March/April 2010

System Integration

Opportunity for valve innovations

Despite economic downturn, opportunities abound for control valve innovation

FAST FORWARD

  • At least 80% of all control valve designs originated in the 1960s.
  • Standards activities for control valves have taken a hit as a result of the severe economic downturn.
  • A modified triple-eccentric butterfly valve is one example of improving control valve design.
 
By Hans D. Baumann

s11The control valve industry, being closely aligned with process control instrumentation, suffers similarly from the current recession. This drastic decrease in order came as a severe blow, following the hay-days in 2008 after the oil boom. Unfortunately, the future outlook is still bleak. The prospect of future high oil prices is expected to materialize only at the end of the current recession. Even then, spending is only expected on the production (upstream) side with refinery construction tabled due to lower gasoline demand and use of smaller cars.

This somber assessment is reflected in the last survey statistic published by Valve Magazine, where at the end of 2009, only 13% predicted an increase in business among their members, while 56% expected a decrease in shipments during 2010.

A somewhat brighter future is offered by the coming renaissance of atomic power plants. Those are the only, large scale, viable alternatives to all other "green" energy providing schemes.

Another avenue towards an increase in business is to export, especially into the developing markets. However, exports require competitive products and a strong manufacturing base. Unfortunately, the latter has suffered due to the past outsourcing boom. This has led to a dramatic shrinkage of manpower employed in the industrial sector. The percentage of workers in manufacturing as percentage of total employment went from 26% in 1965 to less than 8% today. As a result, we now have to import about 40% of all manufactured goods from abroad, mostly from China. This does not come for free, and we have to pay for it in U.S. Treasury Bonds to the tune of $650 billion in 2008 alone. This (current account) deficit, which started in the 1980s, has reached a total of about $6 trillion, about one half of our total national debt.

There is a direct correlation between decrease in industrial manpower and our foreign debt (current account deficit). While manufacturing numbers started to decrease by about 20% between 1960 and 1980, due to the effects of automation, 1980 saw the beginning of outsourcing on a grand scale and with it the accelerated loss of manufacturing jobs. Analyzing foreign countries found a number of 16% of factory employment is needed for a country to have to have a positive trade balance. We reached that point in about 1990. At that time, our trade imbalance was only around $80 billion, mostly due to importation of foreign oil. In a recent interview, Jeffrey Immelt, the chief executive officer of General Electric Co., seemed to agree by suggesting increasing our manufacturing base to 20% of the total employed. That would be a great goal.

What can we do about this problem? We urgently have to reverse the trend and start rebuilding our manufacturing basis. Only by selling manufactured goods, control valves being part of it, can we increase our exports and in turn earn foreign currency to pay our debt. President Barack Obama was only half right when he called for a doubling of our export business. This can not be done without an increase in our current weak manufacturing base.

Here is where the government can help:

  1. Give tax advantages to U.S. manufacturers.
  2. Feed stimulus money into the manufacturing sector.
  3. Provide low-cost loans to build new factories.
  4. Encourage R&D efforts to make our products more desirable.
  5. Allow to let the U.S. dollar to devaluate further. This will increase the cost of imported foreign goods (to be then replaced by local products) and decrease the price of U.S. exported items in order to be more competitive.

State of the art

At least 80% of all control valve designs originated in the 1960s. This to me is regrettable, since it represents a lack of progress and entrepreneurship.

While there was a major leap forward in the design of valve positioners during the 1980s and 1990s, where technologies jumped from analog to digital signals and circuitries enabled valve maintenance and even offered control functions, not much progress has been seen since. Yet, control valves still are a vital part of our control loops and, despite many predictions, have not been substantially replaced by speed-controlled pumps and the like.  Part of the lack of attention for this vital part and its function as the final element in our fluid controlling loops is our seeming obsession with everything electronic.

One can also observe the basic hardware functions of a valve have not changed, leaving few choices for innovation. After all, we have not found a better way to control the rate of fluid flow in a pipe (the basis of all control modes, be it for pressure, temperature, or level). We still do it by creating a pressure differential, which then creates velocity. This in turn is converted by the valve plug or vane into turbulence (and heat), leading to a change in the amount of fluid passing a valve. This is a process called "throttling."

However, relying too much on old, established hardware can bring major disadvantages. The primary problem is old technologies offer no patent protection and can easily be copied. This can happen domestically by low-cost domestic repair facilities or overseas by factories in emerging countries, aided by lower labor costs. Sadly, the latter is unintentionally aided when U.S. manufacturers have valves made in foreign countries and in the process export vital know-how.

Why don't we see more R&D activities in the valve industry? My opinion is all new products are associated with risk, be it customer acceptance or worrying about performance problems. Corporate management, especially with a tight budget, tends to be highly risk-aversive. A second reason has to do with the way R&D activity is conducted-mostly on a computer. This restricts free and independent thinking, the basis of creativity, and limits "hands-on" experience. After all, there is no software as yet telling you how to invent something.

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Source: US Bureau of Census and Labor Statistics

What is new

Yet, there are some efforts, albeit on a smaller scale, to add to the "state of the art" in control valve design. One example is a modified triple-eccentric butterfly valve. Here, is a way to convert a standard, commercial, on-off butterfly valve into a well-performing control valve, by adding a downstream attachment having curved and slotted internal surfaces providing, in conjunction with the camming vane, an equal-percentage flow characteristic and, at the same time, offer low noise and anti-cavitation features. Thus, by combining the advantages of a low-cost, tight shut-off, and the high pressure capabilities offered by such a valve with a replaceable static throttling device, one can offer a better substitute for many standard globe and rotary control valves.

The slotted areas between the teeth are gradually opened by the lower half of the vane. Such reduced flow areas increase turbulent frequencies of passing gaseous fluids. This leads to a substantial attenuation by the downstream pipe wall, hence a lower aerodynamic noise level. A similar effect is achieved with liquids. Here the "coefficient of incipient cavitation" (the pressure ratio signaling the onset of cavitation) is increased, allowing for higher pressure drops. However, even if cavitation should occur, it is only a local phenomena, restricted to near the outlet of the slots, thereby avoiding the pipe-damaging "super cavitation" typical with standard valves discharging directly and unimpeded into a piping system.

Another example is a new control valve design especially developed for the bioprocessing industry. The design challenge is such a valve has to be aseptic, to be self-draining, have a good flow characteristic, and be dynamically stable. Highly polished angle valves meet most of those requirements, since they can drain directly into the top of a vessel, with flow entering from the horizontal port. The problem with such designs is the valve plug is inserted from the top, which means the plug is closing down against the seat where the fluid pressure tends to force the plug down and close the valve. This creates a "positive feedback" force and can lead to dynamic instability, even slamming against the seat. This is especially problematic with larger valve sizes.

One valve design overcomes such problems by installing the plug from below, i.e., pulling the plug up against the seat (and the inlet pressure). This creates a "negative feedback" situation and assures dynamic stability. Another feature of this design is the use of throttling channels in the sides of the outlet ports, where they are easy to clean and polish and where the circular surface areas between such "slots" provide ample guides for the moving valve plug. Removing the throttling surfaces from the plug, as was customary, and placing them inside the slots avoids other potential problems such as unsteady flow caused by wall attachments and the tendencies to cavitate.

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A variation of the flow capacity (Cv) of such a valve can easily be achieved by simply altering the number of parallel slots. Finally, by inserting the plug from below, one can dispense of a removable bonnet at the top of the valve in order to reduce cost and eliminate a potential leak source.

Standards activities

Standards activities for control valves are in the realm of ISA75. Here too, the severe economic downturn has left its mark, and some standards activities are now relegated to the Working Group 9 under International Electrical Commission (IEC), Switzerland, Committee 65B. But even here, activities are relegated to updating existing valve and positioner standards. The most important revision is on IEC 60534-8-3, "Control Valve Aerodynamic Noise Prediction." The new draft, currently in preparation, departs from the current "science-fundamentals" based model to one heavily inspired by empirical data, which makes the document less "vendor neutral" and adds substantial mathematical complexity. Standard 6053-2-1 on control valve sizing also gets updated. There are no basic changes planned in customary sizing equations. What is proposed is to simplify some equations and make them more user-friendly.

ABOUT THE AUTHOR

Hans D. Baumann (baumannh@comcast.net), an ISA Honorary Member, is a senior consultant for H. B. SERVICES PARTNERS LLC. in Rye, N.H.

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