Safety valves discharge gases, vapors, or liquids into the atmosphere or in collective pipelines when the set pressure is exceeded. Here are some design features.

The set pressure is the pressure at which the safety valve starts to open, to blow off the pressure. This pressure is fixed at the safety valve. The set pressure is subject to a tolerance (according to DIN EN ISO 4126-1) of (+/- 3%) or for valves below 3 bar of (+/- 0.1 bar).

The closing pressure is the pressure value at which the safety valve is completely closed again after it has blown off the overpressure. This value is 20% below the set pressure for liquid media (at setting pressure <3 bar, the value is 0.6 bar below).

For gaseous media, the value according to AD2000 is 10% below the set pressure and according to DIN EN ISO 4126-1 15% lower (at setting pressure <3 bar the value is 0.3 bar below the setting pressure).

The opening pressure is also called blow-off pressure and is the point at which the safety valve reaches the maximum lift for the required mass flow to be drained. This is at normal stroke safety valves at max. 10% above the set pressure and with full lift safety valves at max. 5% above the set pressure.

The operating pressure is the working pressure of a plant or system under normal circumstances. Ideally, the operating pressure is 5% below the closing pressure of a sanitary safety valve.

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1. In hot water boilers, non-enclosed with a wrench micro open safety valve can be used.

2. In steam boilers or steam pipes, a non-enclosed wrench full open safety valve can be used.

3. In water and other liquid incompressible media, a closed micro-safety valve or safety relief valve can be used.

4. In the case of high-pressure water supply, closed-type micro-safety valves can be used, such as high-pressure water heaters, heat exchangers, and so on.

5. In the gas and other compressible media, such as gas tanks, gas pipelines, closed all-safety valves, etc. can be used.

6. In Class E steam boilers, deadweight safety valves can be used.

7. In large caliber and large displacement and high-pressure systems, such as temperature and pressure reduction devices, power plant boilers, and pulse safety valves can be selected.

8. In the delivery of liquefied gas train tanker, tank car, storage tank, and built-in safety valve can be used.

9. At the top of the tank, a hydraulic safety valve can be selected. It needs to be used with a breathing valve.

10. Pilot-operated safety valves may be selected for use in downhole drainage or natural gas pipelines.

11. A safety return valve may be used on the liquid return line at the LPG tank pump outlet.

12. In negative pressure or during operation that may produce negative pressure in the system, a vacuum negative pressure safety valve can be used.

Bellows safety valves are available for use in container or piping systems where the backpressure is very variable and toxic and flammable.

14. Insulation jacketed safety valves may be used in systems where the media have a low freezing point.

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The dynamic instability of the safety valve is mainly caused by the following reasons: the discharge capacity of the safety valve exceeds the amount of flow of the medium entering the valve; the spring stiffness is too large; the large back pressure occurred in the upper chamber of the valve flap when the valve is opened; external dynamic interference.

1. The impact of discharge capacity

When the following conditions occur, the discharge capacity of the safety valve may exceed the flow of the medium entering the valve:
a) When the cross-sectional area of the selected safety valve exceeds the cross-sectional area in computing.
b) When the safety valve is installed on a system with a change in emergency displacement.
c) When the cross-sectional area of the inlet pipe is not big enough.

2. The impact of spring stiffness

The spring stiffness is too large can also be the cause of the valve flap oscillation. A full opening safety valve can rely on the medium recoil to fully discharge. But when the spring stiffness is too large, the safety valve can’t fully discharge. In this case, as soon as the safety valve is opened, it goes back to the valve seat, causing oscillation. If the spring stiffness is small, the safety valve will go back to the valve seat under very low pressure. In order to keep this from happening, a suitably designed spring should be installed.

3. The impact of system backpressure

Similar to the effect of excessive spring stiffness, the backpressure of the upper body of the valve flap occurred when the safety valve is opened may also cause valve flap oscillation. To avoid large back pressure, for the open safety valve, use the opening on the valve body to connect the upper body of the valve flap and the atmosphere. For a closed safety valve, the upper body of the valve flap can be connected with the valve body outlet or outlet branch pipe, using the resulting suction effect to reduce the pressure above the valve flap.

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How Do You Adjust the Pressure On a Safety Valve?

1. Before the safety valve leaves the factory, we should adjust its opening pressure to reach the set value user specifies. If a user specifies the working pressure level of the spring, then we should adjust it according to the lower limit of the pressure level.

2. Before the safety valve is installed on the protected equipment, users must re-adjust it at the installation site to ensure the set pressure value of the safety valve meets the requirements.

3. In the range of the working pressure level of the spring specified by the nameplate, by turning the adjustment stem to change the compression amount of the spring, we can adjust the opening pressure.

4. Before turning the adjustment stem, make sure the inlet pressure of sanitary valve is reduced to less than the opening pressure to prevent the valve flap from being turned when adjusting the stem, damaging the sealing surface.

5. To ensure the accuracy of opening pressure value, make sure the medium conditions, such as medium types and temperatures, are as close as possible to the actual operating conditions. When the medium type changes, especially when the dielectric aggregation is different (for example, from the liquid phase to the gas phase), the opening pressure often changes. When the operating temperature rises, the opening pressure is generally reduced. When it’s adjusted at room temperature and used for high temperature, the set pressure value at room temperature should be slightly higher than the required opening pressure value. How high the temperature should be has something to do with the valve structure and material selection, so it should be based on the manufacturer’s instructions.

6. The conventional safety valve is used to fix the additional backpressure. When adjusting opening pressure after the testing (at this time, the backpressure is atmospheric pressure), the set value should be required opening pressure minus additional backpressure.

Conclusion

By adding the 0.1 bar shut-off margin, the safety valve set pressure has to be 10% greater than 6.4 bar. For this example, this means that the safety valve’s set pressure has to be: The set pressure would therefore be chosen as 7.11 bar, provided that this does not exceed the MAWP of the protected system.

Thank you for reading our article and we hope it can help you better understand the adjustment of the opening pressure of the safety valve. If you want to learn more about safety valves, we would like to advise you to visit Adamant Valve homepage for more information.

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Where Should a Pressure Relief Valve be Installed?

The safety valve should be installed as close as possible to the protected equipment or pipe. If the valve can’t be installed close to the layout, then the pipe’s pressure drop from the protected equipment’s inlet to the valve inlet must not exceed 3% of the sanitary valve’s constant pressure.

The safety valve should be installed in places where it’s easy to maintain and regulate, and there should be enough workspace around it to make convenient repairs in the future. The safety valve should not be installed at dead ends of horizontal pipes, so that solid or liquid materials don’t accumulate and affect the normal operation of the valve.

How To Install a Safety Valve?

Should a Safety Valve be Installed Horizontally or Vertically?

Safety valves within equipment or piping systems should be installed upright. But for safety relief valves installed in liquid pipes, heat exchangers, and containers, when the valve is closed, in occasions where the pressure may increase due to thermal expansion, they can be horizontally installed.

What Pressure Should a Safety Valve be Set To?

Safety valve settings are usually set at least 10% above the system’s maximum operating pressure. If your system is designed to tolerate some unstable pressure conditions, you can use a setting of 25-PSIG above the maximum operating pressure. 

In fact, the design of the safety valve should take into consideration the fact that the back pressure doesn’t exceed a certain value of the constant pressure of the valve. For instance, for an ordinary spring safety valve, its backpressure does not exceed 10% of the constant pressure of the valve.

Precautions for the Inlet, Outlet, & Discharge Pipes

• The safety valve inlet pipe should use a long radius elbow.
• The safety valve outlet pipe buried into a closed system should follow the flow direction of the medium and be connected to the top of the pressure relief pipe at a 45-degree slant. This is to prevent the condensate in the general pipe from flowing back into the branch pipe.
• When the outlet pipe is long, a certain slope should be set up to ensure efficient drainage by gravity (except for dry gas systems).
• For the safety of all, the safety valve discharge pipe cannot be directed towards equipment, platforms, ladders, cables, and so on. Discharging excess pressure can cause injuries.
• There should be a “bag-shaped” liquid container inside the discharge pipe of the wet gas pressure relief system.

Other Precautions to Take When Installing Safety Valve

• For large-diameter safety valves, we need to consider the possibility of lifting after disassembly. If necessary, a lifting stem can be used.
• The installation height of the safety valve should be higher than that of the pressure relief system. If the valve outlet is lower than the pressure relief general pipe or the discharge pipe needs to be lifted up to be connected to the general pipe, we should set dispensers at low and accessible points.
• When there’s a shut-off valve on the outlet pipe of the safety valve, a single gate plate or gate valve should be used. The valve stem should be horizontally installed in order to prevent the valve plate from slipping down when the pin connecting the valve stem and valve plate is corroded or loose.
• When the safety valve is installed with a bypass valve, the valve should be sealed.

Thank you for reading these instructions on how to install a safety valve. We hope it can help you to better understand the precautions to take when installing a safety valve. If you want to learn more about safety valves or other types of sanitary valves, please visit Adamant Valves homepage for more information.

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1. Heavy hammer lever type safety valve

Heavy hammer lever type safety valve uses heavy hammer and lever to balance the force on the valve flap. According to the principle of leverage, it can use a heavy hammer of a relatively small weight to get great force through the amplifying effect of the lever and can adjust the opening pressure of the safety valve by moving the heavy hammer (or changing the weight of the heavy hammer).

Heavy hammer lever type safety valve has a simple structure, is easy to adjust, and is rather accurate, and the load will not significantly increase due to the increase in valve flap, so it is suitable for high-temperature occasions. It used to be commonly used, especially in boilers and pressure vessels in high temperatures. But its structure is rather bulky, and the loading mechanism is prone to vibration, which often leads to leakage. Its back seat pressure is low, which makes it not easy to close or keep tight once opened.

2. Spring type safety valve

Spring type safety valve uses the force that compresses the spring to balance the force on the sanitary valve flap. The amount of compression of the helical coil spring can be adjusted by turning the regulating nut above it. The opening pressure of the safety valve can be corrected as needed by using this structure.

Spring type safety valve has a light and tight structure, and its sensitivity is relatively high, its installation location is not limited to a certain position. And because it’s not very sensitive to vibration, it can be used for mobile pressure vessels. The drawback of this kind of safety valve is that the applied load will change with the opening of the valve. That is to say, with the increase in the valve flap, the amount of compression of the spring increases, and the force on the valve flap increases accordingly. This is not good for the quick opening of the safety valve. In addition, the spring on the valve will lose elasticity due to long-term influence by high temperature. When it is used in containers with high temperatures, the issue of insulation and heat dissipation of the spring often need to be considered, which makes the structure complicated.

3. Pulse safety valve

Pulse safety valve consists of main valve and auxiliary valve. The main valve is driven by the pulse of the auxiliary valve. Its structure is complex. Usually, it’s only suitable for use in boilers and pressure vessels with a very large amount of safe discharge. Among the above-mentioned three types of safety valves, the spring-type safety valve is more commonly used.

Conclusion

Thank you for reading our article and we hope it can help you better understand the classification of safety valves. If you want to learn more about safety valves, we would like to advise you to visit Adamant Valve homepage for more information.

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Double sealing sanitary valve seat structure ensures high action precision, good repeatability, quick seat returning, no leakage, the ability to discharge with high back pressure, long service life, stability, and reliability. It can also be adjusted on-site. After repeated start and discharge, it can still return to the seat automatically. Tight closing ensures convenient operation and maintenance.

The pilot-type safety valve is widely used in natural gas, LPG, and chemical pressure vessel equipment and industrial pipelines. It has obvious advantages such as fire-proof and explosion-proof, static-electricity-proof, reliable sealing, quick opening and closing, and a large amount of discharge.

Pilot-type safety valve consists of the main valve, pilot valve, relief valve, fittings, and conduits. Under normal working conditions, the medium pressure of the system is applied to the lower part of the main valve flap and the upper part of the main valve flap. As the medium effect area at the upper chamber of the main valve flap is greater than that of the lower chamber, under the effect of the pressure difference, the main valve is in a closed state.

With the rise in medium pressure of the pipelines, the sealing pressure obtained by the sealing pair will also rise accordingly. This is the opposite of a spring direct loading type safety valve, namely, that the higher the medium pressure, the more reliable the sealing.

When the medium pressure of the pipeline is abnormal and reaches or exceeds the set pressure, the upper valve flap of the pilot valve quickly opens. The medium inside the upper chamber of the main valve flap is quickly discharged through the exhaust fitting of the pilot valve.

Under the strong effect of the lower medium pressure, the main valve flap instantly opens, quickly discharging the medium in large quantity from the outlet of the main valve, so that the medium pressure in the pipeline is restored to the normal working pressure, which ensures the safety of the system.

When the medium pressure in the pipeline drops to around 90% of the set pressure of the system, the upper valve flap of the pilot valve closes, and the medium in the pipeline enters the upper chamber of the main valve flap through the pilot valve. Under the effect of the pressure difference, the main valve closes, ensuring the normal operation of the system.

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The blower safety valve is used to protect the blower and equipment. When the pressure in the blower and equipment is abnormally raised to a certain value (the opening pressure of the safety valve), the safety valve can automatically open and discharge the medium to prevent the pressure from continuing to rise. When the pressure in the blower and equipment falls to a certain value (the back seat pressure of the safety valve), the safety valve automatically closes.

What are the Features of a Blower Safety Valve?

Compared with a traditional safety valve, a blower safety valve has the following features:

1. Since blower is mainly used for low-pressure air medium, blower safety valve doesn’t have outlet discharge flange. Instead, it uses the small holes evenly distributed around the sanitary valve body to directly discharge media while placing the spring chamber directly to the back of the valve flap. With this patented structure, the structure of the valve is more compact, the discharge of the medium is smoother, and the weight of the valve is only one-third to one-fifth of the traditional safety valve.

2. Blower safety valve uses the patented structure of pressure accumulation tank between valve flap and valve seat. Compared with a traditional safety valve that uses regulating ring and positioning screw, it has a simpler structure, and it’s more convenient to use the valve, and the valve has more stable performance.

3. The minimum opening pressure of a traditional safety valve is generally 0.1MPa. For the blower safety valve, its opening pressure is often required to be less than 0.1MPa. Even if the traditional safety valve uses a spring of smaller stiffness, it can’t operate accurately and sensitively under low pressure. The opening pressure range of the blower safety valve is 0.02~0.2MPa, so the blower safety valve can accurately and sensitively operate under low pressure.

4. The point of force of the spring of the blower safety valve on the valve flap through the valve stem is very close to the sealing surface of the valve flap whereas the point of force of the traditional safety valve is far away from the sealing surface of the valve flap. Thus, compared with traditional safety valves, the performance of the blower safety valve is more stable and reliable.

5. Traditional safety valve discharges medium through outlet channel in one direction, so the discharge of medium is likely to cause the vibration of the system. The blower safety valve evenly discharges medium to the surroundings through the small holes evenly distributed on the valve body. Therefore, the operation of the valve is stable, with no vibration.

6. There is no regulation ring on the blower safety valve, so it’s easy to use it. The safety valve has been debugged according to the opening pressure required by the user, so the user can directly install it on the system to use it.

Conclusion

The primary purpose of a blower safety valve is the protection of life, property, and the environment. A blower safety valve is designed to open and relieve excess pressure from vessels or equipment and to reclose and prevent the further release of fluid after normal conditions have been restored.

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Valves of all types are critical components of the fluid, gas, and slurry processing systems that we depend on for production, dispensing, plumbing, and so many more essential activities. Our society truly depends on valves to function efficiently — safety valves are considered by many to be the most important.

From time to time, safety valves fail, no matter how well we take care of them. Oftentimes, we don’t realize how important safety valves are until they’re not working properly. Let’s take a look at the most common reasons why safety valves fail.

Six Common Causes of Safety Valve Failure

1. After discharge, the valve flap doesn’t return to its normal position

This is mainly caused by the spring bending the valve stem, incorrect installation position, or jamming of the valve flap. Check for all of these issues, replace any parts as necessary, and reassemble the valve.

2. Valve Leakage

If leakage exceeds the allowable level between the valve flap and the sealing surface of the sanitary valve seat under normal working pressure, it’s usually caused by built-up debris between the valve flap and the valve seat’s sealing surface. In this case, use the lifting wrench to open the valve several times, removing all debris. If the sealing surface is damaged, repair it using the grinding method according to the level of damage. If the valve stem bends, tilts, or if the lever and fulcrum skew, displacing the valve core and valve flap, you should reassemble or replace it. If the elasticity of the spring is reduced or lost, replace the spring and readjust the opening pressure.

3. The valve doesn’t open when the specified pressure is reached

The reason for this kind of failure is that the pressure setting is not accurate. You should readjust the amount of spring compression or the location of the hammer. If the valve flap is stuck to the valve seat, you should begin testing the safety valve regularly for gas exhaust or water discharge. If the safety valve lever is stuck or the hammer has moved, you should readjust the position of the hammer so it allows the lever to move freely.

4. Exhaust is released effectively but pressure continues to rise

This problem normally occurs when your selected safety valve’s exhaust capacity is too small to safely discharge the system’s pressure. In this case, you should reselect a suitable safety valve that accommodates your necessary pressure levels. If the centerline of the valve stem is not upright or the spring rusts, causing the valve flap to fall short of the required height, you should reassemble the valve stem or replace the spring.

5. Frequent jumping or excess vibration of the valve flap

This is mainly because the stiffness of the spring is too large. In this case, we should use a spring with proper stiffness. If the adjustment ring is not properly set up, it can lead to excess pressure on the valve seat. In this case, you should readjust the adjustment ring’s position. If the resistance of the discharge pipe is too large, causing overly large discharge back pressure, you must reduce the resistance of the discharge pipeline.

6. The safety valve opens below the specified pressure

This is mainly due to the inaccurate pressure settings and aging springs, leading to reduced elasticity. In this case, you should properly tighten the regulating stem or replace the spring.

Conclusion — Safety Valve Failure

Valve leakage is one of the most common faults of boiler safety valves. It mainly refers to leakage between the valve disc and the valve seat under normal working pressure. If you experience any problems with your safety valves, please contact us and we will be happy to help you resolve them.

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