Valves actuation, horizontal

It has been shown that the position of a valve installation has an influence on the frequency of cases of leaks (vertical and horizontal stem valves installed the same system and with similar operating conditions show different behaviour). The horizontally mounted valves are more likely to leak, although the manufacturers usually give assurances that the valves can be mounted in any desired position. In some cases, a modification of a horizontally mounted valve has been successfully implemented. This consists of installing a mechanical support on the stem close to the seal package in order to prevent excessive deformations of the stem itself. It common to see valves mounted vertically but with the actuator in the lower position. Here, as can be predicted, the leaks moved along the stem and damaged both the stem thread and the valve actuator. 

Explosion isolation can also be effected by rapid action barrier valves. At present, they can be arranged only in horizontal pipehnes and are suitable, in general, only for streams with a small amount of dust. Such valves are thus frequently used to protect ventilation lines. As a certain explosion overpressure is necessaiy to close such valves, a distinction is made between self-actuated and externally actuated barrier valves (Fig. 26-46). 

The catalyst preparation area is positioned between the two polyethylene production units with 60 feet separating each one. The aluminum alkyls storage canopy and isopentane horizontal storage tank are located at a remote area at an approximate distance of 250 feet away from the production and utility areas. The isopentane is transported to the catalyst preparation area through a 3-inch pipeline. A remote actuated isolation valve on this supply line that fails closed is located at the isopentane storage tank. This control valve and an associated isopentane feed pump are managed by the operator in the control room. 

It would be very nice to be able to dampen the input fluctuations and to smooth the output from this vessel. To do this requires a control function. One form of control would be to increase the flow rate out of the tank whenever the level in the tank rises or falls above or below a designed set point level ha. For example, the set point level could be the steady-state level that we found from the earlier example with constant input flow, which is the also the bold black horizontal line in level graph above. To increase the flow rate in the case of gravity-driven flow, we must increase the size of the orifice. We can increase it in proportion to the difference between the actual level in the tank at any time and design level. The actual implementation would involve having a level sensor tied to an actuator, which would open the valve more or less depending on the level. The mathematical description of this control function can be given as ... 

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