Gilles' Outlet

November 29, 2009

Installing a compression stop valve

Filed under: Plumbing — Gilles @ 5:35 am

A stubbed out copper pipe is cut and a compression stop valve is installed.


Skill Level: 2 (Basic)

Time Taken: About 15 minutes

Earlier, a cold water supply line for a toilet was roughed in and capped. It is now time to connect the toilet so the copper cap needs to be removed and replaced by a stop valve.

Stop valves make it possible to shut off water at a specific fixture (sinks, toilets …) without having to shut off the water for the whole house. This ability is currently required by plumbing codes, specifically for sinks and toilets.

Before getting too involved with this project and went and shut the water off at the main house shutoff valve. I opened a faucet at the highest point and a faucet at the lowest point, to let the water currently in pipes to drain. It is important to open a faucet at the highest point to let air enter the fresh water piping.

Left: Materials for this project. From left to right:

  • a compression stop valve (1/2 input – 3/8 O.D. output),
  • a silver cover plate to give the project a more finished look

Stop valves can be attached to water piping using two different methods: soldering (the valve gets soldered to the pipe with a torch) or compression (the valve uses a brass mechanism which grabs the copper pipe to achieve a tight seal).

Compression stop valves can be installed and removed easily without soldering. This has made them the preferred stop valve choice for most pros and home owners.

Right: Tools for this project. From left to right:

  • a copper pipe cutter,
  • two adjustable wrenches

Left: I measured about 2’’ from the wall and marked that location with a pen.

Right: I positioned the pipe cutter on the line previously marked and turned the wheel so it was tight around the pipe. The whole cutter is then turned one full turn around the pipe. The scoring wheel makes a small mark in the pipe.

The screw is then tightened slightly and the cutter is turned around the pipe one more time, making the dent deeper. The process is repeated until the pipe is cut.

During the operation, I placed a shallow bucket under the pipe to catch residual water.

Left: the pipe has just been cut. There was still a fair amount of water waiting to drain from the system. I decided to proceed immediately instead of waiting for the whole system to drain.


Right: The pipe cutter leaves burrs inside the pipe so used the reamer on the back of the pipe cutter to remove all copper burrs inside the pipe.

Leaving burrs inside the pipe can cause noise when water is flowing so it is always strongly recommended to ream freshly cut pipes.

Left: I slipped a decorative plate over the pipe. This gives the project a finished look.


Right: The compression stop valve with its business end unassembled. From left to right: the compression nut, the brass ferrule, the valve body. The ferrule gets compressed onto the copper pipe. This causes a water tight seal to be produced.

The ferrule can only be used once: every time the stop valve is removed and re-installed,the ferrule must be replaced.

Left: First, I slipped the nut over the pipe then …

Right: … I slipped the ferrule. It is a tight fit.

Left: I inserted the valve body over the pipe until it bottomed out.


Right: I threaded and tightened the nut by hand, still making sure the valve body remained pushed against the pipe. This is necessary to achieve a long lasting, leak free installation.

Left: When I could no longer tighten the nut by hand, I used two adjustable wrenches to tighten the valve further. One wrench is set on the nut, the other is set on the valve body. I like to use the longer wrench on the nut – this gives me more leverage.

As I tightened, I made sure the output of the valve stayed perfectly vertical.

Unfortunately, I could not take the picture and hold both wrenches at the same time.


Right: Detail of the valve which both wrenches engaged. The valve body acts as a nut.


It is possible to over-tighten a compression fitting. I use the following procedure:

  1. Tighten by hand until no longer possible
  2. Use the wrenches to make at most two additional turns
  3. Turn the water back on and if the fitting leaks, progressively tighten more until the leak stops.

Tools Used:

  • Pipe cutter 
  • Adjustable wrench (2)
  • Pen
  • Measuring tape
  • Bucket
  • Rag

Materials Used:

  • Compression multi-turn angle valve (1/2’’ I.D. – 3/8’’ O.D.)
  • Escutcheon plate (1/2’’ I.D> – 5/8’’ O.D.)


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