Ultimate Guide to Valves: Valve Types, Operations, Functions, and Lockout Tagout

Valves are essential components in various industries, playing a key role in controlling and regulating fluid flow. This comprehensive guide aims to provide an in-depth look at different valve types, their operations, functions, and the importance of proper valve lockout procedures.

Key Takeaways

• Valves are mechanical devices, crucial components in increasing efficiency, improving quality control, and ensuring the safety and reliability of a process.
• The primary function of valves is to isolate or regulate flow of liquids, gases, or other materials by either completely stopping or controlling the passage through a system.
• Valve types can be identified through standardized markings and labels on the valve body, such as the manufacturer, size, pressure rating, material, and flow direction.
• Lockout valves provide a secure means to isolate energy sources, preventing the accidental operation of equipment or the release of hazardous materials during maintenance or repair.

What are Valves and How Does It Work?

Valves are mechanical devices designed to control the flow of fluids (liquids, gases, or slurries) through a piping system. They work by modifying the passageway within the pipe, allowing for precise control over fluid movement. When a valve is open, the fluid flows freely from areas of high pressure to low pressure. By partially or fully obstructing this passageway, valves can reduce or completely stop the flow.

Valves can account for up to 30% of the overall piping cost in a plant, highlighting their critical role in system design and operation. Valves serve multiple functions, including:

• Starting or stopping fluid flow
• Throttling flow rates
• Regulating pressure and temperature
• Redirecting flow between different paths
• Preventing reverse flow
• Ensuring system safety through pressure relief

3 Categories of Valve Operations

Valves can be categorized based on their method of operation:

1. Manual Valves: These valves require direct human intervention to operate. They typically feature handwheels, levers, or other manual mechanisms for control. Gate valves and many ball valves fall into this category.
2. Actuated valves: These valves utilize external power sources for operation, such as electric motors, pneumatic systems, or hydraulic systems. They can be controlled remotely, making them ideal for automated processes or hard-to-reach locations.
3. Automatic Valves: These valves operate based on specific conditions or triggers without direct human intervention. Examples include pressure relief valves and some types of check valves.

Common Types of Valves

Ball Valve

Ball valves utilize a perforated, hollow sphere within the valve body to control flow. These quarter-turn valves rotate 90 degrees between fully open and closed positions. When the valve handle aligns with the pipe, the hole in the ball allows fluid passage; when perpendicular, it blocks flow. Commonly used in on/off applications in oil, gas, manufacturing, and chemical storage sectors, ball valves offer quick operation and visual position indication.

Advantages:

• Excellent sealing capabilities
• Low pressure drop when fully open
• Quick operation

Disadvantages:

• Not ideal for throttling
• Can be more expensive than other quarter-turn valves
• Potential for contamination in the ball cavity

Butterfly Valve

Butterfly valves feature a disc mounted on a rotating shaft to control flow. This quarter-turn valve is fully open when the disc is parallel to the flow and gradually restricts flow as it rotates perpendicular. Widely used in large-diameter pipes, water supply systems, and wastewater treatment plants, butterfly valves are compact and lightweight.

Advantages:

• Compact and lightweight design
• Lower cost compared to other valve types
• Suitable for large-diameter applications

Disadvantages:

• Higher pressure drop compared to gate valves
• Less precise flow control than globe valves
• Potential for disc flutter in partially open positions

Check Valve

Also known as non-return valves (NRVs), check valves allow flow in one direction while automatically preventing backflow. Typically featuring a hinged disc or ball, these self actuated valves open when forward fluid pressure exceeds the cracking pressure and close when downstream pressure surpasses upstream pressure. They're commonly used near pumps and compressors, water supply systems, and fuel lines.

Advantages:

• Automatic operation without external power
• Prevents backflow and protects equipment
• Simple design with few moving parts

Disadvantages:

• Cannot be used for flow regulation
• Potential for water hammer if the closure is too rapid
• May not seal tightly at very low pressures

Gate Valve

Gate valves employ a flat or wedge-shaped gate to control flow. The multi-turn, linear motion valve raises or lowers the gate into the flow path by turning the valve stem. When fully open, the gate is completely out of the flow path. Gate valves are commonly used in water distribution systems, oil pipelines, and as isolation valves in various industries.

Advantages:

• Low pressure drop when fully open
• Bi-directional sealing
• Suitable for high-pressure applications

Disadvantages:

• Slow operation due to multi-turn design
• Not suitable for throttling
• Potential for wedging in partially open positions

Globe Valve

Globe valves use a disc or plug moving perpendicular to the flow path for control. The spherical body typically has two chambers separated by an internal baffle. As a multi-turn, linear motion valve, the disc or plug moves towards or away from a seat in the baffle, regulating flow rate. Globe valves are widely used in flow regulation applications such as cooling water systems, steam systems, and chemical processing.

Advantages:

• Excellent flow control and throttling capability
• Good shutoff characteristics
• Suitable for frequent operation

Disadvantages:

• Higher pressure drop compared to gate valves
• Requires more operating force than quarter-turn valves
• More complex design compared to other valve types

Plug Valve

Plug valves employ a cylindrical or conically tapered plug with one or more passageways to control flow. This quarter-turn valve aligns or blocks these passageways with the flow path to regulate fluid movement. Commonly used in slurry applications, gas and oil piping systems, and sewage treatment, plug valves excel in handling abrasive or corrosive materials. Their design allows for a long service life and high reliability.

Advantages:

• Suitable for corrosive and abrasive materials
• Quick, bubble-tight shutoff
• Can be repaired without removing the body from the system

Disadvantages:

• Not recommended for throttling applications
• Higher cost compared to ball valves
• Requires greater actuation force due to friction

Needle Valve

Needle valves feature a long, tapered, needle-like plunger that fits into a matching seat to control flow. These multi-turn valves offer precise flow regulation due to their finely threaded stem. Typically used in small-diameter piping systems where fine control is crucial, needle valves are common in gauge protection and as bleed valves for pressure relief or fluid sampling.

Advantages:

• Very precise flow control
• Suitable for low flow rates
• Compact design

Disadvantages:

• Limited to small flow rates
• Not suitable for fluids with suspended solids
• Can be damaged by excessive force during shutoff

Pinch Valve

Pinch valves use elastic tubing and a pinching mechanism to control flow. As the mechanism flattens the tubing, it creates a seal, making these valves ideal for handling slurries and solid materials in pneumatic conveying systems. Pinch valves offer simplicity in design and operation, with fewer components compared to other valve types.

Advantages:

• Excellent for handling abrasive slurries
• Minimize turbulence and friction
• Relatively inexpensive and leak-proof

Disadvantages:

• Not suitable for high-temperature or high-pressure applications
• Limited by the elasticity of the tubing material
• Potential for tubing collapse under high vacuum

Diaphragm Valve

Diaphragm valves consist of a flexible diaphragm attached to a compressor. When the compressor is lowered, it presses the diaphragm against a weir or seat, stopping the flow. These valves are widely used in pharmaceutical, food processing, and chemical industries due to their sanitary design and ability to handle corrosive fluids.

Advantages:

• Excellent for sanitary applications
• Good throttling capabilities
• No cavities where fluid can be trapped

Disadvantages:

• Limited pressure and temperature ranges
• Diaphragm may require frequent replacement in certain applications
• Larger and heavier than some other valve types

Comparison Chart: Common Types of Valves

Valve Type	P&ID Symbol	Valve Motion	Common Application
Ball Valve		Quarter-turn	On/off control, oil and gas industry
Butterfly Valve		Quarter-turn	Large diameter pipes, water treatment
Check Valve		Self-actuated	Backflow prevention, near pumps
Gate Valve		Multi-turn, Linear	Water distribution, oil pipelines
Globe Valve		Multi-turn, Linear	Flow regulation, cooling systems
Plug Valve		Quarter-turn	Slurry applications, chemical processing
Needle Valve		Multi-turn, Linear	Precise flow control, instrument connections
Pinch Valve		Linear	Slurry handling, pneumatic conveying
Diaphragm Valve		Multi-turn, Linear	Pharmaceutical, food processing

Valve Function Classification

Valves can be classified based on their primary function within a piping system. The two main categories are isolation valves and regulation valves.

Isolation valves are designed to completely restrict or allow fluid flow without obstruction. They are not recommended for continuous use in partially open states. These valves, such as gate valves and ball valves, provide a tight seal when closed and minimal flow resistance when open. They're ideal for applications requiring full on/off control and are often used in emergency shutoff situations or for system maintenance.

Regulation valves, on the other hand, are used for precise control of pressure and fluid flow. They can safely and efficiently operate in partially open or closed states, allowing for fine-tuning of flow rates. Globe valves and needle valves are common examples of regulation valves. Their design allows for accurate adjustment of the flow passage, making them suitable for applications that require frequent flow modulation or precise control over system parameters.

How to Identify Valve Type?

Valve types can be identified through markings and labels on the valve body. These markings typically include manufacturer information, valve seat, model number, trim, and body material. The first step is to locate these markings, which are usually stamped or cast onto the valve body.

How to Choose a Valve Type?

When selecting a valve type, consider the following factors:

1. Valve size: The valve size is typically specified in inches or with a DN (Diameter Nominal) prefix in millimeters. Ensure the valve size matches the pipe diameter and flow requirements of your system.
2. Pressure rating: Check the valve's pressure class, often denoted by "PN" followed by a number indicating the pressure rating in bars. For example, PN16 indicates a pressure rating of 16 bars (approximately 232 PSI).
3. Materials: Choose valve materials compatible with the fluid being handled and the operating conditions. Common materials include stainless steel, brass, cast iron, and various plastics.
4. Port connections: Consider the type of end connections required, such as flanged, threaded, or welded. Ensure compatibility with your piping system.
5. Nature of the media: Take into account the characteristics of the fluid being controlled, including its viscosity, temperature, and potential for corrosion or erosion.
6. Actuation: Determine whether manual, electric, pneumatic, or hydraulic actuation is most suitable for your application.

What Are Lockout Valves?

Lockout valves are devices used by authorized employees to isolate or shut off operating valves to prevent life-threatening accidents from occurring during repair or maintenance work. These lockout devices are different from the valves themselves. They are devices fitted over the operational section of the valve and secured with lockout hasps or padlocks to prevent unauthorized access.

3 Types of Valve Lockout Devices

1. Gate Valve Lockout
2. Ball Valve Lockout
3. Butterfly Valve Lockout

How Do You Use a Valve Lockout?

There are different types of valve lockout, each tailored to a certain type of industrial valve. We'll discuss each of these in detail below:

Gate Valve Lockout Devices

Gate valve lockout mechanisms are classified into two types: rotating or adjustable and hinged. Rotating gate valve lockout devices have an inward/outward rotating feature, while hinged gate valve lockout devices are made up of two half-moons that are hinged on one side.

While their mechanisms differ, both are designed to enclose and cover the gate valve handle in order to prevent unauthorized or accidental valve opening. Adjustable gate valve lockout devices are also available to fit over a large variety of round gate valves.

Ball Valve Lockout Devices

Ball valve lockout devices come in standard and adjustable designs. The standard ball valve lockout has a simple and efficient single-piece design. To use this, simply clamp the lockout/tagout valve device onto the quarter turn valves lever as far as possible and make sure it sits over the angled portion of the handle. Squeeze the valve handle and the LOTO device together, then secure it with a LOTO lock at its closest fit.

On the other hand, the adjustable valve lockout device comes with a two-piece design. To use this, place the base of the lockout device over the ball valve lever, then slip the sliding piece over the end as far as possible to secure the entire device. To complete the lockout, insert the LOTO lock at its closest fit.

Butterfly Valve Lockout Devices

Butterfly valve lockout devices have a two-piece design that’s quick and easy to install with no extra tools needed. Simply position the main part over the top of the valve lever, then slide the outer sleeve into the handle to block the release trigger. There are also adjustable flanged ball valves to secure the flanged ball valves of larger pipes or high-pressure industrial systems.

FAQs about the Types of Valves

What is the most common valve in plumbing?

Ball valves and gate valves are widely used in plumbing systems due to their reliability and ability to control water flow efficiently. Ball valves are favored for their easy operation and full-flow capabilities, while gate valves are typically used for shut-off purposes in straight-line flow applications.

Where are valves commonly used?

Valves are commonly used in plumbing systems, industrial pipelines, HVAC systems, and irrigation systems to control the flow of liquids, gases, or slurries. They are essential components in regulating flow, pressure, and temperature in various applications.

What are common causes of valve failure?

Common causes of valve failure include corrosion, wear and tear from frequent use, improper installation, and the buildup of debris or foreign materials that prevent proper sealing. Poor maintenance or using valves outside their design limits can also lead to malfunctions.

What size valve should I use?

The size of the valve should match the size of the pipe it is connected to for optimal flow efficiency. Additionally, selecting the right valve size depends on factors such as the flow rate, pressure requirements, and the type of fluid or gas being controlled.

Which valve is best for flow control?

Globe valves are typically the best for flow control due to their design, which allows precise adjustment of the flow rate. They are commonly used when throttling is required, offering better control than ball or gate valves.