guns.
8th May 2018, 06:37 PM
dai sensei

I have one of these in my mobile turning demonstrating kit
Stanley Wall Mount Air Compressor 0.5HP - 14LPM - Supercheap Auto

I use it for small spray gun at 40psi on my turning projects and it works well
Blackridge Air Spray Gun Touch Up - 200mL - Supercheap Auto

It is also fine for the small nailer and other air tools.

For bigger stuff I'm sure it would struggle
8th May 2018, 06:57 PM
david.elliott

I bought the Ryobi AirWave at $199. Worked well... until, I decided I needed an additional Nitto, which started a cascade of crap.

The Manifold is cheap casting which split, then the manifold snapped off flush with the tank, which heat gun fixed, by releasing the thread compound. Spent a few bucks on brass fittings and $60 on a air and moisture filter..A Must Have when painting.

I also suggest an inline filter and pressure regulator At The Gun...I have these two from Supercheap set up as one piece with male and female Nittos, so I add when painting and take off when not..
8th May 2018, 10:27 PM
BobL

Quote:

Originally Posted by Lappa

Common range of CFM requirements for spray guns is 5 to 15 CFM.

https://www.dcjinc.com/wp-content/up...uns-Catlog.pdf

220 litres/min is approx. 7.8 CFM.
So it should suit the range of smaller spray guns.

Unfortunately there's a bit more to it than that.
We don't know what the 7.8 CFM refers to. It could be the swept volume of the cylinders with zero back pressure.
What we need to know what pressure the 7.8 CFM is being delivered at.

It's also only a maximum of 116 Psi and has a 6L tank.
Assume it retriggers at 90 PSI that means after losing 6L of air @26 PSI =11 L or 1/3 of a cubic ft at atmosphere. If a spray gun need 5 CFM the tank will last about 4 seconds till it retriggers.
9th May 2018, 02:52 AM
ian
Quote:

Originally Posted by John G

Does anyone have any experience with the small benchtop air compressors?

Such as https://sydneytools.com.au/lincoln-l...air-compressor

Are they next to useless for anything except pumping up the tires on a kids bike?
The reason I ask is the only spray gun I own is a crappy electric airless unit which tends to spit rather than spray.
I don't have the room, nor do I spray enough to justify a big or expensive compressor.

Would this be hopeless for trying to spray smaller items like furniture? (as opposed to trying to repaint a house)
I would be keen to experiment spraying varnish/poly etc instead of brushing.

Hi John

that sort of compressor is "designed" to run a nail gun or a 16 or 18 ga bradder or a 23 ga pinner -- one tool at a time -- at a bench. Typical use would be shooting a few nails / brads to make a jig or to hold piece in place while the glue dries.

The online info sort of explains it all
- This machine runs on a standard 240 volt domestic outlet making it ideal for pumping up car tyres, blow-up pools, air mattresses, sporting balls and other sport equipment
- It can alternatively be used for stapling and air-brushing applications and can be used with most small air tools
If you want to spray finish, you need air volume and consistent pressure. 6 litres just won't cut it -- as BobL says, 6 l will last about 4 seconds.
I'm estimating that to spray a table top you need about 30 seconds worth of air.
This could be stored in a much bigger tank, or a combination of larger tank and a compressor designed to deliver 15 CFM continuously. Most (if not all) low cost compressors are designed for intermittent running.
9th May 2018, 02:39 PM
Alkahestic

Quote:

Originally Posted by John G

Would this be hopeless for trying to spray smaller items like furniture? (as opposed to trying to repaint a house)
I would be keen to experiment spraying varnish/poly etc instead of brushing.

I'd say yes, it will be hopeless for furniture. For a pen or bowl or a small jewelry box it would probably be ok. The 220 L/min is the pump displacement, the figure to look for is the free air delivery (FAD) and what PSI the FAD is quoted at. Generally the FAD is going to be around 75% of the displacement (don't quote me on that, just what I've observed).

From the information I could gather before I bought a compressor, 200 L/min FAD with a 50L tank tends to be the very minimum you'd look for in a compressor for spraying furniture. Pair it with a LVLP gun and you can get a good ~20s spray time before the compressor kicks in again. The other thing with smaller cheaper compressors is that they are not rated for high duty cycles.
11th May 2018, 01:52 PM
John G

Quote:

Originally Posted by dai sensei

I have one of these in my mobile turning demonstrating kit
Stanley Wall Mount Air Compressor 0.5HP - 14LPM - Supercheap Auto

I use it for small spray gun at 40psi on my turning projects and it works well
Blackridge Air Spray Gun Touch Up - 200mL - Supercheap Auto

Thanks, for the size of my work a 200mL canister is probably enough.

But forgive my ignorance, I don't understand the numbers.
The spray gun says "minimum 65LPM" but the compressor says "14L/min FAD", whereas link in OP says "220L/min"

Which are the relevant numbers when trying to match a compressor to a gun?

(I understand the point about a small tank emptying in about 4 seconds)
11th May 2018, 04:05 PM
ian

Quote:

Originally Posted by John G

But forgive my ignorance, I don't understand the numbers.
The spray gun says "minimum 65LPM" but the compressor says "14L/min FAD", whereas link in OP says "220L/min"

(I understand the point about a small tank emptying in about 4 seconds)

just running the numbers

If the compressor's FAD (free air delivery) is 14 l/min, then the motor would have to work for around 4-1/2 minutes to deliver enough air to power the 65 l/min spray gun for 1 minute. This is only possible via a tank that can store something like 70 litres (or a bit more than 2 cubic feet) of "excess" air at the required pressure.
Please note I've not attempted to consider the effects of pressure, which as air is drawn from the tank will reduce the quantity of available pressurised air.
The best simple analogy might to think of the "usable" air as being the top foot of water in an 8 foot tall water tank.

220 l/min is "believable" on the basis that if the motor could run for a whole minute it could under absolutely perfect conditions deliver 220 litres of air at atmospheric pressure into a pipe that is open at the other end.
11th May 2018, 04:22 PM
BobL

Quote:

Originally Posted by John G

The spray gun says "minimum 65LPM"

A) spray gun needs that or it won't work properly

B)

Quote:

but the compressor says "14L/min FAD",

What Ian said.

C)

Quote:

"220L/min"

This is what the tank and compressor plumbing can deliver at the outlet of the tank, but of course in your case only for a very short period of time
I think this is what Ian said it is, meaning it won't be 220 L/in driving a spray gun.

Quote:

Which are the relevant numbers when trying to match a compressor to a gun?

If the compressor has a big tank and you can run off the tank then you match A and C)

if the tank is small then the compressor will always be running so then you have to match A and B.
14th May 2018, 07:49 PM
John G

Thanks, this is great, it is making more sense now.

Unfortunately, I really don't want a compressor with big tank, even though you can get them for less than $200.

I happened to see on YouTube the other day a HVLP turbine system (which I didn't even know existed) but I can't find them on sale in Australia. They seem a lot of money to pay for a small footprint.
14th May 2018, 08:58 PM
Mobyturns

John,

I had a small SuperCheap compressor (similar to this Blackridge Air Compressor 95LPM 2.0HP Direct Drive - Supercheap Auto) running a Star 106 touch up gun for spraying nitrocellulose lacquer on a medium sized rocking horse. It coped, just, however t
he compressor was cycling continuously
! As Ian has said in practice the numbers in the brochures don't quite stack up.
15th May 2018, 12:07 AM
richmond68

John, HVLP turbine systems are sold here, from Wagner, Graco and possibly others. Like most things, you get what you pay for and four stage turbines aren't cheap. Earlex dual stage were decent and a lot cheaper but I haven't seen them since Wagner took them over.
7th June 2018, 02:09 PM
John G

Hi all, so here is an update:

As as experiment, I've bought a small 36L 115PSI compressor off gumtree, rated for 134L/min FAD.
I will try match this with a small (65Lpm) spray gun.
(I don't know yet what the on/off pressures are but I'll assume 90 / 115 psi.)

If I've done my maths correctly:
Available volume in tank = 36L x (115-90PSI) / 14.7 = 60L air in tank

So if I am spraying at 65 L/min the tank will last almost a minute.
And at 134 L/min FAD, the pump should refill the tank in about half a minute?

So if I spray continuously, the compressor will be able to keep up, but it will be cycling at about 60%?
And if I am spraying for 20 seconds per minute, the compressor will cycle at about 20% (tank will empty in about 3 minutes and then take 30 seconds to refill)?
7th June 2018, 05:05 PM
ian

Quote:

Originally Posted by John G

As as experiment, I've bought a small 36L 115PSI compressor off gumtree, rated for 134L/min FAD.
I will try match this with a small (65Lpm) spray gun.
(I don't know yet what the on/off pressures are but I'll assume 90 / 115 psi.)

If I've done my maths correctly:
Available volume in tank = 36L x (115-90PSI) / 14.7 = 60L air in tank

a 36 litre / 115 psi tank holds 36 litres at 115 psi, which is equivalent to 46 litres at 90 psi.

Quote:

So if I am spraying at 65 L/min the tank will last almost a minute.

nope
if the gun needs 90 psi, then your 36 litre tank only holds about 10 litres of usable air -- the difference between 36 and 46 litres.
at 65 l/min, your gun would run for about 8 seconds before the tank ran out of air at the required pressure.

Quote:

And at 134 L/min FAD, the pump should refill the tank in about half a minute?

if I have the marketing right, the compressor can PULL IN 134 l/min at atmospheric pressure (14.7 psi). This will be compressed to form about 21 l/min at 90 psi. Less than a third of what your gun requires.

Quote:

So if I spray continuously, the compressor will be able to keep up, but it will be cycling at about 60%?

your compressor and it's little tank won't be able to keep up.

Quote:

And if I am spraying for 20 seconds per minute, the compressor will cycle at about 20% (tank will empty in about 3 minutes and then take 30 seconds to refill)?

the compressor will run continuously and you might achieve about 15 seconds of spraying every minute.

I think I had better get BobL to check my maths.
7th June 2018, 10:09 PM
BobL

Hummmm . . .

The 6.5L/min needs to be delivered at 90 pSI but these air requirement volumes for spray gun and tools etc are usually always converted back to atmospheric pressure volumes so I agree with John that he will have about a minute worth of spraying before the compressor needs to recharge.

Same with FAD and recharge.

The questions that need to be asked is how reliable are the 65 L/min on the gun and the FAD. Most manufacturers overstate their FAD and it will degrade with time/wear so you may start out with 60% but you may end up closer to 100%
8th June 2018, 01:56 AM
ian

Quote:

Originally Posted by BobL

Hummmm . . .

The 65L/min needs to be delivered at 90 pSI but these air requirement volumes for spray gun and tools etc are usually always converted back to atmospheric pressure volumes so I agree with John that he will have about a minute worth of spraying before the compressor needs to recharge.

:? scratching head...

although a 36 litre tank at 115 psi may contain the equivalent of 300 or so litres at atmosphere, I understood that only the air that is at or above 90 psi is usable. (90 psi being the pressure required to operate the gun).
This volume is not very great.
8th June 2018, 09:05 AM
BobL

Quote:

Originally Posted by ian

:? scratching head...

although a 36 litre tank at 115 psi may contain the equivalent of 300 or so litres at atmosphere, I understood that only the air that is at or above 90 psi is usable. (90 psi being the pressure required to operate the gun).
This volume is not very great.

yep, that's right usable air (converted back to atmosphere) before going to recharge is 36*(115-90)/14.7 = 61 L

Recharge using 134 L/min should be ~30s but that FAD could be at 90PSI, so FAD will be less above that meaning longer recharge times
8th June 2018, 11:51 AM
John G

Thanks Bob and Ian,
I will report back all the actual numbers vs the theoretical numbers once I have given it a run.
The machine is 2nd hand so I wont be running it until I've given it an overhaul, new oil etc and checked the tank for any damage etc.
So it may be a few weeks before I report back.

No idea what the actual FAD will be as I have no idea the state of the gaskets, valves etc.
The spec in the manual simply says "Delivery 134L/Min, Discharge Pressure 115PSI/8 Bar" and there is a big "134 FAD" sticker on the side.

In theory (if the FAD remains constant), the tank holds (36 x 115)/14.7 = 281L of air, which should fill in 281/134 = just over 2 minutes.
(As I've never used a compressor before this is quite an interesting investigation for me)

John.
8th June 2018, 12:02 PM
BobL

Quote:

Originally Posted by John G

Thanks Bob and Ian,
I will report back all the actual numbers vs the theoretical numbers once I have given it a run.
The machine is 2nd hand so I wont be running it until I've given it an overhaul, new oil etc and checked the tank for any damage etc.
So it may be a few weeks before I report back.

Let the compressor charge itself up several times so it gets hot and then get yourself a container of water and add a squirt of detergent to it and using a paint brush paint all the fittings with the liquid and see if you can spot any leaks you can tighten.

Quote:

No idea what the actual FAD will be as I have no idea the state of the gaskets, valves etc.
The spec in the manual simply says "Delivery 134L/Min, Discharge Pressure 115PSI/8 Bar" and there is a big "134 FAD" sticker on the side.
In theory (if the FAD remains constant), the tank holds (36 x 115)/14.7 = 281L of air, which should fill in 281/134 = just over 2 minutes.
(As I've never used a compressor before this is quite an interesting investigation for me)

If it's real 134 L/m FAD @ 115psi then it should take less than 2minutes to recharge since a great charge rate will happen at the lower pressures.
If the compressor is in good condition t could be as little as half that time but most likely it will be between 1 and two minutes.
How many HP is the motor?
8th June 2018, 12:42 PM
ian

Quote:

Originally Posted by BobL

Recharge using 134 L/min should be ~30s but that FAD could be at 90PSI, so FAD will be less above that meaning longer recharge times

Dr Google suggests that FAD is typically quoted as cylinder volume x number of piston strokes per minute -- i.e. it's measured at atmospheric pressure.
so 134 litres FAD would be around 22 litres at 90 psi
8th June 2018, 03:01 PM
John G

Quote:

Originally Posted by BobL

Let the compressor charge itself up several times so it gets hot and then get yourself a container of water and add a squirt of detergent to it and using a paint brush paint all the fittings with the liquid and see if you can spot any leaks you can tighten.
...
How many HP is the motor?

It is 2.5hp motor direct drive. It is basically the same as this model (but not this brand).
First problem with changing the oil (if it even has any!) is the sump bolt isn't one with the oil level window, so I don't know how much oil to add. So I need to get one of those first to change the oil before I can even start. Also clean out the breather plug and a whole bunch of other stuff I am still learning about.