Last updated on Sep 20, 2024

How do you interpret the control valve symbols on a piping and instrumentation diagram (P&ID)?

A piping and instrumentation diagram (P&ID) is a graphical representation of the process flow, equipment, and control devices in a plant or facility. It shows how the piping, valves, instruments, and other components are connected and interact to achieve the desired process conditions. One of the most important elements on a P&ID is the control valve, which regulates the flow, pressure, temperature, or level of a fluid or gas. But how do you interpret the control valve symbols on a P&ID? Here are some tips to help you understand the different types and functions of control valves and their symbols.

1 Control valve types

Control valves can be classified into two main types: linear and rotary. Linear control valves move the valve stem in a straight line, opening or closing the valve port. Examples of linear control valves are globe, gate, diaphragm, and pinch valves. Rotary control valves rotate the valve stem or disc, changing the angle or position of the valve port. Examples of rotary control valves are ball, butterfly, plug, and eccentric disc valves. The type of control valve affects the flow characteristics, performance, and suitability for different applications.

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Chris Vogel

Principal at C.F.M.E.
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If we are talking about flow control vs mechanical control we need to further classify valve functions. Ball, gate and butterfly type valves are better applied for isolation as the flow rates are non linear. At about 50% these valves are approaching almost 90% flow. Globe, needle or screw port valves offer tighter control. Companies add restriction plates or supplement control by doing things like a wedge shape plate or pressure reset of valves to enhance flow characteristics.

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Hossein R.Maleki

Instrument Dep Chief at OICO
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Also it is very important the fail condition of valve for control concept and safe condition the Symbole of FC that mentioned the Valve is Fail close and the Symbole of FO that mentioned the Valve is Fail open

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Gladstone Samuel

Qualified Independent Director | ESG Practitioner | PMP®
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Example Interpretation For instance, consider the following P&ID representation: Symbol: A circle with a label "CV-101" and an arrow indicating flow direction. Interpretation: CV-101 is a control valve designed to regulate flow. The arrow indicates the direction of fluid flow through the valve. If there’s an accompanying line to a flow meter (e.g., FM-102), it indicates that the control valve adjusts based on flow measurements.

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2 Control valve symbols

Control valve symbols are composed of three parts: the actuator, the valve body, and the accessories. The actuator is the device that provides the force or motion to move the valve stem or disc. It can be pneumatic, hydraulic, electric, or manual. The valve body is the part that contains the valve port and the sealing element. It can have different shapes and sizes depending on the type of control valve. The accessories are the additional components that enhance the functionality or performance of the control valve. They can include positioners, solenoids, limit switches, transmitters, regulators, and filters.

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Mohamed Yehia Mursi

Instrumentation & Control Engineer | Maintenance & Reliability | Technical Support | Asset Performance Management | RCM Methodolegy
(edited)
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Any P&IDs drawing should clearly describe the control valve symbols in a way that can be easily understood, in my experience, control valve body (Gate, Butterfly, Ball, etc..) will be the same either if this is a (control valve) or a switch (ON/OFF) valve, the difference will be in actuator symbol. According to ISA 5.1, a control valve actuator sometimes takes the half-circle shape and in the Switch or On-Off Valve it takes square shape, for accessories part, for example if we have a valve tag is (HV-01) the i/p positioner symbol could be (HIC-01) and solenoid valve could be (HN-01 or HX-01) and the feedback limit switches could be (ZSC-01) and (ZSO-01). Also there is a self-actuated (Pressure PCV or Temperature TCV) regulator valves.

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3 Actuator symbols

Actuator symbols indicate the type and action of the actuator. A simple circle represents a manual actuator, such as a handwheel or a lever. A circle with a diagonal line represents a spring return actuator, which returns to its original position when the power source is removed. A circle with two diagonal lines represents a double acting actuator, which can move in both directions by applying or releasing the power source. A circle with a letter inside represents a powered actuator, such as P for pneumatic, H for hydraulic, or E for electric. A triangle inside the circle represents a fail-safe action, such as fail open (FO) or fail close (FC).

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Philip Brown

Operations Team Leader @ Perenco | FS Eng, BEng
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From my experience this depends on which standard you follow. The three oil and gas companies I have worked for all follow ISA 5.1 and do not typically represent actuators as described above. It is common for the actuator type to be determined by the signal/supply line type, which also follow their own symbols to differentiate between pneumatic, hydraulic, electric

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4 Valve body symbols

Valve body symbols indicate the type and shape of the valve body. A simple line represents a gate valve, which has a flat disc that slides across the valve port. A line with a gap represents a globe valve, which has a spherical disc that moves up and down to regulate the flow. A line with a ball inside represents a ball valve, which has a spherical ball with a hole that rotates to align or block the flow. A line with a butterfly inside represents a butterfly valve, which has a thin disc that pivots to control the flow. A line with a plug inside represents a plug valve, which has a cylindrical plug with a hole that rotates to align or block the flow.

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5 Accessory symbols

Accessory symbols indicate the type and function of the accessory. A square with a letter inside represents a positioner, which adjusts the actuator position according to the signal from the controller. A square with an S inside represents a solenoid, which switches the power source to the actuator on or off. A square with an LS inside represents a limit switch, which detects the end position of the actuator and sends a feedback signal. A square with a T inside represents a transmitter, which measures and transmits a process variable, such as flow, pressure, temperature, or level. A square with an R inside represents a regulator, which maintains a constant pressure or flow in the system. A square with an F inside represents a filter, which removes impurities from the fluid or gas.

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Elahe Shahabzadeh

Instrumentation and Control Engineer |Project Engineer|Electrical Control Engineer| Artificial Intelligence
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According to ISA 5.1 to show control valves first of all you need to show the type of valve body. Then you need a Tag and failsafe situation, if for example your valve in control system has a loop with flowmeter This Tag will be FCV_xxx. Then you should show the actuator type and tag that must be selected as ISA said if it is motorized or pneumatic. Also you may need to show the positioner if it is a transmitter use ZT_xxx. in many P&IDs there is no need to show Air filter regulator, it will be mentioned in control valve datasheets.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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How do you interpret the control valve symbols on a piping and instrumentation diagram (P&ID)?

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1 Control valve types

2 Control valve symbols

3 Actuator symbols

4 Valve body symbols

5 Accessory symbols

6 Here’s what else to consider

Control Valves

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