Motorized valves

A three-state controller is used to drive either a pair of independent on/off actuators such as heating and cooling valves, or a bidirectional motorized actuator. The controller is actually two on/off controllers, each with deadband, separated by a dead zone. When the controlled variable lies within the dead zone, neither output is energized. This controller can drive a motorized valve to the point where the manipulated variable matches the load, thereby avoiding cychng. 

Buildup of condensate in a heat exchanger can cause operating problems as well as water hammer. If the steam supply is controlled by a motor valve and the valve is not fully open, the steam pressure may be too low to expel the condensate, and its level will rise. This will reduce heat transfer, and ultimately the steam supply valve will open fully and expel the condensate. The cycle will then start again. This temperature cycling is bad for the heat exchanger and the plant and may be accompa-... 

The second area will be feedwater pumps. It is normal to have a duplicate standby feedwater pump. Sometimes this may be two for each boiler or one duplicate pump to serve any selected boiler. These will usually require manual changeover in the even of failure of the duty pump. It is practical to automate this changeover by using pressure sensors and motorized valves. The same can apply to oil-circulating pumps, gas boosters, water-treatment plant and any other valves and motors. It is possible to do most things, but in the end there is the cost to be considered. An... 

A three-way motorized valve is modulated between full flow to the coil and full bypass to satisfy the room thermostat. 

Steam flow to vessels can be controlled by motorized valves, allowing timed control of the valve. Such valves can also be made to modulate rather than on/off operation. 

AVhen a noun is used, the interviewer may need to clarify hy asking, What, exactly For example, a motor valve may he electric or air operated the difference may he important to the investigation. 

This difficulty too can be obviated by decreasing the flow rate to just compensate for the decrease in activity owing to catalyst deactivation. To accomplish this, it is necessary to incorporate some device to sense conversion in a recycle reactor as shown in Figure 3. The signal from this sensor is then fed back to a motor valve and positions it to follow a flow rate profile in time so that the conversion is maintained constant. This type of reactor provides data on a deactivating catalyst in which the catalyst is exposed to reactant and product concentrations for a particular reaction and temperature that are constant in both space and time. In principle, then, the... 

On top of the cyclone is located a cross-tee which is equipped with two manually operated, and one motorized butterfly valve. The manual valves are employed to direct the gas to a particular end use. The motorized valve controls the gas entering the flare. 

The presence of a trench/pipe system in Option B, used to remove rain accumulations, increases the risk that contaminated fire water might be inadvertently discharged into the sanitary sewer system. In order to reduce this risk, it is necessary to install a motorized valve in the drainage piping. This valve could be arranged to close automatically in the event of a fire through a signal from the fire alarm panel and manually as needed. It may also be desirable to use a valve which will automatically close in the event of loss of power. Alternatively, this valve could be normally closed and opened when needed. 

The methylcyclohexane and hydrogen entered at the top of the reactor. The total effluent passed through a motor valve at the exit of the... 

Much has changed since the first commercial FIA analyzer was introduced by Bifok. This FIA 05 instrument (Ref. 153, Fig. 5.1), developed by the Swedish group of R. Lundin, T. Anfalt, and B. Karlberg in a then typical garage enterprise (actually an abandoned milk store) had a motorized valve, modular flow system but no computer control of the analyzer functions. Later, FIAtron, Lachat and Control Equipment (all U.S.), Hitachi, Jasco, and Soma Kazaku (Japan) as well as Micronal (Brazil) entered the market with different designs. Meanwhile Bifok developed a new generation of FIA instruments and in a joint venture with Tecator (Sweden) marketed these analyzers worldwide. 

Finally, it should be added that automated injection with a motorized valve can be used to reduce peak width (and increase the sampling frequency) if the valve can be returned from inject to fill position after a chosen period of time. Thus the volumetric sample cavity can either be emptied completely by leaving the valve in the inject position for a sufficiently long time [5 s. Fig. 6.10(4 )] or partly by letting the valve remain in the inject position for shorter periods of time (curve b, 2.8 s c, 1.8 s dy 1.3 s). Shorter injection periods, however, will lead to decreasing peak heights and may result in loss of reproducibility (cf. also Chapter 5.1). 

PRIMARY CONTROL - A device which directly or indirectly controls the control agent in response to needs indicated by the controller. Typically a motor, valve, relay, etc. 

The Adaptive Prosthesis uses two microprocessor-controUed motor valves to control a hybrid hydrauHc and pneumatic system. The hydraulic system controls stance, flexion, and terminal impact. The pneumatic portion of the system control both swing phase and knee extension. The Adaptive Prosthesis also offers a... 

Valve common causes include deposited salt or broken motor valve. 

NaK (pronounced nack), as the eutectic is called, as well as the alkali metals in general, have found new interest as heat dissipating and heat transfer agents in nuclear reactors and in motor valve stems of internal combustion engines. These uses have led to a sp ecial series of articles in the literature on the subject of handling these substances and their properties. - ... 

Control systems generally consist of three main elements. A sensing element (sensor) is used for measuring the actual valne of the parameter to be controlled. The control device serves for forming commands for intervention, if necessary. The element for intervention (e.g., a motoric valve) executes the command of the controller. 

CUl and CU4 are value-keeping controllers for the control of the outlet temperatures of the collector and of the HWS heat exchanger, respectively. Control signals are produced by the temperature sensors Tqc and Tw- Control is realized by changing the mass flow rates with one-way motor valves Vq and respectively. 

Figure 9 Tomlin s static vapour-pressure apparatus with injection of liquids. A, vapour-pressure cell B, capacitance null manometer C, motorized valve D, variable leak E, F, metal bellows valve G, Teflon valves H, degassing apparatus M, nitrogen pressure regulator L, nitrogen ballast tank (35 1) V, to high vacuum line (Reproduced by permission from Royal Australian Institute of Chemistry, 5th National Convention, Papers of Physical Chemistry Division)...

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