Dewar

We have had some failures of the StanCam dewar temperature and pressure. During an inspection it was found that the O-rings for both the pressure and vacuum sensor were damaged and needed replacing. Since all the O-rings are the same age it was decided to replace them all. Details for all the O-rings were requested from Copenhagen and two full sets have been purchased.

Some of the O-rings have been replaced, but to minimise the risk of damaging the CCD the O-rings for the connections to the CCD were left untouched. After pumping and starting to cool it was clear there was a problem with the vacuum and the dewar was warmed up. Since the size of the O-ring specified for the dewar window was slightly different to the original, the old O-ring was put in again and all the other O-rings checked. After this, the vacuum has been maintained properly.