Views: 5893 Author: Site Editor Publish Time: 2025-04-29 Origin: Site
Valves are essential components in piping systems, controlling the flow of fluids ranging from water and steam to corrosive media and oil. Proper valve selection and maintenance are critical to system safety, reliability, and operational efficiency.
This article provides a systematic overview of valve classification, characteristics, selection procedures, and common failure troubleshooting.
By Drive Method
Type | Description | Examples |
|---|---|---|
Automatic | Self-actuated by media | Check valves, safety valves, regulators |
Actuated | Operated by external force | Gate valves, globe valves, ball valves |
By Structure
Gate type: disc moves perpendicular to seat
Globe type: disc moves along seat center
Ball/plug type: rotates around its axis
Swing type: rotates around shaft outside seat
Butterfly type: disc rotates around shaft inside seat
By Application
Isolation: gate, globe, ball, butterfly valves
Check: check valves
Regulation: control valves, pressure reducing valves
Distribution: three-way plugs, distribution valves
Safety: safety valves, relief valves
Special purpose: steam traps, blow-down valves
By Pressure
Category | Pressure Range |
|---|---|
Vacuum | < 0.1 MPa |
Low pressure | PN ≤ 1.6 MPa |
Medium pressure | PN 2.5–6.4 MPa |
High pressure | PN 10.0–80.0 MPa |
Ultra-high pressure | PN ≥ 100.0 MPa |
By Temperature
Category | Temperature Range |
|---|---|
Standard | -40℃ to 425℃ |
High temperature | 425℃ to 600℃ |
Heat resistant | > 600℃ |
Low temperature | -150℃ to -40℃ |
Ultra-low temperature | < -150℃ |
By Size
Category | Size Range |
|---|---|
Small bore | DN < 40mm |
Medium bore | DN 50–300mm |
Large bore | DN 350–1200mm |
Extra large | DN ≥ 1400mm |
By Connection
Flanged, threaded, welded, clamp, ferrule
Functional Characteristics
Valve category and type
Material of major components
Drive mechanism
Structural Characteristics
Face-to-face dimensions, overall height
Connection type
Sealing surface configuration
Stem type (rising or non-rising)
Nine-Step Selection Process
Define service conditions (media, pressure, temperature)
Determine connection size and type
Select actuation method
Choose body and trim materials
Determine valve category
Select valve type
Define performance parameters
Determine geometric dimensions
Reference product catalogs for final selection
Key Selection Criteria
Service conditions and control requirements
Media properties (corrosivity, viscosity, particulates)
Flow characteristics (resistance, capacity, sealing class)
Installation space and dimensional constraints
Reliability, service life, and special requirements
Gate Valves
Preferred for most applications; suitable for steam, oil, and particulate media
Low-temperature service requires specialized designs
Globe Valves
Suitable for DN < 200mm steam lines
Not recommended for high-viscosity or particulate-laden media
Ball Valves
Ideal for low-temperature, high-pressure, high-viscosity media
Suitable for media with suspended solids
Full-port designs not recommended for flow regulation
Butterfly Valves
Preferred for DN > 600mm applications
Suitable for water, oil, and air at ≤80℃, ≤1.0MPa
Higher pressure loss than gate or ball valves
Check Valves
For clean media; not suitable for particulate-laden fluids
DN ≤ 40mm: lift type
DN 50–400mm: swing type
DN ≥ 450mm: silent or buffered type
Diaphragm Valves
For temperatures < 200℃, pressures < 1.0MPa
Suitable for media with suspended solids
Not recommended for vacuum service
Closure Component Detachment
Cause | Corrective Action |
|---|---|
Improper operation | Follow proper procedures; reverse handwheel slightly after full opening |
Loose connection | Ensure secure connection with anti-rotation devices |
Corrosion or wear | Select corrosion-resistant materials with adequate strength |
Packing Leakage (Most Common)
Cause | Corrective Action |
|---|---|
Incorrect packing material | Select appropriate packing for service conditions |
Improper installation | Install rings individually with staggered joints at 30° or 45° |
Packing老化 | Replace aged or damaged packing |
Bent or worn stem | Straighten, repair, or replace stem |
Insufficient compression | Tighten evenly with at least 5mm preload clearance |
Sealing Surface Leakage
Cause | Corrective Action |
|---|---|
Uneven lapping | Repair and lap surfaces; perform dye check |
Misalignment | Adjust assembly to ensure proper alignment |
Incorrect material selection | Select appropriate materials for service conditions |
Seal Ring Connection Leakage
Cause | Corrective Action |
|---|---|
Insufficient rolling | Apply adhesive and reroll |
Poor welding quality | Reweld according to specifications |
Loose threads | Clean, replace damaged parts, and reassemble |
Body and Bonnet Leakage
Cause | Corrective Action |
|---|---|
Casting defects | Perform strength testing before installation |
Freezing damage | Insulate or trace heat; drain when not in service |
Poor welding | Follow welding procedures; conduct NDT and strength tests |
Impact damage | Avoid stacking heavy objects; provide supports for large valves |
Valves serve as the final control elements in piping systems. Proper selection requires comprehensive consideration of media properties, operating conditions, actuation methods, and installation constraints. Effective maintenance demands targeted approaches for different failure modes.
Mastering valve classification, selection methodologies, and troubleshooting techniques is essential for engineers seeking to ensure safe, reliable, and efficient piping system operation.
