Technical Report on Relief Valves
Abstract
The work gives a brief description of the relief valve construction. The functions of the tools are described on the examples of several valve types and the best environment for their use is explained. The main requirements for the valves according to the developed standards are listed.
In any working system a dangerous overpressure can occur as a result of a variety of external factors` malfunction together with internal physical processes causing unpredictable events not provided for normal exploitation. To prevent such problems a relief valve was designed. Relief valve is a tool designed for protection against mechanical damage of pressurized equipment and pipelines by automatic release of excess liquid, steam and gas from the systems and vessels to remove the excessed pressure. Usually an electronic control member for controlling and enabling the release of pressure is used to increase the prevention accuracy (Theobald & Kokko, 2014). It usually works directly in the operating environment along with the majority of the protective structures reinforcement and direct pressure regulators.
The main components of a relief valve are the shut-off switcher and controller providing a force on the sensor associated with the valve shut-off structure. Shut-off valve consists of a valve and seat. With the help of controller the valve is configured so that the force on the spool pressed it against the seat lock body in such case preventing the working environment from further flowing. When the relief valve is closed its sensor element is effected by the strength of the protected system operating pressure tending to open the valve but the shut-off controller force prevents the opening. With the emergence of the system perturbations causing an increase in pressure the amount of force pressing the valve seat is decreased. At the moment when this force becomes zero, an equilibrium of active system pressure force and the force pushing the sensitive element of the valve is set. Shut-off valve opens and if the pressure grow in the system continues, it resets the working fluid through the valve. With decreasing pressure the disturbing effects disappear and the shut-off valve body is closed.
The closing pressure in some cases is 10-15% lower than the operating pressure due to the fact that in order to create a seal closure a significantly greater force than that which was sufficient to maintain the valve opening before sealing is required. This is due to the need to overcome the landing traction molecules of the medium passing through the gap between the sealing surfaces of the spool and seat to oust this environment. Also, a decrease in pressure is caused by the delay in the closure body associated with the impact of a dynamic effort of the flow-through media and the presence of friction requiring additional efforts for its total closure.
Relief valves usually have a corner form but may also have crossed one though regardless of that they are installed vertically so that the stock goes down when closing. Most relief valves are made …
