Method for Differentially Pumping Endblock Seal Cavity

Abstract

A system for providing a seal between a rotating part and a stationary part that comprises two seals in series separated by a cavity is disclosed. The cavity may be at low pressure and failure of either seal may be detected by a change in cavity pressure. An alarm may be triggered when cavity pressure rises above a threshold, or when it remains above a threshold for more than a predetermined period of time. In a system comprising multiple cavities, a cavity may be selectively isolated to determine if a seal associated with that cavity is experiencing a leak.

1 .- 4 . (canceled) 
   
   
       5 . An apparatus that maintains vacuum integrity of a chamber that has a coupling, the coupling having movable parts in a vacuum environment mechanically coupled to movable parts external to the vacuum environment, comprising:
 a plurality of evacuated cavities, a cavity formed by a first seal between a static part and a movable part and a second seal between the static part and the movable part;   a manifold that is selectably connectable to individual ones of the plurality of evacuated cavities;   a pressure gauge that measures the pressure in the manifold; and   a source of vacuum connected to the manifold by a conduit that restricts the flow of gas from the manifold to the source of vacuum, such that the flow from the manifold to the source of vacuum is more restricted than the flow from a cavity to the manifold.   
   
   
       6 . The apparatus of  claim 5  wherein the conduit is a gas line that is of smaller cross-section than a gas line used to connect a cavity to the manifold. 
   
   
       7 . The apparatus of  claim 5  wherein the conduit includes a fixed orifice restrictor. 
   
   
       8 . The apparatus of  claim 5  wherein the pressure gauge is connected to a monitoring system that provides an alarm if the pressure measured by the pressure gauge exceeds a predetermined pressure for a predetermined period of time. 
   
   
       9 . The apparatus of  claim 5  wherein the source of vacuum is a vacuum pump or an evacuated volume. 
   
   
       10 . A method of detecting a leak in a chamber having a plurality of cavities, a cavity formed by a dual seal surrounding a rotating shaft, the plurality of cavities connected through a common conduit to a vacuum source, comprising:
 forming a vacuum in the plurality of cavities by connecting the plurality of cavities to the vacuum source through the common conduit;   selectively isolating individual cavities from the common conduit while monitoring pressure in the common conduit and while the vacuum source draws gas from the common conduit; and   identifying a leaking cavity by the pressure in the common conduit when the leaking cavity is isolated from the common conduit while the vacuum source draws gas from the common conduit.   
   
   
       11 . The method of  claim 10  wherein a leak is detected because the pressure in the common conduit exceeds a predetermined pressure for a predetermined time and the leaking cavity is identified when the pressure drops below the predetermined pressure in response to isolating the leaking cavity from the common conduit.