Rupture disks are designed for reliable emergency relief of excess pressure since they instantaneously rupture at a specific predetermined pressure range. Model BP420 rupture disk is designed specifically for use in plastic extruders. Each assembly consists of a stainless steel body and rupture disk. A rupture disk may be specified for primary relief in applications where pressure build-up can occur so rapidly that the response time of a relief valve is inadequate, such as in a polymerization reaction vessel.