Liquid level control is one of the most important considerations in the safety and overall function of facilities in the process industries including gas and oil, chemical, and food processing.
Liquid level control devices like valve bodies, float balls, and connectors, arms are an integral part of safety and quality standards with long-lasting and corrosion-resistant.
The float valve is also commonly known as a ball-cock, It is a small device used for regulating flow/level in tanks of liquid.
Since a float is employed in numerous industries and applications, float valves are absolutely mechanical in their operation.
The purpose of the float valve is to control the flow and fill the level of the tanks and stop overflow or overfilling while the valve connector connects the valve to the incoming liquid.
When the float rises to a selected level, the valve is then opened or closed by the lever attached to the float.
All the related components, the valve, float, and connector all work together to make sure that the liquid stays at the perfect set level with minimal monitoring required by the technicians.
In certain cases, one piece of control equipment may consists of more than one control items, e.g. a ball-float valve (ball-cock) which is a complete level controller loop in one package.
The float valve will have an air-filled ball, it will stop the water until a certain level is reached. Water can’t go back. The float ball valve is air-filled is available both in PVC, bronze, brass, or stainless steel.
In household applications such as overhead tanks, or bathroom cisterns, generally float valves close when the level rises but in industrial applications, the float valve closes the main valve opens.
The float valves are available in two types.
In the direct float control, the float valve rise with rise of liquid level in the tank.
In this simple arrangement, the main valve open or close by the movement of float valve arm unit.
As can be seen from the loop diagram, in the below figure, it illustrates a simple proportional controller.
The float valve is a assembly of measurement device, controller and also a final control device built into one unit. The measurement device is the ball-float itself.
The final control device is the valve, and the bell crank linkage is the controller which changes the direction of force by 90 degrees.
As with the increase in liquid level in the tank, float raise to close the pilot valve. The developed liquid on the upper chamber of the main control valve.
The upper chamber consists of a diaphragm that exert pressure on the main valve to close.
The float come down as with the level and allow liquid pass through the pilot line of float valve. Now the main valve gets open to allow liquid to fill in the tank.
The main valve may be located near the float valve or mounted at a suitable location, either nearer or away from float valve.
The float valve is selected based on the following process limitations.
Reference: Practical process control by A.M Seal.
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