|McLeod Gauge Information relating to reading,
actuation of plunger / magnetic assembly.
a thin layer of vacuum grease is highly recommended for assembly. The gauge will degas
rapidly when the gauge is leak tight and connected to a good vacuum pump. The gauge can be
actuated up and down into the red indicator fluid and when no bubbles (excess gas) are
apparent the gauge is degassed (at vacuum) and ready for use. If the gauge is going to be
in use regularly during the day, the maintenance of the gauge at full vacuum pressure is
recommended to assure limiting the need for degassing prior to use.
The inner glass bell / scale assembly of the gauge has some
metal pieces at the assemblies top. One of these items is a small magnet. Actuation when
reading of the gauge is accomplished by using the magnetism of the large outside magnet
(2" OD) and by slowly lowering the inner bulb into the red vacuum reading liquid at
the bottom of the gauge until the mercury is engaged and the gauge scales.
When finished reading a vacuum pressure, the inside
assembly can be "parked" at the top of the gauge. This is accomplished with the
large magnet physically, not using the gauge magnetism. The magnetism is primarily for
inner gauge actuation. It is possible to "park" the gauge by using the knurled
aluminum piece at the top of the outside of the gauge. Adjusting this knurled knob up so
that the inside lip of the large magnet housing assembly (2" OD), is able to catch
top of gauge tube on which the large magnet assembly rides.
It is advantageous to have the gauge in a location that is
relatively vibration free and where it is not going to be disturbed. Remember, all that is
holding the inner bulb up is the magnetism of the gauge, it is possible for the gauge
inner bulb to be accidentally knocked down. Although it a short fall, and it often happens
here, it has the potential to damage the inside bulb.
There is really no difficulty with parking the gauge in the
down position because of the rapid degass times of the gauge. If the gauge is maintained
at full vacuum, degass times become very small or even non-existent.
Use off a good vacuum valve off the inlet of the gauge
allows for the gauge to be quickly moved from point to point before adjusting for a new
reading. Simply allow some time for evacuation of your tubing before opening the valve.