Showing posts with label plug valve. Show all posts
Showing posts with label plug valve. Show all posts

Monday, July 22, 2019

Introduction to Gas Pipeline Block Station Valves

Gas Pipeline

When a gas pipeline is constructed it is divided up into segments using block valve stations. This enables various sections to be isolated for inspection and maintenance. The block valve is typically a full-bore, soft seated ball valve to allow for "pigging", a practice that includes cleaning and inspecting the pipeline. However, it is not recommended that soft seated ball valves be opened against full differential pressure as damage to the valve seats can occur. To mitigate valve seat damage, a bypass system is installed around the main block valve to balance the pipeline pressure prior to opening. For these bypass requirements, plug valves are commonly used because their inherent design tolerates full differential pressure and allows for the opening and throttling without damage.

Why You Need a Bypass 

Full port ball valve
Full port ball valve
For any given section of pipeline, the block station valve opening process begins after completion of inspection and/or maintenance has been completed and this section is now ready to be returned to service. 

Because the block valve (often is a soft seated ball valve) is exposed to full differential pressure, it faces a huge pressure drop across the valve as it opens. The pressure drop generates high velocity flow, very often accompanied by scale, rust and dirt particles. These particles come in contact with the valve seats resulting in seat erosion and damage. Once the valve seats are damaged, the block valve cannot seal bubble tight once closed. To avoid the block valve seats from being exposed to high velocity, erosive particles, a bypass is utilized to balance the pressure either side of the block valve prior to the opening of the block valve.

Prevention of Block Valve Seat Deterioration Using Bypass Valves

plug valve
Plug valve (CRANE Xomox)
A typical bypass system includes two (2) bypass valves and One (1) vent valve. With the vent valve closed, the first of two bypass valves (Bypass Valve 1) is opened allowing pressure into the bypass piping. Usually, a plug valve is be used because it can tolerate full differential pressure without seat damage. Next, bypass the second bypass valve (Bypass Valve 2) is slowly opened, gradually building pressure in the downstream section of the pipeline until the pressure either side of the main block valve is equalized. Plug valves are also commonly used here because they are capable of controlling the flow without seat damaged.

With the pressure now equalized in the pipeline, the block valve can be opened safely, without the risk of seat damage. Bypass valves 1 & 2 have done their jobs and are now fully closed, providing bubble tight shutoff for the main pipeline.

Pipeline Venting to Atmosphere

Block stations are required occasionally vent a section of the pipeline to atmosphere. This too is a demanding application, with the valve being  exposed to full differential pressure. This operation starts with all valves in the system being closed. Bypass valve 1 is then opened allowing pressure into the bypass station system. The vent valve is now slowly opened to release the pipeline pressure.  Plug valves are commonly used here again to ensure bubble tight isolation to the atmosphere once closed.

For more information, contact Mountain States Engineering and Controls by visiting https://mnteng.com or by calling 303-232-4100.

Wednesday, February 7, 2018

Plug Valves - Right For Your Application?

industrial plug valve with manual operating handle
Plug valves incorporate design features making them
a positive choice for many fluid process applications.
Image courtesy Fluoroseal, Inc.
There are common components to be found on almost every process system that involves fluid control. Regardless of the operation's scale, pumps, piping, tanks and valves are likely to be part of the system.

Valves, of which there are many types, provide control over the flow rate, direction and routing of fluids in a processing operation. Flow can be started, stopped or modulated between zero and full rate using a properly sized and configured valve. Some valves enable media flow to be diverted to a selection of outlets, in lieu of a single inlet and outlet pair. Specialized valves regulate inlet or outlet pressure, or prevent fluid flow from going in an undesirable direction. All of these capabilities are packaged into differing valve product offerings that present a very large selection array to a process designer or engineer.

Industrial flow control valve types are generally classified according to the structure or arrangement contained within the valve body that provides obstruction to fluid flow. Some of the common types are ball, butterfly, gate, globe, and plug. Surely, there are more valve types, and this article is not intended to list them all. Some of our previous blogs have discussed selection considerations for gate, ball and butterfly valves. This article will focus on one of the oldest valve types, the plug valve.

Plug valves, like ball and butterfly valves, span from fully open to fully closed positions with a shaft rotation of 90 degrees. The “plug” in a plug valve is installed in the flow path within the valve body and rotated by means of a stem or shaft extending to the exterior of the body. Plugs are often tapered toward the bottom and are fitted to a seating surface in the valve body cavity that prevents fluid from bypassing the plug. An opening through the plug, the port, can be shaped to provide particular flow characteristics. There are numerous variants of the basic plug valve which may make it suitable for particular applications. One common variant is the lined or sleeved plug valve, with an insert or interior lining of material that creates an isolating barrier between the valve body and the media. This allows use of less expensive materials for the body construction that may be otherwise subject to corrosion by exposure to aggressive media.

Positive attributes of plug valves.

  • 90 degree rotation from open to closed provides fast operation.
  • With proper configuration, can be well suited for frequent operation.
  • Availability of corrosion resistant liner may provide comparative cost savings because valve body can be constructed of less expensive material.
  • Design is simple and employs a low parts count.
  • Valve can be serviced in place.
  • Generally, low resistance to flow when fully open.
  • Reliable leak-tight service due to tapered plug wedging action, replaceable sleeve, and injection of lubricant in some variants.

Potential issues of concern.

  • Higher friction in the plug closure mechanism may require comparatively higher operating torque than other valve types.
  • Without a specially designed plug, generally not well suited for throttling applications.
  • Rapid shutoff delivered by plug design may not be suitable for some applications where hammering may occur.

Share your fluid control application challenges with a valve and automation specialist. Leverage your own knowledge and experience with their product application expertise to develop an effective solution.

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, July 21, 2015

Selecting the Right Valve Type - Plug Valves

Valves are the primary fluid flow control device employed in the industrial process control arena. The widely varied applications and requirements have led to an almost daunting array of vendors. valves and options from which to choose. For your particular project or application, the selection candidate pool can be shrunk down to a manageable size if you first select the type of valve that will best suit your needs.

industrial plug valve internal part
The "Plug" in a Plug Valve
Courtesy Fluoroseal Inc.
Valves are generally used to start, stop, redirect, or throttle (control at some intermediate level) the flow of a fluid. They may also be tasked with preventing fluid flow from going in an undesirable direction or regulating pressure. Industrial flow control valve types are generally classified according to the structure or arrangement within the valve body that provides the obstruction to fluid flow. Some of the common types are ball, butterfly, gate, globe, and plug. Surely there are more valve types, and this article is not intended to list them all. Some of our previous blogs have discussed selection considerations for ball, butterfly, and gate valves. Let’s look at one of the oldest valve types, the plug valve.

Plug valves are similar to ball and butterfly valves, with their rotational movement of 90 degrees from the fully open to the closed positions. The “plug” in a plug valve is installed in the flow path within the valve body and rotated by means of a stem extending to the exterior of the body. Plugs are often tapered toward the bottom and are fitted to a seating surface in the valve body cavity. An opening through the plug, the port, can be shaped to provide particular flow characteristics. There are numerous variants of the basic plug valve which may make it suitable for particular applications. One common variant is the lined plug valve, with an interior lining of material suited to provide a measure of corrosion resistance for special media applications.

industrial plug valve
Industrial Plug Valve With Manual Operation Handle
Courtesy DHV Industires
What are the general positives for plug valve application?

  • 90 degree rotation from open to closed provides fast operation.
  • With proper configuration, can be well suited for frequent operation.
  • Availability of corrosion resistant liner may provide comparative cost savings because valve body can be constructed of less expensive material.
  • Design is simple and employs a low parts count.
  • Valve can be serviced in place.
  • Generally, low resistance to flow when fully open.
  • Reliable leak-tight service due to tapered plug wedging action, replaceable sleeve, and injection of lubricant in some variants.

What are some potential negatives for plug valves?

  • Higher friction in the closure mechanism may require comparatively higher operating torque than other valve types.
  • Generally not well suited for throttling applications without special design modifications.
  • Rapid shutoff may not be suitable for some applications where hammering may occur.

As part of your own assessment and selection process, share your application requirements and concerns with an experienced sales engineer. Their product knowledge and application experience can provide the additional input needed to make the best choice for your project.