Where to use single and double union ball valves
We are often asked to supply single union PVC ball valves. The main reason for this is that people look at the price and, as single union valves are cheaper, think that they will be OK. This is a decision that very often comes back to haunt the user, and sometimes the installer, with plastic pipe systems. This video sets out where single union ball valves are most appropriate for use (which is actually in very few situations). The general rule of thumb should be that if in doubt, install a double union valve.
So, is this because we will make more money from you…ummm…no, it is because if you ever need an access point, have a blockage or a leak or need to make a repair, you can simply unscrew the unions and take the valve body out of the line. As well as making the valve easy to service, this gives an access point for rodding should it be required and also gives a gap in the pipework. This availability of this gap is very important when repairs are required as it allows the plastic pipework to be moved enough, in one or another direction, to fit a pipe into a socket. Without such movement availability, the pipe would need to be cut in two places and additional unions fitted, to make a repair or retrofit.
Single union ball valves are relay only of use on the ends of plastic pipe lines, where the fluid flows out freely with no fixed pipes afterwards. In most cases, and if in any doubt...use a Double Union!