One of the major advantages of compression fittings is that the installer joins the tube by mechanical means. This heat-free system means no hot works permits are required, and joints can be made where it would otherwise be dangerous to use a naked flame. How do the two types differ? Why do large pipes require a different type of joint?
The major benefit of brass compression fittings
Compression joints can be taken apart and remade without adversely affecting their performance. Joints can be made on wet pipework, making them ideal for use in maintenance and repair applications where the complete draining of pipework is difficult.
Manufactured from duplex brass, dezincification resistant alloy (DZR) or gunmetal, the fitting type offers choice and versatility. Large compression joint systems are regularly used to join soft copper copper pipe (R220) These fittings have been developed and improved for well over fifty years and if connected correctly, are extremely reliable.
Two types of compression fittings
Type 'B' (Not covered here) or manipulative fittings are used with soft (R220) copper tube and require the installer to flare the tube end before the joint is assembled.
Type 'A' or non-manipulative fittings enable the installer to make a compression joint without carrying out any work on the tube ends other than ensuring that they are clean, burr free, and cut square.
Smaller sizes Type 'A' compression sizes (as above) start at 6mm and go up to 54mm and these joints are made by tightening the joint with two spanners. The joint consists of a body with a built-in stop to receive the tube, a compression ring the same size as the tube’s outside diameter, and a compression nut.
To make the joint, the tube and fitting are assembled, and the compression nut tightened with spanners.
This quick and simple action compresses the compression ring onto the tube, creating a sound mechanical joint.
Larger size between 67mm to 108mm are a different beast and use bolts to complete the joint.
Making Large Sized Joint
- A good hacksaw with a fine toothed blade
- Suitable burr removal tool
In general a hacksaw should be used to cut the pipe - tube cutters should not be used for this application. Ensure that the tube and fitting sizes are compatible.
Cut the tube end square but ensure tube retains its shape.
The tube will then make even contact with the tube stop in the body of the fitting.
Remove any burrs from the tube, both inside and out.
1. Place the flange and compression ring onto the tube.
2. Insert the tube firmly into the compression fitting, ensuring that the compression ring seats centrally in the fitting body and that the tube makes firm contact with the tube stop.
3. Bring up the compression flange, and tighten the nuts by hand. Using a spanner, continue to tighten the nuts diagonally in increments of half a turn, to a minimum of 2 two turns and a maximum of 2 and a half turns.
DO NOT OVER TIGHTEN. This may distort the flange or shear the nuts.
4. The compression flange should be parallel to the face of the body to indicate that a sound joint has been made.
5. If after assembling the joint a slight weep can be seen (as happens occasionally) it will readily be corrected by the application of a smear of an approved sealing compound to the sealing faces.