Showing posts with label flow control. Show all posts
Showing posts with label flow control. Show all posts

Thursday, October 26, 2017

When to Use a Globe Valve for Fluid Process Control

cast iron globe valves
Cast iron globe valves are utilized extensively in steam,
HVAC, and other commercial and industrial applications
Image courtesy of Crane Co.
Industrial process control often involves the regulation of fluid flow. There are almost uncountable types and variants of flow control valves, each with a particular set of attributes that can make it the advantageous choice an application.

When the process calls for controlling flow over a range of possible values, known as throttling, a globe valve may be a good candidate for the application.

Globe valves are characterized by the change in direction of fluid flow as it passes through the valve and around the plug positioned in an opening through which fluid must pass. The plug is connected to a stem extending to the exterior of the valve body through the bonnet. Movement of the stem will reposition the plug in relation to the opening, providing a successively larger or smaller opening area through which fluid can pass.

Globe valves are available in tee, angle, and wye configurations, as well as an enormous range of special configurations to suit specific applications.
simplified globe valve diagram
Simplified globe valve diagram
Image courtesy Wikipedia


What are some potential advantages of globe valves?
  • Good throttling and shutoff capability
  • Comparatively easy maintenance
  • Comparatively short travel of plug from open to closed position
  • Seats can usually be resurfaced when worn
What are some limiting factors for globe valves?
  • Higher valve pressure drop than some other designs
  • No straight through fluid path
  • Potentially higher actuator torque requirements than other valve types
  • Seal area is unprotected from exposure to process fluid flow
When flow throttling capability is the overriding concern for an application, a globe valve is a good candidate for consideration. Share your flow control challenges with valve and automation specialists. Combining your process knowledge and experience with their product application expertise will produce effective solutions.

Wednesday, March 9, 2016

Sleeved Plug Valves - Design Features and Variants

Industrial process control often involves the management of fluid flow, either by simple on-off flow control, throttling, or diversion of flow to alternate destinations. Valves of many differing designs and construction features provide distinct advantages for particular applications depending upon a variety of media characteristics, operational requirements, physical restrictions, and regulatory requirements.

Plug valves, so named for the generally tapered or parallel sided structure held in the flow path by the valve body, have wide application throughout the fluid control field. Their advantageous features include simple design, low maintenance, moderate size, minimal flow resistance when fully open, and quarter turn operation.
Cutaway view sleeved plug valve for industrial process use
Cutaway view of sleeved plug valve with design features labelled
Courtesy Fluoroseal

One subset of the plug valve family, the sleeved plug valve, has an additional advantage. It does not require lubrication. The metal plug is wedged within a sleeve, usually PTFE or a similar material, which provides a seal around the plug and a self lubricating surface to facilitate rotation of the plug within the body. One manufacturer, FluoroSeal, provides a broad offering of sleeved plug valves. The illustration (left) provides a cutaway view of one of Fluoroseal's valves of this type with primary design features labelled by the manufacturer as follows:
  1. Bidirectional in-line bubble-tight seal independent of line pressure
  2. Multiple external bubble-tight seals independent of line pressure
  3. Direction mechanical three-point adjustment independent of line pressure
  4. Independent travel stops
  5. Full encapsulation and retention of all leading edges of PFE sleeve and top seal components
  6. Full lip at port openings protects PTFE sleeve
  7. Contoured waterway ensures minimum flow turbulence characteristic
  8. No body cavities to entrap flow media
  9. Positive flow direction indication
  10. Drilled and tapped flange actuation mounting pads independent of cover and top sear assembly.

This versatile valve type is available in a number of variants suited to particular applications. Thes variants include:

  • Multiport configurations for flow diversion.
  • Caged plug version for use with a range of abrasive fluids
  • Double block and bleed design
  • Fire safe versions with additional sealing and venting to prevent leakage if the valve is overheated in a fire
  • Severe service variant to provide tight emission control and suitability for demanding applications with thermal cycling or a high operating rate
  • Special cleaning, testing, production methods, or other specialized tasks needed to assure safety or performance under very specific application conditions found in various industries.
An illustrated document with technical performance data for much of what is described above is included below. Browse the document for a more complete understanding of where sleeved plug valves can be applied and how they work. For more information, contact a valve specialist. Share your fluid control challenges with them and work toward a winning solution. The combination of your process expertise and their deep product application knowledge will yield good results.




Tuesday, January 13, 2015

Cavitation in a Water Pump and Valve - Excellent Visual and Audible Demo...

Cavitation is the formation of gas bubbles in a flowing liquid when the pressure of the liquid drops below its vapor pressure. Sometimes a difficult concept to grasp, this video offers an excellent demonstration on what actually happens inside process piping, pumps and valves during this phenomena.


Thursday, July 31, 2014

Basics of Flow Meters

flow meter
Flow Meter

Measuring the flow rate of solids, liquids, and gases is referred to as flow measurement, and is a very important and widely used control variable. Many industries such as power, chemical, water, waste-water treatment, energy, mining and petroleum have many requirements for flow measurement and control.

A flow meter is a device that measures the rate of flow or quantity of a moving fluid in an open or closed conduit. There are two basic ways of measuring flow: volumetric basis and weight basis.

Flow measuring devices are generally classified into four groups:
  1. Mechanical type flow meters: Fixed restriction, variable head type flow meters using different sensors such as orifice plates, venturi tubes, flow nozzles, pitot tubes, quantity meters such as positive displacement meters, mass flow meters, etc. 
  2. Inferential type flow meters: Variable area flow meters (Rotameters), turbine flow meters, target flow meters, etc.
  3. Electrical type flow meters:  Electromagnetic flow meters, Ultrasonic flow meters, laser doppler anemometers etc.
  4. Other flow meters: Purge flow regulators, flow meters for solids flow measurement, cross-correlation flow meter, vortex shedding flow meters, flow switches, etc.
Flowmeters need to be integrated into existing piping or new installation. There are two methods for flowmeter installation: inline and insertion. With the inline method, connectors are provided for upstream and downstream pipes. For the insertion method, a sensor probe is inserted into the pipe.

Most flowmeters are installed with straight sections of pipe on either side for flow to normalize. For the inline method, the diameter of pipes should be same as the flowmeter size. Insertion design is easier to install and more economical in large diameter pipes.

To select the suitable flowmeters many factors should be taken in mind. The most important is fluid phase (solid, liquid, gas, steam) and the other is flow condition (clean, dirty, viscous, open channel etc.). The next important factor is line size and flow rate. Other properties that will affect the selection of flowmeter are density, pressure, temperature, viscosity etc. You should consult an application engineer before specifying a flow meter to assure proper installation, lowest installed cost and safety.


Thursday, July 3, 2014

Swing Check Valve Operation - The Basics

check valve symbol
Check Valve Symbol
There are several types of industrial check valves such as piston, ball, diaphragm, wafer and swing. The following video introduces the viewer to the inner workings of the swing check valve.

According to Wikipedia, "Check valves are used in many fluid systems such as those in chemical and power plants, and in many other industrial processes.

Check valves are also often used when multiple gases are mixed into one gas stream. A check valve is installed on each of the individual gas streams to prevent mixing of the gases in the original source.
"

The swing check uses the directional flow to push open a swinging disk. As long as flow continues, the disk stays raised. But as flow stops, gravity allows the disk to re-seat itself and any reverse flow is prevented by the closed disk. As reverse flow pressure increases, the swing check valves seating increases as well.


Tuesday, July 1, 2014

A Fluid Velocity Tutorial

Here is another video describing the concepts of fluid velocity, pressure, and flow. It's from the Hydraulics collection offered by Columbia Gorge Community College.  In this video,  Instructor Jim Pytel, drives home fluid velocity concepts in a very entertaining and easy to understand way.  The video uses a humorous "application", where Mr. Pytel equates pressure to the system "strength", and flow as the system "speed". The video then goes on to explain the roles of pressure relief valves and flow control valves and how they allow for changes in force and speed of the sample system. It also introduces parallel and series hydraulic circuits, laminar and turbulent flow, flow rate, and flowmeters.



Saturday, May 31, 2014

Great Flow Control Tutorial Series on YouTube

Came across a great tutorial series of flow control basics, control valve basics, check valve basics and a bunch of other stuff. The videos are from the Columbia Gorge Community College and are done by a teacher there named Jim Pytel. Here's one on Flow Control Valve basics. Enjoy.