Cleaning The Series 421 Sensor - MKS HPS 937A Series Owner's Operation And Maintenance Manual

To disassemble the Sensor, remove the backshell subassembly as follows
(Steps 1 through 4 are not necessary when replacing internal parts):
1 Remove the two 4-40 x ¼" Phillips head SEMS screws
the backshell
2 Remove the two 4-40 x ¼" button head screws
Use needle nose pliers to pull the #22 contact
3
ion current feedthrough
Pull the #20 contact
4
bulkhead 4
from the bulkhead).
5 Remove the six ¼-28 x 0.875" socket head cap screws
the back flange
lubricity and should be used only once. They may be relubricated with
a dry lubricant such as molybdenum disulfide, though new silver-
plated screws are recommended. The copper gasket
replaced with a standard 2
The cathode and anode assemblies are attached to the flange. Here
disassembly generally proceeds from bottom to top of the internal
assembly drawing.
To remove the cathode
6
ears hooked over the shoulder of the ceramic insulating support
7 Gently pull up on the ear until it just clears the outer diameter of the
insulating support .
the position of the small Elgiloy
current feedthrough
cathode with respect to the leaf is not critical, but take care to not
bend the leaf .
8 Slide the cathode
9 The insulating support is captured by the guard bolt
with a spanner wrench and unscrew the guard bolt from the flange .
the presence of the small curved spring washer
the guard bolt . The spring washer holds the insulating support tight,
preloads the guard bolt to resist unscrewing due to possible vibration,
and provides compliance for differential thermal expansion during bakeout.

Cleaning the Series 421 Sensor

The procedure for cleaning the internal parts of the 421 sensor is the same as
that used for the Series 423 I-MAG Cold Cathode Sensor (see p. A.3).
A.8
off the sensor.
9
17 .
7 off of the 5kV feedthrough taking the entire
with it (do not remove the SHV and SMA connectors
free. Note that these screws are silver-plated for
13
1
/8" CF flange gasket.
23 , release the two integral, spring-loaded
®
leaf
to the cathode . Rotational position of the
17
and washer
23 22
937A Multi-Sensor System
and slide
2
.
1
8 carefully off of the
and pull
10
24 must be
used to connect the ion
18
off the insulating support .
. Remove
21
under the head of
20
.
19
13