Brooks Instrument 5850E - Manual (Page 42)

4-10
Installation and Operation Manual
X-TMF-5850E-MFC-eng
Part Number: 541B102AAG
September, 2009
Section 4 Maitenance &
Troubleshooting
Brooks ® Model 5850E
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 not be
sufficient to raise the plunger and the valve will not open.
The airgap is the space between the top of the plunger and stem. The
airgap determines the force between the plunger and stem at a given
voltage and the total travel of the valve. If the airgap is too small, the
plunger travel may not be sufficient to fully open the valve. Also, the
magnetic force may be too high for a given valve coil voltage. If the airgap
is too large, the magnetic force will not be sufficient 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.
1. Adjustment Procedure (Refer to Section 5, Spare Parts, for the 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.
c. Disassemble the control valve following the procedure given in
Section 4-4a, above. Note the number, locations and thicknesses of
all the spacers (9 and 10).
d. Decrease the preload of the valve by 0.005 inches either by remov-
ing a 0.005" small preload spacer or by adding a 0.005" large
preload spacer. Refer to Fig.4-2.
e. Reassemble the valve following the assembly procedure in Section
4-4a.
f. Command 0% flow, apply normal operating pressure and check for
valve leak-through by observing the output signal.
g. If the valve leaks-through, increase the preload by 0.005" and go to
Step h. If the valve does not leak-through, repeat Steps d, e, f and g.
h. Apply the normal operating gas pressure and command 100% flow
(5.000 Volts on Terminal A, Pin 2).
Note: Due to possible heat capacity and density differences between
the test gas and actual process gas for which the mass flow control-
ler was sized, it may be necessary to increase the inlet pressure to
obtain proper control at 100% flow.
i. Measure the valve voltage by connecting a voltmeter between Test
Point 3 (TP3) and Test Point 4 (TP4). Refer to Figure 4-3.
Valve Voltage =
(1.53 x TP3) + 20.7
j1. If the flow controller output signal is 100% (5.0V) and the valve
voltage is less than 11.5 Volts, the valve adjustment is complete.