Everything You Need to Know About Valves

Contents

• Introduction
• What is a Valve?
• Valve Classification
  • Shutdown Types
  • Check Types
  • Regulating Types
  • Safety Protection Types
  • Special Purpose Types
• Valve Structure
  • Gate Valve
  • Globe Valve
  • Ball Valve
  • Butterfly Valve
  • Check Valve
• How to Select a Valve
• Valve Applications
• Flange, Thread, and Welding Standards
• Summary

Introduction

Valves play a crucial role in fluid piping systems. They are not only control elements but also key devices for isolating equipment and piping systems, regulating flow, preventing backflow, and regulating and releasing pressure.

Today, this article introduces the classification, structure, applications, and selection criteria of valves, hoping to provide you with a clearer understanding of valve knowledge.

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What is a Valve?

Valves are control components in fluid transport systems, used to regulate the direction, pressure, and flow rate of fluids, and possess functions such as shut-off, flow diversion, backflow prevention, pressure stabilization, flow splitting, or overflow pressure relief.

Their core function is to achieve precise control of fluids such as air, water, steam, corrosive media, slurry, and oil by changing the cross-sectional area of ​​the passage or the direction of medium flow.

Valve Classification

Valves can be classified into the following main types according to their application and structure, each type having a unique function:

Shutdown Types

Gate valve: Controls fluid flow by raising and lowering a gate, suitable for fully opening or closing large-diameter, high-pressure pipelines, but not suitable for flow regulation. Globe valve: Regulates flow by moving a valve disc up and down; offers good sealing but has high fluid resistance; commonly used in steam and hot water systems.

Ball valve: Controls flow by rotating a ball; opens and closes quickly and provides a reliable seal; suitable for water, steam, oil, and other media.

Butterfly valve: Regulates flow or cuts off fluid by rotating a butterfly plate; compact in structure; suitable for large-diameter, low-pressure pipelines.

Plug valve: Controls fluid by rotating a cylindrical or conical plug; opens and closes quickly, suitable for frequent operation.

Check Types

Check valve: Prevents backflow of medium. It automatically switches on and off based on fluid pressure, requiring no external power. It is commonly used at the outlet of water pumps and in drainage systems.

Regulating Types

Control valves: These adjust flow rate, pressure, or liquid level by changing the valve core stroke according to the signal direction and magnitude. They are divided into manual and automatic control valves.

Needle valves: These precisely adjust flow rate by rotating a needle-shaped valve core. They are suitable for high-pressure, low-flow systems.

Safety Protection Types

Safety valve: Automatically opens to relieve pressure when system pressure exceeds a set value, protecting equipment and the system from overpressure damage.

Pressure reducing valve: Reduces high-pressure fluid pressure to the required level and maintains a stable outlet pressure.

Special Purpose Types

Steam trap: Automatically drains condensate, prevents steam leakage, and improves energy efficiency.

Air vent: Removes excess gas from pipelines, improving pipeline efficiency and reducing energy consumption.

Valve Structure

Valves come in a wide variety of structures, mainly categorized as follows:

Gate Valve

Structure: Composed of valve body, gate, valve stem, valve cover, etc., with the gate perpendicular to the fluid direction.

Principle: Fluid flow is controlled by raising or lowering the gate. Resistance is low when fully open, but it is not suitable for flow regulation.

Globe Valve

Structure: Composed of valve body, valve disc, valve stem, valve cover, etc., the valve disc and valve seat sealing surfaces are tightly fitted.

Principle: Relying on the pressure of the valve stem to seal the valve disc against the valve seat, preventing the flow of media, suitable for flow regulation and frequent operation.

Ball Valve

Structure: Composed of valve body, ball, seat, and stem, the ball has an internal hole with the same diameter as the pipe.

Principle: Opening and closing is achieved by rotating the ball 90 degrees, resulting in low fluid resistance and rapid opening and closing.

Butterfly Valve

Structure: Composed of a valve body, butterfly plate, valve stem, and sealing ring, the butterfly plate is circular.

Principle: Fluid flow is controlled by rotating the butterfly plate; a 90-degree rotation of the valve disc achieves a fully closed to fully open operation.

Check Valve

Structure: Composed of valve body, valve disc, valve seat, etc. The valve disc can rotate around a pivot or move along the vertical centerline of the valve body.

Principle: Automatically switches on and off based on fluid pressure to prevent backflow of the medium.

How to Select a Valve

Fluid Conditions

Pressure: Select the valve’s nominal pressure based on the system’s highest operating pressure, such as low-pressure valves (PN≤1.6MPa), medium-pressure valves (2.5MPa≤PN≤4.0MPa), and high-pressure valves (10.0MPa≤PN≤80.0MPa).

Temperature: Select the valve material based on the medium temperature, such as cryogenic valves (-101℃≤t≤-29℃), ultra-low temperature valves (t<-101℃), and high-temperature valves (t≥120℃).

Fluid Properties

Corrosivity: Corrosive media require corrosion-resistant materials, such as stainless steel, plastics, or special alloys.

Viscosity: High-viscosity media require valves with high flow capacity, such as ball valves or butterfly valves.

Containing Solid Particles: Media containing suspended particles require valves with wiping properties, such as ball valves or plug valves.

Valve Function

Stop and Open Media: Select straight-through valves with low flow resistance, such as gate valves or ball valves.

Controlling Flow: Select valves with easily adjustable flow rates, such as gate valves or needle valves.

Reversing flow: Select a multi-channel valve, such as a plug valve or a ball valve.

Valve Applications

Petrochemical Industry: Used for the transportation and control of crude oil, natural gas, and chemical raw materials.

Power Industry: Used for flow and pressure regulation in boilers, steam turbines, and steam pipelines.

Metallurgical Industry: Used for media control in equipment such as blast furnaces, converters, and continuous casting machines.

Water Supply and Drainage Systems: Used for flow regulation and shut-off in urban water supply, drainage, and sewage treatment systems.

HVAC Systems: Used for flow distribution and temperature control in air conditioning and heating systems.

Gas Systems: Used for the transportation and safety control of natural gas and liquefied petroleum gas.

Flange, Thread, and Welding Standards

Flange Standards

GB/T 9113: Specifies the types and parameters of steel pipe flanges.

HG/T 20592: Applicable to the design and manufacture of steel pipe flanges in the chemical industry.

Thread Standards

GB/T 7306: Specifies the dimensions and tolerances of 55° sealing pipe threads.

ISO 228: Standard for non-sealing pipe threads developed by the International Organization for Standardization.

Welding Standards

GB/T 12459: Specifies the dimensions and tolerances of steel butt-welded pipe fittings.

ASME B16.9: Standard for factory-manufactured forged steel butt-welded pipe fittings developed by the American Society of Mechanical Engineers.

Summary

The article above provides a detailed understanding of valves, helping us make better choices.

Metleader specializes in manufacturing various types of valves and fittings, offering high quality at low prices, and can customize products to meet customer requirements.

We welcome global partners to visit our factory and support third-party on-site quality testing.

For more information on our valve and fitting catalog, please email Metleader.