Principle Operations of the Regulation Units - Essay Example

• Modify pressure in any system depending on the preset turndown ratio for pressure drop applications.
• Modify the flow of fluids e.g. direct flow of fuel to the fuel port for fueling and direct the flow of fuel out of the fuel port for refueling.

Thus it can be generalized to say that control valves, as the name suggests, are used to regulate the output after taking any input. The regulation depends on their size and structure.

2. Characteristics of regulating units
A damper is a regulating unit that consists of pivotally mounted damper blades. Adjustment of the blades which is done by another part pivotally connected to the blades controls the airflow. For dampers used in refrigerators, a circuit board is used on which a sliding door is mounted to control the airflow to the freezer.
A louver is a set of parallel slats in a door or window that allow air but restrict rain. A picture can be seen below:

A power cylinder is an electromechanical linear actuator which provides push-pull movement. It can be used in remote-controlled operations and integration with computer-controlled systems.
A valve positioner is a device that exactly positions a control valve to the required position as per the signal given to it. The positioner senses the valve opening through a position feedback link connected to the valve. Controlled external supply air to the positioner provides power to the positioner to position a valve.
A globe valve is one in which inlet and outlet openings are arranged in several ways to suit varying requirements of the flow. It can give straight flow, angular flow, and cross flow. The major application is to get good flow control. Picture below:

Ball valves are stop valves that use a ball to stop or start the flow of fluid. When operated, the ball rotates to a point where the hole through the ball is in line with the valve body inlet and outlet. Picture below:

The Diaphragm valve is that which closes using a flexible diaphragm attached to a compressor. When the compressor is lowered by the valve stem, the diaphragm seals and cuts off the flow.
Gate valves are used when a straight-line flow of fluid and minimum restric¬tion is desired. The part that either stops or allows flow through the valve acts somewhat like the opening or closing of a gate and is called, the gate.
Double seated has two valve plugs on a common spindle, with two valve seats due to which the differential pressure is partially balanced.
A three-way valve has three ports. The inlet from one port can be sent to a second or third port. It can also be put in an intermediate position so that all flow is stopped.
A solenoid valve controls the flow of fluid or gas through an electric current where a coil of wire passes through the body of the valve
Split Body valves have the body in two parts where each part normalizes the drop in flow or pressure in the other end.
Butterfly valves are used in a variety of systems aboard ships. These valves can be used effectively in freshwater and saltwater. It consists of a butterfly disc which when rotated determines the flow of liquid through it. It is used for Good flow control at high capacities.
3. Use of valve positioners.
Valve positioners compare a control signal to a valve actuator’s position and move the actuator accordingly. The most modern valves come with the following specifications. Deadband - <0.15%, linearity – 1%, hysteresis - <0.75%, repeatability - <0.5%, air connection – ¼” NPT, gauge connection – 1/8” NPT, conduit entry – ½” NPT, air consumption – 12.8 scfm at 60 psi. the latest digital valve positioners use Foundation Fieldbus technology which controls the position of single- and double-acting valve actuators with linear or rotary mountings. It features a FISCO-compliant user interface board, potentiometer, piezoelectric technology, and host interoperability. Commissioning, calibration, tuning, and setup are accomplished in 2 min from the local user interface, and all parameters from the user interface are automatically updated.
4. Plug characteristics
A safety valve is a valve mechanism for the automatic release of a substance from a boiler, pressure vessel, or any other system. The other three plugs can be seen as:

In an equal percentage plug, equal increments of valve travel produce an equal percentage of flow change. Thus it is used in processes where large process drop is expected. For linear plugs, valve travel is directly proportional to the valve stroke. It is used in liquid level or flow loops and where pressure drop across the valve is fairly constant. In quick-opening valves, a small change in valve stroke makes a large increase in flow. Thus it is used for frequent on-off service.
5. Conclusion
Regulating units i.e. control valves can be operated manually (by hand, lever, or pedal) or can also be automatic (driven by changes in pressure, temperature, or flow). However used, valves have been a major invention and they form the very basis of most of the machinery used in modern times.