Honeywell SV2 Series User Manual page 84

SV2 Series Safety Shut-off Valves
Fig. 42: FARMOD orientation and pulse line connections.
The flow restrictors (O1 ... O4) are chosen such that the system will operate with airflow through the sensors (S1, S2a and S2b)
only. The sensor signals represent an airflow depending on the sensor pressure differentials.
Filters (F1 and F2) protect the sensors and flow restrictors against pollution. The S1 sensor signal depends on the differential of
the air and reference pressure, which in turn depend on the actual combustion airflow, and thus represents the actual airflow.
The S2b sensor signal depends on the differential of the air and gas pressure, which in turn depends on the actual combustion
air and gas pressure, and thus represents the gas pressure.
Note that the S1 and S2b signals do not represent the actual combustion air or gas flow values, but a derivative of the flows.
The SV2 Series Fuel/Air Ratio control depends on the ratios of the S1 and S2b signals, which are derived from the stored
amplification values at different burner loads during the commissioning of the appliance. The FARMOD sensor S2a and the
valve (CV) are part of the built-in safeguards to assure the plausibility of the sensor signals.
All sensor signals are fed to the SV2 Series electronics, which actuates the stepper motor controlled gas Flow Control Valve
(FCV) to the required gas flow to meet the required S2b value.
For ease of commissioning, the interface between the set-up tool (see the Accessories chapter of this manual for available set-
up tools), requires entry of the amplification factor [(Pgas – Pref)/(Pair – Pref)]. The SV2 Series electronics then translates the
entered amplification factor into the required S2b to S1 ratio.
Pressure Pick-up Point Requirements
Due to the flexibility of setting up the fuel/air ratio per specific burner load, some attention should be paid to the design of the
pressure pickup locations:
• To avoid a dynamic pressure behavior, the pressure pick-up should be perpendicular to the air, the fuel and, for the premix
reference pressure, the (fuel/air) mixture/flow.
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