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Problem-Driven Innovation

Problem-Driven Innovation

Developing Alternative Technology to Imp...

Valve Repair Takes Center Stage in Houston

Valve Repair Takes Center Stage in Houston

Attendees gathered June 2-3 in Houston t...

What Internal Best Practices Can Do for Valve Selection

What Internal Best Practices Can Do for Valve Selection

As time goes by, technology moves forwar...

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Problem-Driven Innovation

Problem-Driven Innovation

Monday, 20 June 2016  |  Mark A. Lobo, P.E.

Developing Alternative Technology to Improve Product Performance

Industrial product engineering teaches us to understand the difference between problem...

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Industry Headlines

Curtiss-Wright Awarded Contracts for U.S. Naval Defense Platforms

1 DAY AGO

Curtiss-Wright announced that it has been awarded contracts valued in excess of $80 million to provide valves for the U.S. Navy’s Virginia-class submarines and Ford-class aircraft carriers. The awards were received from Bechtel Plant Machinery, Inc. and General Dynamics Electric Boat Division ...

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DeZURIK Adds Dedicated Clean Room to Sartell Plant

3 DAYS AGO

In order to ensure proper cleaning procedures are performed on valves intended for oxygen, ozone, chlorine, hydrogen peroxide, isocyanate and other applications, DeZURIK has constructed a new dedicated clean room within its Sartell, MN manufacturing plant.

Operated by trained cleaning technicians, DeZU...

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Global Upstream Spending Slashed by $1 Trillion

1 DAY AGO

Global upstream development spending from 2015 to 2020 has been cut by 22% or $740 billion since the oil price started to drop two years ago, according Wood Mackenzie's research . When you include cuts to conventional exploration investment, the figure increases to just over $1 trillion. Expect to see...

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EPA Bans Fracking Wastewater Disposal at Public Treatment Plants

3 DAYS AGO

The EPA has finalized a rule establishing pretreatment standards for discharges of wastewater from onshore unconventional oil and gas (UOG) extraction facilities to municipal sewage treatment plants (also known as publicly owned treatment works, or POTWs). The rule is designed to prevent the discharge...

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U..S. Durable Goods Orders Down 2.2% in May

1 DAY AGO

New orders for manufactured durable goods in May decreased $5.3 billion or 2.2% to $230.7 billion, the Commerce Department announced today. This decrease , down following two consecutive monthly increases, followed a 3.3% April increase. Excluding transportation, new orders decreased 0.3%. Excluding d...

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Federal Judge Halts New BLM Fracking Rules

1 DAY AGO

“The Obama administration will fight a federal judge’s ruling overturning its effort to regulate hydraulic fracturing on public lands,” Bloomberg reports . The White House says they will take the case to the U.S. Court of Appeals.

“The ruling, issued late Tuesday by Wyoming-based...

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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.

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