So when a review or model maker says “set 15psi” is that before or after you press the airbrush button, and what effect does the drop in pressure on the gauge when using the brush have?
I set 15psi. I press the airbrush button, pressure drops. So is this an actual drop in pressure or should I ignore?
Hope that makes sense!
It’s an actual drop in pressure. To properly measure the pressure, I set the regulator while spraying air at full blast through my AB.
It could be either, depending on the modeler. It doesn’t really matter. The right pressure is the one that works best with your paint and airbrush. Play with it a bit and you’ll see what works the best for you.
Don
The pressure gauge should measure the static pressure at the compressor outlet. If set up correctly, the reading should not change. With a good setup, the compressor pressure should not have changed according to the amount of air or thickness of the paint you use. Otherwise, the airbrush user loses control of the airbrush.
If the reading changes when you press the trigger, it is either the compressor is too low powered to maintain pressure, or the gauge not set up correctly to measure the static pressure. Yes, my first compressor, a Silentaire Scorpion-1 clone, did that. The motor does not have enough power. I set the pressure at 25 psi with a Paasche H. The reading drop to less than 10 psi when I airbrush. My Paasche DA400 will not do that. I set the pressure at 17 psi for my Iwata HP-CS, it stays at 17 psi when I press the trigger.
The bottom line is to get a good quality compressor. In today’s market, it does not have to be expensive. There are some good choices among the name brand and some house brand. For the cheaper single cylinder, w/o tank compressor, it is not unusual for the pressure reading to drop 2-3 psi when pressing the trigger. It is ok as long as the reading is stable and repeatable.
If the pressure reading drops more than that or continue to drop when you hold down the trigger, the compressor is probably too low powered for your airbrush.
I would say that is slightly misleading. Without air flowing the pressure guage is reading static pressure, but as soon as air starts to flow the guage is then reading dynamic pressure & a guage drop between the two is inevitable. The quality of the guage will have some effect on the indicated pressure drop, the quality of the pressure switch (sensitivity / reaction) will also have an effect, as will the available air storage of the compressor. Lower quality gages, large receivers & finer nozzles will all reduce the indicated drop, but it still exists
If the drop were considerable (more than say 5>10psi), it may indicate an issue with the regulator or guage arrangement, but if it’s below that level & the compressor can maintain the lower dynamic reading I would suggest that the compressor is powerfully enough.
Unless you’re using a storage tank right?
I am talking about basic engineering principles. The dynamic pressure is dependent on the mass flow rate and the airspeed. We usually measure dynamic pressure both parallel and perpendicular to the flow. It is not practical to do that in a hobby compressor and it yields too much information for airbrush use. With the airbrush drawing less than 0.5 CFM, a properly positioned pressure gauge should measure very close to the no flow delivery pressure and not change much when the user press the airbrush trigger.
In my Paasche DA400 setup, the reading never change more than 0.5 psi. The DA400 is not an expensive compressor. It will be interesting to see some reports on what other compressor does. For example, the Iwata Power Jet or the Sparmax TC-2000.
I agree with your basic suggestions, but like to recommend getting a compressor that drops no more than 2-3 psi in use.
The pressure gauge should read the delivery pressure to airbrush. The storage tank will not have higher pressure than the compressor can produce. The tank should make no difference in the pressure reading.
I would just set it to 15psi, static, and tweak from there if needed.
The point is that you should not have to guess. The gauge’s pressure reading should be repeatable.
It is possible to get reliable pressure reading with better compressor. Unfortunately, your recommendation of guessing makes sense for most cheaper ones.
By the time the air gets to the brush and depending somewhat on the brush itself you kind of are guessing anyway.
I use spray equipment for a living including A/B’s and the setting at the tank/compressor is only the start, by the time the air gets to my gun the gauge on the gun reads different and I’m only using a 6’ hose.
The gauge on the compressor is a good start but not that accurate at the A/B itself.
[*-)]
2>10psi over a range of decent compressors, being dependent on the flow requirement of the brush/nozzle combination.
Hi,
thanks for all the replies but I’m still confused.
I have an Iwata airbrush and compressor SilverJet from memory (@ £200 its at the cheaper end of the market but still a nice brush). I can deduce from the responses that the compressor gauge is measuring static pressure. When I use the airbrush the gauge drops significantly but I don’t notice a significant drop in airbrsh pressure. So could I still be getting that same pressure at the brush? If not then it kind of defeats the object of the gauge.
Thanks,
Ted.
The value of the gauge is repeatability, not absolute accuracy. When you find a setting that works well, you can always come back to it.
How much do you tighten a violin string? Until it sounds right.
Don
[dto:]
Don’t get to hung up about spraying at the “correct” pressure because it’s big variable, it depends on a large number of things other than the compressors guage accuracy & the pressure drop. The airbrush, the nozzle size, paint consistency, job in hand & user technique all play a part in getting the “correct” pressure & one mans optimum will not be another’s.
Start at one end of say a 10>30psi range & work through it at 5 or 10psi adjustment at a time, spraying on some scrap material until you find what suits you - when you become more experienced you will be adjusting the pressure more by feel than by number. Paint not coming out or spattering heavily suggest not enough pressure, paint bouncing from your model or drying to a grainy finish suggest too much.
Last week I found myself painting some boots (ladies) with pink Createx paint at 50psi, only later to be doing some 1/72 detailing with Tamiya acrylic at 10psi…
Compressor gauges are necessary and set the limits for the compresser. They also set a good starting reference (Gets you close), but I doubt your getting the exact same pressure at the A/B aircap.
Especially given the, length and expansion of different hoses, efficiency of the compressor and cfm of any given A/B etc. Air cools within the hose and pressure can drop some.
The only way to tell for sure would be with a special gauge that measures at the aircap .
We do this with our spray guns at work… HVLP guns for instance can have no more than 10 psi at the air cap. Regardless of who manufacures it. So we adjust at the gauge initialy then at the gun itself.
Compressor tanks can have a significant effect on what the gauge indicates.
Your compressor must still be delivering " sufficient" cfm and pressure with the trigger pulled and developing the proper vacuum at the nozzle tip.
I always get a laugh out of engineers. [whstl]
And you believe everyone can build their own airbrush and compressor in the garage? We have no use of the manufacturers who hire engineers for their products?
Or you are green of envy? Next time, when you get on an airplane or get behind the wheel of a car, you may wish that whoever designed and built that thing took the job seriously.
Anyway, 9 of 10 models we build are modeling product of engineering. [;)]
No Keilau it is how they over-analyze everything that makes me laugh.
Envy? Hardly. I work around engineers and physicists every day. Some are just out there so to speak.
You would like to talk to a fighter pilot sometime and ask him/her if he thinks that engineer “over-analyze everything”. When their life is on the line all the time, I can understand why the pilots are so critical of the engineers and always push them further.
Working “around engineers and physicists every day” is not quite the same as working with them. Different line of work, different outlook of life.