# Understanding Pump Ratings for Air-Assisted Airless Equipment

Finishers explain how air pressure relates to fluid pressure in an air-assisted airless situation, and what it means when a AAA pump is rated "14:1," "10:1," et cetera. February 17, 2014

Question
I'm not planning on getting a AAA pump anytime soon, but looking at some of the pumps available, what is this ratio I keep seeing - 14:1, 20:1, etc.?

Forum Responses
(Finishing Forum)
From contributor J:
You should change your mind and get one sooner than later. Once you have one, you will wonder how you worked without it.

The ratio is simply the multiplier to find the fluid pressure at a given air pressure. For example if you have a 14:1 pump, and feed it with 40psi of air, you will have 14*40=560psi of fluid pressure.

If you look on the TDS of many of the products you spray, they will recommend a fluid pressure when spraying the product with an AAA.

From the original questioner:
Thanks for clearing that up. So when you buy a pump like that, the fluid psi is dictated by how you set the air pressure. How do you know witch ratio pump you need? At this time I don't do a whole lot of spraying. Maybe if I get more jobs I will look into it.

From contributor J:

For the typical fluids we cabinetmakers spray, a 10 or 14:1 is fine. You need larger pumps if you plan on spraying extremely thick materials, or want to run more than 1 gun at a time off a single pump.

Refer to the TDS of the materials you plan to spray. Most will recommend a fluid pressure of around 600psi give or take. So with a 10:1, you feed the pump with 60psi of air, and a 14:1 you feed the pump with ~40psi. Most air tools have a max pressure rating of around 100psi, meaning that you can get a max fluid pressure of 1000psi from a 10:1 and 1400psi from a 14:1.

Any of the typical units from Binks, Kremlin, CAT, Graco, will all be suitable. I would base your decision more on the availability of parts and support from your dealer than the actual brand. They are all capable of laying down a quality finish. The Kremlin is by far the most popular. I use a CAT bobcat, and have nothing but great things to say about it.

From contributor N:
The third thing to look at (as well as ratio and availability of parts) is volume - how much material the unit can pump. If you'll just running one gun, .3 to .5 gpm is more than adequate and will use a lot less solvent when cleaning up.