Can I Substitute a Plastic Valve for a Metal Valve?

Plastic Valves Installed in a Metal Piping System

Many times people with a metal piping system are attracted to a plastic valve or strainer because of its low cost compared to a stainless steel or bronze one. And also for all of the benefits plastic offers.

The engineer that designed that system chose metal pipe for a specific application reason so you have to make sure a plastic component will work.

Plastic components can, however, be used successfully in metal systems. But you have to be aware of several factors that will affect the success of the application. If these factors are not taken into consideration the chance of success is reduced. Applied and installed correctly, however, the valve or strainer will perform as expected.

First, you have to be sure that the plastic valve or strainer will be used within its temperature and pressure rating. Metal piping is often used because of high operating temperatures. Make sure the temperature/pressure range of the application is within the acceptable range for the plastic product you are considering. Chemical resistance needs to be checked, as well, to ensure that there will not be a problem. Part of your application analysis should include the potential for shock pressure generation, i.e., water hammer in the system that could damage the plastic valve or strainer. Things to look for include a system flow rate of greater than 8 feet per second, quick starting pumps, positive displacement pumps, fast opening or closing actuated valves, and solenoid valves.

Once it's determined that ALL of the application parameters are OK for the plastic component, it is impotrant to look at how the plastic component is installed.

Stress on the plastic valve or strainer is the single most important installation factor to consider. Stress can cause immediate damage or it can build up over time and cause damage later on. There are several ways that this stress can be induced during installation and/or operation.

One is improper alignment of the plastic component in the metal piping system. If either one has to be forced into position, it ís sure to cause problems. A second problem to look out for is oversize face-to-face dimensions of the mating pipe flanges, as well as misalignment of the flanges.

Thermal expansion can be a problem is some applications. Expansion joints can help compensate for this. Another solution is to install plastic pipe on the inlet and outlet of the valve or strainer to isolate it from the metal pipe.

Plastic valves and pipeline strainers can be used successfully in many metal piping systems. You just have to be aware of all of the application parameters and how they relate to the plastic component. Not all applications are the same and the recommendations that have been made here may not apply in all cases.