【2026 Safety Valves】Difference between safety valves built into pumps and pipeline safety valves
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The key difference between the safety valve built into the pump and the safety valve installed separately on the pipeline lies in their respective objects of protection and functional roles. In simple terms, one is to protect the “pump” device, and the other is to protect the entire “pipeline system”.
The pump is equipped with a safety valve: the device’s “self-protection” mechanism. The safety valve built into the pump is commonly referred to as an internal pressure relief valve or pressure limiting valve. Protection target: Primarily aimed at the pump body itself. Core function: Its role is to prevent the pump from being damaged due to sudden pressure surges during startup, shutdown, or operation. For example, when the outlet pipeline becomes suddenly blocked, it can open quickly, allowing the fluid to circulate inside the pump or over a short distance, thereby preventing the pump from damaging its motor or internal components due to pressure buildup. Limitations: These valves are typically designed for protection over short periods of time at low flow rates. It may be unable to handle continuous, high-volume overpressure conditions in the entire export pipeline system that result from prolonged blockages or improper operations.
Piping safety valve: the “final line of defense” of the system. A safety valve installed separately on the pump outlet pipe is a standard system safety relief device. Protected objects: What is protected is the entire export pipeline system, including pipes, flanges, valves, and all equipment downstream. Core function: Acting as the \"last line of defense\" for the system, it activates automatically when the pressure in the pipeline system exceeds a preset safe level, allowing a large amount of fluid to be discharged to a safe location (such as back into the inlet tank or a designated discharge system), thereby ensuring that the pressure throughout the system remains within safe limits and preventing catastrophic incidents such as pipe bursts.
Regulatory requirements: According to standards such as the \"Design Code for Petrochemical Enterprises\" (GB 50160), safety valves must be installed on the outlet pipes of positive displacement pumps (such as reciprocating pumps and gear pumps), unless it can be proven that the valves built into the pump itself are sufficient to protect the entire system.
A common misconception is that having valves on the pump means the system is protected. In fact, the built-in pressure relief valves in many pumps only provide short-term protection for the pump itself, and do not offer protection for the operation of the entire system.
In engineering design and safety inspections, if it cannot be confirmed that the valves built into the pump are capable of protecting the entire piping system, an independent safety valve must be installed on the outlet pipeline to meet regulatory requirements and ensure system safety.
The following information on “fully open safety valves and slightly open safety valves” is for reference only. Starting from July 1, 2026, the \"Safety Technical Regulations for Safety Accessories of Pressure-Type Special Equipment\" (TSG 92-2026) will come into force. TSG 92 stipulates that \"(1) When the working medium is gas, steam, liquefied gas, or a liquid whose maximum operating temperature is equal to or higher than its standard boiling point, a full-open safety valve should be used\" ； When the working medium is a liquid, a slightly open safety valve can be selected ； ” Should: As a legal term, “should” implies a mandatory obligation and is essentially no different from “must”; it is used to regulate legal obligations. Yes: one has the power to do so, or not to do so.
TSG 92 mentions “regular self-inspections” and “regular calibrations”; if “improper selection” is detected and cannot be addressed in a timely manner, the safety valve should be taken out of use.
In China, safety valves are classified according to their opening height into fully open safety valves (with an opening height of 4/25 or more of the channel diameter), slightly open safety valves (with an opening height ranging from 1/20 to 4/25 of the channel diameter), and moderately open safety valves (with an opening height between those of the fully open and slightly open types) (see Figure 1).
Fully open safety valves and slightly open safety valves are classified based on their opening height, which involves the flow area, curtain area, and discharge area. Flow channel area: The minimum cross-sectional area of the flow channel between the inlet end of the valve and the sealing surface of the closing element, used to calculate the theoretical flow rate in the absence of any resistance effects. (See Figure 2). Curtain area: The area of the cylindrical or conical passage formed between the sealing surfaces when the valve disc rises above the valve seat. (See Figure 2). Discharge area: The minimum cross-sectional area of the flow path when the valve discharges fluid. For fully open safety valves, the discharge area is equal to the area of the flow path; for slightly open safety valves, the discharge area is equal to the area of the curtain.