CCS has created a few matrices that can be useful in determining the correct o-ring seal for a given pressure switch application. The o-ring seal is important in that it seals the pressure port to the rest of the pressure switch and prevents any leakage of the medium being sensed.
This picture shows a cutaway portion of the pressure port for a 604 series pressure switch. You can see the o-ring seal sits right below the polyimide diaphragm for the 604 series. The o-ring and the diaphragm both make direct contact with the medium so it is very important that they are both chemically compatible with that medium otherwise the seal could fail.
The first matrix that CCS has developed shows what O-Rings are available for a specific CCS hazardous or non-hazardous model.
The availability is color coded where green means that o-ring is standard for that model part number, yellow means the part is available but typically with a part number modifier or a suffix. For example in the 604G series a Viton O-ring would be available with the letter “A” as the part number modifier.
A red color means that the o-ring may be available for this part, however it may require a special part number and CCS must determine its availability for use. Teflon, Neoprene, and Fluorosilicone o-rings are typically o-rings that may be available that would require a special part number.
Another option available for some of our models is a 316 stainless steel welded capsule, designated by the letter “C” in CCS part numbers. This option eliminates the o-ring seal altogether and is the best option for very corrosive materials or very cold temperatures.
The next matrix compares the characteristic strengths and weaknesses of the various o-ring materials we have available, for example in the list below we see tensile strength, heat resistance, cold resistance, abrasion resistance, acid resistance, and others.
We can see that Teflon has universally excellent O-Ring properties, but they are typically a bit more expensive than a standard Buna-N O-ring. Usually Buna-N O-rings make a good enough seal for most non-corrosive applications.
Finally, our last matrix shows a large list of possible mediums that may be used in pressure applications and what the chemical compatibility those mediums are with each CCS O-Ring.
This chart comes directly from the Parker Hannifin o-ring guide and is truncated to feature the o-rings that CCS uses in their products.
In the chart a “1” means that the o-ring material and the medium being sensed is completely chemically compatible and will make a good seal. A “2” means that the two materials are fairly compatible and are still likely to make a good seal, however other factors such as cold, or heat may affect the properties to where a seal is no longer tight. A “3” means that the two chemicals are likely not compatible, and a “4” means that the two chemicals are completely incompatible. If an o-ring is rated a “3” or “4” in compatibility it should definitely not be used with that medium and a better o-ring or possibly a stainless steel welded capsule should be used.
As an example of this, to the right, we see that acetone is rated a “4” which is unsatisfactory for use with a Buna-N or Viton o-ring, however acetone for an Ethylene Propylene o-ring it is perfectly acceptable for use.