Editing Compression fitting (section)

==Operation principle==
In small sizes, the compression fitting is composed of an outer ''compression nut'' and an inner ''compression ring'' (ferrule) that is typically made of brass, copper, or steel.  Ferrules vary in shape and material but are most commonly in the shape of a ring with beveled edges. To work properly, the ferrule must be oriented correctly, in the case of copper olives they are normally barrel shaped and this means they cannot be fitted incorrectly, but where this is not so, particularly in Hydraulic and high pressure applications, the ferrule is fitted such that the longest sloping face of the ferrule faces away from the nut.
[[File:Fitok_Tube_Fittings.jpg|thumb|Fitok tube fittings]]
When the nut is tightened, the ferrule is compressed between the nut and the receiving fitting; causing both ends of barrel shaped copper olives to be clamped around the pipe when the middle of the ferrule bows away from the pipe, in the case of hydraulic style ferrules they currently have one end which is larger with a 45 degree chamfer which tapers away  (from installation contact with the nut) and the small end generally has two internal biting edges, for applications demanding much higher pressure, that penetrate the  outside diameter of the tube, the fittings must be tightened to guidelines as per DIN2353 as not to exceed the elastic limit of the steel ferrules, The result is that the ferrule seals the space between the pipe, nut, and receiving fitting, thereby forming a tight joint. The clamping support of the pipe by the force at the taper at both ends help prevent movement of the pipe in the fitting, but it is only the taper at the receiving fitting itself that needs to seal completely, since if it does seal (to both the pipe and the compression fitting) then no fluid can get to the nut threads or the taper at the nut end to result in any leaks. As a result, some similar fittings can be made using an olive with only one taper (or a fixed cone sealed to the pipe) where the sealing at that taper prevents fluid from reaching the nut.

Larger sizes of compression fitting do not have a single nut to compress the ferrule but a flange with a ring of bolts that performs this task. The bolts have to be tightened evenly.

Thread sealants such as joint compound ([[pipe dope]] or [[thread seal tape]] such as [[PTFE]] tape) are unnecessary on compression fitting threads, as it is not the thread that seals the joint but rather the compression of the ferrule between the nut and pipe. However, a small amount of [[silicone grease|plumber's grease]] or light oil applied to the threads will provide lubrication to help ensure a smooth, consistent tightening of the compression nut.

It is critical to avoid over-tightening the nut or else the integrity of the compression fitting will be compromised by the excessive force. If the nut is overtightened the ferrule will deform improperly causing the joint to fail. Indeed, overtightening is the most common cause of leaks in compression fittings. A good rule of thumb is to tighten the nut first by hand until it is too difficult to continue and then tighten the nut one half-turn more with the aid of a wrench; the actual amount varies with the size of the fitting, as a larger one requires less tightening. The fitting is then tested: if slight weeping is observed, the fitting is gradually tightened until the weeping stops.

The integrity of the compression fitting is determined by the ferrule, which is easily prone to damage. Thus care should be taken when handling and tightening the fitting, although if the ferrule is damaged it is easily replaced.