WP #6472 

Today I modified the electric actuators (LLCVs) controlling CP4, CP3, CP6 and CP5 (the mid-stations).  I will do the four remaining ones (end-stations and corner-station) during this upcoming Tuesday maintenance day.  This process required pulling the vacuum rack fuses for the 24VDC supplying the actuators and the 4-20 mA read back signals.  For some unknown reason, it appears that the PT245A pirani interlock was disabled as a result of pulling these fuses.  This, in turn, caused PT245B to be disabled.  We will investigate (some new Beckhoff interrelationship? Voltage spike via common DC pwr supply?).  

The "as found" problem needing fixing is that water has been entering the actuator housings due to a lack of sealing where the 1/2" conduit elbow threads into the housings.  The issue is that the tapped hole is too tight/shallow effectively preventing the "Seal Tight" plastic elbow from penetrating deep enough so as to compress its sealing O-ring (see attached image).  I remedied this by running a tap deeper into the hole (see attached image).  Now the sealing O-ring is compressed and should be water tight (see attached image).  Embracing my eternal pessimism, I went ahead and drilled and tapped a drain hole (see attached images) which should prevent the level of water from rising high enough within the housing to cause any problems should water some how still get into the housing.  The hose was added to allow for a later insertion of steel wool to discourage insect entry into the housing (see attached image).