Since diaphragms are the high-wear component of most valves, we thought it would be useful to show some of the common failures that occur with diaphragms. In this article we will discuss the most common failures we have observed, and we’ll show an example of a specific case and how the problem was resolved.
Over the years we have seen or heard about various types of diaphragm failures. Most of them fall into one of two categories:
1. Chemical incompatibility
2. Incorrect assembly
Here is an example of chemical incompatability:


The diaphragm shown here was exposed to a 10% (2.5M) solution of NaOH overnight. Sometime during the night this failure occured.
The system where this diaphragm was installed was set-up with a downstream valve that was closed, and then the tank valve (where this diaphragm was installed) was opened. The piping from the downstream valve through the tank valve, and into and including the vessel, were flooded with NaOH. This solution was left in place overnight, with the tank valve left open during this time as well. In the morning the NaOH was found on the floor and, as you can see, the diaphragm was destroyed.
The customer, in this case, choose silicone because it was already approved in their system and, according to most chemical compatability/resistance charts (example chart), is rated as being minorly (0-5% swell) to moderately (5-10% swell) affected by sodium hydroxide. While these guides are useful starting points for choosing an elastomer, they are generally limited by type of exposure, time of exposure, and the elastomer is generally static not dynamic. These additional factors can have a significant affect on elastomer performance.
In this case, the major contributing factor to the destruction of this diaphragm was the high stress point combined with the level of compatability of the silicone with NaOH.
How can this be avoided? There were two options that were available to this customer:
1. Process change
2. Material change
Since there were factors that prevented a material change, the customer made a process change. After flooding the line, tank valve and vessel, the customer closed the tank valve – relieving the high stress point and preventing pre-mature material failure.
Have you experienced problems with a diaphragm? Let us know and we can work with you to resolve the problem. Send us an email or post a comment.
Chemical incompatability can be a difficult problem to resolve. In most cases you’re left with an increase in diaphragm replacement or a change in materials, and if you don’t have a certain material approved for use in your system it can be difficult to change to a more compatible material.
Next post: Incorrect assembly
©2006 ASEPCO Corporation