Instrumentation control valves

Use multiple parallel instruments/control valves of different ranges for the for same service... 

From the basic process-containing flowsheet other engineering specialties develop their own details. For example, the instrument engineer often takes the requirements of the process and prepares a completely detailed flowsheet which defines every action of the instruments, control valves, switches, alarm horns, signal lights, etc. This is his detailed working tool. 

Instrument Failure assume instrument control valves freeze or fail in open position (or closed, which ever is worse), determine capacity for relief based on flows, temperatures, or pressures possible under these circumstances. The judicious selection of instrument failure sequence may eliminate or greatly reduce relief valve requirements. 

Develop a complete plant layout for the sodium dodecylbenzene sulfonate plant that is described in Chap. 2. Indicate location of instruments, control valves, and panel boards. Provide possibilities for future expansion or revision of the plant. 

Turn on the nitrogen supply for instruments, control valves, mixing resins and for blanketing RO product water storage tank. 

Cleaned and flushed (instruments, control valves, check valves protected)... 

Instrumentation, controls, valves and chemical addition points should be located, as much as practicable, outside the process equipment enclosures unless the anticipated radiation level within the enclosure is not signiEcant. 

Field instrument, control valves and relief valves preinstallation inspection and test records and calibration... 

Control valve fails to respond 3. Same 3. Place valve on critical instrumentation JFL 1/93... 

From a dynamic-response standpoint, the adjustable speed pump has a dynamic characteristic that is more suitable in process-control apphcations than those characteristics of control valves. The small amphtude response of an adjustable speed pump does not contain the dead baud or the dead time commonly found in the small amphtude response of the control valve. Nonhnearities associated with frictions in the valve and discontinuities in the pneumatic portion of the control-valve instrumentation are not present with electronic... 

The two principal elements of evaporator control are evaporation rate a.ndproduct concentration. Evaporation rate in single- and multiple-effect evaporators is usually achieved by steam-flow control. Conventional-control instrumentation is used (see Sec. 22), with the added precaution that pressure drop across meter and control valve, which reduces temperature difference available for heat transfer, not be excessive when maximum capacity is desired. Capacity control of thermocompression evaporators depends on the type of compressor positive-displacement compressors can utilize speed control or variations in operating pressure level. Centrifugal machines normally utihze adjustable inlet-guide vanes. Steam jets may have an adjustable spindle in the high-pressure orifice or be arranged as multiple jets that can individually be cut out of the system. 

In.strument air failure. The consequences of the loss of instrument air should be evaluated in coujuuc tiou with the failure mode of the control valve ac tuators. It should not be assumed that the correct air failure response will occur on these control valves, as some valves may stick in their last operating position. 

For the purpose of this chapter, instrumentation will be considered everything from the primary element monitoring the controlled variable through the control valve performing the throttling action. The process equipment interacts with the instrumentation to provide the process... 

In addition to failure as a result of their utihty supply, items of equipment are subject to individual failure through mechanical malfunction. Such items include pumps, fans, compressors, mixers, instruments and control valves. The process upset resulting from such malfunctions (e.g., loss of a reflux pump) may in turn result in emergency conditions and the potential for overpressure. These contingencies should be examined and evaluated. 

In addition, a further mechanism of chattering may be introduced in some liquid PR valve installations if the response characteristics of a control valve in the same system are such that hunting between the two occurs. Generally, this can be eliminated by adjustment of instrument settings or by installation of two valves with staggered set points... 

Data on spare and parallel equipment are often omitted. Valving is also generally omitted. A alve is shown only where its specification can aid in understanding intermittent or alternate flows. Instrumentation is indicated to show the location of variables being controlled and the location of the actuating device, usually a control valve. To help the reader better understand the process flow sheet, a list of commonly used symbols is presented in Fig. 5.9.1. 

Control valves carry the same designation as the instrument to which they are connected. 

In general, the final pump selection and performance details are recommended by the manufacturers to meet the conditions specified by the process design engineer. It is important that the designer of the process system be completely familiar with the action of each pump offered for a service in order that such items as control instruments and valves may be properly evaluated in the full knowledge of the system. 

These last three are special valves from the viewpoint of chemical and petrochemical plant applications, but they can be designed by the major manufacturers and instrumentation manufacturers as these are associated with instrumentation controls. Care must be taken in the system design to make certain it meets all ASME code requirements. 

It is very important to note that in this loop system the parameter To, which must be kept constant, is measured, though all subsequent action is concerned with the magnitude of the error and not with the actual value of To. This simple loop will frequently be complicated by there being several parameters to control, which may necessitate considerable instrumental analysis and the control action will involve operation of several control valves. 

Standard symbols for instruments, controllers and valves are given in the British Standard BS 1646. 

Handbook of Control Valves, Instrument Society of America, p. 17. 

Whenever a test 1s to be run, the sample composition and Instrument control parameters must be defined. This Is done with three (or more) data-entry screens. The first data-entry screen, shown In Figure 4, deals with experiment identification and base fluid composition. The operator simply types in the desired information Into unprotected fields of the screen. Information requested Includes such Items as experiment ID, submitter s name, base fluid type and base fluid additives. The base fluid pump rate and valve selection are also requested for later use by the control programs. The second data-entry screen is used to select the desired test temperatures and also to record any comments related to the experiment. The third data-entry screen Is used to input the in-line additive compositions. This screen is filled out for each set of additives to be tested with the base fluid as described on Data-Entry Screen No. 1. Also input are the pump rates for each of the three additive pumps. This information is used by the control programs when the additive set is being tested. (The pump rates are preset by the operator, but the pumps are turned on and off by the control programs as necessary during the course of an experiment.)... 

Baumann HD. Control Valve Primer. Durham, NC Instrument Society of America, 1991. 

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