Pressure-Relief Valve
A pressure release valve is an essential safeguard in any pressurized system, ensuring safety by automatically venting excess pressure. Selecting the right relief valve is crucial for long-term reliability and compliance with industry standards.
With a commitment to precision engineering and high-quality materials, we provide durable, efficient, and industry-compliant solutions designed to meet the demands of various applications, ensuring optimal performance and safety in every system.
Our Collection of Pressure-Relief Valves
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What is a Pressure-Relief Valve? What are Its Functions?
A pressure-relief valve is a mechanical safety device designed to control or limit the pressure in a system. When the system's pressure exceeds a predetermined limit, the valve opens to allow excess fluid or gas to escape, thereby preventing potential equipment failure or hazardous situations.
The primary function of a pressure-relief valve is to safeguard equipment and personnel by releasing excess pressure from a system. For example, in boiler systems, these valves release steam when pressure gets too high, preventing it from reaching dangerous levels and reducing the risk of explosions.
They also help maintain consistent pressure, which is crucial in machinery that relies on steady flow. This regulation is vital in various applications, from chemical processing plants to hydraulic systems, where precise pressure control is key to optimal performance. Without them, these systems wouldn’t be nearly as reliable and efficient—or as safe.
How Do Pressure-Relief Valves Work?
Pressure-relief valves are direct-acting devices, meaning the system’s pressure directly affects its internal components. These valves stay closed under normal conditions, with their internal parts creating a tight seal with pressure to prevent fluid or gas from escaping. However, when pressure rises too high, it pushes against the poppet or diaphragm, eventually overcoming the spring’s force. This causes the valve to automatically open, allowing excess pressure to vent. Once the system pressure drops back to a safe level, the valve then shuts again, and the spring pushes the valve shut again, stopping the flow.
To understand how this works exactly, let’s break it down into three key parts:
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Valve Element (The Main Control Part)
This is the core of the valve, responsible for opening and closing based on pressure changes. It’s usually a spring-loaded poppet valve—a small movable component with a seal that presses tightly against the valve seat to keep the system closed.
Under normal conditions, the spring pushes the poppet against the seat, keeping the valve shut so no fluid escapes. As system pressure increases, it pushes against the poppet. If the pressure gets too high, it overcomes the spring force, causing the poppet to lift and open the valve. When the pressure drops back to a safe level, the spring pushes the poppet back down, sealing the valve again.
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Sensing Element (Detecting Pressure Changes)
The sensing element detects the system's pressure and helps control when the valve opens. This part is usually a piston or a diaphragm:
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Piston-based designs are durable and handle high pressures well, but they may have slower response times due to friction in the seal.
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Diaphragm-based designs work better for low-pressure applications and offer greater accuracy since they eliminate friction. These are usually made of elastomers (rubber-like materials) or metal for special applications.
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Reference Force Element (Controlling the Valve's Set Pressure)
This is typically a spring that determines when the valve opens. The spring applies force to keep the valve closed until the system pressure becomes too high. Most pressure-relief valves allow users to adjust the relief pressure by tightening or loosening the spring:
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Tightening the spring means more pressure is needed to open the valve.
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Loosening the spring lowers the pressure threshold, allowing the valve to open more easily.
Common Types of Pressure-Relief Valve
Selecting the appropriate type of pressure-relief valve depends on factors such as system pressure, the nature of the fluid, required accuracy, and maintenance considerations. Understanding these types helps in making an informed decision to ensure system safety and efficiency.
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Spring-loaded
Spring-loaded valves are one of the simplest the most reliable types of pressure-relief valve that uses a spring force to hold the valve closed under normal conditions. Note that there are actually no springs inside the valves. When the system pressure increases beyond the set pressure, which is the force applied by the spring, the valve opens to allow excess process fluid to escape. Once the pressure returns to a safe level, the valve closes again.
These valves are self-actuated, meaning they don't need an external power source to operate. They are widely used in various applications such as piping systems, boilers, and pressure vessels. However, they are sensitive to back pressure and may not be suitable for very high-pressure applications.
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Piston-type
Piston-type pressure relief valves utilize a piston as a sensing element and often incorporate a pilot valve to control the main valve. These valves are frequently chosen for applications involving higher relief pressures and where ruggedness is a primary concern.
They combine a pilot valve, similar to a direct-acting valve, with a main valve. The pilot valve's exhaust pressure acts on the piston to open the main valve, using inlet pressure when needed. They offer higher capacity and extreme accuracy compared to direct-acting valves. However, they can be more sluggish than diaphragm designs due to piston seal friction. Also, they need regular maintenance and replacement as they are prone to erosion.
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Diaphragm-type
Diaphragm-type pressure relief valves utilize a diaphragm as a sensing element to control the valve's opening and closing. These valves can be used with a double diaphragm in place of a piston in the inner pilot valve, which increases the diaphragm area and allows for the opening of a larger main valve.
This design results in a higher capacity than inner pilot piston valves of the same pipe size. They are also very sensitive to pressure changes and can achieve a high level of accuracy. They often incorporate a downstream sensor line located outside the valve, which reduces turbulence in the gas or liquid and further enhances their accuracy.
Diaphragm valves are suitable for low-pressure applications or when high accuracy is required. These valves are flexible and can be used with different pilot valves, including pressure, temperature, air load, or solenoid valves. The design of diaphragm valves essentially eliminates friction, unlike piston-style valves.
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Acting-type
Acting-type pressure relief valves are the simplest type of pressure relief valve, characterized by a flat diaphragm or bellows. These valves are designed as an independent structure, so they do not need an external sensor line downstream. These valves are specifically designed for medium and low-flow amounts, where high accuracy is not the primary concern.
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Nozzle-type
Nozzle-type pressure relief valves are designed with a nozzle and orifice to regulate fluid flow instead of a disc and seat, making them suitable for systems with particulate-filled or unclean fluids. This design helps prevent clogging, ensuring reliable operation even in challenging conditions.
While they offer robust performance, nozzle-type valves are generally more expensive and require more maintenance than other types of relief valves. In comparison to other designs, which may use a disc and seat, nozzle-type valves are well-suited for situations where maintaining consistent operation despite the presence of contaminants in the fluid is important.
Pressure-Relief Valve vs. Pressure-Safety Valve
Pressure valves are essential for keeping systems safe by preventing overpressure. Two common types are pressure-relief valves and pressure-safety valves. They may seem similar because they both protect equipment from excess pressure, but they function differently.
The biggest difference is how they release pressure. A pressure-relief valve opens gradually and proportionally as pressure builds up or drops, making it ideal for liquid systems where controlled pressure release is needed. On the other hand, a pressure-safety valve (PSV) is designed to quickly release pressure when it reaches a dangerous level as a fail-safe measure.
It pops open instantly when pressure is about to hit the set point, allowing excess gas or fluid to escape rapidly. PSVs are commonly used in gas systems, steam boilers, and other applications where sudden pressure spikes could cause serious hazards or emergencies like explosions, rather than control pressure.
Feature
Pressure-Relief Valve (PRV)
Pressure-Safety Valve (PSV)
Function
Gradual pressure release
Instant full opening
Best for
Liquid systems
Gas and steam systems
Response Time
Opens slowly
Opens immediately
Closing Action
Closes gradually
Closes instantly
Application
Hydraulic systems, water treatment, HVAC
Boilers, gas pipelines, steam systems
What is a Pressure-Relief Valve Used for?
Pressure-relief valves play a crucial role in various industries by ensuring systems operate safely and efficiently. In industrial settings, such as chemical processing plants and manufacturing facilities, these valves protect critical equipment like reactors, pipelines, and storage tanks. By automatically releasing pressure, these valves keep operations safe and reliable.
In water supply systems, especially in high-rise buildings, pressure-relief valves help regulate water flow and prevent damage to plumbing infrastructure. Excessive force could lead to pipe bursts or inconsistent water supply without proper pressure control, making these valves essential for maintaining a steady and safe water distribution.
In hydraulic systems, pressure-relief valves prevent excessive force from damaging components like hoses, pumps, and cylinders. By controlling pressure levels, they protect sensitive machinery and ensure smooth operation, reducing wear and tear on essential parts.
How to Choose Pressure-Relief Valves
Picking the right pressure-relief valve is key to keeping your system safe and working properly. Here’s what you need to consider:
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Materials and Medium
The material of a pressure-relief valve must match the fluid or gas it will handle. Picking the wrong material can cause corrosion, leaks, or failure, so always choose based on the system’s needs. Stainless steel resists corrosion and is great for chemical processing. Brass is cost-effective and works well with water and non-corrosive fluids, making it common in HVAC systems.
High-end materials like Hastelloy or titanium offer superior durability, but they can be expensive. Budget is a key factor, especially in large-scale systems. For low-pressure or non-corrosive environments, plastic and composite materials like PTFE provide a lightweight and cost-effective alternative, commonly used in water treatment and certain chemical systems.
Beyond fluid compatibility, environmental factors matter. Humidity, harsh chemicals, and extreme temperatures can affect durability. The fluid’s viscosity and specific gravity also play a role. Thicker fluids need specialized valves to ensure proper function. For example, medical systems like blood analysis require inert materials that won’t react with fluids. Finally, it’s also important to follow industry standards like ANSI to ensure the materials match safety and compliance.
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Size and Weight
The valve's size should align with your system's requirements. An undersized valve may not relieve pressure adequately, posing safety risks, while an oversized valve can lead to chattering, causing wear and tear. It's crucial to calculate the required relief capacity based on your system's parameters and select a valve size that meets this capacity.
Also, consider the valve's weight, especially in systems where support structures have weight limitations. Proper sizing ensures the valve operates effectively without compromising system integrity.
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Flow Rate Requirement
A relief valve must release enough fluid to keep the system from reaching dangerous pressure levels. Flow capacity depends on the system’s fluid volume, how quickly pressure builds, and the amount of fluid that needs to be displaced.
For example, a large storage tank requires a valve with a higher flow capacity than a small piping system. The flow rate is measured at the flow point pressure, which is slightly above the valve’s opening pressure. Make sure the valve can handle pressure surges without failing to relieve enough fluid.
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Working Temperature
Temperature affects both the medium and the valve itself. High temperatures can make certain materials brittle or cause them to degrade over time. If your system deals with extreme heat—like in steam applications—choose a valve rated for high-temperature conditions, such as those made from stainless steel.
Cold temperatures can also impact performance by making some materials less flexible. Before choosing a valve, check its minimum and maximum temperature ratings to ensure it will function reliably in your system.
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System Pressures
Setting the relief valve at the right pressure is key to keeping your system safe. It should open at a pressure high enough to avoid unnecessary activation but low enough to prevent dangerous overpressure.
There are 4 important pressure ratings you need to keep in mind:
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Operating Pressure – The typical pressure the valve handles during normal system use.
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System Pressure – The maximum pressure the system may reach under working conditions.
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Proof Pressure – The highest pressure the valve can withstand without suffering permanent damage.
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Burst Pressure – The point where the valve will fail or rupture.
Your valve needs to handle all these pressures to ensure durability and long-term reliability. Always check these ratings to make sure the valve is tough enough for your system’s demands.
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Leakage
Both internal and external leakage matter. External leakage happens when fluid escapes from the valve’s body, while internal leakage means the valve isn’t fully sealed when closed. Some applications allow a small amount of leakage, but in high-pressure or sensitive systems, even minor leaks can be a big problem. Consider your system’s needs—does it require zero leakage, or can it tolerate a slight loss of fluid?
What to Know When Using Pressure-Relief Valves
Using a pressure-relief valve correctly is essential for keeping your system safe and working efficiently. Proper installation and pressure adjustment help prevent leaks, equipment damage, or system failures. Here’s what you need to know:
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Installation Tips
Always mount the valve in an upright, vertical position to ensure it functions correctly. Be careful not to overtighten it, as this can cause damage or leaks. If you're installing a flanged relief valve, tighten the bolts evenly to create a secure seal.
For piping connections, make sure the inlet pipe is not smaller than the valve opening, as this can restrict flow. The outlet pipe should be larger than the valve outlet to allow pressure to escape smoothly. Also, support the outlet piping properly to prevent strain, warping, or leaks.
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Adjusting Pressure Settings
The cracking pressure is the pressure at which the valve starts to open and release excess pressure. It must be set correctly for the system to operate properly. If the cracking pressure is too low, the valve might open too soon, leading to inefficient operation. If it's too high, the valve might not open in time to protect the system.
Many pressure-relief valves allow manual pressure adjustment using a reference spring. By tightening or loosening the spring, you can increase or decrease the pressure at which the valve activates. Always follow the system’s design requirements when setting the relief pressure to ensure proper protection.
Kuhnway - Your Choice for Pressure-Relief Valve Distributor
At KUHNWAY Corporation, the leading supplier of pressure relief valves, we know that the right pressure relief valve isn’t just a component—it’s the key to safety, efficiency, and long-term performance. That’s why we design high-quality, precision-engineered valves to protect your systems and keep them running smoothly.
With decades of expertise, innovative designs, and top-tier materials, we ensure every valve meets the highest industry standards. Whether you're upgrading or building from scratch, KUHNWAY has the solutions you need. Let’s work together! Contact us today and experience the difference of reliable, high-performance valves built for success.