NOTICABLY INNOVATIONS IN CONTROL VALVES
Stan: We're fortunate to possess had the chance to talk to Hendes Baumann, a worldwide engineering, and management consultant. Hendes may be the finest innovator in
control valve designs that offer precise throttling for probably the most difficult conditions experienced in process applications. Hendes developed special valves for power plants, breeder reactors, truck refrigeration, nuclear submarines, bioprocesses, high rangeability and very low flows. Also, he developed the "critical flow factor," "hydraulic jet diameter" and "reducer correction factors." He upon the market as senior v. p . of Fisher Controls Worldwide in 2000. Just before founding H.D. Baumann Assoc. Limited. in 1977, Hendes was corporate v. p . at Masoneilan-Worldwide Corporation., manager of R&D at Worthington, director of engineering at Cashco Corporation., and chief engineer in a valve supplier to Siemens. Hendes is part of the procedure Automation Hall of Fame.
Greg: Pinch (boot) valves employed for sanitary applications and slurries were built with a quick-opening characteristic, crude controlling capacity, and excessive capacity. Sequence mechanism diaphragm valve offers precision throttling of flow. The diaphragm eliminates the requirement for stem packing and offers a little, smooth path for fine adjustment of very small flows that fit sanitary valve needs. The low friction from the packless and roller bearing linkage design enables the valve to reply to incredibly minuscule alterations in the signal. These valves can be used as a fine charge of additives and nutrients in drug and food production. The flow varies using the third power with stroke. The exceptional resolution and flow characteristic offer remarkable rangeability of higher than 15,000:1 for any stroke selection of 25:1. The flow needs to become laminar. Pressure drop is less space-consuming than available pressure. Consequently, the installed characteristic is near to the natural characteristic, enabling a precise linearization from the controller output within the DCS, provided there's a minimum of a 16-bit output card. pH control systems have incredible reagent delivery rangeability and precision needs, and reagent demands so low for strong acids and bases (particularly during the last stage) the flow is laminar. For greater flows, I still use Baumann sliding stem valves since the low-friction design and multiple spring diaphragm actuator offered the very best precision, particularly below 10% stroke. It was proven in "Improve Loop Control Loop Performance," March 2007, in Chemical Processing. The majority of the manufacturer tests and statements regarding resolution (really threshold sensitivity) are suitable for tests near mid-throttle range, to ensure that seating friction isn't seen.
Stan: Hendes, what are a few of your more notable innovations aside from the roller
diaphragm valve?
Hendes: Because of financial aspects, users are interested in
butterfly valves. However, these valves generally have poor flow characteristics, excessive flow capacity, stick-slip from high seal friction and dead band from backlash in shaft connections and linkages. There is commonly a dreadful breakaway torque close to the closed position along with a torque reversal around 70 levels. To assist satisfy the interest in rotary valves without having to sacrifice controllability, I developed the Camflex valve at Masoneilan. I developed the reduced-noise and occasional-torque "Low-T" butterfly at Baumann. Later, I helped get the Control-Disk butterfly valve at Fisher which has a contoured disk, low torque, a natural equal percentage characteristic and throttling at low flow rates. Butterfly valves with teeth cut lower on cavitation. You can do this having a Sharktooth attachment from Arthur Yeary Associates in Chicago. The reduced torque requirement eliminates shaft windup observed in rotary valves, in which the shaft twists and lastly breaks free, jumping to some position past the preferred position, an answer worse than stick-slip.
Greg: How's backlash eliminated in rotary valves?
Hendes: A good clamp can be used between your actuator shaft and
valve stem. Spline shafts will also be used instead of pinned shafts. The translation from a straight line to rotary motion is eliminated through actuators with rotary shafts.
Stan: So why do we have a lot of rotary valves with an excessive dead band?
Hendes: Most of the rotary valves marketed as control valves were initially on-off valves. With on-off valves, you do not worry about a dead band. The valves were already within the piping spec, and also the cost was low. Users did not be aware of the effects of the dead band so that they installed them.
Greg: There's hardly any data provided by on-off valve manufacturers on dead band. After I requested a presenter of the valve having a piping valve heritage about a dead band in a recent ISA conference, he'd not a clue in regards to what dead band was and why it's important. What's your take on positioners, thinking about that signal portrayal, as needed, is preferably completed in the DCS?
Hendes: For that small sliding stem valves, I designed multiple spring diaphragm actuators. Positioners weren't necessary. The pneumatic positioners were well known to be hard to keep calibrated, and using cams for signal portrayal gave an incorrect feeling of improvement from linearization since the alternation in output signal was very small around the steep slope from the valve characteristic. I developed a small pneumatic positioner for globe valves with simply eight parts. With the introduction of digital positioners with advanced diagnostics and position read-back, the extra information for predictive maintenance is beneficial. Flexible tuning enables the positioner to become enhanced for an actuator and valve type and operating conditions. Digital signal portrayal and 16-bit I/O cards have reduced the priority of lack of resolution or threshold sensitivity during linearization. You still need to lessen the gain should you encounter high valve friction.
Stan: What's your latest innovation?
Hendes: I've just created a compact three-way valve getting merely a single vane you can use for bypass, and for mixing service. The valve includes a single curved vane with double shutoff at one-third the price. I am presently designing a butterfly valve for beer processing having a sanitary liner and without any breakaway friction.
Greg: There are plenty of various kinds of actuators. Excluding individuals initially produced for on-off valves, (e.g., link-arm and rack-and-pinion pistons), that is terrible news, and just what would you see as choices?
Hendes: I favor diaphragm actuators as their pistons have a sliding friction. Diaphragm actuators happen to be produced for operation at actuation air pressures as much as 100 psig rather from the previous 30-psig limit, extending their application to bigger valves and greater pressure drops. Ballscrew drives can handle .002-in. the resolution having a response duration of a couple of tenths-of-a-second limitation mainly because of inertia. Electrical actuators neglect to the final position, whereas pneumatic actuators use springs to pressure a preferred fail position (e.g., fail available to prevent surge, high-pressure or high-temperature journeys). Additionally, electro-hydraulic actuators having a walking motor driving the oil pump along with a spool valve reversing flow between your pump and also the actuator will also be able to extremely fast responses. However, issues with leaks, ambient temperatures, and maintenance make these packages unattractive.
Stan: A great deal could be stated about using valves like a final control element, but the final word originates from.