Gerardo, Janos

Today at ~9 am the actuation range of CP7's LLCV valve was shifted towards "more open". This was necessary, as the actuator could not open up enough to maintain the 92% LN2 content in the cryopump's LN2 reservoir, if the LN2 amount in the dewar was less than ~40% (more data about this issue can be found in aLog 84846).
The lowest impact solution was to add a shim washer between the bonnet and the cast aluminum frame of the actuator. On the valve's drawing, the bonnet is no. 2 (on the drawing, the actuator frame is not highlighted). The procedure was simple: loosen the locknut (no. 12), lift the actuator assembly (along with the stem), and put a shim washer between it an the bonnet. In order to reach the nut, the only suitable tool is a so-called crowfoot-wrench (see in the picture, along with the U-shaped shim washer).
The thickness of the shim washer is 0.1"; the change on the valve "openness" is ~15% (from 95% to 80%). This is enough to handle the issue, however, the stem and/or the whole valve assembly needs replacement or cleaning in the long run, as either there is contamination at the orifice, or the stem is not properly assembled (too long). This will be handled after O4.