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Chapter 4 Maintenance Series 830/840/860 Instruction Manual
4-12 IM-83/84/86-H
840 L, M and H series
Valve Adjustment Procedure
The Sierra 840 L, M and H (low, medium or high-flow units) con-
trol the flow with a proportional electromagnetic valve that is set
up for certain process conditions. Variables, which affect their op-
eration, include orifice size, spring selection and adjustment, input
and output pressures and gas-flow orientation (horizontal or verti-
cal). If operating conditions change it may be necessary to make a
valve spring adjustment. An adjustment may also become neces-
sary due to a valve-seat depression or spring sag, both of which
can cause a change in the internal tension of the valve spring and
electrical current. An incorrectly adjusted valve can be detected by
OSCILLATION (UNSTABLE OUTPUT), NOT OBTAINING
MAXIMUM FLOW, OR LEAKAGE AT A ZERO SET
POINT (LEAK-BY).
The following valve adjustment procedure may correct the above
conditions.
Equipment needed:
L and M:
1/16” hex wrench
5/16” nut driver
H:
Standard screwdriver
3/8” nut driver
(Quick fix for leak-by). If your unit is experiencing leak-by, first
confirm that this condition is mechanical in nature rather than elec-
trical by shutting down the power. If leak-by stops (check for
downstream flow), the problem is electrical in nature and the in-
strument may require factory repair. If leak-by continues, the
problem is mechanical and may be fixed by an adjustment. Re-
move the small cover that is on top of the silver solenoid to the
right of the rectangular electronic enclosure. (On some 840L-units
this may require removing the plastic electronic enclosure to ex-
pose the valve coil.) With the power off, apply the appropriate in-
let pressure to the controller per the inlet/outlet operating pres-
sures listed on your label and apply a zero setpoint. Loosen the
lock nut. Adjust the center adjustment screw slowly clockwise
(increasing the spring tension) 1/4 turn at a time until this leak-by
subsides. (Putting your finger over the outlet fitting can confirm