The PD and PDL valves are provided with non-metallic plates. The thermoplastic materials special chemical properties make them suitable for a wide range of gases, from inert to those with aggressive components and presence of impurities.

Amongst the available compounds the most used one is glass fibre filled Peek™ in alternative to other thermoplastic materials such as carbon fibre filled Peek™ which is more suitable at working also at high temperatures. The PDLT series distinguishes itself for the use of thermoplastic caps protecting the spring by eliminating the metal contact between the spring and its housing cavity. Such spring protections may be in different configuration