Compression Fittings: What They Are & How To Use Them

What are compression fittings?

A compression fitting has three components: the body of the fitting, a brass olive and a threaded compression nut. As the compression nut is screwed onto the fitting it squeezes the olive against the pipe and makes a completely waterproof seal.

They can also be used for connecting a gas supply, where the assembly technique is similar to that for water. However, the UK’s Gas Safety Regulations make it illegal for anyone other than a Gas Safe registered engineer to install or work on a gas appliance.

What are the benefits of using compression fittings?

While plumbers tend to have their preferred methods of joining pipes and fittings, compression joints offer several advantages that are particularly useful for DIY plumbers but are also appreciated by professionals.

Compression joints are easy to assemble without special tools or skills

Soldered pipe joints require special tools and the skill to use them so that each joint is guaranteed to be watertight. In contrast, compression fittings only require one adjustable wrench to hold the fitting and another to tighten the compression nut.

Compression fittings don’t require heat or naked flames

Soldered joints also carry a risk of fire as a blowtorch is used to melt the solder. As no heat is required to make a compression joint, this is another advantage for the DIY plumber but also for professionals working on sites where a hot works permit cannot be given, or in situations where a naked flame carries a particular risk.

Compression joints can be made in wet conditions

Plumbers don’t always have the luxury of a dry working environment or an empty plumbing system. If they are working in damp conditions or repairing a leak in an existing system, Compression fittings eliminate the need to drain and dry the pipework before making the joint.

Compression joints can be undone and reassembled

Unlike soldered joints, the compression nut can be unscrewed and the joint taken apart for repairs or maintenance and then reassembled. Again, this can be done with water present.

Compression fittings can be reused

If a plumbing system that features compression fittings is removed or reconfigured for any reason, the compression fittings can be salvaged and reused on another installation, saving costs and reducing construction waste. All that is needed to make a new compression joint is an inexpensive replacement olive.

Compression fittings can be used with different pipe materials

While soldered joints are only compatible with copper pipe, providing the installation instructions for the pipe type are followed correctly, compression fittings can be used with copper, stainless steel, carbon steel and plastic pipe with copper inserts.

How do you make a compression joint?

To make a compression joint, you will need a few tools which are likely to already be in your tool bag or are inexpensive to buy for the job.

• You will need something to cut the pipe to length; we recommend the type that rotates around the pipe, gradually tightening blades against the pipe to cut through it, as this offers the fastest, cleanest cut.
• You will also need a deburring tool to clean up the inside of the cut pipe end. Some pipe cutters even feature an integral deburrer.
• Finally, you will need two adjustable wrenches to tighten the joint. A plumber’s wrench is easily adjusted and allows you to tightly grip the body of the compression fitting, while an adjustable spanner can be set to the correct size for the compression nut and will offer a better grip on its flat surfaces.

1. Cut the pipe to length

Measure and cut the pipe to the correct length. This should be such that the end of the pipe rests firmly against the backstop inside the fitting.

1. Deburr the pipe

Even with a rotary pipe cutter, a slight burr will be left on the cut end of the pipe which can prevent a tight seal and release particles into your plumbing system. Use your deburring tool to remove this and create a clean, even edge, taking care to prevent any debris from dropping into the pipe.

1. Assemble the compression fitting

Place the compression nut onto the pipe with the ‘open’ end of the nut facing the end of the pipe. Follow this with the olive, positioning this so that it fits flush with the end of the pipe.

Carefully push the end of the pipe into the compression fitting, pressing until it is seated against the backstop inside the fitting. Holding the fitting and pipe together with one hand use your other hand to screw the compression nut onto the fitting as tightly as you can with your fingers.

1. Tighten the compression fitting

Use your adjustable wrenches to hold the compression fitting and tighten the compression nut. Use reasonable force to ensure a snug fit without over-tightening, as this can damage the pipe or fitting and result in leaks. Stop tightening as soon as the nut stops turning.

1. Test your system

Once all your pipes and fittings have been connected and the system is sealed, turn on the water supply and check each fitting for leaks. Slight leaks may be fixed by tightening the compression nut a bit further, but larger leaks may require you to turn off the water and disassemble the joint to check for damage or incorrect assembly.

We hope you have found this information interesting and helpful. If you have any further questions you are always welcome to call our friendly team of experts on 01420 555600 or email [email protected]. 

Also, look out for more articles in our ongoing series of blog posts, bringing you useful information, insights, guides and tips on all things drainage!