1. Main Boiler Feedwater Control Valve
This control valve is used to control the boiler drum level to ensure that there is always enough feedwater in the boiler to generate steam. The boiler feedwater control valve must have an equal-percentage characteristic to compensate for the difference between the characteristic of the boiler feedwater pump and the boiler itself (Arca Ecotrol® Series 8C and 6H and Series 350 and 380).

2. Filling / Boiler Feedwater Control Valve
This control valve fills the boiler drum when the plant is started. Significant differential pressures and cavitation must be controlled at this time, subjecting the valve to high forces whcih may lead to excessive wear. Often small in design, these valves are equipped with hard, graduated valve trims and are positioned parallel to the main boiler feedwater control valve (Arca Ecotrol® Series 8C and 6H and Series 190 and 350).

3. Burner Control Valve
These burner control valves regulate the supply of natural gas to the gas burner or heating oil to the oil burner in the boiler. During gas operation, these valves regulate to maintain the defined control characteristic and reduce any noise. When heating oil is used, this valve functions as an overflow valve and keeps the pressure upstream of the oil burner nozzle constant (Arca Ecotrol® Series 8C and 6N).

4. Sludge Control Valve
This valve will open quickly for a brief moment to drain a small quantity of boiler feedwater for desludging the boiler water drum. Hard wearing internal components are required to withstand the high differential pressure, cavitation, and abrasion that present. The seat surfaces of this control valve are subject to severe wear, which is why Arca recommend installing an additional shut-off valve here (Arca Ecotrol® Series 8C and 6H and Series 190, 350 and 380).

5. Start-Up Control Valve
This start-up control valve will typically blow steam through a silencer system into the atmosphere when the boiler is started. The valve will almost always have an asymmetrical shape because the steam will expand when the pressure is suddenly reduced (Arca Ecotrol® Series 8C and 6H and Series 350 and  380).

6. Soot Blower Control Valve
The walls of the heat exchangers in the boiler are steam-cleaned to remove soot particles which optimizes heat transfer efficiency inside the boiler. These sootblower control valves feed live steam to the sootblower nozzles with a quick response time (Arca Ecotrol® Series 6H and Series 190, 350 and 380).

7. Air Preheater Control Valve
Air to the burner is preheated to optimize the effectiveness of the combustion process. The temperature of the air to the burner is determined by the steam fed to the air preheater via this control valve (Arca Ecotrol® Series 8C and 6N).

8. 3-Way Mixing Valve (Variant I)
While running, the steam to the turbines is superheated to increase plant efficiency and prevent the turbine blades being damaged by any condensed drops of liquid. An intermediate superheating facility is installed for power plants with higher steam pressures in order to better harness the energy produced by the steam. The heat transferred to this superheater varies greatly due to fluctuating loads and soot deposits in particular. The temperature of this superheater must therefore be regulated. To achieve this, hot steam is channeled through a serpentine in the water-filled section of the steam drum via the 3-way mixing valve. The colder drum water, at saturated steam temperature, then cools the hot steam (Arca Series 200 and 220).

9. Injection Cooler (Variant II)
Another common way of controlling the superheater temperature for new plants is to inject boiler feedwater using a controllable injection cooler / desuperheater (Arca Series 590).

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