What are the setting pressure, adjustment pressure, and discharge pressure of a safety valve?
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The setting pressure, adjustment pressure, and discharge pressure of a safety valve are its key technical parameters, which play an important role in ensuring the safe operation of the system. Although the three are closely related, they each have their own differences. (1) The following is an introduction to these three parameters: 1) Setting pressure: The setting pressure is the predetermined pressure at which the safety valve begins to open, that is, the gauge pressure measured at the inlet of the valve. At this pressure, the force generated by the medium pressure to open the valve balances the force that keeps the valve disc in place on the valve seat. This is the threshold at which the safety valve opens automatically when adjusted to a specific pressure. 2) Starting pressure: The starting pressure refers to the pressure point at which the safety valve actually begins to release pressure. When the actual pressure of the system reaches this value, the safety valve will begin to operate. The starting pressure reflects the sensitivity and protective performance of the safety valve, and is a parameter used to describe the dynamic response characteristics of the safety valve. 3) Discharge pressure: Discharge pressure refers to the set pressure plus the excess pressure. The excess pressure is usually expressed as an increment in percentage of the set pressure. (II) The following illustrates the relationship among the three parameters: 1) Setting pressure and trip pressure a) Definition difference: The setting pressure is the predetermined pressure at which the safety valve begins to open; it is a set value ； The starting pressure is the pressure point at which the safety valve actually begins to release pressure, and it is a dynamic parameter in actual operation. b) Relevance: The set pressure is usually determined at a level that is lower than or equal to the system’s maximum operating pressure. When the system pressure reaches this set pressure, the safety valve begins to open; at this point, the system pressure is actually the trip pressure. Ideally, the set pressure and the start-up pressure should be equal, but in practice differences may arise due to factors such as valve performance and environmental conditions. c) Conversion relationship: Typically, the opening pressure of a safety valve is slightly higher than or equal to the set pressure, as the valve needs to overcome static friction and mechanical resistance before it can open. 2) Set pressure and discharge pressure a) Definition of the difference: The set pressure is the pressure at which the safety valve opens for the first time, while the discharge pressure is the pressure when the safety valve is fully open and discharging fluid steadily. b) Relevance: The discharge pressure is usually the set pressure plus a certain excess pressure. Excess pressure refers to the increase in pressure above the set pressure, usually expressed as a percentage of the set pressure; it is used to ensure that the safety valve opens fully once the set pressure is reached, thereby allowing excess pressure to be effectively released. c) Influencing factors: The discharge pressure depends not only on the set pressure but also on the structural characteristics of the safety valve and the discharge medium. The standards for setting the discharge pressure of safety valves in different media (such as steam, air or other gases, water or other liquids) also vary. d) Conversion relationship: Discharge pressure = Set pressure + Excess pressure. The excess pressure is generally expressed as a percentage of the set pressure; for example, if the excess pressure is set at 10% of the set pressure, then the discharge pressure will be 1.1 times the set pressure. 3) Starting pressure and discharge pressure a) Functional relationship: The starting pressure represents the beginning of the discharge process, indicating that the safety valve begins to release pressure ； The discharge pressure represents the end of the discharge process, indicating that the safety valve has reached its maximum discharge capacity. b) Transition relationship: As the system pressure increases, the safety valve will gradually open starting from its setting pressure, until it reaches the discharge pressure at which point discharge occurs steadily. During this process, the opening height and flow rate of the safety valve gradually increase until the maximum discharge requirement is met. c) Conversion relationship: There is no direct numerical conversion relationship between the starting pressure and the discharge pressure, as these two parameters reflect the performance of the safety valve at different operating stages. The starting pressure refers to the sensitivity with which the safety valve begins to operate, while the discharge pressure relates to the discharge capacity of the safety valve when it is fully open. In general, the relationship among the setting pressure, the discharge pressure, and the opening pressure of a safety valve is closely linked, and it is crucial for ensuring that the safety valve responds properly to system overpressure. Understanding these parameters and their relationships helps to select, configure, and maintain safety valves more effectively, ensuring the safe operation of the system.
Can the set pressure be higher than the trip pressure? What are the regulatory requirements?
Jump pressure is a term used in academic research; it is not standard terminology. The only standard term is set pressure, and there is no such requirement that the set pressure should be higher than the jump pressure. Due to practical constraints, in reality the starting pressure = discharge pressure = set pressure; no one goes to the trouble of measuring the difference between them, nor are there any standard requirements for this. The setting pressure of the safety valve is determined based on the equipment’s set pressure, and the sealing pressure is also determined based on that set pressure. Be sure not to be misled by those so-called experts. Under normal circumstances, the user only needs to determine the operating pressure of the equipment; the set pressure and the sealing pressure are determined by the calibration agency based on the operating pressure.
The user must identify the most critical pressure, which is the 【operating pressure】. This operating pressure represents the maximum gauge pressure that can be reached at the top during actual use. There’s no need to worry about other pressures; professionals will handle confirming those for you.
Too many users fail to understand the working pressure, which results in the customized equipment not meeting the required standards and the safety accessories failing to function properly. Moreover, there’s confusion caused by all those technical terms. Many experienced workers even invent values such as the maximum working pressure or the highest allowable pressure in order to mislead others. The more pressure values provided, the greater the likelihood of confusion and misguidance; it’s even possible to confound less experienced professionals completely. Yet it is still the users who end up bearing the consequences. Remember, you only need to figure out the work-related stress; leave the rest of the stresses to professionals to deal with – there’s no need for you to worry about them. 【Working pressure】 refers to the maximum pressure (gauge pressure) that may be reached at the top of the equipment under normal operating conditions. 1. The Special Equipment Safety Law determines special equipment based on this pressure ； 2. The design pressure is one that you provide to the design firm for determination ； 3. The maximum allowable operating pressure is determined by the design team through actual calculations ； 4. The setting pressure of the safety valve is determined by the calibration institution based on the operating pressure ； 5. The test pressure is determined by the design unit, manufacturing unit, and inspection unit based on the operating pressure. Almost all sources of stress stem from work-related pressures; don’t worry about other types of stress. If someone expects more stress from you, it means they are not professional enough.