User Manual - P series
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6.2. Procedure C2: Diaphragm-actuated differential instrument
For reasons related to production and metrology, low- and medium-pressure differential instruments are adjusted
relative to each other, with the LP chamber vented to atmosphere.
The procedure is identical to the procedure described in the previous point (C.1. Single instrument).
The HP chamber is connected to the pressure bench, and the LP remains at atmospheric pressure.
6.3. Procedure C3: Bellows-actuated differential instrument
Example: Set the first threshold to 1 bar downwards and the second threshold to 5 bar upwards, with static pressure
10 bar.
6.3.1. Set the first LP switch threshold.
1. Inhibit the dead band spring (RE) by fully loosening the screw (VE).
2. Go up to the desired static pressure in both chambers (10 bar), and stabilise.
3. Isolate both chambers.
4. Create a pressure differential in favour of the HP chamber corresponding to lowering the first required
threshold “1 bar“ (HP=10 bar, LP=9 bar).
5. Using set point adjustment screw VG, relax range spring RG until the exact points when the two switches
are triggered on the way up.
6. Retighten until the exact point where the first threshold is triggered on the way down (LP switches).
6.3.2. Set the second HP switch threshold.
7. Return to the desired static pressure in both chambers (10 bar), and stabilise.
8. Isolate both chambers.
9. Fully extend spring RE.
10. Create a pressure differential in favour of the HP chamber equal to the second desired high threshold
value “5 bar“ (HP=10 bar, LP=5 bar).
11. Using dead band adjustment screw VE, relax dead band spring RE until the exact point when the second
threshold is triggered on the way up (HP switch).
6.3.3. Checking/adjusting thresholds
12. Repeat operations 2 and 3, and then slowly pressurise and depressurise the HP chamber to measure the
changeover values of the switches on the way up and the way down.
13. Fine-tune the settings using the threshold adjustment screw (RG = 1st threshold and RE = 2nd threshold).
14. Disconnect the instrument from the bench.
15. Apply a seal to adjustment screws VG and VE using a Georgin seal kit (torque: 1.7 N∙m ±10%).
16. Close the cover and tighten the two captive screws (torque: 1.2 N∙m).
