Vacuum closed venting valve

Claim 1

A venting valve comprising: a body having a first port which is open to atmosphere and an axially opposed second port which is, in use of the valve, located within a chamber to be evacuated; a valve member located in a cavity within the said body for axial movement therein; a venting passage extending axially through said valve member such that said venting passage connects said first and second ports when said valve member is in a first position within said cavity; spring biassing means located within said cavity to bias said valve member to said first position; first sealing means on said valve member slidingly engaged with the wall of said cavity and located adjacent said first port when said valve member is in said first position; second sealing means on said valve member spaced from said first sealing means; a valve chamber defined by the valve member, the first and second sealing means and the wall of said cavity, said valve chamber being closed from said second port by said second sealing means; and said valve member when said valve member is in a second position; a third port opening into said cavity to communicate with said valve chamber, said third port in use, being connected to a vacuum source such that sub-atmospheric pressure within the valve chamber causes the valve member to move axially against the spring biassing means to said second position whereupon said valve chamber is opened into communication with the second port, the valve further including passage sealing means which close said passage to isolate said first port from said second port when the valve member is in said second position.