Automatic valves

In addition to the use of such manual valves, automatically operated valves may be considered as an additional safeguard in certain installations. These can be connected to (among other interlocks) panic buttons sited within the building, which they are protecting. This is a recommended requirement for buildings containing plant of over 2 MW total heat input and supplied with gas at above 1 bar. 

Water tube boilers have a pressure gauge, vent cock, and drum safety valve on the top of the steam drum. Where superheaters are fitted, the steam takeoff line leads to the superheater, which is followed by a superheater safety valve, automatic nonreturn valve, and stop valve with a pressure-equalizing line and valve. 

When these latent conditions create an unfolding situation, the safety barriers present in an organization can be seriously affected. Svenson (Svenson, 2001) identifies three functional categories of safety barriers, e.g. technical, human, organizational. These safety barriers can be activated by different safety barrier systems, such as the closure of a valve automatically by a computer or manually by an operator. Moreover, a safety barrier system can (simultaneously) operate more than one safety barrier, like an operator who can close a valve, connect a hose, or a computer which closes down a machine and alerts an operator, etc. 

The most sophisticated way of coupling the two chromatographs is a fraction transfer system comprising one eight-port injection valve (see Fig. 15). With two storage loops, it is possible to collect fractions continuously without losses. When starting the separation, loop 1 is in the LOAD position, whereas loop 2 is in the INJECT position. Each of the loops has a volume of 100-200 pi. When the first fraction leaves the HPLC system, it enters loop 1 and fills it. When loop 1 is completely filled with the fraction, the injection valves automatically switch to the opposite positions, i.e. loop 1 is then connected to the SEC system in the... 

In most chemical reactors, temperature is a critical variable that must be controlled. Cooling water circulates in the reactor jacket, removing the enthalpy of reaction. To control the reaction temperature, the cooling-water flow rate to the jacket is controlled. Set the desired tenqjerature on the tenqjerature-indicator-controller (TIC), which is measured by a temperature sensor installed in the reactor. The control valve automatically corrects any deviations from the desired temperature by adjusting the cooling-water flow rate into the jacket. 

Check valves. A check valve permits flow in one direction only. It is opened by the pressure of the fluid in the desired direction when the flow stops or tends to reverse, the valve automatically closes by gravity or by a spring pressing against the disk. Common types of check valves are shown in Fig. 8.4. The movable disk is shown in solid black. 

When pyrolysis temperatures are reached, the six-port Valeo valve is switched and the 34-port Valeo valve automatically takes 15 samples of the gas stream for later analysis in the Hewlett-Packard 5834a Gas Chromatograph (HPGC). Unsampled gas is collected in a Teflon bag for later analysis. 

ESDI is located at the well and consists of pressure switches, relay logic, and the flow-line valve. This trip system closes the flow line valve automatically if the line pressure drops below or goes above... 

The filling of a tank is monitored with the help of a level indicator with alarm LIA by the operator. The written operating instruction states that the pump P has to be switched olf on alarm and the valve V has to be closed. For safety reasons an additional level switch LSHH is installed. It turns off the pump and closes the valve automatically. However, as in case of the Buncefield accident (vid. Table 1.1) it may remain in a deactivated position. 

Thus, the composition of air is 20 percent oxygen gas and 80 percent nitrogen gas hy volume. When a diver is submerged, the pressure of the water on the diver is greater than atmospheric pressure. The air pressure inside the body cavities (for example, lungs, sinuses) must be the same as the pressure of the surrounding water otherwise they would collapse. A special valve automatically adjusts the pressure of the air breathed from a scuba tank to ensure that the air pressure equals the water pressure at all times. For example, at a depth where the total pressure is 2.0 atm, the oxygen content in air should be reduced to 10 percent by volume to maintain the same partial pressure of 0.20 atm that is,... 

Less Less flow Excess chlorine in (1) Caustic valve Automatic closure of... 

There are many different combinations of sensors and control valves on production machines. The sensor is usually mounted above the slip in the reservoir behind the doctor blade. In the case of puddle casting, where the slip is pumped onto the carrier behind the doctor blade, there is no reservoir, and the sensor detects the spread of the slip backward from the doctor blade itself. The most common sensors are based upon capacitance or inductance and are known as proximity sensors. These sensors detect the surface of the slip and generate an electrical impulse when the slip is within range. The electrical impulse in turn controls either an on-off valve or a proportional valve to control the flow of slip to the reservoir. When the slip falls below the range of the sensor, the valve automatically opens to allow more slip to flow into the reservoir until the electrical impulse begins the controlling cycle once more. 

Dump valves and Inlet emergency supply valves automatically open k. Building pressure reaches l/k pslg and fog spray system la automatically actuated ... 

The chemical processing industry uses a complex network of automated systems to control its processes. The smallest unit in this network is called a control loop. Control loops usually have (1) a sensing device, (2) a transmitter, (3) a controller, (4) a transducer, and (5) an automatic valve. Automatic valves (see Figure 5-7) can be controlled from remote locations, making them... 

Does the tire inflation control valve automatically shut off the airflow when the valve is released ... 

An acetylene supply plant consists of a high-pressure, medium-pressure and possibly a low-pressure section. In addition to the pressure regulators, safety devices such as manual safety cylinder or bundle connectors, non-retum valves, automatic quick acting shut-off devices, flame arrestors and multifunctional safety devices have to be installed. 

The letdown flow outside containment isolation valve is a normally closed, fail closed, air-operated globe valve that isolates letdown to the liquid radwaste system. This valve automatically opens and closes on a plant control system signal from the pressuriser level control system or a containment isolation signal from the protection and safety monitoring system. Ibis valve operates in the same fashion as the letdown flow inside containment isolation valve. The letdown flow outside containment isolation valve eloses more quickly than inside containment letdown flow isolation valve to limit seat wear of inside containment isolation valve. This valve operator has a flow restricting orifice in the air line, so it opens more slowly than inside containment letdown flow isolation valve. In addition, during brief periods of shutdown, when the reactor coolant system is water solid, this valve throttles to maintain the reactor coolant system pressure. Manual control is also provided in the main control room and at the remote shutdown workstation. 

The hydrogen addition contairunent isolation valve is a normally open, fail closed, air-operated globe valve is located outside containment in the hydrogen addition line. The valve automatically closes on a containment isolation signal from the protection and safety monitoring system. Manual control is provided in the main control room and at the remote shutdown workstation. 

The two feed water control valves and the two feed water isolation valves automatically close. 

---