Differences between a diaphragm and a dual-piston compressor?

A dual-piston design is less prone to pulsation in the airflow and can provide a higher, more consitent output pressure compared to a diaphragm type.

You will get pulsation in the airflow of a diaphragm compressor because by its very nature, (for want of better terms) there is a "compression" (up) stroke and a "return" (down) stroke. The diaphragm must return to its starting position and while this happens, it's not pumping air.

In a dual piston system, one piston is "compressing" while the other is "returning", so it is able to maintain a consistent output

Due to the flexible nature of a diaphragm, it can have a lower maximum output pressure (though it's still sufficient for most airbrushing purposes). 

In extreme cases, excessive backpressure in a diaphragm compressor can rupture the diaphragm. (hence the need for a "bleeder" valve in a diaphragm compressor).

Thank you!  I've been pondering getting a nice Iwata Power Jet compressor for some time to replace my Paasche D500 (diaphragm) compressor, but have been put off by the expense.  Perhaps it may be worth it....however, I'm going to need to spend more time than I have lately building to make such an expense worthwhile.  Are the Dual-Piston compressors any quieter?

Diaphragm and dual piston compressors are "about" the same noise level. As there are two pistons that have to stop and reverse direction, they do tend to be a little bit noisier. If you want quiet there are no inexpensive solutions.

A true "silent" compressor is pretty expensive and uses a screw for compression. They are the same type of compressors found in refrigeraters and make a similar amount of noise.

Even quieter is CO2. If you have the ability to transport a tank safely, that is. Around my parts a CO2 system costs about $150 to set up. The benefit is the CO2 is completely dry, no need for a moisture trap, and is completely silent except for the hiss of the escaping gas. One caveat is CO2 is poisonous and should only be used in a well ventilated room. 

My inexpensive solution to noise is to use a tanked "garage" style compressor. It is kept outside in a ventilated box for protection and I run a hose through the wall to the spray booth. From where I sit and spray I can only hear a distant noise from the compressor, and then only when it is refilling the tank. 

Bgrigg wrote:

A true "silent" compressor is pretty expensive and uses a screw for compression. They are the same type of compressors found in refrigeraters and make a similar amount of noise.

Bill,

Silent compressors are not screw compressors, they are piston driven with cast iron heads and oil lubrication to make them quiet.

That all depends on how silent, Mike.

Silentaire for example can be piston or screw, oil or oiless. Depends on how much you want to spend!

Most of the ones advertised as "silent" are anything but. Those kinds tend to be piston. "Super-Silent" like the Silentaire Eco-20 is the same kind of compressor you'll find in your fridge and are much quieter.

Bgrigg wrote:

That all depends on how silent, Mike. Silentaire for example can be piston or screw, oil or oiless. Depends on how much you want to spend! Most of the ones advertised as "silent" are anything but. Those kinds tend to be piston. "Super-Silent" like the Silentaire Eco-20 is the same kind of compressor you'll find in your fridge and are much quieter.

Bill,

Are you saying the "Super Silent compressors are screw driven?

A refrigerator compressor is piston driven I believe.   

I have A Jun-Air and a Badger Million air and both are about as loud as a refrigerator (roughly 30 dB) and both are piston driven.

Even Airbrushtalk.com has an article about Silentaire compressors and the article states:

All silent compressors are piston-driven and oil-filled, which reduces friction in the motor.

Maybe there are silent screw driven compressors but they are not the ones you find from Silentaire, Jun-Air, and other well-known airbrush compressors.

Look here for a view of the inside of a Jun-Air compressor:

http://www.jun-air.com/graphics/pdf/data_sheets/3motor.pdf