What is Mobrey in Steam Boilers?

Mobrey is an automatic boiler water level control included in the category of mountings and fittings in a steam boiler. Mobrey is usually found in smoke tube boilers due to its greater shell diameter compared to water tube boilers, regardless of the running capacity and working pressure of both types of boilers.

Mobrey is placed on the external of the smoke tube boilers, on the nozzles coming out of the boiler shell. It comprises a hollow cylindrical unit that hangs a float. The feed water is provided to the boiler shell by the feed pump to fill the shell. The water enters the hollow cylindrical of the mobrey through nozzles that cause the float to rise upwards.

As the steam boiler operates, the water gets heated and generates steam. As a result, the water in the boiler shell is reduced, leading to the float coming down as well. When the float covers a determined distance, the mobrey passes an electrical signal to the electrical panel that, resultantly, starts the feed pump to balance the water shortage. It causes the float to move up once again after refilling.

The coordination system between mobrey and feed pump is termed Cascade Control System. The Cascade Control System uses the output of the primary controller to influence the output of the secondary controller, as the second controller output is the required one. In this case, the primary controller is mobrey, and the secondary controller is the feed pump.

Components of Mobrey in Steam Boilers:

Modulating controller:

The modulating controller mounted on the steam boiler includes a chamber with a float and float rod attached to an actuator that moves freely up and down inside a steam tube around a mounted inductive coil A. The inductance of this coil varies by the movement of the actuator, changing in water level.

Modulating control valve:

Modulating control valve is placed in the boiler feed water line with an actuator and inductive coil B. The inductance of this coil varies by the movement of the valve spindle. The feedwater flow to the steam boiler is controlled by the modulating valve lid, operated by a piston, actuated by two solenoid valves on the modulating valve. The inlet solenoid valve allows water at feedline pressure to the cylinder and piston, reducing the modulating valve opening. The exhaust solenoid valve releases water from the cylinder and piston to increase the modulating valve opening.

Control box:

The control box includes a circuit board connecting mains input, solenoid valves, sensing coils, and the low-level alarm/burner cut-out functions. The control box identifies any difference in inductance balance between the modulating controller, thereby letting the appropriate solenoid valve to open.

Application of Mobrey in Steam Boilers:

Automatic cold start conditions:

It is utilized for all pumps capable of operating against closed discharge. With an increasing water level in the steam boiler, the modulating valve lid is decided by the capacity of the steam boiler.

Rising water level:

As the float rises, the actuator changes the inductance at coil A the control box detects the change and opens the inlet solenoid valve that allows feed pump pressure onto the piston to move the modulating valve lid downwards, reducing the flow of water into the steam boiler. The modulating valve continues its downward movement until the inductance at coil ‘B’ is in balance with coil ‘A’. The control box closes the inlet solenoid valve to lock the modulating valve in its new position.

Falling water level:

The falling water level is the reverse of the rising water level sequence, with the outlet solenoid valve releasing hydraulic pressure from the piston, causing the modulating valve to open. It results in increasing the flow of water to the steam boiler.

Conclusion:

Mobrey is essential equipment to maintain the water level in the steam boiler to enhance its overall safety in process operation by reducing manual intervention.

Rakhoh Boilers have been consistently contributing to the thermal sector since their inception in 1983. We have manufactured and successfully delivered our efficient and reliable steam boilers, waste heat recovery boilers, thermic fluid heaters, and boiler accessories in over 26 countries worldwide.

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