Throttle control

Fig. 7. Control of fan performance with inlet vane control. SoHd lines marked A and N show normal performance without vanes (vanes wide open). As vanes are progressively closed, static and power curves are modified as indicated by dashed lines. Intersection ( - ) of the system resistance curve with these reduced pressure curves at points B, C, D, and E shows how imparting more spin to the inlet air reduces flow. Projecting points A to E vertically downward to the corresponding power curve locates fan power points A through E7 Power savings achieved over throttling control can be estimated by projecting points B through E vertically downward to the A power curve and comparing the value with that from the proper reduced power curve. To...

V ri ble Frecjuency Drives. An important energy by-product of soHd-state electronics is the relatively low cost variable speed drive. These electronic devices adjust the frequency of current to control motor speed such that a pump can be controlled direcdy to deUver the right flow without the need for a control valve and its inherent pressure drop. Eigure 11 shows that at rated load the variable speed drive uses only about 70% as much power as a standard throttle control valve system, and at half load, it uses only about 25% as much power. 

A control valve consists ot a valve, an actuator, and possiblv one or more valve-control devices. The valves discussed in this section are applicable to throttling control (i.e, vviiere tlovv through the valve is regulated to anv desired amount betvv een maximum and minimum limits). Other valves such as check, isolation, and relict valves are addressed in the next subsection. As defined, control valves are automatic control devices that modify the tliiid tlovv rate as specified bv the controller. 

Multi-Port This term refers to any vaWc or manifold of s ah es with more than one inlet or outlet. For throttling control, the three-way body is used for blending (two inlets, one outlet) or as a dh ertor (one inlet, two outlets), A three-way S ah e is most commonly a special globelike body with special trim that allows flow both o cr and under the plug. Two rotaiw s ah es and a pipe tee can also be used. Special three-, four-, and fh e-way ball- ah e designs are used for switching applications. 

As most throttling control valves are still operated bv pneumatic actuators, the control-valve device descriptions that follow relate primarily to devices that are used with pneumatic actuators. The function of hydraulic and electrical coimteiparts are very similar. Specific details on a particular valve-control device are available from the vendor of the device. 

On springless actuators where the actuator is not usable for throttling control without position feedback,... 

Motorized sluice valve - To throttle the flow of fluid Figure 6.38 Conventional throttle control... 

Figure 6.39 Power requirement and rate of discharge on a throttle control...

There is thus an obvious energy saving by employing sttitic control over the conventional anil more energv-consuming throttle control. 

Thus the energy saving in this particular case by employing the method of speed control over that of throttle control will be... 

Figure 6.41 Power saving with the use of static control compared to throttle control...

Opwatad ValVM 3.5.3.1 Hvdraulic. 1 Fail Close Actuator. 2 Fall Open Actuator. 3 Fail in Position Actuator. 1 AMamating (2-position Control). 2 Continuous (Throttling Control). 3 Standby Open. 4 Standby Closed 1-4 All Modes Catastrophic a. External Leakage b. Internal Leakage > 1% c. Spurious Operation d. No Change of Position on Demand... 

Proportional control is also referred to as throttling control. 

If the molecular weight rises by 20 percent and we control the drum pressure by suction throttle control, the motor amps will increase by about 10 percent. 

In addition to the throttling control valve, other types of process valves can be used to manipulate a process. 

Isolation A means for pressure-isolating control valves, pumps, and other piping hardware for installation and maintenance is another common application for an on/off valve. In this application, the valve is required to have tight shutoff so that leakage is stopped when the piping system is under repair. As the need to cycle the valve in this application is far less than that of a throttling control valve, the wear characteristics of the valve are less important. Also, because many are required in a plant, the isolation valve needs to be reliable, simple in design, and simple in operation. 

Permanent temperature constituent inside the hill would make it possible to determine the between-shroud temperature difference. Throttling control in air pipe would allow adjusting the temperature balance. 

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