Brooks Instrument 5850i - Manual (Page 38)

Brooks ® Model 5850i
4-10
Section 4 Maintenance Installation and Operation Manual
X-TMF-5850i-MFC-eng
Part Number: 541B108AAG
December, 2008
Tighten the assembly until there is no looseness, but do not over-
tighten.
7. Install the valve plunger assembly (7, 8, 9 and 11)(NC Valve) or
(35,31,32,8,9,11)(NO Valve) on the preload spacers (10). Install air gap
spacers (10), if used on top of the valve spring.
8. Install the valve stem assembly (6), secure with the valve retaining plate
(4) and four hex socket screws (3). When installing the screws they
should first make light contact with the plate, which should be checked
to insure that it makes full contact around the stem assembly. Torque
the screws securing the valve retaining plate in diagonal pattern (Refer
to Figure 4-1) to 17 in/lbs.
9. Install the coil assembly (2) over the valve stem assembly (6)(NC
Valve) or (34)(NO Valve) install extension spacer nut (3)(NO Valve) and
secure with jam nut (1).
10.Install the printed circuit (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
vessel codes.
C. Adjusting the Control Valve
The 5850i 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