Control though

The group of industrial valves that are responsible for controlling the physical parameters of a fluid, such as pressure, temperature, flow, and surface, are called control valves .

For example, regulators in industry are a type of these valves that are solely responsible for pressure control. Control valves are displayed in instrumentation maps according to the parameter they control with names such as FV, ​​PV, TV, LV. .

In instrumentation projects, Globe, Ball and Butterfly valves are used for more control work, diaphragm valves are also used in chemical, food and health industries for control work, Globe valves up to 24 inches are made.

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These types of valves are more expensive than others in the same size, however, they have the best control properties.

Also, the leak class intended for them is usually IV. These valves are also made in sizes smaller than 2 inches with leakage classes V, VI.

The size of the valve controls is usually considered to be at least half the size of the upstream line. For example, if the line is 6 inches, the size of the valve control will be at least 3 inches.

 

Prices of industrial valves

In order to design and select the desired valve, the valve coefficient must be considered.

The valve coefficient is defined as: If an American gallon per minute passes through the control valve at 60 degrees Fahrenheit (ISA standard conditions), one pound per square inch creates a pressure difference between the two ends of the valve.

Iran Industrial Valves

Therefore, it can be concluded that the larger the coefficient, the higher the transit capacity. Also, a smaller valve coefficient will mean a greater pressure drop at both ends of the valve.

Since the valve coefficient is directly related to the flow, the valve should be selected in such a way that the maximum possible flow in a line is considered to be a maximum of 80% of the valve coefficient.

In other words, after performing the calculations and finding the coefficient of the valve in the maximum value, we will multiply the calculation by approximately 1.2 and we will reach the coefficient of the valve for selection and design.

Iran Industrial Valves

Experimentally, if the globe control valve is about 20% open, it should flow at a minimum, if it is 50% open, it should pass the normal flow (Operation), and if it is about 80% open, it should pass the maximum flow. The end (100%) does not open. Because in these conditions, a lot of force and torque will be needed to close it.

Petrochemical industrial valves

The control valves make a noise during operation that the maximum allowable volume of 85 decibels can be heard at a distance of one meter in 8 hours of continuous operation of the valve and is not dangerous for the operator.

One of the cases that is known as severe and difficult phenomena inside the control valves is corrosion caused by cavitation. This common phenomenon is caused by excessive pressure drop at both ends of the valve, which causes the fluid inside the valve to evaporate.

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Due to the pressure drop, the velocity of the fluid in the valve also increases, the bubbles from evaporation hit the internal devices of the valve and because they also have high kinetic energy, they cause corrosion of the internal devices.

To prevent corrosion, special materials such as steel with hardened coatings (tungsten carbide or cobalt and chromium) can be used.

Equipment such as Restriction Orifice can also be used to break the pressure in two steps.

Internal devices, however, consist of the main part: Seat, Plug, Stem

 

Foreign industrial valves

The plug is responsible for closing the flow path and the seat will be the seat of the plug. The stem also applies the force required by the operator to open or close the plug.

Usually in oil and gas projects, the internal devices, which are also called Trim, are made of stainless steel and the valve body is selected from carbon steel.

Second hand industrial valves

In order to access the internal devices of the valve, the valve bonnet that is closed on the body must be opened and separated from the control valve.

One of the most important external parts of the valve control is its actuator.

The actuator is the part that provides the necessary force to open and close the valve.

Valve control actuators are usually considered pneumatic and diaphragmatic.

Adequate air flow and proper pressure for the operator are some of the things that should be considered when designing and supplying equipment.

The size of the operating air tube is usually considered to be ½ ”, which can be larger depending on the pressure and torque applied.

Industrial and construction valves

The air pressure applied to the diaphragm moves the control valve to open or close. If this air does not exist, it will go to the initial state, which is called (Fail).

The opening and closing time of the valve is another issue that must be considered when designing the operator. This time (in seconds) can be detected in project specifications or control-related standards.

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Another piece of equipment outside the body is known as the Positioner. In fact, the main air line first enters the positioner and exits it and connects to the operator.

The position of the positioner is to determine the location of the plug in relation to the seat with high accuracy.

In other words, it is the position that determines what percentage of the control valve is open or closed.

Prices of industrial valves

This process is done in such a way that the signal sent from the control room (signal 4 to 20 mA) inside a part of the positioner called I / P is converted into a pneumatic control signal. (Eg 3 to 15 pounds per square inch) This pneumatic control signal will control the air pressure applied to the actuator diaphragm.

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