Wherever possible, bonnet gasket seals have been eliminated in an effort to minimize the number of potential leak paths. Valves fitted with bonnet seals have been so designed to facilitate gasket replacement. The size and orientation of the valve body ports on bonnet fitted valves precludes gasket removal through its ports. 

Seal Design
A vacuum seal is made by pressing the poppet OFE copper gasket onto a conical stainless steel knife edge seat as depicted in the diagram at top-right. The sealing pressure deforms the copper gasket, which conforms to the conical knife-edge seat. During thermal cycling the valve’s loading mechanism counteracts component differential expansion to maintain a uniform pressure necessary for seal integrity. 

Poppet Gasket Replacement
Poppet gasket replacement for the 1-1/2" and 2-1/2" all-metal angle valves must be done by removing the valve from the system, as these two valves have welded bonnets. Once detached from the system, gasket replacement is easily accomplished by inserting a standard blade screw driver into the bottom port and unscrewing the copper gasket, which is then extracted through the side port of the valve. The 3/4" angle valve and all inline valves are fitted with bonnet seals and do not require complete removal from the system for gasket replacement. Gasket removal and replacement is performed by detaching the bonnet flange from the valve body. Once the bonnet has been opened the gasket is easily detached by unscrewing with a standard blade screw driver.

Seal Torque
The first seal or closure in an all-metal valve causes plastic deformation of a virgin copper gasket leaving a permanent impression. This first closure is made at the factory and shipped to the customer in a ready to install sealed condition. Upon breaking this seal, resealing can be accomplished by torquing the valve according to the “Poppet Sealing Torque” data found in the specifications chart. To aid in the process of subsequent seal cycles the top of each valve body is fitted with a radially graduated vernier plate. The vernier plate provides a visual cue for previous and subsequent cycle or torque positions.

Valve Compatibility
MDC offers Varian and Vacuum Generators (VG ) compatible all-metal angle and inline valves. The Varian compatible valves have been labeled as "V" in the valve type column found in each product table. Vacuum Generators compatible valves are identified by a "VG" designation in the valve type column. Compatibility is defined herein as the ability to replace or interchange Varian and/or Vacuum Generators valves with MDC all-metal valves. Compatibility is limited to valves fitted with Del-Seal™ CF port flanges and exclusively to the port to port dimensional  characteristics. In other words, the dimensions from any valves’ flanged port centerline to the opposite ports’ flange face are direct equivalents to Varian and VG valves. Other MDC all-metal valve dimensions may vary from those found on Varian and Vacuum Generators products. The "T" designation in the valve type column pertains to valves designed for either tube weld installation or custom flange attachment.