Often the question is asked why can we not replace one with the other. The general comment is that the double diaphragm is usually much cheaper and more commonly available?
DON'T DO IT!
Piston Diaphragm Spring Force (@25mm stroke)= 11000N
The piston type actuator or commonly known as a Tri-Stop is most often found on trucks and disc braked trailers. The reason for the 40% extra parking force is that the truck tractor is by law required to hold the truck and trailer fully laden on a 12% gradient. The additional force is required to stop a run away and the Tri-Stop has been designed and chosen for use on the Truck!
In addition, the Piston Diaphragm actuator has additional stroke and a more constant force over its actuation stroke which may be essential as the brake linings wear in a truck application. The double diaphragm actuator may have a shorter stroke than its equivalent size Tri Stop which may result in brake fade if used in the wrong application.
For additional information in this regard, CLICK HERE to contact your nearest WABCO branch and we will be happy to assist.