Is my compressor too big!

[KrisW77]

As title of thread my compressor is a big Clarke 150L twin piston which the previous owner of my house left in the garage. It great for air tools and tyre inflating but is it to big for my H&S Ultra airbrush? It does blast the paint out and is is tricky to get the pressure set right.

[Dave Swindell]

It's a bit overkill for what you're using it for, I wouldn't suggest going out and buying one just to run an airbrush, but as you've inherited it and assuming it's working ok/in good condition I wouldn't be dashing out to replace it either. The big compressor and tank should mean you can pump it up to pressure and it will run the airbrush without cutting in again for anything but really extended spraying sessions. The pressure output won't be any greater than a dedicated airbrush compressor (6-7 bar), but what you do need is a pressure regulator to drop the tank pressure down to a comfortable working pressure for your airbrush (around 1 bar, might be higher or lower depending on what you are spraying, your airbrush setup and personal preference) a good quality pressure regulator will be easily adjustable and have an output pressure gauge on it, most airbrush compressors come with one already fitted, but your compressor might not, if it hasn't you'd be best fitting one, if it has it sounds like you need to check it's working and adjust it to a much lower pressure.

[KrisW77]

43 minutes ago, Dave Swindell said:

It's a bit overkill for what you're using it for, I wouldn't suggest going out and buying one just to run an airbrush, but as you've inherited it and assuming it's working ok/in good condition I wouldn't be dashing out to replace it either. The big compressor and tank should mean you can pump it up to pressure and it will run the airbrush without cutting in again for anything but really extended spraying sessions. The pressure output won't be any greater than a dedicated airbrush compressor (6-7 bar), but what you do need is a pressure regulator to drop the tank pressure down to a comfortable working pressure for your airbrush (around 1 bar, might be higher or lower depending on what you are spraying, your airbrush setup and personal preference) a good quality pressure regulator will be easily adjustable and have an output pressure gauge on it, most airbrush compressors come with one already fitted, but your compressor might not, if it hasn't you'd be best fitting one, if it has it sounds like you need to check it's working and adjust it to a much lower pressure.

The way it's setup it comes out of the compressor into a water catcher/pressure gauge then into a big reel which I then connect to my airbrush. Sorry if this is a stupid question but could I be loosing pressure as it goes through the big reel because the pressure on the regulator is set to only say 20psi? And its got a long way to go before it reaches the airbrush? Would it be better to have the airbrush connected to the regulator so it's not going through the massive reel?

[malpaso]

My cheapy compressor “says” 25psi static and 20psi when flowing through the airbrush.  But as it’s quality is debatable and I doubt many others have had their compressor gauges properly calibrated, the actual psi is fairly nominal, what the gauge gives is a guide to the consistency of the airflow, so you can adjust up and down and get back again as needed.  Whatever my gauge says I’d bet a lot it won’t be exactly the same pressure at the end of the 10ft hose, nor at the tip of the airbrush as each change of direction or constriction will affect.

 

In other words once you have found whatever pressure works for you, record it and use as your baseline for any experimentation with different paints, thinning ratios and so forth.

 

With a very long hose you may want to consider an inline water trap at the airbrush end, as you may get appreciable condensation as the air heated by the compressor cools along the hose and can’t retain the moisture.

[Ade H]

@KrisW77 Kris, as you've inherited this workshop compressor, I don't suppose that you know its specification, but perhaps try to find out what flow it has (usually expressed as cubic feet per minute). This is overlooked but quite important; most airbrush compressors, as far as I've noticed, are in the region of 4-8cfm at base pressure. Giving an airbrush less than it needs reduces performance, but I wouldn't be too surprised if giving it very much more than it was designed for may not be ideal either and may result in the effect which you describe. Flow and pressure can feel like the same thing, but are not. A MAC valve reduces flow (think of it like a tap -- the water pressure is what it is, but the flow is adjustable) and fitting one under the airbrush may help you to get more control. Just surmising and I hope that it helps somewhat. The advice from Dave and malpaso is also spot on, I think.

See also

 

Edited September 2, 2021 by Ade H
typo

[Dave Swindell]

2 hours ago, KrisW77 said:

The way it's setup it comes out of the compressor into a water catcher/pressure gauge then into a big reel which I then connect to my airbrush. Sorry if this is a stupid question but could I be loosing pressure as it goes through the big reel because the pressure on the regulator is set to only say 20psi? And its got a long way to go before it reaches the airbrush? Would it be better to have the airbrush connected to the regulator so it's not going through the massive reel?

Yes, the hose reel could be causing a pressure drop.

If you need the hose length to get the air from the compressor to your airbrush position consider moving the moisture trap/regulator to the airbrush end of the hose or get another one to fit at that end and set the compressor end one to an intermediate pressure)

If you're airbrushing close to the compressor, disconnect the hose reel and connect the airbrush directly to the moisture trap/regulator.

Don't get too hung up on the actual pressure, it just needs to be adjustable and stable when set. 

32 minutes ago, Ade H said:

@KrisW77 Kris, as you've inherited this workshop compressor, I don't suppose that you know its specification, but perhaps try to find out what flow it has (usually expressed as cubic feet per minute). This is overlooked but quite important; most airbrush compressors, as far as I've noticed, are in the region of 4-8cfm at base pressure. Giving an airbrush less than it needs reduces performance, but I wouldn't be too surprised if giving it very much more than it was designed for may not be ideal either and may result in the effect which you describe. Flow and pressure can feel like the same thing, but are not. A MAC valve reduces flow (think of it like a tap -- the water pressure is what it is, but the flow is adjustable) and fitting one under the airbrush may help you to get more control. Just surmising and I hope that it helps somewhat. The advice from Dave and malpaso is also spot on, I think.

 

The compressor flow rate is irrelevant  so long as it's supplying more than the airbrush demands ( and with the OP setup this won't be a problem) A higher flow rate will fill up the tank quicker and the compressor will cut out sooner than one with a lower flow rate. Flow to the airbrush will be governed by the regulator capacity and hose size and length..

Yes, flow and pressure are different, but they're interrelated in a dynamic system. 

Yes, a MAC valve adjusts the flow, but it's a simple throttle valve and it also adjusts the pressure. Fully open it will have little or no effect on flow and there will be little or no pressure drop across it. Start shutting it in and you reduce flow, but also increase pressure before the valve and drop the pressure after the valve..

 

[Ade H]

Either you have misunderstood me or I have misunderstood you. I'm not sure which.

[KrisW77]

I've ordered a Moisture trap/regulator from Screwfix to put at the airbrush end as suggested. Be interesting to see what happens.

Edited September 2, 2021 by KrisW77

[Mike]

7 minutes ago, KrisW77 said:

I've ordered a Moisture trap/regulator from Screwfix to put at the airbrush end as suggested. Be interesting to see what happens.

I've never seen a bragging thread about the size of someone's compressor before Glad you've had some advice, and I just had to put the extra O in your "to".  It was doing my head in

 

If the moisture trap/regulator doesn't work out, you should have a word with someone like Martin @ Aircraft.net.  He'll be able to set you up with something like a shorter hose etc., and get you up and running without fear of exploding your airbrush

[Dave Swindell]

15 minutes ago, Ade H said:

Either you have misunderstood me or I have misunderstood you. I'm not sure which.

The compressor has a 150l tank, a compressor with a higher flow rate will fill the tank quicker than one with a lower flow rate.

The flow rate out of the tank will be governed by demand (the airbrush) up to the capacity of the regulator but no more.

Flow rate through the airbrush will be governed by the airbrush design and input pressure, the compressor flow rate won't affect this unless it's insufficient t keep up with demand.

If the compressor flow rate is higher than airbrush demand, the pressure in the tank will increase until a pressure switch stops the compressor, or a safety valve lifts.

As the pressure increases in the tank the regulator will shut in to maintain desired output flow at the set pressure.

If the demand alters (opening or closing the airbrush needle valve) the regulator will adjust to compensate and keep the pressure constant.

[KrisW77]

Bit of an update. I installed the flow regulator/Moisture trap today and its holding pressure nicely not like the setup before where it was dropping. Not been able to shoot any paint yet but looking forward to seeing the difference 👍

Edited September 4, 2021 by KrisW77