04242017Mon
Last updateMon, 24 Apr 2017 2pm

i

Relevance in a Digital Age

Relevance in a Digital Age

The distribution model of the past 50 ye...

Video Game Technology Changing the  Offshore Industry

Video Game Technology Changing the Offshore Industry

One of the most powerful innovations in ...

Reshoring, Robots and What Happens if We Do Bring Jobs Back?

Reshoring, Robots and What Happens if We Do Bring Jobs Back?

While offshoring is painted as the major...

The Weekly Report

New Products

  • ja-news-2
  • ja-news-3

Industry Headlines

Natural Gas Inventories Above Five-Year Average

Monday, 24 April 2017  |  Chris Guy

Working natural gas in storage as of March 31, the traditional end of the heating season, totaled 2,051 billion cubic feet, or almost 15% above the fi...

Readmore

Loading...
Advertisement
i

Industry Headlines

VanAire Names Steven Soderman CEO, Quality Manager

4 DAYS AGO

Steven Soderman has joined the leadership team of VanAire, Incorporated as CEO and quality manager. Bill VanDeVusse will continue in his role as president having previously filled the positions of both president and CEO.

Soderman has held key quality positions throughout his career most recently fillin...

Readmore

Chromatic Industries Adds Two Former Cameron Executives

4 DAYS AGO

Mark Gamber has joined Chromatic Industries as CEO effective April 10, 2017. Wayne Hall will continue in his role as president. Gamber most recently served as vice president of operations at Cameron in its Distributed Valves Group.

Additionally, Mark Cordell has joined Chromatic as a senior advisor. Be...

Readmore

Natural Gas Inventories Above Five-Year Average

-1 DAYS AGO

Working natural gas in storage as of March 31, the traditional end of the heating season, totaled 2,051 billion cubic feet, or almost 15% above the five-year average according to EIA 's Weekly Natural Gas Storage Report . The total inventory of U.S. natural gas in storage tends to follow seasonal patter...

Readmore

Alliance Pipeline Proposing Expansion to Chicago Market

-1 DAYS AGO

Alliance Pipeline Co. has made a non-binding request for expressions of interest for additional natural gas transportation service on its system with an anticipated commencement date of Nov. 1, 2020. In response to high demand for its transportation service to the Chicago market hub , Alliance is asse...

Readmore

Are Women the Key to Closing U.S. Skills Gap?

-1 DAYS AGO

The Manufacturing Institute, Deloitte and APICS have just released, “Women in Manufacturing: Stepping up to make an impact that matters.” The joint study is the result of more than 600 survey responses from women professionals in the manufacturing industry, along with nearly 20 manufactu...

Readmore

Fed Beige Book Showing Continued Economic Expansion

3 DAYS AGO

Economic activity increased in each of the twelve Federal Reserve Districts between mid-February and the end of March, with the pace of expansion equally split between modest and moderate . In addition, the pickup was evident to varying degrees across economic sectors.

Manufacturing continued to expand...

Readmore

Valve Live Loading Using Belleville Springs

The "live loading" of valve packing has been the topic of many articles and papers over the past few years. While highly recommended by some, others claim it has no value. The truth is both statements can be correct-it all depends on the individual application.

The problem is determining if a valve is a candidate for live loading. In most cases this can be decided by answering a few questions:

  • Is it a packed valve?
  • Does the valve cycle frequently?
  • Is it motor operated?
  • Is the valve difficult to get at?
  • Is the valve subject to high temperatures and pressures?
  • Is the valve in a critical application?
  • Does the valve have a history of packing leaks?
  • Does the valve have to be monitored under EPA regulations?

If the answer to the first question and any of the others is "yes," there is a good possibility the valve is a candidate for live loading.

Many different packing materials can and have been live loaded, but since the graphite-based materials are the most commonly used in live-load applications, the data referred to is based on these materials.

Live Loading
In its simplest form, live loading is the application of a spring load to the gland follower of a packed valve. A Belleville spring between the gland follower and its fastening studs and nuts provides an effective way to establish and maintain a controlled amount of stress in the packing set. The amount of the packing stress in a live-loaded system can be controlled by the size of the Belleville spring used and how far it is compressed or deflected. In a live-loaded packing system, the follower will continue to push against the packing even when packing volume is lost (by friction, extrusion, consolidation, etc.) The spring load will be slightly reduced as the springs expand, but this reduction in load will be much less than the load that is lost if the packing set was not live loaded. This remaining load allows the packing stress to remain at a level above the minimum sealing stress and enables the packing to remain leak free. There are many reasons why packed valves leak.

The most common problems are listed here, though some cannot be overcome by live loading alone:

  • Wrong packing material for the application.
  • Bent, scored, or pitted valve stems. No amount of spring load can overcome the damage these can cause to a packing set.
  • Improper packing installation. This may be the single biggest reason repacked valves leak. Graphite-based materials are not as forgiving as asbestos. These materials must be installed properly. This includes initially consolidating the packing by cycling the valve and retorqueing. This may take from as few as three to five times, to as many as 15 to 20. Installation procedures can vary from one packing manufacturer to another. Follow the manufacturer's procedures, whether the repacking is being done in house or by an outside contractor. The benefits of live loading are greatest when the packing has been installed properly.

Infrequent Use
A valve that is not used often, like an isolation valve, tends to leak when it has opened or closed after remaining unused for an extended period of time. What has happened is that the packing has consolidated over time, and the initial compressive load is reduced. Also, when the valve is actuated, additional compressive load is lost. If this reduction in packing stress falls below the minimum seal pressure, the valve will leak. Valves that fall into this category are not typically live loaded, but the addition of a single set of springs has been beneficial.

Frequent or High Cycles
When a valve is cycled, the packing around the stem wears. As the packing is lost, the stress on the packing is reduced. If left unchecked, the valve will eventually leak, which becomes very apparent on highly cycled valves, typically control and motor-operated valves. The normal method of overcoming this is frequent retightening of the gland follower bolts. Live loading can alleviate this stress reduction and eliminate the need for constant retightening.

High Temperatures, Pressures and Critical Applications
When valves work at high temperatures and pressures, they are usually in a critical application. Keeping these valves from leaking can be a difficult job. They are subjected to additional factors that make it harder to keep the proper stress on the packing set.

High temperatures can cause the gland follower bolts to creep or relax, which will reduce the stress on the packing set. High pressures usually mean higher packing loads, which can be difficult to maintain. Critical application usually means a need for a higher standard of safety. Live loading can be used to help eliminate these problems.

Maintenance Headaches
Valves that have been chronic leakers and valves that are inaccessible also are good candidates for live loading. Live-loaded valves require less packing maintenance, and the controlled load on the packing set may just help those chronic leakers.

EPA Monitoring

The Clean Air Act has made everyone take a closer look at packing leaks. If a valve has to be monitored, it must not only meet the EPA standard leak rate, but must be able to maintain that leak rate. Also, it must be able to do this without being adjusted. Controlled load on the packing set is essential in attaining this. Live loading may be the most cost-effective way to meet the EPA's standards.

Almost all of the major valve manufacturers, valve rebuilders, packing manufacturers, and packing distributors now have live-loading programs. Some are more complex then others, but all of them work basically the same way: Belleville springs are used to maintain the load on the packing set.

  • Latest Post

  • Popular

  • Links

  • Events

Advertisement

Looking for a career in the Valve Industry?

ValveCareers Horiz

To learn more, watch the videos below or visit ValveCareers.com a special initiative of the Valve Manufacturers Association