Developments in Control Valves Technology [May 2012]

May 26, 2012 7:31 am

Kiran Diwanji, President at Qu Con Inc. talks about the latest developments in the control valves technology
Now as technology advancement is on rise, new concepts and newer process technologies make plants very advanced. Such plants use and need state-of-the-art technologies and products in all areas including valves. With massive globalisation, now there is no physical limitation for buy and sell. In such competitive market, every industry has to be one up in everything – process technologies, waste control, productivity and zero maintenance. Therefore, dynamic progressive industrial units want long lasting fit and forget valves requiring zero or very little maintenance with guaranteed performance. There is more and more stress now on size and weight of valve provided they do not sacrifice performance in doing so. Industry needs small, compact, low weight reliable valve with ‘fit & forget’ feature. Here is one such valve for control functions.
Small is beautiful!Small, compact, light-weight, smart, and precise control valves. For handling low temperature media, air and water, there are such valves available locally. These valves with Belimo actuation are very reliable, high performance, low weight, compact ball valves with built in electronics for precise control. Normal ball valves have severely distorted flow characteristics on account of very high CV value as compared to globe valve used for control function. Belimo ball type control valves have special contoured ball so, actual flow of media flowing in valve opening is controlled by not the hole in ball but buy contour of the ball. This design offers many advantages like, equal percentage flow characteristics, higher rangability, high close off pressure, tight sealing and no sudden pressure jump while opening or closing. In a 3 way ball valve, operation from 0 to 15° of rotation of ball result in tight shut off performance. Further rotation from 15 to 90° gives regulating performance.
For critical service applications, it is desired that valve should not have leakage through seat when it is closed. Valves with Belimo actuation too offers such zero leak ball type valves with excellent seat leakage values which are less than 1/50,000 of maximum CV value for given valve.
These ball valves coming in size from ½ inch to 8 inches – are now used for control functions. These valves are offered with round or profiled opening for very precise flow control. For precise flow control of media, valves are fitted with fast response motorized actuators with minimal loose linkage, complete with feedback potentiometer and smart control electronics for very precise flow control. The smart control electronics of Belimo need just sensor having 4-20mA output signals, and an auto tuned PID controller with fuzzy logics.
Whenever valve is actuated, the Belimo actuated valves go in to self diagnostics and span monitoring. It is automatically travelling to fully open to fully close position for self re calibration. Secondly, the valves have no end limit switches at all. Smart electronics sense and fix end limits themselves. Thirdly, actuator is protected for over torque stress failures. When ever there is valve jamming or obstructions etc., the torque starts increasing. Each Belimo valve is selected and fitted with dedicated actuator with designed torque rated for said valve. When this torque increase beyond safe limit provided, valve stop automatically. Thus the valve stops functioning before external parameter damage them. These features make Belimo valves unique.
In most valves, due to hard stem movement, static friction exceeds dynamic friction and so initially, static friction prevents stem from moving for small input changes. Then stem suddenly moves when force is large enough to free it. Since force is excessive than needed to go to desired stem position, Movement is jumpy and control is shoddy. Underpowered actuator pronounces this effect. It can de-stabilise loop if action is fast. Secondly some valves do not behave same way during opening as during closing. Further since the torque that moves valve varies according to valve opening and process parameters, valve dynamic behaviour is not constant over entire range and that varies dead time, and positioner overshoot. As a result, control valve fail to control temperature precisely. Most control action for precise temperature control need very small incremental change, even 1 per cent or so, to which standard control valve may not even respond at all. These common problems associated with conventional control valve make valve to operate bumpy and jumpy.Belimo actuated flow control system is basically a decentralized intelligent-control loop that operates on its own. It has control put in to valve which receives temperature signal directly from sensor and responds immediately and also in proper algorithm moved into valve electronics giving feedback signal and command to PID controllers so as to position valve opening in such a way that its movement is just incremental in proportion to signal change received. Belimo actuated valves have so simple calibration and commissioning procedure that the whole procedure takes hardly few minutes. It is documented that the reason of failure to reduce process variability to acceptable level in as much as 80 per cent control loops audited was on account of poor dynamic performance of control valve due to not so good interfacing of communication module with valve actuator. A good valve positioner must control valve accurately in terms of dead band, Hystersis, Repeatability and Sensitivity. Smart valve have to have process gain less than 3, linearity less than 3 and hysteresis and dead band also less than 3. This is what Belimo does.
Auto-tuned PID controller with fuzzy logics evaluates close loop response from its existing PID setting and compare with set value. Deviations are converted in to corrections to PID settings, and then it actually and automatically close loop around PID controller. As long as this tuning loop is closed, it can readjust PID settings to correct any variations in process parameters as soon as they occur by observing resulting variations in damping, period etc.
PID controller acts in such a way that valve opens or closes just enough in response to intelligent signal required to position valve opening to regulate flow and hence desired parameter accurately.
Thus, by selecting Belimo actuated smart control ball valve, PID controller with auto tuned fuzzy logics and sensor, the plant is assured long trouble free flow control in given service conditions. Belimo actuated ball type control valves are especially suited for used in closed water circuit of heating, ventilating, and air conditioning system. These valves do have temperature limitations. They are not meant for temperature higher than 125°C. For high temperature controls up to 340°C, Qucon KZ zero leak globe type smart control valves with Belimo actuator is the ultimate answer.
These valve not only do not leak at all from anywhere including gland packing, but also provide very precise temperature control to the tune of 1°C plus minus even at 340°C. Secondly, as these valves are painted with high temperature paint, the valve colour do not burn/peel off even while handling hot oil at 340°C. The company offers 24-months unconditional warrantee with valves that confirms reliability and performance accuracy.
Effect of high temperature on performance of panelThe plants that need precise controls or have high speed high output production lines, invariable have state of art microprocessor based electronics in control panels. To ensure maintenance free, shut down free machine running, these panels too have to operate shut down free. For which they must be temperature controlled. Every control panel has heat generated from components within. Also, there is ambient to consider. They all add up to heat electronic components within control panel. For every 10°C rise temperature in electric/electronic control panel enclosure, on-line production shut down increases twice as often. Heat and dust in compact/multi function electrical/electronic control panels, variable speed drives, electric distribution panels, servos and programmed logic controllers make components to deteriorate, reduce its active life, make it malfunction, cook digital displays to misread, make controls to drift, and breakers to trip prematurely bellow their rated loads. To avoid these, the panels must be climatically controlled.
Starting with display, LED efficiency is directly related to junction temperature at junction where individual diode is connected to the base. Maintaining low junction temperature ensures longer life of LED and low loss of lumens. In addition to drive current and thermal path; ambient temperature affects light output, life expectancy and colour. Temperature has very serious effect on capacitors. At high temperature, capacitor ages fast and cause dielectric failure of capacitor even after it has served for long time. As temperature increases, insulation resistance decreases due to increased electron activity. Similarly dissipation factor of capacitor increases with temperature decreasing capacity to perform. Even in hermetically sealed capacitor, at high temperature, pressure inside sealed capacitor increases causing breakage of capacitor seal, leading to leakage of impregnated liquid or allowing ingress of moisture.
In any given control panel, technically power is fed to perform a function and it is switched off when function is completed. This on-off function induces alternate stress in structural elements as a result assembly heats up and cools down cyclically. Every stress cycle uses up small part of total life of system, leading to ultimate stress cracking of structural parts like solder joints, plated through holes lead wires etc. When axially loaded devices on PCB are exposed to such thermal cycling environments, overturning moments can occur which can force PCB to bend. Bend PCB means big trouble. .
Understanding the seriousness of keeping controls cool, normally control cabinets in plants are cooled with fans as providing air conditioning may not be viable all the time. Unfortunately, fans cannot cool enough, plus it draws dusty humid air inside panel cabinets, creating other source of failure. To some control panels, air conditioners are provided with equipment itself, or plant adds it on later if possible. While conventional air conditioning is relatively costly, needs electrical power, is unsuitable in hazardous explosive ambient, have more on-going maintenance, and are large in size and sometimes, are difficult to install in given space; gas free air conditioning technology is desired in these instances which overcomes all these problems at lower cost. Vortex tube cooling technology is the answer.
Advents in control panel air-conditioningAir conditioning of control panel without motor, electricity, refrigerant or moving parts by vortex tube cooling technology. The panel air conditioning with vortex tube is most simple, compact, light weight, maintenance free, economical and time proven technology. The vortex tube is a mechanical device with no moving parts at ll.One has to just inject /feed dry clean air at 7- 8 bar pressure into small vortex tube and outcomes chilled air from within. In vortex tube, dry air is fed tangentially in to swirl chamber where it is accelerated at sonic speed of 10 lac rpm, creating a cyclone – vortex inside. The cyclonic air stream travels length of tube and reaches the end where the conical nozzle allows very small amount of air to escape in atmosphere whereas majority of air is forced back as inner vortex of smaller diameter within outer vortex of larger diameter. As both vortices rotate at same angular velocity, inner vortex loses angular momentum. This decrease of angular momentum imparts very high kinetic energy to outer vortex resulting in increase of temperature of air in outer vortex. Since outer vortex is under higher pressure due to higher centrifugal force on account of larger diameter, temperature of outer vortex is higher than inner vortex. The effect is similar to peltier effect resulting in clear heat transfer at boundary layer separation and separate flow of hot and cold stream of air. The cold air flow is directed towards cold end in to control panel and hot air is exhausted out of other end of vortex tube through valve. The air flow can be adjusted by turning the knob at hot end. This in turn can adjust cold air temperature inside control panel. The tube needs no electrical power, no evaporator, no compressor or no refrigerant and since has no moving parts there is no maintenance at all.
Secondly, vortex cooling creates positive pressure inside panel at pressure slightly higher than atmospheric; hence it does not allow foul dusty, corrosive plant air into control panel. This feature is very important for plants handling corrosive resins etc. By installing solenoid valves and low cost temperature controller circuit, one can set within control panel operational temperature and close air supply as long as set temperature is maintained within. Thus duty cycle of vortex tube would be minimal and so would be air consumption.
These are time-tested technologies serving hundreds of end users worldwide, resulting in ‘fit & forget’ maintenance-free precise temperature controls at elevated temperature reducing shut downs and saving money. Money saved is money earned.