Control Valve Innovations

McMillan and Weiner Asks Hans Baumann About His Most Notable Innovations in Control Valves.

By Greg McMillan, Stan Weiner

Share Print Related RSS
Page 1 of 2 « Prev 1 | 2 View on one page

Stan: We are fortunate to have had the opportunity to talk with Hans Baumann, an international engineering and management consultant. Hans is the greatest innovator in control valve designs that provide precise throttling for some of the most difficult conditions encountered in process applications. Hans developed special valves for power plants, breeder reactors, truck refrigeration, nuclear submarines, bioprocesses, high rangeability and extremely low flows. He also developed the "critical flow factor," "hydraulic jet diameter" and "reducer correction factors." He retired as senior vice president of Fisher Controls International in 2000. Prior to founding H.D. Baumann Assoc. Ltd. in 1977, Hans was corporate vice president at Masoneilan-International Inc., manager of R&D at Worthington, director of engineering at Cashco Inc., and chief engineer at a valve supplier to Siemens. Hans is a member of the Process Automation Hall of Fame.

Greg: Pinch (boot) valves used for sanitary applications and slurries had a quick-opening characteristic, crude regulating capability and excessive capacity. The roller mechanism diaphragm valve offers precision throttling of flow. The diaphragm eliminates the need for stem packing, and provides a small, smooth path for fine adjustment of extremely small flows that meets sanitary valve requirements. The very low friction of the packless and roller bearing linkage design enables the valve to respond to incredibly minuscule changes in signal. These valves can be used for fine control of additives and nutrients in food and drug production. The flow varies with the third power with stroke. The exceptional resolution and flow characteristic offers extraordinary rangeability of better than 15,000:1 for a stroke range of 25:1. The flow is forced to be laminar. The pressure drop is small compared to available pressure. As a result, the installed characteristic is close to the inherent characteristic, enabling an accurate linearization of the controller output in the DCS, provided there's at least a 16-bit output card. pH control systems have incredible reagent delivery rangeability and precision requirements, and reagent demands so low for strong acids and bases (particularly for the last stage) that the flow is laminar. For higher flows, I still use Baumann sliding stem valves because the low-friction design and multiple spring diaphragm actuator offered the best precision, particularly below 10% stroke. This was shown in "Improve Loop Control Loop Performance," Oct 2007, in Chemical Processing. Most of the manufacturer tests and statements as to resolution (actually threshold sensitivity) are for tests near mid-throttle range, so that seating friction is not seen.

Stan: Hans, what are some of your more notable innovations besides the roller diaphragm valve?

Hans: Due to economics, users want to buy butterfly valves. However these valves tend to have poor flow characteristics, excessive flow capacity, stick-slip from high seal friction and dead band from backlash in shaft connections and linkages. There tends to be a terrible breakaway torque near the closed position and a torque reversal around 70 degrees. To help meet the demand for rotary valves without sacrificing controllability, I developed the Camflex valve at Masoneilan. I developed the low-noise and low-torque "Low-T" butterfly at Baumann. Later, I helped develop the Control-Disk butterfly valve at Fisher that has a contoured disk, low torque, an inherent equal percentage characteristic and better throttling at low flow rates. Butterfly valves with teeth cut down on cavitation. This can be done with a Sharktooth attachment from Arthur Yeary Associates in Chicago. The low torque requirement eliminates shaft windup seen in rotary valves, where the shaft twists and finally breaks free, jumping to a position beyond the desired position, a response worse than stick-slip.

Greg: How is backlash eliminated in rotary valves?

Hans: A solid clamp is used between the actuator shaft and valve stem. Spline shafts are also used rather than pinned shafts. The translation from linear to rotary motion is eliminated by the use of actuators with rotary shafts.

Stan: Why do we have so many rotary valves with excessive dead band?

Hans: Many of the rotary valves marketed as control valves were originally on-off valves. With on-off valves, you don't care about dead band. The valves were already in the piping spec, and the price was low. Users didn't know the consequences of dead band, so they installed them.

Page 1 of 2 « Prev 1 | 2 View on one page
Share Print Reprints Permissions

What are your comments?

Join the discussion today. Login Here.

Comments

No one has commented on this page yet.

RSS feed for comments on this page | RSS feed for all comments