Within Industrial Plant settings Stainless Steel Compression Fittings are the fitting of choice for misting solutions. Why? The answer is pretty obvious. Stainless Steel (SS) fittings have a very high working pressure rating, typically above 6000 psi. This provides a high safety factor during operation.
The size of the SS fittings used in misting systems are 3/8" and 1/2" tubing, occasionally one size larger and smaller, 3/8" for medium size system up to 100 nozzles. 1/2" for larger systems. The pressure ratings are actually limited by the tube rating being used. Pressure rating of Stainless Steel tubing used in this size range are from 2000 psi to 6000 psi depending on wall thickness and construction. That is plenty of cushion for safe operation when misting systems hardly ever go over 1000 psi.
Single Ferrule or Double Ferrule
There are two types of compression fittings, single ferrule and a double ferrule. The single ferrule have a slightly less pressure rating the double ferrule. The advantage of the double ferrule is the second ferrule assists in holding (locking) a firm connection. This is great when the fitting is subject to abnormal vibration, temperature or pressure variations. Industrial Plants where mechanical equipment abounds is the good application for double ferrule.
3/8" Double ferrule Stainless Steel Tube Union with 10/24unc
The inside ferrule, the ferrule closest to the middle of the fitting is considered the locking ferrule. The outside ferrule, ferrule closest to the end is considered the sealing ferrule.
1/4" Single ferrule Stainless Steel fitting
There are several manufactures of Stainless Steel fittings. In the USA, Parker and Swagelok are the two big manufactures. You can Google them to find more info.
Back to our misting application, double ferrule fittings are used in most industrial applications because of their inherent capacity to work in environments of heavy vibrations and temperature ranges. Single ferrule would work fine in less demanding application like printing facilities and woodworking humidification applications.