Compression fittings are also used extensively for hot and cold water faucets and toilet stop valves. These valves generally control water to one fixture, such as a toilet, to allow it to be serviced without turning off the water to the entire house. Compression fittings are well suited to this application, as these valves are usually located in confined spaces where copper pipe would be difficult to solder without creating a fire hazard.
Compression fittings are the industry standard for chemical, oil and gas, R &D, Bio-tech, and the Semiconductor industry. They are used due to their ability to provide leak tight seals. These fittings can be remade.
The compression fitting is composed of an outer "compression nut" and an inner ring called a "ferrule" or "olive" in the UK. This is usually made of brass or copper. When the nut is tightened, it clamps-down on the ferrule, causing it to conform to the circumference of the pipe. Ferrules vary in shape and material according to the pipe material. To work properly, the ferrule must be oriented correctly. Typically the ferrule is fitted such that the longest sloping face of the ferrule faces away from the nut.
It is important to remember to not apply joint compound or teflon tape to a compression fitting's threads. The compression is the means of sealing the joint, not the sealing of the threads themselves. Pipe compound or teflon tape will frequently lead to a leak in the fitting by causing the fitting to loosen as a reaction to the compression. Joint compound is usually applied to the ferrule or Olive to seal imperfections in the fitting. In a standard threaded connection, pipe compound and teflon tape act to seal the threads from the water pressure.
In addition, it is critically important to the integrity of the fitting that excessive force is avoided in tightening the nut. If the fitting is overtightened, the ferrule will deform and cause leaks. Overtightening is the most common cause of leaks in compression fittings. As a general rule, a compression fitting should be "finger tight" and then tightened 1 turn with a wrench. The fitting should then be tested, and if slight weeping is observed, the fitting should be slowly tightened a bit more until the weeping stops.
A standard fitting can be installed using an ordinary wrench to tighten the surrounding nut. To remove it, a specialized pulling tool is often used to slide the nut and ferrule off the tube.