Spallation: what is it and why you should care about it?

Authors:   Charles Golub – Market Development Manager
Heidi Lennon -  Senior Research Engineer

Peristaltic pumping over compresses the tube in order to form the seal that enables positive displacement of a liquid.  This over compression is referred to as percent occlusion. The occlusion required for peristaltic pumping causes the polymeric material to be exposed to a shear-compression force. Some materials do not perform well under shear and can form micro defects resulting in portions of the tube to come off in the fluid path and/or on the roller assembly. The external spallation can sometimes be confused for a grease or wax like build-up on the pump roller and housing.  A critical consideration that is understated is that the rate of spallation generation as well as the size particulates can vary greatly even within the same family of materials. This means that not all PVC’s will have the same spallation profiles, and the same is true for silicones. 

Peristaltic pumping will always have some level of spallation, but it is important to understand the size and amount of spallation that is critical in your specific application.  In some pharmaceutical applications, smaller particles can affect the drugs manufactured, but larger particles can often be easily filtered out.  However, in many medical procedures, larger particles can be more critical since the smaller particles pose less of a threat towards the occurrence of an adverse health event.  

Spallation within medical procedures have been widely studied, but most of the literature published only looks at material classes, not at factors within each material family.  In looking at silicone families there are many different formulations that change things like: durometer, crosslink density, modulus, and even catalyst systems used, all of which will affect how a tube spallates. PVC formulations can be drastically different based on plasticizers used, stabilizers, and types of PVC resins; each of which will result in changes in how they behave. There are so many factors in material formulations that can impact how they wear that for pump manufacturers it is important to collaborate with a tube manufacturer who has an understanding of this and can work to provide technical support. 

If you are looking only at material families for your spallation profile, you may be missing a unique opportunity to balance the pump performance you want with the spallation profile that is critical to your application. 

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