Valves, interrupter

In the production head, each stream is in pumped circulation continuously, to maintain uniformity of composition and temperature. When it is time for an injection, valves interrupt the circulation to allow the required metered quantities into the mixing chamber. Figs. 13.9 and 13.10. 

Solvent-divert system. Used in conjunction with an interface, it permits temporary interruption of the flow from a chromatograph to a mass spectrometer by briefly opening a valve to a pumping line. Thus effluent present at a high concentration (usually solvent) does not enter the mass spectrometer ion source. 

Actuators often provide a failsafe function. In the event of an interruption in the powder source, the actuator will place the valve in a predetermined safe position, iisiiallv either full open or full closed. Safety systems are often designed to trigger local failsafe action at specific valves to cause a needed action to occur, vv4uch rnav not be a complete process or plant shutdown. 

Eail-Safe Design features which provide for the maintenance of safe operating conditions in the event of a malfunction of control devices or an interruption of an energy source (e.g., direction of failure of a control valve on loss of signal). A system is fail-safe if failure of a component, signal, or utility that would create a hazard initiates an action that maintains the system in a safe condition. 

Small interrupters and MCCBs particularly may be electrically operated through a solenoid valve. 

Valve or non-linear resistor In this version, a nonlinear SiC resistance is provided across the gap and the whole system works like a preset valve for the follow current. The resistance has an extremely low value on surge voltages and a very high one during normal operations to cause a near-open circuit. It is now easier to interrupt the follow currents. 

Filters must be provided for all gas buffers in places where the gas will pass through the gas seal. The gas should be filtered to a nominal value of 2 microns. On most critical systems, dual filters will be required to permit servicing the filters without having to shut down the compressor. This requires the use of a transfer valve that can be switched without causing a flow interruption. If liquids are anticipated, heat tracing or an alternate gas source should be the first consideration. Should this not prove to be practi-... 

Cooley. Specify twin coolers with non-interrupting transfer valve. Spevily materials of construction, utilities, and fouling factor,... 

Recently, dry wire-pipe ESPs are being cleaned acoustically with sonic horns (Flynn, 1999). The horns, typically cast metal horn bells, are usually powered by compressed air, and acoustic vibration is introduced by a vibrating metal plate that periodically interrupts the airflow (AWMA, 1992). As with a rapping system, the collected particulate slides downward into the hopper. The hopper is evacuated periodically, as it becomes full. Dust is removed through a valve into a dust-handling system, such as a pneumatic conveyor, and is then disposed of in an appropriate marmer. 

A limit stop or open bypass around each valve so that flow cannot be completely interrupted, or... 

Fail-safe Design features that provide for the maintenanee of safe operating eonditions in the event of a malfunetioning eontrol deviee or an interruption of an energy souree (e.g., direetion of failure of a motor-operated valve on loss of motor power). 

Some radioactive bromine (half-life 36 hours), in the form of ammonium bromide, was put into a brine stream as a radioactive tracer. At another plant 30 km away, the brine stream was electrolyzed to produce chlorine. Radioactive bromine entered the chlorine stream and subsequently concentrated in the base of a distillation column, which removed heavy ends. This column was fitted with a radioactive-level controller. The radioactive bromine affected the level controller, which registered a low level and closed the bottom valve on the column. The column became flooded. There was no injury, but production was interrupted. 

Also available for the prevention of bit plugging are backflow valves that prevent cuttings suspended in water from backing up through the bit into the drill pipe when the flow of air or gas is interrupted. 

In the case of an interrupted pilot, de-energize the safety shut-off valves. 

LPG cylinders are filled only at purpose-designed filling plants and (if refillable) are returned there when exhausted. To provide a continuous gas supply, two, four or more cylinders are connected to a changeover valve so those empty cylinders can be exchanged without interrupting the supply. Automatic changeover devices are available, which switch to the reserve supply when necessary, and indicate that they have done so. A typical wall-mounted ACD is illustrated in Ligure 20.9. 

System components, such as pumps, valves and gauges, create both turbulent flow and high friction components. Pressure drop, or a loss of pressure, is created by a combination of turbulent flow and friction as the fluid flows through the unit. System components that are designed to provide minimum interruption of flow and pressure should be selected for the system. 

Although the problems associated with septum injectors can be eliminated by using stop-flow septumless injection, currently the most widely used devices in commercial chromatographs are the microvolume sampling valves (Fig. 8.3) which enable samples to be introduced reproducibly into pressurised columns without significant interruption of the mobile phase flow. The sample is loaded at atmospheric pressure into an external loop in the valve and introduced into the mobile phase by an appropriate rotation of the valve. The volume of sample introduced, ranging from 2 piL to over 100 /iL, may be varied by changing... 

NOTE Water hammer is caused by sudden interruptions in flow as when steam meets draining condensate. The steam produces instantaneous surges of pressurized water that hits valves, elbows, and tees at high velocity. This produces a hammering sound and leads to metal stress and possible failure. 

Valves and regulators are used in pipeline networks to perform a variety of functions. Isolating valves are used to interrupt flows and to shut off... 

Other devices which find varying degrees of success in the treatment of thixotropic materials include rotary beaters and pulsating valves to interrupt the air flow in the drying zone. Both of these result in movement of the cake, giving a reduction in moisture content. 

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