MDC bakeable all-metal angle and inline
valves are designed for use in ultrahigh vacuum environments where elevated
temperatures preclude the use of elastomers and low temperature gasket
metals. These valves provide reliable high temperature seals from atmospheric
pressures to below 10-11 Torr. 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.
When operated at ambient temperatures,
all-metal valves provide hundreds of leak
free cycles between routine poppet gasket
replacements. In high temperature
applications, life cycles are inversely
proportional to the bakeout temperatures. When operated at the maximum bakeout
temperature of 450°C, the poppet seal
gasket life is reduced to approximately 50
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.
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.
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