The valve on ours has three positions:
Vent - instrument essentially unusable
Fore Vac - seems to work just fine
High Vac - it's there for a reason...
It appears the FV position is to get decent vacuum before applying the
HV turbo pumps to avoid stressing them.
Maybe remove and clean the big o-ring and the grooves in which it
resides, and the thinnest coat of vacuum grease upon it -that fixed the
leaky HD amp housing here- before digging deeper into valve and tubing.
On 9/6/2019 3:50 AM, Wolfgang Bevern wrote:
> Hello Melanie,
> I think the amplifier housing should be evacuated in any case! The
> high-resistance resistors tolerate absolutely no moisture.
> We also had leaks in the area. As far as I can remember, it was once the
> three-way valve itself and once the hose connection to the amplifier
> Greeting Wofgang
> Am 06.09.2019 um 11:20 schrieb Melanie Gimpel:
>> Hi all,
>> some time ago I've asked for help for my unstable MAT 253 (poor
>> stability and no linearity). I got a lot of input of the community.
>> Thanks a lot for it! But until now, I couldn't solve the problem.
>> Embarrassingly I never had a look at the pumps. Otherwise, I would
>> have found out, that the amplifier housing is not evacuated (knob on
>> position "vent" instead of "HV") since we reinstalled the MAT 253.
>> Evacuation has failed, probably due to a leaky O-ring in the amplifier
>> housing or due to a defect pump valve? A service engineer left the
>> IRMS in this condition and assumed that measurement will be possible
>> without evacuation of the amplifier housing.
>> Is it probable that my problems concerning the stability and linearity
>> are caused by the amplifier housing? Has anyone experiences with this?
>> Unfortunately it isn't easy to get a new O-ring. Otherwise, I would
>> simply replace the O-ring.
>> Best regards
>> /// Wissenschaft im Dienst des Menschen ///