Pressure Control Valve

Pressure Control Valve


Who invented the Pressure Control Valve? 

Erastus Boise Kunkle, born on December 1836, learned the machine trade from his dad. Kunkle laboured in a high-pressure job before inventing the control valve. He worked in the locomotive shops for Pennsylvania Railroad where he invented a lock-up pop safety valve, designed to release steam pressure in locomotive engines. Boiler over pressure was a serious problem, yet control valves were unheard of at the time. Kunkle wanted to make his work site safer and chase the American Dream. He was a curious inventor and diligent problem solver.
E.B. patented the safety valve invention in 1875. The Fort Wayne Safety Valve Works, operated by E.B. Kunkle & Company grew and a100 years later a modified version of the original invention was still in production.

Where it is possible to find the Pressure Control Valve? 

It is possible to find Pressure-Control Valves in practically every pneumatic and hydraulic system. They help in a variety of functions, from keeping system pressures below a desired limit to maintaining a set pressure level in part of a circuit. The conventional technical solution normally adopted is to install a series of components designed, sized and manufactured in accordance with the process and the products of the storage system. In particular, an adequate dust abatement system is needed that allows the release of the air, but which retains the same, in order to avoid harmful emissions into the atmosphere. It is mandatory to install a pressure control device that intervenes if a risk situation arises. In the event that the internal pressure of the silo reaches a limit value, both in positive and negative terms, the valve must open and allow the evacuation / introduction of air, with a consequent and connected emission of dusty material into the atmosphere. An adequate powder loading system, therefore, must let the air pass and at the same time retain the material, avoiding the increase in internal pressure of the silo during the loading phase. Most pneumatic and hydraulic power systems are designed to operate within a defined pressure range. This range is a function of the forces the actuators in the system must generate to do the required work. Without controlling these forces, the power components and expensive equipment could damage. Control valves make it possible to avoid this hazard.

Technical features 

During the filling phase, inside the silo there is a separation of the two phases: while the solid part deposits in the silo, the air must be evacuated. An excessive increase in pressure inside the container can lead to the swelling of the silo, with consequent structural damage to it, or in a limit situation to its explosion with very serious effects for people, structures and the environment. The most critical phase of the entire process is that of the loading end, in which the flow rate of flours is much lower than that of air: the pressure, in fact, passes from 1.2-1.5 bar to atmospheric pressure, resulting in an increase in air speed. It is at this time that it is possible to have a rapid develop in pressure inside the silo, leading to a rise in risk for the structure, for the accessories and complementary components of the storage system. Similarly, a rapid change of pressure during the emptying phase of the container can equally lead to implosion, resulting in high levels of risk for the workers, the plant structures and for the environment. The silos roof, from a design point of view, can also be equipped only with an opening that allows the air to be vented to the outside or, alternatively, but with the same efficiency and safety, with vent pipes of variable diameter. Since the gaseous system is still full of dust particles, a simple opening would involve venting not only the air, but also the emission of pollution into the atmosphere and the possibility that the product can contact external factors. This design approach turns out to be a non-viable path and, above all, of non-respect for the environment protection. 

From a technical point of view, the valve is a device for restoring normal operating conditions and should intervene rarely, only in cases of system anomaly. As for its operation, any external device does not control the VCP valve. Its operation can be in pressure and under pressure. During the pneumatic loading of the silo the pressure increases inside, exceeding the calibration value of the VCP, the valve disc rises allowing the fluid under pressure to escape. During the silo-emptying phase a depression is generated inside, exceeding the valve calibration value, the lid lowers allowing the entry of air inside to balance the depression generated. The VCP, pressure control valve, represent the last possibility of venting if abnormal pressure conditions inside the silo endanger the structure. In the VCP, helical springs keep the valve lids closed if pressure conditions remain within the setting limits. The three external spring bars keep the outer ring-shaped lid hermetically closed until the pressure inside the silo exceeds the force generated by the springs. If the pressure exceeds the set value, the lid will open for venting. The smaller disc-shaped lid closes a circular opening in the centre of the pressure relief disc from below. It is held in closed position by a spring bar and pressed on the external disc by the normal pressure existing inside the silo. In the event that a depression occurs inside the silo, the spring is compressed causing the lid to open. The air entering the silo from the external atmosphere ensures a rapid balance of pressure: at this point, the spring returns to the disc in closed position.

Reliability and productivity: protection systems must always be available and operational. The possibility of false interventions that would reduce the productivity of the plant must be excluded. They are installed above the silos and hoppers to avoid pressure values, during loading, or depression, during unloading, which would compromise the structure of the silo and / or filter. The intervention values can be calibrated with special kits of springs or counterweights.

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