Rotary control valve

Rotary Control Valves. A rotary control valve utilizes an eccentric plug that rotates nominally 50° to an open position or to intermediate positions for throttling control. The eccentric action of the plug ensures that rubbing contact with the valve seat occurs only within a few degrees of the closed position, minimizing friction and optimizing controUabihty (Fig. 5.196). 

Most control valves used for automatic process control are either globe or rotary control valves. Their parts are briefly discussed here. 

Figure 4 Some typical rotary control valves. [Courtesy of Fisher Controls Intemationai LLC, Emerson Process Management.]...

Fr is a control valve s Reynolds number factor, Cvs is laminar flow control valve Cv. Cv is turbulent flow Cv. Fs is laminar or streamline flow factor. Fd is valve type modifler. Fd equals 1.0 for globe control valve and ball type rotary control valve. It equals to 0.71 for butteifly type rotary control valve. 

Most reciprocating compressors have inlet and outlet valves (on the piston heads) that are actuated by a pressure difference. These are called self acting valves. There are some larger multistage reciprocating piston compressors that do have camshaft-controlled valves with rotary slide valves. 

Although most fluid power motors are capable of providing rotary motion in either direction, some applications require rotation in only one direction. In these applications, one port of the motor is connected to the system pressure line and the other port to the return line. The flow of fluid to the motor is controlled by a flow control valve, a two-way directional control valve or by starting and stopping the power supply. Varying the rate of fluid flow to the motor may control the speed of the motor. 

Directional control valves may be classified in several ways. Some of the different ways are by the type of control, the number of ports in the valve housing, and the specific function that the valve performs. The most common method is by the type of valving element used in the construction of the valve. The most common types of valving elements are the ball, cone, sleeve, poppet, rotary spool, and sliding spool. The basic operating principles of the poppet, rotary spool, and sliding spool types are discussed in this text. 

The rotary spool directional control valve. Figure 40.24, has a round core with one or more passages or recesses in it. The core is mounted within a stationary sleeve. As the core is rotated within the stationary sleeve, the passages or recesses connect or block the ports in the sleeve. The ports in the sleeve are connected to the appropriate lines of the fluid system. 

The rate of feed of solids may be controlled using screw feeders, rotating tables or vibrating feeders, such as magnetically vibrated troughs. Volumetric rates may be controlled by regulating the speeds of rotation of star feeders or rotary vaned valves. 

Figure 16.13. Indirectly heated rotary dryer. A-Firing door. B-Air regulator. C-Fumace. D-Control valves. E-Feed chute. F-Furnace flue. G-Feed screw. H-Fan. J-Driving gear. K-Discharge bowl. L-Duct lifters.

Rotary stem-valve designs are normally offered only in their naturally occurring characteristic, since it is difficult to appreciably alter this. If additional characterization is required, the positioner or controller may be characterized. However, these approaches are less direct, since it is possible for device nonlinearity and dynamics to distort the compensation. 

If whole tires are used, they are usually added manually to the reactor. If the processor is using chipped tires, the chips are stored in a chip silo (see Figure 8-1, Item 1), and are fed from the silo into the reactor using a vibratory feeder or a screw conveyor to achieve a controllable and known feed rate. The feed passes through an air lock system consisting of two valves or a rotary star valve. From the air lock, the feed enters the pyrolysis reactor (Item 2). 

The preneutralizer slurry is pumped at a controlled rate to a rotary-drum, ammoniator-granulator there it is distributed onto a rolling bed of recycled solids. The most commonly used metering system for the preneutralized slurry is a variable-speed centrifugal pump with automatic control from a magnetic flowmeter. Some plants have had success with a magnetic flowmeter and automatic control valve of a special ball type. 

Injection valves designed for FIA are produced by a number of manufacturers. These valves are often microprocessor controlled (26) and are quite versatile. However, for all of the analyses described later, a simple low-pressure rotary injection valve designed for liquid chromatography is adequate (e.g., Rheodyne Model 50). Pneumatic and electric actuators are available for automated operation. An injection valve that can be machined quite easily from poly(tetrafluoroethylene) (PTFE, Teflon) and Plexiglas is described elsewhere (25, 27). 

The most widely used control valves for liquid and high pressure gas streams are the various sliding stem valves such as the bevel plug, V-port, parabolic plug, and for small flows the needle valve. For corrosive materials and slurries, pinch-type valves like the Saunders patent valves are used. Rotary stem valves include plug types and for gas flows butterfly valves, dampers, and louvers. 

Include the same length of upstream straight-run piping before control valves as for orifices. This is particularly important for rotary valves. 

Rotary, star valve feeder used especially as solids feeders for dilute-phase pneumatic conveying to provide an air lock and to feed solids. Seal/wear depends on Ap and abrasiveness of powder. For pressure systems keep Ap <80 kPa for vacuum systems Ap <40 kPa. Provide an air vent to take the air loss away from the gravity flow of the solids and to control the filling of the star. 

The control valve adjusts the flow rate by changing the size and shape of the flow area offered to the fluid passing through it. There are two main categories of control valve used on process plant globe valves and rotary valves. The flow area in a globe valve is dictated by the position of the valve plug relative to its seat, while the flow area in a rotary valve depends on the... 

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