How to determine PSI on air brush?

You need a pressure gauge.

One with a regulator will allow you to adjust the pressure.

They look like this:

Clear thing on the bottom is a water trap.  Also very handy.

Ok, attached between the can and the gun correct (dummy question but I have never used one before)?  Who sells them please? Thanks . . .

Are you using canned air? I'm not sure a pressure gauge will work on those. I would think you will lose part of a limited air supply trying to adjust the pressure.

If you are using a propellant can rather than a compressor, a pressure gauge won't be much use. There's no way to connect one. Generally speaking, when using a propel can, it's all or nothing.

In addition, you will encounter the inevitable pressure loss as the can cools during use. This is unavoidable due to basic physics. In simple terms, a gas cools as it expands. The propellant in the can consists of a low-boiling point liquid. Normal room temperature exceeds the boiling point of the liquid in he can. In the closed environment of a propellant can, the static pressure of the gas in the can prevents more liquid from boiling off. When the can valve is opened and gas is released, the reduction in pressure allows the liquid propellant to boil off, releasing more gas. There is a trade off, however, In that the expansion of the gas absorbs heat from its surroundings. As this liquid to gas conversion continues, the liquid propellant gets progressively colder and closer to the boiling point of the liquid. As this happens, the molecules on the liquid become less energetic and less gas is released from the liquid, causing a loss in pressure in the can.

In user terms, it means you'll spray for a few minutes, and the pressure will gradually drop, eventually reaching the point where the airbrush will no longer pick up paint. Sometimes the can will cool to the point where frost will form on it. Set it all down for a few minutes and wait for the can to warm up.

Resume, repeat.

You can help this process along by putting the cold can in a basin of warm (not hot) water, but the cycle is unavoidable.

Sorry Thlorian.  I thought you meant for a compressor.  As was said above, a regulator is of no use with a can of propellant.  No worries though. I used them when I first started airbrushing and they do fine without one.  You'll just have make adjustments in the paint/thinner ratio vs a regulator.

A Propel can will not give a constant pressure.  As you use the propellent the expansion of the gas flowing out the opening cools the can, and the pressure is highly temperature-sensitive. I read about the trick of sticking the can in a pan of water.  Result- a pan full of ice!

You need to get a compressor or an air tank and regulator.  However, free air at service stations (needed to maintain air in tank) is disappearing, so you will eventually want a compressor.  If you can stand the noise, a little pancake compressor can sometimes be found for about fifty bucks or a bit less. In these days of hundred and fifty buck kits, compressors are not as relatively expensive as they used to be.

Here's what I did. I waited until Michael's had one of the 50% off coupons days. I bought a $300 Paasche compressor, for, of course, 50% off. So, that was a big deal. Then I went to Home Depot and bought a simple in-line pressure gauge with a dial adjuster for about $20. Very happy with the system and even bought a in-line water separator, but, that was from the LHS. \

So, not a terribly expensive way to upgrade to an advanced system.

Save even more by getting the compressor and fittings at Harbor Freight.   I bought a tank type comp. used for nail guns and it works just fine for my airbrush.

Wow!  Thanks so very much for all this great info and tips!  MUCH APPRECIATED from each of you!!

I've had this one for about 8-9 months. It is quieter than the exhaust fan on my spray booth. The built-in tank smooths out the air pulses too. It's cheap and often there are combos that even include an airbrush.

1/5 hp MASTER AIRBRUSH TANK COMPRESSOR is sold by Amazon, TCP Global

Ken

Just a reminder that there is a forum just for Painting and Airbrushing.  Selecting compressors, and fittings for same, are frequently discussed there.  It is a great forum, one of my "must read" forums each day.

Thlorian, I, like many others here, started out using canned propellant with my airbrush. After 4 cans, and a lot of wasted air and paint, it was obvious that if I really wanted to use an airbrush, I needed a different set up. I did a little math, and it was obvious that if I spent a little money up front by buying an air compressor, I'd save a lot of money in the long run. I bought an Iwata Smart Jet. It was one of the best decisions I have made. Now, I just spray away and don't count the dollars every time I think about using my airbrush. I can spray indefinitely and the pressure is constant. If I hadn't gotten the compressor, I doubt that I'd still be using an airbrush. If you plan on using an airbrush regularly, and can afford a couple hundred dollars up front, I highly recommend that you invest in a compressor. You'll actually save money, you won't be breathing some pretty nasty fumes from cans, and you'll like the results a lot better as well. You could even put the compressor on a credit card and pay it off a little each month. Just consider it your monthly can allotment. You're just using the money you would have spent on cans for the compressor instead. Eventually, it will be paid off, and you'll still have the compressor instead of a room full of empty cans to show for your money.

Thanks everyone!  BarrettDuke - You have sold me on a compressor before I have even used either a can or a compressor yet!  I do have a can here for my first test sprays this weekend on some cardboard and scraps (Had hoped to spray last weekend but time go t away from me).  I posted a new thread re confusion on psi/compressors and I see you have replied to it - thank you!

Look on line at TCP Global like  kinjitak  said, I bought  the one he said about 8 months ago and it works great, quiet and never has missed a beat and was only $89.00 and comes with a regulator and gauge. In my opinion best deal out there for the money.