difference between a safety valve and a relief valve in stock

As you already know, there are a multitude of pressure relief valves out there. In the industry, we tend to use terms like safety valve and relief valve interchangeably. And for the most part, this makes sense. Most pressure relief valves are designed to do the same thing — release pressure in a system.

But is there a difference between some of these commonly used terms, and if so, what does it mean for you? Here’s a quick breakdown of two popular terms: safety valve vs. relief valve.

While both terms refer to valves used to release pressure from a pressurized system, their technical definitions are a bit different. In general, the term relief valve refers to a valve within a pressurized system that is used to control pressure for the optimal functionality of the system. Relief valves are designed to help your facility avoid system failures, and protect equipment from overpressurized conditions.

The term safety valve, on the other hand, refers to pressure valves that are designed to protect people, property, and processes. In other words, the term safety valve refers to a failsafe, last resort valve that will release pressure to prevent a catastrophe, usually in the event that all other relief valves have failed to adequately control pressure within a system.

The general purpose of both safety valves and relief valves are the same. Both are pressure relief valves, and they are designed to let off pressure in any situation where a system becomes overpressurized. That said, relief valves and safety valves do function slightly differently:

Relief Valves are designed to control pressure in a system, most often in fluid or compressed air systems. These valves open in proportion to the increase in system pressure. This means they don’t fly all the way open when the system is slightly overpressure. Instead, they open gradually, allowing the system to return to the preset pressure level. When that level is reached, the valve shuts again.

Safety Valves are used for one reason — safety. Instead of controlling the pressure in a system, they’re designed to immediately release pressure in the event of an emergency or system failure. Unlike relief valves, safety valves open immediately and completely to avoid a disaster, rather than to control the pressure of a system.

While both safety valves and relief valves work to release excess pressure, the way they go about it is a little different. Check out this table, courtesy of Difference Between, for a little more information about the differences between the two valves:

Industrial equipment often uses either safety or relief valves to prevent damaging pressure levels from building up. Though they perform similar functions, there are some critical differences between safety and relief valves. Understanding these two valves’ differences is essential for proper pressure system operation. So here we discuss the pressure safety valve vs pressure relief valve.

A pressure relief valve is a device that releases pressure from a system. The relief valve is generally immune to the effects of back pressure and must be periodically stripped down. Pressure relief valves are one the essential parts of a pressure system to prevent system failures. They are set to open at a predetermined pressure level. Each pressure system has a setpoint that is a predetermined limit. The setpoint determines when the valve will open and prevents overpressure.

Pressure relief valves are typically used in gas or liquid systems where there is a need to prevent excessive pressure from building up. When the pressure in the system reaches a certain level, the valve will open and release the pressure. Pressure relief valves are an essential safety feature in many designs and can help to prevent damage to the system or components.

PRVs are generally considered to be safe and reliable devices. However, before installing a PRV in a system, some potential disadvantages should be considered. Here are five pros and cons of pressure relief valves:

Pros: Pressure relief valves are anessential safety feature in many systems. They protect against over-pressurization by relieving excess pressure from the system. This can help to prevent severe damage or even explosions.

Pressure relief valves can help to improve the efficiency of a system. The system can operate at lower overall pressure by relieving excess pressure and saving energy.

Pressure relief valves can be used as a safety device in systems that are susceptible to overpressurization. By relieving pressure before it builds up to a dangerous level, they can help to prevent accidents and injuries.

Cons: Pressure relief valves can be a potential source of leaks. If not properly maintained, the valve may not seat properly and can allow fluids or gasses to escape.

Pressure relief valves can sometimes cause problems if they do not open or close properly. This can lead to process disruptions and may cause safety issues.

A pressure safety valve is a device used to release pressure from a system that has exceeded its design limit. This safety valve is a fail-safe device. This type of valve is typically used in systems that contain fluids or gasses under high pressure. Pressure safety valves are designed to open and release pressure when the system has exceeded its maximum pressure limit. This helps to prevent the system from rupturing or exploding.

Pressure safety valves are an essential part of many different types of systems and can help keep both people and property safe. If anyone is ever in a situation where they need to release pressure from a system, it is essential to know how to use a pressure safety valve correctly.

A pressure safety valve (PSV) is a type used to relieve a system’s pressure. PSVs are commonly used in chemical and process industries, as well as in some kinds of pressure vessels. There are both advantages and disadvantages to using a PSV. Some of the pros of using a PSV include: PSVs can help to prevent overpressurization, which can be dangerous.

A safety valve is a pressure relief device used to prevent the over-pressurization of a system. On the other hand, a relief valve is a device used to relieve pressure from a system that is already overpressurized. Function Of Pressure Relief Valve Vs Safety Valve

The function of a pressure relief valve is to protect a system or component from excess pressure. A safety valve, on the other hand, is designed to protect from overpressurization. Both types of valves are used in various industries, but each has unique benefits and drawbacks.

Pressure relief valves are typically used in systems where a small amount of overpressure can cause damage. On the other hand, safety valves are designed for systems where overpressurization could be catastrophic. Both valves have advantages and disadvantages, so choosing the right type of valve for the specific application is essential.

Relief valves are usually set to open at a specific pressure and will close once the pressure has been relieved. Safety valves are similar in that they are also used to protect equipment from excessive pressure. However, safety valves are designed to stay open until they are manually closed. This is because safety valves are typically used in applications where it is not safe to have a closed valve, such as in a gas line. Operation Of Safety Relief Valve Vs Pressure Relief Valve

Two types of valves are commonly used in industrial settings: relief valves and safety valves. Both of these valves serve essential functions, but they operate in different ways.

Relief valves are designed to relieve pressure build-up in a system. They open when the system pressure reaches a certain point, which allows excess pressure to be released. On the other hand, safety valves are designed to prevent accidents by preventing system pressure from getting too high. They open when the system pressure reaches a certain point, which allows excess pressure to be released before an accident can occur.

So, which valve is better? That depends on the situation. A relief valve is the better option to protect the system from pressure build-up. If anyone need to protect the system from accidents, then a safety valve is the better option Setpoint Of Pressure Relief Valve Vs Safety Relief Valve

The relief valve is made to open when it reaches a specific pressure, commonly described as a “setpoint”. Setpoints shouldn’t be misinterpreted as the pressure set. A setpoint on a relief valve is set to the lowest possible pressure rating, which means it is set to the lowest system pressure before an overpressure situation is observed. The valve will open as the pressure increases to a point higher than the setpoint. The setting point is determined as pounds per square inch (PSIG) and should be within the maximum allowed operating pressure (MAWP) limits. In safety valves, the setpoint is typically placed at about 3 percent over the working pressure level, whereas relief valves are determined at 10 percent.

No, the safety valve and relief valve can not be used interchangeably. Though both valves are seal butterfly valve and used for safety purposes, they serve different functions. A safety valve relieves excess pressure that builds up in a system, while a relief valve regulates the pressure in a system.

Knowing the difference between these two types of valves is essential, as using the wrong valve for the intended purpose can potentially be dangerous. If unsure which type of valve to use, it is always best to consult with a professional.

A few key points help us understand the safety valve vs pressure relief valve. Safety valves are designed to relieve pressure in a system when it gets too high, while relief valves are designed to relieve pressure when it gets too low. Safety valves are usually set to open at a specific pressure, while relief valves are generally open at a particular vacuum. Safety valves are typically intended for one-time use, while relief valves can be used multiple times. Choose the trusted valve manufactureraccording to the specific business needs.

Both the terms are used interchangeably in the process industry as every pressurized system requires safety devices to protect life, property, and environment. Relief valves and safety valves are the two principle safety devices designed to prevent overpressure conditions in process industries. Although, both the devices are used almost for the same purpose, the difference lies mainly in how they operate.

Relief valves, or commonly known as pressure relief valves (PRVs), belong to the family of protective devices specifically designed to protect pressure-sensitive systems and equipment from the damaging effects of overpressure conditions. A relief valve device is basically immune to the back pressure effects of a system and is subject to periodic stripdown. Pressure relief valves are one of the most critical parts of a pressure system that are set to open at a preset pressure level in order to avoid system failures. Every pressure system is set with a predetermined design limit called a setpoint, above which the valve begins to open to prevent overpressure conditions.

A safety valve is the last resort of people, property, and processes in the process industry comprising of power plants, petrochemicals, boilers, oil and gas, pharmaceuticals, and many more. It’s kind of a fail-safe device that actuates automatically in order to prevent the accumulation of pressure in a vessel or system beyond a preset limit. The device is so designed so that the safety valve trips automatically when the given pressure is attained. It simply allows the excess pressure to escape in order to prevent any damage to the vessel. Additionally, it also makes sure the pressure remains within the limits in the future. Even a slight increment in pressure lifts the safety valve and it closes as soon as the pressure is reduced to the prescribed limit.

A relief valve, also known as pressure relief valve (PRV) or safety relief valve, is type of a safety valve device used to limit or control the pressure level in a system within a safe threshold limit to avoid an overpressure condition. In simple terms, a relief valve is a device designed to control the pressure in a vessel or system to a specific set level. A safety valve, on the other hand, is a device used to let go excess pressure from a vessel or equipment when the pressure crosses a certain predetermined limit. It simply allows liquids or gases to escape if the pressure gets too high to prevent any damage.

Pressure relief valves are mainly used in hydraulic systems to limit the pressure in the system to a specific preset level and when the pressure reaches the safety design limit, the relief valve responds by releasing the excess flow from an auxiliary passage from the system back to the tank in order to prevent equipment failure. The main purpose of a safety valve is to protect life, property, and environment against failure in the control system pressure. Simply put, a safety valve opens when the pressure exceeds the designed set pressure limit.

For a safety relief valve, the opening is directly proportional to the increase in the vessel pressure. This means the opening of the valve is rather gradual than sudden, allowing it to open only at a preset pressure level and release fluids until the pressure drops to the desired set pressure. A safety valve, on the other hand, will open immediately when the system pressure reaches the set pressure level in order to system failure. It is safety device capable of operating at all times and is the last resort to prevent catastrophic failure in systems under overpressure conditions.

A pressure relief valve is designed to open at a certain pressure level which is generally called as a “setpoint”. A setpoint should not be confused with the set pressure. In fact, a setpoint of a relief valves is adjusted to the lowest maximum pressure rating meaning it is set below the maximum system pressure allowed before the overpressure condition occurs. The valve begins to open when the pressure reaches up to some level above the setpoint. The setpoint is measured in pounds per square inch (PSIG) and must not exceed the maximum allowable working pressure (MAWP). In safety valves, the setpoint is usually set at 3 percent above the working pressure level whereas in relief valves, it is set at 10 percent.

Both relief valves and safety valves are high-performance pressure-sensitive safety devices so designed to control or limit the pressure inside the system or vessel by releasing the excessive pressure from the auxiliary passage out of the system. Although both are common terms used for safety valves, the difference lies mainly in the capacity and setpoint. While the former is operator-assisted and is designed to relieve pressure in order to avoid overpressure condition, the latter is a self-operated device which opens automatically when the maximum allowable pressure is reached. Relief valves are mostly used in fluid or compressed air systems, whereas safety valves are mainly used to release vapor or steam into the atmosphere.

Sagar Khillar is a prolific content/article/blog writer working as a Senior Content Developer/Writer in a reputed client services firm based in India. He has that urge to research on versatile topics and develop high-quality content to make it the best read. Thanks to his passion for writing, he has over 7 years of professional experience in writing and editing services across a wide variety of print and electronic platforms.

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Safety valves and relief valves have similar structure and performance, both of which discharge internal media automatically when the pressure exceeds the set value to ensure the safety of the production device. Because of this essential similarity, the two are often confused and their differences are often overlooked as they are interchangeable in some production facilities. For a clearer definition, please refer to the ASME boiler and pressure vessel specifications.

Safety Valve: An automatic pressure control device driven by the static pressure of the medium in front of the valve is used for gas or steam applications, with full open action.

The basic difference in their operating principle: The safety valve relieves the pressure into the atmosphere i.e. out of the system, it can be a pressure relief device of fluid vessels, when the set pressure value reached then the valve opens almost fully. On the contrary, relief valve relieves the pressure by relieving the fluid back into the system, that’s the low-pressure side. Relief valve opens gradually if the pressure increased gradually.

The difference is also generally shown in capacity and setpoint. A relief valve is used to relieve pressure to prevent an overpressure condition, the operator may be needed to assist in opening the valve in response to a control signal and close back once it relieves the excess pressures and continues to operate normally.

A safety valve can be used to relieve the pressure that does not need a manual reset. For example, a thermal relief valve is used to bleed off pressure in a heat exchanger if it is isolated but the possibility of thermal expansion of the fluid could cause overpressure conditions. The safety valve on a boiler or other types of fired pressure vessels must be capable of removing more energy that is possible to be put into the vessel.

In short, Safety valves and relief valves are the two most commonly used types of control valves. The safety valve belongs to the pressure release device, which can only operate when the working pressure exceeds the allowable range to protect the system. The relief valve can make the high-pressure medium quickly to meet the pressure requirements of the system and its working process is continuous.

In the process industry, both terms refer to safety devices, which generally come in the form of valves, cylinders, and other cylinders that protect people, property, and the environment. Safety valves and relief valves are integral components of process safety. However, they are used for almost identical purposes. Their main difference lies in their operating mechanisms.

In the event of an overpressure, a safety valve or pressure relief valve (PRV) protects pressure-sensitive equipment. It is recommended to strip down relief valves regularly and prevent serious damage due to backpressure. Pressure relief valves are a crucial part of any pressurized system. In order to prevent system failures, you can set the pressure to open at predetermined levels. A setpoint, also known as a predetermined design limit, is set for all pressure systems. When the setpoint is exceeded, an overpressure valve opens.

A relief valve, illustrated in Below Figure, gradually opens as the inlet pressure increases above the setpoint. A relief valve opens only as necessary to relieve the over-pressure condition.

A safety valve, illustrated in Below Figure, rapidly pops fully open as soon as the pressure setting is reached. A safety valve will stay fully open until the pressure drops below a reset pressure.

The reset pressure is lower than the actuating pressure setpoint. The difference between the actuating pressure setpoint and the pressure at which the safety valve resets is called blowdown.

Relief valves are typically used for incompressible fluids such as water or oil. Safety valves are typically used for compressible fluids such as steam or other gases.

There are various types of safety valves used in several types of industries, including power plants, petrochemical plants, boilers, oil and gas, pharmaceuticals, and more. Using safety valves helps to prevent accidents and injuries that can harm people, property, and processes. Pressure builds up in vessels and systems automatically when the device is activated above a preset level. Safety valves must be configured so that their prescribed pressure is exceeded in order for them to function (i.e., relieve pressure). Ideally, excess pressure should be released either to the atmosphere or back into the pneumatic system to prevent damage to the vessel. In addition, excess pressure should be released to keep pressure within a certain range. As soon as a slight increase in pressure above the desired limit has lifted the safety valve, it opens.

As indicated in Below Figure, system pressure provides a force that is attempting to push the disk of the safety valve off its seat. Spring pressure on the stem is forcing the disk onto the seat.

At the pressure determined by spring compression, system pressure overcomes spring pressure and the relief valve opens. As system pressure is relieved, the valve closes when spring pressure again overcomes system pressure.

Most relief and safety valves open against the force of a compression spring. The pressure setpoint is adjusted by turning the adjusting nuts on top of the yoke to increase or decrease the spring compression.

Valve relief removes excessive pressure from a system by limiting its pressure level to a safe level. Often referred to as pressure relief valves (PRVs) or safety relief valves, these valves provide relief from pressure. The purpose of a relief valve is, for example, to adjust the pressure within a vessel or a system so that a specific level is maintained. The goal of a relief valve, unlike a safety valve, is not to prevent damage to the vessel; rather, it is to control the pressure limit of a system dynamically depending on the requirements. Conversely, safety valves have a maximum allowable pressure set at a certain level, which allows escaping liquid or gas whenever the pressure exceeds it, eliminating damage to the system. It is imperative that safety valves are installed in a control system to prevent the development of pressure fluctuations that can cause property damage, life loss, and environmental pollution.

The hydraulic system relies on a pressure relief system in order to regulate the running pressure. By allowing excess pressure to escape from the pressurized zone, pressure relief valves and safety valves prevent overpressure when the pressure in the system reaches a predefined limit. By venting excess pressure through a relief port, or returning it through a return line, a pneumatic system can enable the excess pressure to escape into the atmosphere. Pump-driven pressure generators and control media that cannot be vented into the atmosphere are typical examples of this type of application.

Excess pressure may be relieved from the system using relief valves and safety valves. The valve opening increases proportionally as the vessel pressure increases with the relief valve. Gradually opening the valve rather than abruptly releasing only a prescribed amount of fluid. As pressure is reduced, the release proceeds at this rate until the pressure drops. By contrast, an emergency safety valve operates automatically when a predetermined pressure is reached in the system, preventing a catastrophic system failure. When the system is under excessive stress, the safety valve regulates the pressure within the system and prevents overpressure.

Defining a “setpoint” is the process of defining a pressure level that triggers the device to vent excess pressure. Setpoint is different from pressure. Overpressure is prevented by setting these devices lower than the highest pressure the system can handle before overpressure occurs. Setting the device below this pressure prevents overpressure. The valve opens when pressure rises above the setpoint. A setpoint also known as the maximum allowable working pressure (MAWP) cannot be exceeded when deciding the pressure in pounds per square inch (PSIG). The adjustment points for safety valves are generally 3 percent above working pressures, while adjustment points for relief valves are 10% above working pressures.

Pressure in an auxiliary passage can be controlled by a safety valve as well as a relief valve by releasing excess pressure. Safety valves of this type are pressure-sensitive and reliable. Safety valves can be categorized according to their capacity and setpoint, although both terms often refer to safety valves. Self-opening devices open automatically when maximum allowable pressure has been reached rather than being manually activated to prevent over-pressurizing. Contrary to relief valves, safety valves are typically used for venting steam or vapor into the atmosphere. Relief valves regulate fluid flow and compressed air pressure and gases, whereas safety valves typically regulate steam and vapor venting. Put simply, relief valves are used for more gradual pressure control requiring accurate, dynamic systems, whereas safety valves are used for one set to prevent damage to a system.

Pilot-operated relief valves are designed to maintain pressure through the use of a small passage to the top of a piston that is connected to the stem such that system pressure closes the main relief valve.

Thus, its operation is automatic; it will open only to release the pressure and not exceed the liquid force; therefore, its use is more common with fluids (although, they can also be used with vapours or moderate gases). In terms of capacity, they can withstand low pressures and their processes are continuous.

Whenever we talk about the pressure in the process industries we come across two types of safety equipments and that is the safety v/v and the relief v/v.

Most of us think that both are same thing but that’s not the case. Though their functions are same yet there are certain differences among them. Both of them are used in the industry to prevent the accumulation of excess pressure, but there are operational differences between them.

Relief valves which are also known as Pressure relief valves are one of the protective devices which are used to protect a pressurize working system and equipments from getting damaged due to an over-pressure or excessive pressure conditions.

In every pressurized working system there is a set pressure under which the system works properly and efficiently, this set pressure is known as set point and when the pressure is above set point the relief valve opens and the excess pressure is released.

It is made very sensitive such that even for a slight increment in the pressure lifts the safety valve and gets closed quickly as soon as the pressure is released to maintain the desired pressure in the vessel.

1. A relief valve is a device used to limit the pressure in the system within certain specified limit or a set level.A safety valve is a device designed to actuate automatically when the pressure becomes excess.

2. The opening of a relief Valve is directly proportional to the increase in the vessel pressure.2. A safety valve opens almost immediately and fully in order to prevent over pressure condition.

3. A relief valve opens when the pressure reached the specific limit and it is usually operated by an operator.3. The purpose of the safety valve is mainly to safeguard people, property and the environment. It operates without any human intervention.

4. The set point of a relief valve is usually set at 10% above working pressure.4. The set point of safety valve is usually set at 3 % above working pressure.

5. Relief valves are categorized into pop-type, direct-operated, pilot-operated, and internal relief valves.5. Safety valves are divided into wide variety of types based on their applications and performance in different areas of use.

From the definition of both the valves we can conclude that the relief v/v which is also known as the pressure relief v/v is a safety device which is used to maintain a proper preset pressure in the vessel or the system within a prescribed limit condition to prevent a situation of over pressure.

On the other hand, the safety valve is a protective device which is used in a system to control the pressure inside the system under a predetermined limit.

The pressure relief valves are generally used in the hydraulic systems to control the pressure within specified limit and when the pressure increases than the preset value.

It lifts up and provide an escape of the excess pressure through an alternate channel or bypass provided in the system back to the source from where the input is coming or may be a different chamber provided to accept the excess of the liquid.

On contrary in case of safety valve, the main function of the safety valve is to provide safety to the property, life, and the environment which can get damaged due to failure of the system because of the excess pressure.

The pressure relief valves are generally used in the hydraulic systems to control the pressure within specified limit and when the pressure increases than the preset value, it lifts up and provide an escape of the excess pressure through an alternate channel or bypass provided in the system back to the source from where the input is coming or may be a different chamber provided to accept the excess of the liquid.

On contrary in case of safety valve, the main function of the safety valve is to provide safety to the property, life, and the environment which can get damaged due to failure of the system because of the excess pressure.

We used the set point in case of the relief valve, the “Set Point” basically refers to a point set to the lowest maximum pressure rating which means that the pressure is set below the maximum operative pressure which is allowed for a system to operate without being get into the state of overpressure.

In Simple words we can say that the relief valve pressure is set to maintain and control the pressure inside the system, the set pressure is dependent on the working pressure of the system.

On the other hand , the pressure of safety valve is set on the basis of various factors of consideration like the material used, the environment in which it has to be used, the type of work it has to perform.

The boilers material used for 6 Bar will have the materials which can withstand upto 12 Bar (it depends on the manufacturer) So the Safety valve will be set to 7-8 bar so as to prevent the boiler failure.

A series of anomalies occurred in the boiler room that evening. The steel compression tank for the hydronic loop flooded, leaving no room for expansion. Water will expand at 3% of its volume when heated from room temperature to 180° F. When the burner fired, the expansion of the water increased the system pressure within the boiler. The malfunctioning operating control did not shut off the burner at the set point which caused the relief valve to open.

The brass relief valve discharge was installed with copper tubing piped solid to a 90° ell on the floor and the tubing further extended to the floor drain. The combination of hot water and steam from the boiler caused the discharge copper tubing to expand, using the relief valve as a fulcrum. The expansion of the copper discharge tubing pressing against the floor was enough to crack the brass relief valve, flooding the boiler room. The damage was not discovered until the next morning, several hours after the leak occurred. Thousands of dollars in damage was sustained and luckily no one was injured.

Each boiler requires some sort of pressure relieving device. They are referred to as either a safety, relief or safety relief valve. While these names are often thought of as interchangeable, there are subtle differences between them. According to the National Board of Boiler and Pressure Vessel Inspectors, the following are the definitions of each:

• Safety valve— This device is typically used for steam or vapor service. It operates automatically with a full-opening pop action and recloses when the pressure drops to a value consistent with the blowdown requirements prescribed by the applicable governing code or standard.

• Relief valve— This device is used for liquid service. It operates automatically by opening farther as the pressure increases beyond the initial opening pressure and recloses when the pressure drops below the opening pressure.

• Safety relief valve— This device includes the operating characteristics of both a safety valve and a relief valve and may be used in either application.

• Temperature and pressure safety relief valve— This device is typically used on potable water heaters. In addition to its pressure-relief function, it also includes a temperature-sensing element which causes the device to open at a predetermined temperature regardless of pressure. The set temperature on these devices is usually 210°.

• Relief valve piping— The boiler contractor installed a bushing on the outlet of the safety relief valve. Instead of 1 1/2-in. pipe, the installer used 3/4-in. pipe. When asked about it, he answered that he did not have any 1 1/2-in. pipe but had plenty of 3/4-in. pipe. I explained and then had to show the disbelieving contractor the code that states that the relief valve discharge piping has to be the same diameter as the relief valve outlet (see 2012 International Mechanical Code, 1006.6). By reducing the discharge pipe size, the relieving capacity of the safety valve may not be adequate to properly relieve the pressure inside the boiler, causing a dangerous situation.

The code also states that the discharge material shall be of rigid pipe that is approved for the temperature of the system. The inlet pipe size shall be full diameter of the pipe inlet for the relief valve. Some manufacturers suggest using black iron pipe rather than copper tubing. If using copper, it should have an air space that allows expansion should the relief valve open to avoid the accident that I referenced above. The discharge piping has to be supported and the weight of the piping should not be on the safety relief valve. Valves are not permitted in the inlet piping to or discharge piping from the relief valve. If you are using copper tubing on discharge piping, verify that there is room for expansion.

• Installation— Read the manufacturer’s installation manual as each may have different requirements. For instance, Conbraco requires that the discharge piping must terminate with a plain end and use a material that can handle temperatures of 375° or greater. This will preclude PVC or CPVC pipe for the discharge piping. The instruction manual for its model 12-14 steam relief valve stipulates that you cannot use a pipe wrench to install it. That would be good to know.

I once visited Boiler Utopia as the floor was clean and waxed. All the pipes were covered and exposed pipes were painted. There were large stickers detailing what was inside each pipe as well as directional arrows. Nothing was stacked next to the boilers. Yellow caution lines were painted on the floor around each boiler. I was in heaven. As I walked around the rear of the boiler, something clicked and triggered a warning bell. The discharge of the relief valve piping was about 6 in. from the floor but instead of a plain or angled cut end, the pipe had a threaded pipe cap on the termination. I asked the maintenance person about it and he said that the valve was leaking all over his newly waxed floor and this was the only way he could stop it. When I said that the discharge pipe should not have been threaded, he explained that it was not threaded and he had to take it to the local hardware store to thread it. I informed him that the cap had to be removed. We cut the pipe on an angle to prevent this.

• Steam boiler— Most manufacturers recommend a drip pan ell on the discharge of the steam boiler relief valve to eliminate the weight of the discharge piping on the relief valve. Some codes require the discharge to be vented outdoors.

• Testing— I will ask the attendees in my classes, “How often do you test the relief valves?” Most do not make eye contact and when I follow up with, “Why are they not tested?” I often hear that opening the relief valve will cause it to leak. I suggest that you refer to each manufacturer’s directions for testing. For instance, one will recommend once a year while another recommends twice a year. One manufacturer says, “Safety/relief valves should be operated only often enough to assure they are in good working order.” I am not sure what that even means. You want to also verify the proper test procedure as some will only want the relief valve tested when the boiler is at 75% of the rated pressure or higher of the relief valve.

Pressure relief valves are a type of safety valve that are commonly used to protect a system and the people operating it. Whereas pressure regulators take incoming line pressure and regulates it down to the pressure that is required by the downstream system. Pressure Regulators can be used for reasons of safety and/or cost. Both of these valves are very important to its specific application. In this article, we will discuss the difference between a pressure relief valve and regulator.

Pressure Regulators take an incoming line pressure and regulate it down to the pressure that is required by the downstream system. This may be for other instrumentation to operate effectively or simply to control the output flow of a pipe. Lower system pressures mean less risk and lower running costs and a reduced risk of air loss through a system. Pressure regulators can be used in many applications including pneumatics, compressed air and water.

There are various kinds of pressure regulators available within MGA Controls range – from general purpose units covering everyday industrial applications to more specialised precision pressure regulators, manifold regulators, pilot operated regulators and large capacity pilot operated versions. View our full range of pressure regulators in our store.

Pressure relief valves are used to control or limit pressure spikes in a compressed air system. When the system pressure increases beyond a predetermined set point, the valve opens and relieves that pressure, bringing it back in line with normal operating parameters. The main function of a Pressure relief valve is to vent excess pressure and protect other system components, all the while maintaining optimum performance.

Air systems benefit highly from pressure relief valves, however different types of pressure relief valves can be used in a wide range of industries. For example, the water industry utilises the valve to make sure water pressure doesn’t reach such a level that it will burst pipes.

The IMI Norgren Olympian Plus pressure relief valve is designed to protect compressed air systems against over-pressurisation. It has high relief capacity while being sensitive and accurate. As part of the Olympian Plus range of products, it is suitable for in-line or modular installation and is compatible with other products in the Olympian Plus range, such as the B64G Filter/Regulator and the L64 Series Lubricator. Some of the key pressure relief valve features include:

Choosing a pressure relief valve isn’t always easy, but here at MGA Controls, we specialise in helping you choose the correct valve for your application. There are six basic factors to consider before choosing your pressure relief valve:

You must also consider the physical dimensions of the application and the plant, as well as factors related to the environment in which the valve will operate.

Here at MGA Controls, pressure relief valves can be fitted to an existing system and can be specified in sizes ranging from 1/4″ to 1.1/2″. We carry a wide range of stock that is available for quick delivery in your time of need.

To speak to a member of our technical team about choosing a pressure relief valve or the difference between a pressure relief valve and regulator contact us today on 01704 898980 or email sales@mgacontrols.co.uk. To request a free quote or view our general range of products contact our team.

Pressure Relieving Devices (PRD) are components used in refineries, chemical plants, and other similar facilities to prevent pressure vessels and other equipment from over pressurization by relieving excess pressure when necessary. They can be used to release gas, steam, liquids, or vapours. Properly functioning pressure relief devices are essential for protecting plant personnel and equipment, since unexpected overpressure events can potentially cause equipment damage, loss of containment, and result in costly plant shutdowns.

Pressure relieving devices include mechanisms such as Pressure Safety Valves (PSV) and Pressure Relief Valves (PRV), although there are other types of pressure relieving devices as well, such as Rupture Disk Devices and Pin-Actuated Devices. These devices can come in many different sizes and shapes and allow pressurized fluids or gasses to escape through a secondary passage out of the system so that pressure cannot build up beyond safe operating limits.

A Pressure Safety Valve (PSV) is a type of valve used to quickly release gasses from equipment in order to avoid over pressurization and potential process safety incidents. PSVs are activated automatically when pressure exceeds prescribed pressure limits in order to return equipment pressure to a safe operating level.

A Pressure Relief Valve (PRV) is a type of valve used to release stored gas in various equipment in order to maintain an optimal pressure level. PRVs open gradually as pressure builds up in order to release the necessary amount of pressure. While the term PRV is sometimes used interchangeably with PSV, there is a difference between the two. A PRV opens gradually in relation to the pressure, while a PSV is opened suddenly once the pressure hits a certain level in order to avoid over pressurization and a potential process safety incident.

The function of both PSV and PRV is that they relieve the excess pressure from the system by opening automatically and they get closed automatically when the pressure in the system normalizes.

The valve has a spring which is attached to adjusting screw. The screw can be adjusted to compress the spring thus imparting flexibility in adjusting the spring force. The spring is attached to a disc using a spindle. The location of the disk is where the fluid enters the valve when the system is over pressurized.

If the pressure force is less than the spring force then the fluid will not be able to move the disc. Such condition represents normal operating condition. If the pressure force is equal to the spring force then the disc starts to move. The fluid enters from the equipment to the valve and starts moving out of the system.

In case of PSV, when the pressure force becomes greater than the spring force the valve opens instantly and a ‘pop’ sound occurs whereas the PRV opens proportionally to the increasing pressure. It can be said that the opening is relatively gradual as compared to PSV.

The escaping fluid results in decrease of the pressure. When the pressure force becomes smaller than the spring force again then the disc returns to the same location again and seals the equipment.

As soon as mankind was able to boil water to create steam, the necessity of the safety device became evident. As long as 2000 years ago, the Chinese were using cauldrons with hinged lids to allow (relatively) safer production of steam. At the beginning of the 14th century, chemists used conical plugs and later, compressed springs to act as safety devices on pressurised vessels.

Early in the 19th century, boiler explosions on ships and locomotives frequently resulted from faulty safety devices, which led to the development of the first safety relief valves.

In 1848, Charles Retchie invented the accumulation chamber, which increases the compression surface within the safety valve allowing it to open rapidly within a narrow overpressure margin.

Today, most steam users are compelled by local health and safety regulations to ensure that their plant and processes incorporate safety devices and precautions, which ensure that dangerous conditions are prevented.

The principle type of device used to prevent overpressure in plant is the safety or safety relief valve. The safety valve operates by releasing a volume of fluid from within the plant when a predetermined maximum pressure is reached, thereby reducing the excess pressure in a safe manner. As the safety valve may be the only remaining device to prevent catastrophic failure under overpressure conditions, it is important that any such device is capable of operating at all times and under all possible conditions.

Safety valves should be installed wherever the maximum allowable working pressure (MAWP) of a system or pressure-containing vessel is likely to be exceeded. In steam systems, safety valves are typically used for boiler overpressure protection and other applications such as downstream of pressure reducing controls. Although their primary role is for safety, safety valves are also used in process operations to prevent product damage due to excess pressure. Pressure excess can be generated in a number of different situations, including:

The terms ‘safety valve’ and ‘safety relief valve’ are generic terms to describe many varieties of pressure relief devices that are designed to prevent excessive internal fluid pressure build-up. A wide range of different valves is available for many different applications and performance criteria.

In most national standards, specific definitions are given for the terms associated with safety and safety relief valves. There are several notable differences between the terminology used in the USA and Europe. One of the most important differences is that a valve referred to as a ‘safety valve’ in Europe is referred to as a ‘safety relief valve’ or ‘pressure relief valve’ in the USA. In addition, the term ‘safety valve’ in the USA generally refers specifically to the full-lift type of safety valve used in Europe.

Pressure relief valve- A spring-loaded pressure relief valve which is designed to open to relieve excess pressure and to reclose and prevent the further flow of fluid after normal conditions have been restored. It is characterised by a rapid-opening ‘pop’ action or by opening in a manner generally proportional to the increase in pressure over the opening pressure. It may be used for either compressible or incompressible fluids, depending on design, adjustment, or application.

Safety valves are primarily used with compressible gases and in particular for steam and air services. However, they can also be used for process type applications where they may be needed to protect the plant or to prevent spoilage of the product being processed.

Relief valve - A pressure relief device actuated by inlet static pressure having a gradual lift generally proportional to the increase in pressure over opening pressure.

Relief valves are commonly used in liquid systems, especially for lower capacities and thermal expansion duty. They can also be used on pumped systems as pressure overspill devices.

Safety relief valve - A pressure relief valve characterised by rapid opening or pop action, or by opening in proportion to the increase in pressure over the opening pressure, depending on the application, and which may be used either for liquid or compressible fluid.

In general, the safety relief valve will perform as a safety valve when used in a compressible gas system, but it will open in proportion to the overpressure when used in liquid systems, as would a relief valve.

Safety valve- A valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to re-close and prevent further flow of fluid after normal pressure conditions of service have been restored.

There is a wide range of safety valves available to meet the many different applications and performance criteria demanded by different industries. Furthermore, national standards define many varying types of safety valve.

The ASME standard I and ASME standard VIII for boiler and pressure vessel applications and the ASME/ANSI PTC 25.3 standard for safety valves and relief valves provide the following definition. These standards set performance characteristics as well as defining the different types of safety valves that are used:

ASME I valve - A safety relief valve conforming to the requirements of Section I of the ASME pressure vessel code for boiler applications which will open within 3% overpressure and close within 4%. It will usually feature two blowdown rings, and is identified by a National Board ‘V’ stamp.

ASME VIII valve- A safety relief valve conforming to the requirements of Section VIII of the ASME pressure vessel code for pressure vessel applications which will open within 10% overpressure and close within 7%. Identified by a National Board ‘UV’ stamp.

Full bore safety valve - A safety valve having no protrusions in the bore, and wherein the valve lifts to an extent sufficient for the minimum area at any section, at or below the seat, to become the controlling orifice.

Conventional safety relief valve -The spring housing is vented to the discharge side, hence operational characteristics are directly affected by changes in the backpressure to the valve.

Balanced safety relief valve -A balanced valve incorporates a means of minimising the effect of backpressure on the operational characteristics of the valve.

Pilot operated pressure relief valve -The major relieving device is combined with, and is controlled by, a self-actuated auxiliary pressure relief device.

Power-actuated safety relief valve - A pressure relief valve in which the major pressure relieving device is combined with, and controlled by, a device requiring an external source of energy.

Standard safety valve - A valve which, following opening, reaches the degree of lift necessary for the mass flowrate to be discharged within a pressure rise of not more than 10%. (The valve is characterised by a pop type action and is sometimes known as high lift).

Full lift (Vollhub) safety valve -A safety valve which, after commencement of lift, opens rapidly within a 5% pressure rise up to the full lift as limited by the design. The amount of lift up to the rapid opening (proportional range) shall not be more than 20%.

Direct loaded safety valve -A safety valve in which the opening force underneath the valve disc is opposed by a closing force such as a spring or a weight.

Proportional safety valve - A safety valve which opens more or less steadily in relation to the increase in pressure. Sudden opening within a 10% lift range will not occur without pressure increase. Following opening within a pressure of not more than 10%, these safety valves achieve the lift necessary for the mass flow to be discharged.

Diaphragm safety valve -A direct loaded safety valve wherein linear moving and rotating elements and springs are protected against the effects of the fluid by a diaphragm

Bellows safety valve - A direct loaded safety valve wherein sliding and (partially or fully) rotating elements and springs are protected against the effects of the fluids by a bellows. The bellows may be of such a design that it compensates for influences of backpressure.

Controlled safety valve - Consists of a main valve and a control device. It also includes direct acting safety valves with supplementary loading in which, until the set pressure is reached, an additional force increases the closing force.

Safety valve - A safety valve which automatically, without the assistance of any energy other than that of the fluid concerned, discharges a quantity of the fluid so as to prevent a predetermined safe pressure being exceeded, and which is designed to re-close and prevent further flow of fluid after normal pressure conditions of service have been restored. Note; the valve can be characterised either by pop action (rapid opening) or by opening in proportion (not necessarily linear) to the increase in pressure over the set pressure.

Direct loaded safety valve -A safety valve in which the loading due to the fluid pressure underneath the valve disc is opposed only by a direct mechanical loading device such as a weight, lever and weight, or a spring.

Assisted safety valve -A safety valve which by means of a powered assistance mechanism, may additionally be lifted at a pressure lower than the set pressure and will, even in the event of a failure of the assistance mechanism, comply with all the requirements for safety valves given in the standard.

Supplementary loaded safety valve - A safety valve that has, until the pressure at the inlet to the safety valve reaches the set pressure, an additional force, which increases the sealing force.

Note; this additional force (supplementary load), which may be provided by means of an extraneous power source, is reliably released when the pressure at the inlet of the safety valve reaches the set pressure. The amount of supplementary loading is so arranged that if such supplementary loading is not released, the safety valve will attain its certified discharge capacity at a pressure not greater than 1.1 times the maximum allowable pressure of the equipment to be protected.

Pilot operated safety valve -A safety valve, the operation of which is initiated and controlled by the fluid discharged from a pilot valve, which is itself, a direct loaded safety valve subject to the requirement of the standard.

The common characteristic shared between the definitions of conventional safety valves in the different standards, is that their operational characteristics are affected by any backpressure in the discharge system. It is important to note that the total backpressure is generated from two components; superimposed backpressure and the built-up backpressure:

Subsequently, in a conventional safety valve, only the superimposed backpressure will affect the opening characteristic and set value, but the combined backpressure will alter the blowdown characteristic and re-seat value.

The ASME/ANSI standard makes the further classification that conventional valves have a spring housing that is vented to the discharge side of the valve. If the spring housing is vented to the atmosphere, any superimposed backpressure will still affect the operational characteristics. Thiscan be seen from Figure 9.2.1, which shows schematic diagrams of valves whose spring housings are vented to the discharge side of the valve and to the atmosphere.

By considering the forces acting on the disc (with area AD), it can be seen that the required opening force (equivalent to the product of inlet pressure (PV) and the nozzle area (AN)) is the sum of the spring force (FS) and the force due to the backpressure (PB) acting on the top and bottom of the disc. In the case of a spring housing vented to the discharge side of the valve (an ASME conventional safety relief valve, see Figure 9.2.1 (a)), the required opening force is:

In both cases, if a significant superimposed backpressure exists, its effects on the set pressure need to be considered when designing a safety valve system.

Once the valve starts to open, the effects of built-up backpressure also have to be taken into account. For a conventional safety valve with the spring housing vented to the discharge side of the valve, see Figure 9.2.1 (a), the effect of built-up backpressure can be determined by considering Equation 9.2.1 and by noting that once the valve starts to open, the inlet pressure is the sum of the set pressure, PS, and the overpressure, PO.

In both cases, if a significant superimposed backpressure exists, its effects on the set pressure need to be considered when designing a safety valve system.

Once the valve starts to open, the effects of built-up backpressure also have to be taken into account. For a conventional safety valve with the spring housing vented to the discharge side of the valve, see Figure 9.2.1 (a), the effect of built-up backpressure can be determined by considering Equation 9.2.1 and by noting that once the valve starts to open, the inlet pressure is the sum of the set pressure, PS, and the overpressure, PO.

Balanced safety valves are those that incorporate a means of eliminating the effects of backpressure. There are two basic designs that can be used to achieve this:

Although there are several variations of the piston valve, they generally consist of a piston type disc whose movement is constrained by a vented guide. The area of the top face of the piston, AP, and the nozzle seat area, AN, are designed to be equal. This means that the effective area of both the top and bottom surfaces of the disc exposed to the backpressure are equal, and therefore any additional forces are balanced. In addition, the spring bonnet is vented such that the top face of the piston is subjected to atmospheric pressure, as shown in Figure 9.2.2.

The bellows arrangement prevents backpressure acting on the upper side of the disc within the area of the bellows. The disc area extending beyond the bellows and the opposing disc area are equal, and so the forces acting on the disc are balanced, and the backpressure has little effect on the valve opening pressure.

Bellows failure is an important concern when using a bellows balanced safety valve, as this may affect the set pressure and capacity of the valve. It is important, therefore, that there is some mechanism for detecting any uncharacteristic fluid flow through the bellows vents. In addition, some bellows balanced safety valves include an auxiliary piston that is used to overcome the effects of backpressure in the case of bellows failure. This type of safety valve is usually only used on critical applications in the oil and petrochemical industries.

In addition to reducing the effects of backpressure, the bellows also serve to isolate the spindle guide and the spring from the process fluid, this is important when the fluid is corrosive.

Since balanced pressure relief valves are typically more expensive than their unbalanced counterparts, they are commonly only used where high pressure manifolds are unavoidable, or in critical applications where a very precise set pressure or blowdown is required.

This type of safety valve uses the flowing medium itself, through a pilot valve, to apply the closing force on the safety valve disc. The pilot valve is itself a small safety valve.

The diaphragm type is typically only available for low pressure applications and it produces a proportional type action, characteristic of relief valves used in liquid systems. They are therefore of little use in steam systems, consequently, they will not be considered in this text.

The piston type valve consists of a main valve, which uses a piston shaped closing device (or obturator), and an external pilot valve. Figure 9.2.4 shows a diagram of a typical piston type, pilot operated safety valve.

The piston and seating arrangement incorporated in the main valve is designed so that the bottom area of the piston, exposed to the inlet fluid, is less than the area of the top of the piston. As both ends of the piston are exposed to the fluid at the same pressure, this means that under normal system operating conditions, the closing force, resulting from the larger top area, is greater than the inlet force. The resultant downward force therefore holds the piston firmly on its seat.

If the inlet pressure were to rise, the net closing force on the piston also increases, ensuring that a tight shut-off is continually maintained. However, when the inlet pressure reaches the set pressure, the pilot valve will pop open to release the fluid pressure above the piston. With much less fluid pressure acting on the upper surface of the piston, the inlet pressure generates a net upwards force and the piston will leave its seat. This causes the main valve to pop open, allowing the process fluid to be discharged.

When the inlet pressure has been sufficiently reduced, the pilot valve will reclose, preventing the further release of fluid from the top of the piston, thereby re-establishing the net downward force, and causing the piston to reseat.

Pilot operated safety valves offer good overpressure and blowdown performance (a blowdown of 2% is attainable). For this reason, they are used where a narrow margin is required between the set pressure and the system operating pressure. Pilot operated valves are also available in much larger sizes, making them the preferred type of safety valve for larger capacities.

One of the main concerns with pilot operated safety valves is that the small bore, pilot connecting pipes are susceptible to blockage by foreign matter, or due to the collection of condensate in these pipes. This can lead to the failure of the valve, either in the open or closed position, depending on where the blockage occurs.

The terms full lift, high lift and