Chapter 4 Maintenance | Series 830/840/860 Instruction Manual |
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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
