Airbrush mac valve

[MrProd]

Apologies if this is a stupid question but I've seen contradictory advice on other sites/ youtube. 

 

Is there any practical difference between reducing the pressure at the compressor or dialing down the air with the mac valve on my ps270. I've tried both and can't tell any difference and logic makes me think if the air is flowing at a certain rate then its irrelevant whether the rate is dictated at the far end of the airline or just before the nozzle.

 

But I see mac valves described as splatter valves or stipple valves and I'm puzzled. Perhaps I should just stay away from Reddit.

[Kev The Modeller]

In theory no, but due to things compressor spec/quality, length of line, line/tank integrity (leaks) and the gauge.  The air you think is coming out of the compressor as shown by the gauge, could well be very different from what is reaching and coming out of the nozzle not to mention any fluctuation.  The Mac valve on the brush is much closer to the nozzle so you've got a far more accurate control over what's coming out.   

[dromia]

Your compressor gives pressure the "MAC" valve adjust the volume of air going through the brush at whatever pressure the compressor is delivering.

 

I like to spray small and close up, I can drop the pressure to around 8 psi as indicated on my compressor, real value unknown, and still get decent paint atomisation. With the "MAC" valve, I have mine mounted on the quick release end of my air hose so I can use it with all my airbrushes, I can reduce the volume and this will give me an even finer spray than the lowest working pressure can. When you get to the edge of the working volume for your airbrush you will then get the "splatter" effect which can have its uses.

 

So the two can seem to be doing the same thing but they are different, as to whether that is of any help to your style of airbrushing then only you can answer that.

 

 

[Dave Swindell]

2 hours ago, MrProd said:

Is there any practical difference between reducing the pressure at the compressor or dialing down the air with the mac valve on my ps270. I've tried both and can't tell any difference and logic makes me think if the air is flowing at a certain rate then its irrelevant whether the rate is dictated at the far end of the airline or just before the nozzle.

There's no difference, as you've found they both reduce the air pressure and volume flow at the airbrush nozzle. 

The advantage of the MAC valve is it's immediately accessible on the airbrush, you don't have to go scrabbling about on the floor if your pressure regulator is on your compressor outlet under your bench. 

The pressure regulator gauge might not read the exact pressure at your airbrush, but the pressure losses will be constant, and the gauge will give a reading that is directly proportional to that at the airbrush, so you can use the reading as a reference, which is a bit more difficult to do with a MAC valve.

[Ray_W]

I see little advantage in a MAC valve for our modelling purposes unless you cannot reach the regulator on your compressor and if that was the case I would be moving it closer with a decent regulator and water trap. I suppose if your running a large workshop then yes although I would still install a decent regulator and water trap within reach. I can reach my compressor and dial 8 to 22 psi regularly depending on what I am doing and it works for me. 

 

However, @dromia nailed it. He is up close and if you're hunting for special effects like an airbrush artist, then there is advantage in one as you try to create different effects by varying paint volumes such as normal spray and a variety of shading effects to splatter/stipple as mentioned. It gets down to your individual artistic needs. Think less about giving pressure control at the airbrush (yes, which it does) and more about the convenience of varying paint effects right at the airbrush. 

 

Ray

[Dads203]

I find it invaluable, it’s more precise than the comp regulator so you can really fine tune the pressure. It is one of the main things that need to be balance if you are spraying very fine intricate work. 

[Simon Cornes]

I wish I could get hold of one!! I have a couple of Badger brushes (a 200 and a Revell Professional, which is a Vega) and both attach to the compressor with standard Badger plastic airlines. At one point I almost got one from Paul at Little Cars but the last time I saw him was at Bolton in January and he didn't have the right end connectors! I e-mailed him subsequently, at his suggestion, but no reply was ever forthcoming. If someone can tell me what I need then maybe I should start searching on eBay?

Thank you in advance

Simon

[P_Budzik]

I'm with Ray, I use a tank air supply that feeds a manifold.  Each air outlet has it's own pressure regulator and it's located at my fingertips of where I'm painting. The only thing about the MAC valve versus the pressure regulator is that the MAC valve is more instantaneous because you don't have to let the air bleed out of the hose.  That said, I have several airbrushes with a MAC valve and I've yet to ever use it.

 

As far as stippling, I'd rather use something more predictable, that was designed for the task, like a Paasche AB.  And actually the Paasche H does stippling better than an internal mix.

 

If you don't need it, it's just one more thing to clean around and another valve in the air supply.

 

 

Paul

 

[MrProd]

I've read this about one changing the pressure and the other changing the volume but in actual use what difference should I be seeing.

 

I've tried mac valve wide open with the regulator at 10 psi and then psi at about 30 with the mac valve restricting until the air flow felt and sounded the same as before. 

I can't see any difference in how the paint goes down. 

What difference should I expect?

[Ray_W]

40 minutes ago, MrProd said:

What difference should I expect?

 

Do it the other way, using a paint that you spray regularly, and has a known performance, set the main regulator at your normal value. Say, 18 psi and keep it there.  Have the MAC valve wide open. Then play with screwing the MAC valve down and see what effects you achieve. 

 

Also try being an artist and use a super thin semi-transparent acrylic paint, not like our thinned modelling style opaque paints. Super thin paints have their challenges and the fine MAC valve adjustment can be handy. 

 

Frankly, once I have set a pressure for a particularly paint and thinner based on what works best for that particular paint (I usually need to up the pressure slightly higher for metallics), I find the airbrush works effectively over a wide range of pressures and the need to change pressure is more related to how close I want to work from the surface. For example I'll drop the pressure to get up very close for a fine line and higher pressure to move away and get greater coverage. I use an IWATA HP-CS with a 0.35 needle and have a finer IWATA, but find the HP-CS does most of what I want to do over a broad range. I do not get too hung up on pressure. Correct thinning and trigger control are to me far more critical. 

 

The other thing is the MAC valve is all about effect with an unknown value. Micro final adjustment. For our modelling needs I much prefer the main regulator and a gauge and can quickly say "I am spraying AK Xtreme it goes down nicely for me when I up the pressure to 22 psi" or "Gunze Aqueous with Mr Color Levelling Thinner close work, fine line, I'll go to 8 psi".  No guesswork.

 

Have fun with the MAC valve and come back with your conclusions.

 

Ray

 

 

 

 

[dromia]

1 hour ago, MrProd said:

I've read this about one changing the pressure and the other changing the volume but in actual use what difference should I be seeing.

 

I've tried mac valve wide open with the regulator at 10 psi and then psi at about 30 with the mac valve restricting until the air flow felt and sounded the same as before. 

I can't see any difference in how the paint goes down. 

What difference should I expect?

As I said in my post the difference the MAC valve makes for me is that it allows a finer spray than just reducing the pressure alone, the airbrush and paint mix will need a minimum pressure to atomise the paint and spray well, go below that and you will not get the atomisation and 'twill spit and grumble.

 

With the MAC valve I can set my lowest working pressure on the compressor and then use the MAC valve to reduce the volume of air this gives me an atomised spray finer than the lowest pressure will, as I said I like to spray small and close up so this facility is a great asset for me. If you are more a stand back and hose it on just to get the colour down then adjusting the volume really won't give you much difference within those parameters and just using the pressure to get the optimum spray for you paint and application.

 

I am sure that the vast majority of airbrush using modellers do very well with out an air volume control and in the majority of cases it is of no value. That is probably why most airbrushes don't have MAC valves it is not essential to getting a good spray.