Shanghai Xiazhao: Comprehensive FAQ on Pressure Relief Valves

Shanghai Xiazhao specializes in the R&D, production, and sales of pressure relief valves, with in-depth expertise in industrial piping, high backpressure working conditions, fire protection water supply systems, and other fields. To help customers quickly resolve core questions regarding the selection, application, and installation of pressure relief valves, we have compiled the following high-frequency FAQs. The content is strictly based on industry standards and practical experience, providing you with professional and reliable references.

I. Basic FAQs on General Pressure Relief Valve Selection

1. How to correctly select a pressure relief valve? What are the core steps for selection?
Correct selection must follow the 5-core step process: "Clarify Requirements → Select Type → Calculate Parameters → Screen Models → Verify and Adjust".
Step 1: Clarify the system's operating pressure, design pressure, medium type (liquid/gas/steam), temperature, flow range, and pressure control accuracy requirements.
Step 2: Select the type based on working conditions—direct-acting pressure relief valves are suitable for low-pressure, small-flow scenarios with stable pressure, while pilot-operated pressure relief valves are preferred for high-pressure, large-flow scenarios requiring high control accuracy.
Step 3: Calculate key parameters—set pressure must match the system's design/operating pressure, consider the impact of backpressure, and accurately calculate the relief capacity.
Step 4: Screen product models with reliable brands and comprehensive after-sales service based on type and parameters.
Step 5: Verify against the actual system conditions and adjust the plan if necessary. Shanghai Xiazhao provides customized selection consulting services to ensure optimal compatibility.

2. If the pipeline pressure is unstable, is it related to incorrect pressure relief valve selection?
It is highly likely related. Incorrect pressure relief valve selection is one of the core causes of pipeline pressure fluctuations. Common scenarios include: mismatched set pressure with actual system requirements, leading to premature or delayed valve opening; selected valve type incompatible with system backpressure changes, affecting normal valve operation; insufficient relief capacity failing to discharge excess pressure in a timely manner.
Solutions: Re-calculate system parameters and adjust the set pressure; replace with a suitable valve type based on backpressure conditions (e.g., backpressure balanced pressure relief valves for large backpressure fluctuations); select a pressure relief valve with relief capacity matching requirements. For precise troubleshooting, contact Shanghai Xiazhao's technical team for working condition analysis services.

3. What are the core differences between direct-acting and pilot-operated pressure relief valves? How to choose?
The core differences lie in structure, performance, and application scenarios:
① Structure: Direct-acting valves consist of a disc, spring, and valve body, with a simple structure; pilot-operated valves consist of a main valve + pilot valve, with a complex structure.
② Performance: Direct-acting valves have fast response and low cost but low control accuracy, easily affected by media and environment; pilot-operated valves offer high control accuracy, strong stability, and adaptability to a wide pressure range and complex working conditions, but with slower response and higher cost.
③ Selection recommendations: Choose direct-acting valves for low-pressure, small-flow scenarios with stable pressure (e.g., small hydraulic systems, low-pressure water pipelines); select pilot-operated valves for high-pressure, large-flow scenarios with large pressure fluctuations and high control accuracy requirements (e.g., large industrial equipment, high-pressure pipelines).

4. How to determine the set pressure, backpressure, and relief capacity of a pressure relief valve?
These three parameters directly determine the performance of the pressure relief valve.
Determination methods are as follows:
① Set pressure: Must be combined with the system's design pressure, operating pressure, and relevant standards, usually higher than the operating pressure but not exceeding the design pressure to avoid failure to relieve pressure in time (if too high) or unnecessary media waste (if too low).
② Backpressure: Consider the static and dynamic backpressure on the system outlet side, obtained through actual measurement or working condition calculation, to select a suitable valve type (e.g., backpressure balanced pressure relief valves for high backpressure scenarios).
③ Relief capacity: Calculate using industry formulas based on the system's maximum overpressure, physical properties of the medium (density/temperature/pressure), and pipeline parameters (diameter, length) to ensure the relief capacity can quickly reduce system pressure. Shanghai Xiazhao provides parameter calculation tools and technical support.

5. What is the general price range of pressure relief valves? What factors affect the price?
There is no fixed standard for pressure relief valve prices, which are mainly affected by the following factors:
① Type: Pilot-operated valves are more expensive than direct-acting valves; special working condition valves (e.g., backpressure balanced, fire protection-specific) are pricier than general-purpose types.
② Specification and model: Larger caliber, higher pressure rating, and greater relief capacity result in higher prices.
③ Material: Stainless steel valves are more expensive than cast iron or cast steel ones; corrosion-resistant materials (for special media) cost more.
④ Brand and service: Well-known brands (e.g., Shanghai Xiazhao) have slightly higher prices due to quality assurance and comprehensive after-sales service.
⑤ Purchase quantity: Bulk purchases are eligible for manufacturer discounts. Specific prices need to be calculated based on selection requirements; it is recommended to clarify working condition parameters before consulting for quotes.

6. What is the essential safety device for the outlet of a water pump? Why?
The essential safety device for the water pump outlet is a pressure relief valve.
Reasons: Water hammer is likely to occur when the pump starts or stops; if the outlet pipeline is blocked or the valve is closed during operation, the pressure inside the pump will rise sharply, damaging the pump impeller, pipeline, and related components. The pressure relief valve stabilizes the system pressure through automatic pressure relief, prevents water hammer impact, and protects the safety of the pump and pipeline system. Shanghai Xiazhao's water pump-specific pressure relief valves are compatible with different pump power working conditions, ensuring safe operation.

II. Special FAQs on Pressure Relief Valves for High Backpressure Working Conditions

1. What is a high backpressure working condition? What impacts does it have on ordinary pressure relief valves?
A high backpressure working condition refers to a scenario where the backpressure on the system outlet side is high (usually exceeding 10% of the set pressure) or fluctuates frequently and drastically. It is common in chemical reactor exhaust systems, compressor outlets, high-pressure steam pipelines, and other applications.
The main impacts on ordinary pressure relief valves include:
① Set pressure deviation: The actual opening pressure increases with backpressure, failing to relieve pressure at the preset value and easily causing overpressure accidents.
② Reduced relief capacity: Backpressure increases the resistance of medium discharge, making the actual relief capacity lower than the design value and unable to reduce pressure effectively.
③ Improper valve closing: Small pressure difference on both sides of the disc leads to medium leakage, resulting in energy waste and shortened valve service life. Therefore, special pressure relief valves are required for high backpressure working conditions.

2. How do bellows-sealed pressure relief valves solve backpressure problems?
Bellows-sealed pressure relief valves balance backpressure through special structural design:
① Core principle: A bellows is used as the sealing and balancing element to introduce system backpressure to the other side of the disc, balancing the pressure on both sides of the disc and eliminating the impact of backpressure on opening pressure and relief capacity.
② Additional advantages: The bellows effectively isolates the system medium from the external environment, avoiding medium corrosion of internal valve components, while improving sealing performance and preventing leakage.
③ Application scenarios: Suitable for medium-to-high backpressure working conditions with corrosive media, such as high backpressure pipelines in the chemical and petroleum industries. Shanghai Xiazhao's bellows-sealed pressure relief valves use high-quality bellows materials, adapting to complex high backpressure working conditions.

3. What are the performance differences between backpressure balanced pressure relief valves and conventional valves?
Core performance difference comparison:
① Opening pressure stability: Backpressure balanced valves are less affected by backpressure and have high stability; conventional valves are greatly affected by backpressure, prone to opening pressure deviation.
② Relief capacity accuracy: Backpressure balanced valves eliminate the impact of backpressure on relief capacity, with precise values; conventional valves have significantly reduced relief capacity under high backpressure.
③ Backpressure adaptability: Backpressure balanced valves are suitable for high backpressure and large fluctuation working conditions; conventional valves are only applicable to low backpressure, stable working conditions.
④ Sealing and service life: Backpressure balanced valves adopt advanced sealing structures, with good sealing performance and long service life; conventional valves are prone to sealing failure under high backpressure, shortening service life. Backpressure balanced pressure relief valves are preferred for high backpressure working conditions.

4. How to calculate and correct the relief capacity under high backpressure working conditions?
Under high backpressure, the relief capacity needs to be adjusted using a correction factor.
The core method:
① Basic idea: First calculate the theoretical relief capacity using ideal state formulas, then determine the correction factor based on backpressure magnitude and valve type; actual relief capacity = theoretical value × correction factor.
② Determination of correction factor: For backpressure balanced pressure relief valves, the correction factor is close to 1 when backpressure ≤ 30% of the set pressure; beyond 30%, it needs to be specifically calculated based on working conditions. For bellows-sealed pressure relief valves, the correction factor is determined according to bellows material, structure, and backpressure conditions, which can be referenced in product manuals or industry standards.
③ Notes: The correction must consider factors such as medium properties and pipeline resistance to avoid calculation deviations. Shanghai Xiazhao provides precise calculation services for relief capacity under high backpressure to ensure selection compatibility.

5. Which valve type is more suitable for the renovation of pressure relief valves in high backpressure pipelines of a chemical plant?
For high backpressure pipelines in chemical plants (e.g., reactor exhaust with corrosive media), backpressure balanced or bellows-sealed pressure relief valves are recommended, with specific selection based on working condition parameters:
① If backpressure fluctuates greatly and the medium is non-corrosive: Choose backpressure balanced valves, which eliminate backpressure impact through balanced pistons/diaphragms to ensure stable pressure relief.
② If the medium is highly corrosive and backpressure is medium: Select bellows-sealed pressure relief valves, which have both backpressure balancing and corrosion resistance properties.
③ Key renovation steps: First calculate pipeline operating pressure, design pressure, backpressure fluctuation range, medium properties, and other parameters, then screen matching models to ensure relief capacity and opening pressure meet requirements. Shanghai Xiazhao has multiple successful renovation cases of high backpressure pressure relief valves in chemical plants and can provide customized renovation solutions.

III. Special FAQs on Pressure Relief Valves for Fire Protection Water Supply Systems

1. What are the requirements for pressure relief valves in the national standard "Code for Design and Construction of Fire Protection Water Supply and Hydrant Systems" (GB 50974-2014)?
Core requirements of the code are as follows:
① Installation location: Pressure relief valves must be installed on the outlet pipelines of fire pumps and pressure stabilizing pumps.
② Performance requirements: The rated pressure of the pressure relief valve must be greater than the system's design operating pressure, and the relief capacity must meet overpressure relief needs; the set pressure of the pressure relief valve at the outlet of the pressure stabilizing pump must be higher than the system's automatic start pressure and lower than the fire pump's start pressure.
③ Installation requirements: The installation location, direction, and connection method must comply with the code—for example, the pressure relief valve at the fire pump outlet should be installed between the check valve and the gate valve.
④ Commissioning requirements: The set pressure, relief capacity, and sealing performance must be commissioned to meet design and code requirements.
⑤ Product qualification: Qualified products with fire protection product certification certificates and inspection reports must be selected. Shanghai Xiazhao's fire protection pressure relief valves all comply with GB 50974-2014 and can pass fire protection acceptance smoothly.

2. What are the differences in the installation of pressure relief valves at the outlets of fire pumps and pressure stabilizing pumps?
Core differences are reflected in four aspects:
① Installation purpose: The valve at the fire pump outlet prevents overpressure during pump start/operation/stop and protects the pump and pipeline; the valve at the pressure stabilizing pump outlet prevents frequent start of the pressure stabilizing pump and maintains stable system pressure.
② Set pressure: The set pressure of the fire pump outlet valve ＞ system's design operating pressure and ＜ pump's maximum allowable operating pressure; the set pressure of the pressure stabilizing pump outlet valve ＞ system's automatic start pressure and ＜ fire pump's start pressure.
③ Installation location: The fire pump outlet valve is installed between the check valve and the gate valve; the pressure stabilizing pump outlet valve is installed between the pressure stabilizing pump outlet and the check valve.
④ Relief capacity: The relief capacity of the fire pump outlet valve must meet the overpressure needs under the pump's maximum flow working condition; the relief capacity of the pressure stabilizing pump outlet valve is determined according to the pressure stabilizing pump's flow and pressure fluctuation conditions.

3. How to prevent overpressure in fire protection pipe networks? What are the requirements for the installation location of pressure relief valves?
The key to preventing overpressure in fire protection pipe networks is the reasonable installation of pressure relief valves.
Core installation locations and requirements:
① Fire pump outlet pipeline: Installed between the check valve and the gate valve to prevent water hammer during pump start and overpressure during operation.
② Pressure stabilizing pump outlet pipeline: Installed between the pressure stabilizing pump outlet and the check valve to stabilize system pressure.
③ Zone division of zoned water supply systems: Prevent high-zone pressure from being transmitted to the low zone, causing overpressure in the low-zone pipe network.
④ Pipeline after pressure reducing valve: Respond to sudden pressure increases caused by pressure reducing valve failure. Installation principles: The location must be easy to operate, inspect, and maintain, away from humid, corrosive environments and mechanical damage areas. Shanghai Xiazhao provides consulting services for the layout design of pressure relief valves in fire protection pipe networks.

4. Which is more suitable for fire protection systems: piston-type or diaphragm-type pressure relief valves?
Selection must be based on the type of fire protection system:
① Diaphragm-type pressure relief valves: Advantages include fast response, good sealing performance, small leakage, and strong pollution resistance; suitable for systems requiring high pressure control accuracy and clean media, such as automatic sprinkler systems. Disadvantages: Diaphragms are prone to aging, resulting in slightly higher maintenance costs.
② Piston-type pressure relief valves: Advantages include durable components and low maintenance costs; suitable for systems with low pressure control accuracy requirements and media containing a small amount of impurities, such as hydrant systems. Disadvantages: Slow response, general sealing performance, and easy clogging by impurities. It is recommended to select based on system function, medium cleanliness, and control requirements. Shanghai Xiazhao provides targeted recommendations.

5. What are the specific requirements for pressure relief valves in fire protection acceptance? How to ensure passing the acceptance?
Core requirements for fire protection acceptance:
① Product qualification: Provide fire protection product certification certificates, inspection reports, product qualification certificates, and installation and operation manuals to ensure complete and valid documentation.
② Specification and model: Must be consistent with design requirements; parameters such as rated pressure, relief capacity, and caliber must meet system needs.
③ Installation quality: Correct installation location, direction, and connection method; firm fixation; no water leakage; accessories (pressure gauges, gate valves, check valves) installed before and after in accordance with the code.
④ Performance parameters: On-site testing of set pressure, relief capacity, and sealing performance must meet code and design requirements.
⑤ Technical documentation: Provide complete selection calculation documents, commissioning records, and other materials. Key to ensuring acceptance: Select qualified products complying with the code (e.g., Shanghai Xiazhao's fire protection pressure relief valves), strictly follow the code for selection, installation, and commissioning, and sort out complete technical documentation in advance.

IV. Introduction to Shanghai Xiazhao's Pressure Relief Valve Products and Services

With years of focus on the pressure relief valve field, Shanghai Xiazhao's product range covers a full series of general-purpose, high backpressure-specific, and fire protection-specific valves. All products have passed strict quality inspections and relevant certifications, adapting to working conditions in various industries such as industry, chemical engineering, fire protection, and water treatment. We provide full-process services including "selection consulting → product customization → installation guidance → commissioning and maintenance", helping customers solve problems throughout the entire application cycle of pressure relief valves. For more questions or needs, please contact Shanghai Xiazhao's official customer service or technical team.