Brooks Instrument 5851i - Manual (Page 38)

4-10
Installation and Operation Manual
X-TMF-5851i-MFC-eng
Part Number: 541B109AAG
September, 2009
Brooks ® Model 5851 i
Section 4 Maintenance
& Troubleshooting
9. Install the coil assembly (2) over the valve stem assembly (6) and
secure with a jam nut (1).
10. Install the PC Board (15), secure with the bracket (24) and two screws.
Plug the connector from the sensor assembly onto the PC Board. The
flow arrow on the connector should be pointing toward the valve
assembly.
11. Install the electronics cover (23) on the controller, secure with three
screws (20). Plug the connector from the valve coil into the PC Board
through the hole in the electronics cover.
12. Prior to installation, leak and pressure test to any applicable pressure
requirements.
C. Adjusting the Control Valve
The 5851i control valve has been factory adjusted to insure proper
operation. Readjustment is only required if any of the following parts have
been replaced:
orifice (12)
valve stem (6)
plunger (7)
lower guide springs (8)
valve seat (11)
The valve is adjusted in Brooks Mass Flow Controllers by adding spacers
(9 and 10) to the control valve assembly to vary the air gap and initial
preload. Spacers are used to affect the proper adjustment because they
provide a reliable and repeatable means for adjustment. Screw type
adjustment mechanisms can change with pressure or vibration and
introduce an additional dynamic seal that is a potential leak site and source
for contamination. Refer to Figure 4-2 for spacer locations.
The preload determines the initial force that is required to raise the valve
seat off the orifice and start gas flow. If the preload is insufficient, the valve
will not fully close and gas will leak through. If the preload is excessive, the
magnetic force generated between the plunger and stem will be insufficient
to raise the plunger and the valve will not open.
The air gap is the space between the top of the plunger and stem. The air
gap determines the force between the plunger and stem at a given voltage
and the total travel of the valve. If the air gap is too small, the plunger travel
may be insufficient to fully open the valve. Also, the magnetic force may be
too high for a given valve coil voltage. If the air gap is too large, the
magnetic force will be insufficient to raise the plunger and the valve will not
open.
NOTE: Prior to starting the valve adjustment procedure, check to insure
that the orifice is properly seated and that the valve parts are not bent or
damaged.
Adjustment Procedure
(Refer to Section 5, Spare Parts for Spacer Kit)
a. Remove the electronics cover (23) from the controller. Insure that the
connector from the coil assembly (2) is properly reconnected to the PC
Board after the electronics cover is removed.
b. Perform the electrical and gas connections to the controller following
the instructions in Section 2 of this manual. Use a clean dry inert gas,
such as nitrogen, for this procedure. Do not apply gas pressure to the
controller at this time.