Inst ToolsInst ToolsInst Tools
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Search
  • Books
  • Software
  • Projects
  • Process
  • Tools
  • Basics
  • Formula
  • Power Plant
  • Root Cause Analysis
  • Electrical Basics
  • Animation
  • Standards
  • 4-20 mA Course
  • Siemens PLC Course
Reading: Control Valve Cavitation and Flashing
Share
Notification Show More
Font ResizerAa
Inst ToolsInst Tools
Font ResizerAa
  • Courses
  • Design
  • PLC
  • Interview
  • Control System
Search
  • Courses
  • Automation
    • PLC
    • Control System
    • Safety System
    • Communication
    • Fire & Gas System
  • Instrumentation
    • Design
    • Pressure
    • Temperature
    • Flow
    • Level
    • Vibration
    • Analyzer
    • Control Valve
    • Switch
    • Calibration
    • Erection & Commissioning
  • Interview
    • Instrumentation
    • Electrical
    • Electronics
    • Practical
  • Q&A
    • Instrumentation
    • Control System
    • Electrical
    • Electronics
    • Analog Electronics
    • Digital Electronics
    • Power Electronics
    • Microprocessor
  • Request
Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Inst Tools > Blog > Control Valves > Control Valve Cavitation and Flashing

Control Valve Cavitation and Flashing

Last updated: March 21, 2019 11:15 pm
Editorial Staff
Control Valves Guest Articles
No Comments
Share
4 Min Read
SHARE

Flashing is the first stage of cavitation. However, it is possible for flashing to occur by itself without cavitation occurring.

Contents
Control Valve Cavitation and FlashingErosionReduced CapacityCavitation

Flashing occurs in liquid flows when some of the liquid changes permanently into vapour. This is brought on by a reduction in pressure forcing the liquid to change to gaseous state.

The reduction in pressure is caused by the restriction in the flowstream generating a higher flow rate through the restriction and therefore a reduction in pressure.

The two main problems cause with flashing are:

  • Erosion
  • Reduced capacity

Control Valve Cavitation and Flashing

control valve flashing effectA photograph showing a badly eroded valve plug (from a cage-guided global valve) reveals just how destructive flashing can be:

Flashing Problems in Control Valve
A characteristic effect of flashing in a control valve is a “hissing” sound, reminiscent of what sand might sound like if it were flowing through the valve.

Erosion

When flashing occurs, the flow from the outlet of the valve is composed of liquid and vapour. With increased flashing, the vapour carries the liquid. As the velocity of the flowstream is increased, the liquid acts like solid particles as it strikes the internal parts of the valve.

The velocity of the outlet flow can be reduced by increasing the size of the valve outlet which would reduce the damage. Options of using hardened materials are another solution.

Angle valves are suitable for the application as the flashing occurs further downstream away from the trim and valve assembly.

Control Valve Erosion Effect

Another cause of erosion in control valves is wet steam, where steam contains droplets of liquid water propelled at high velocity by the steam flow.

A dramatic example of wet steam damage appears in this next photograph, where the cage from a Fisher valve has been literally cut in half from the flow.

Valve Erosion Problem
Reduced Capacity

When the flowstream partly changes to a vapour as in the case of flashing, the space that it occupies is increased. Because of the reduced available area, the capacity for the valve to handle larger flows is limited.

Chocked flow is the term used when the flow capacity is limited in this way.

Chocked flow of valve
Cavitation

Cavitation is the same as flashing except that the pressure is recovered in the outlet flowstream such that the vapour is returned to a liquid. The critical pressure is the vapour pressure of the fluid.

Flashing occurs just downstream of the valve trim when the pressure drops below the vapour pressure, and then the bubbles collapse when the pressure recovers above the vapour pressure. When the bubbles collapse., they send severe shock waves into the flow stream.

The main concern with cavitation, is the damage to the trim and body of the valve. This is primarily caused by the collapsing of the bubbles.

Depending on the extent of the cavitation developed, its effects can range from a mild hissing sound with little or no equipment damage to a highly noisy installation causing severe physical damage to the valve and downstream piping.

Severe cavitation is noisy and can sound as if gravel were flowing through the valve. The noise produced is not a major concern from a personal safety point of view, as it is usually low in frequency and intensity and as such does not pose a problem to personnel.

Photographs of a fluted valve plug and its matching seat are shown here as evidence of flashing and cavitation damage, respectively:

valve cavitation picturescontrol valve cavitation conditions

Also Read: Control Valve Basics

Don't Miss Our Updates
Be the first to get exclusive content straight to your email.
We promise not to spam you. You can unsubscribe at any time.
Invalid email address
You've successfully subscribed !

Continue Reading

Instrument Panel Cooling Efficiency Enhancement
5 Port 2 Position Valve Working Principle
Difference between Globe Valve and Gate Valve ?
Different Types of Control Valve Actuators
What is Instrument Air Manifold ?
Thermostatic Valves Working Principle
Share This Article
Facebook Whatsapp Whatsapp LinkedIn Copy Link
Share
Leave a Comment

Leave a Reply Cancel reply

Your email address will not be published. Required fields are marked *

Stay Connected

128.3kFollowersLike
69.1kFollowersFollow
210kSubscribersSubscribe
38kFollowersFollow

Categories

Explore More

What is Poppet Valve? When we Use a Poppet Valve?
What is a 4-way Solenoid Valve?
Open Tank DP Level Transmitter Calculations
Face to Face Dimension of Control Valve
Importance of Proper Control Valve Sizing
What is a Hydraulic Valve? and their Types
Control Valve Working Animation
Basic Requirements of Control Valves Sizing

Keep Learning

Emergency Shutdown Valve

Emergency Shutdown Valve : Advantages

Control Valves Pre-Commissioning Checklist

Control Valves Pre-Commissioning Checklist

PLC Program for Car Parking

PLC Program for Entry and Exit Control of Car Parking

Dual Solenoid Valve on Control Valve

Why we Require Dual SOV on a Control Valve?

Compressor and Compressor valves Maintenance

Compressor & Compressor Valves Maintenance

What is a Servo Valve?

What is a Servo Valve? – Principle and Advantages

Pressure Control Valve

What is Pressure Control Valve?

Full Bore or Reduced Bore Valves

When to choose Full Bore Valve or Reduced Bore Valve ?

Learn More

Control Valve Selection Guide

Control Valve Selection Guide

How to Prevent Ground Loops in Analog Circuits?

How to Prevent Ground Loops in Analog Circuits?

Emergency Stop Push button

Emergency Stop Switch Spurious Trip

Engineering Materials Objective Questions

Engineering Materials Objective Questions

How PLC controls a ON-OFF Valve

PLC Valve Control Ladder Logic Programming

Electrical Terminology

Electrical Terminology

Remote Diaphragm Seal Transmitter for Vacuum Application

Remote Diaphragm Seal Transmitter for Vacuum Application

Chemical Battery

Batteries

Menu

  • About
  • Privacy Policy
  • Copyright

Quick Links

  • Learn PLC
  • Helping Hand
  • Part Time Job

YouTube Subscribe

Follow US
All rights reserved. Reproduction in whole or in part without written permission is prohibited.
Welcome Back!

Sign in to your account

Username or Email Address
Password

Lost your password?