The pressure relief valve is a kind of self-powered regulating valve. It throttles using a valve member, reducing the inlet pressure to the desired outlet pressure. When the inlet pressure and the amount of flow change, it relies on elastic components and the power of transmitting the medium to keep the outlet pressure largely unchanged.

What are the types of sanitary pressure relief valves?

The commonly used sanitary pressure relief valve is usually level one throttle whose valve flap is cone-shaped. The pressure relief valve of level one throttle has a better effect under the low-pressure drop. Under high-pressure drop, cavitation is prone to occur, which will lead to premature damage of throttling members. In light of this, two or more pressure relief valves are often used in parallel, which increases the operating cost of the system and the instability. In order to solve the problem of pressure-relieving under the high-pressure drop, a kind of two-stage throttle balanced sleeve type pressure relief valve was designed.

According to structural forms, the pressure relief valve can be divided into direct-acting film type, direct-acting bellows type, pilot film type, pilot bellows type, and pilot piston type. Regardless of the structural form, they all automatically balance the pressure of the medium using the elastic component to regulate the opening of the valve flap to throttle and reduce pressure.

What is Balanced Sleeve Type Pressure Relief Valve?

The valve flap is the core component of the pressure relief valve. Whether its design is reasonable or not directly affects the operating performance of the pressure relief valve.

The valve flap of the pressure relief valve uses two-stage balanced sleeve type throttle. In the middle of the valve flap, six throttle holes of the same area are drilled and are evenly distributed circumferentially. These are level two throttle holes. The medium enters the cylindrical space of the valve flap from the inlet of the pressure relief valve, through the six throttle holes in the middle of the valve flap. Because the upper and lower area of the cylindrical space is the same, the liquid pressure sustained by the upper and lower sleeves is offset to reach a balance. Thus, the area of throttling is not affected by the change in the pressure of the inlet. Then, the medium enters the outlet of the pressure relief valve through the upper and lower throttle holes.

The total area of the upper and lower twelve two-stage throttle holes is the same as the total area of the six first-stage throttle holes in the center. Two-stage throttling pressure is close, that is, the total throttling pressure of the pressure relief valve is basically evenly distributed, which controls the speed of the liquid flow. In addition, the respective six throttle holes at the upper, middle, and lower parts are circumferentially positioned, eliminating the lateral force.

A two-stage throttle balanced sleeve type pressure relief valve has many advantages:

1. Two-stage throttling can be achieved, which solves the problem of pressure reducing under the high-pressure drop, alleviates the hydraulic shock, avoids cavitation, and lowers the noise. It can also be used to reduce pressure under a low-pressure drop.

2. Through simple structural design, the valve flap is horizontally balanced while being vertically balanced, which reduces the cost of design and manufacturing.

3. The lateral thrust of the valve flap is balanced, the piloting is smooth, the service life of the sealing surface of the valve seat improves, the structural optimization is reasonable.

4. The valve flap can be quickly disassembled in whole, which is easy for repair and maintenance.

5. The elastic component only corresponds with the outlet pressure of the two-stage throttling, which can improve the stability of the outlet pressure.

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A pressure relief valve is a kind of self-regulating valve that uses throttling to reduce the inlet pressure to desired outlet pressure. When the inlet pressure and the amount of flow change, it relies on elastic components and the force of transmitting the medium to keep the outlet pressure unchanged.

Sanitary pressure relief valve that is now commonly used is first-grade throttling. The valve flap is cone-shaped. The pressure relief valve of first-grade throttling has a better effect in low-pressure drop. But in high-pressure drops, cavitation is prone to occur, leading to premature damage to the throttle.

Usually, two or more pressure relief valves are used in parallel, increasing the operating cost of the system and its instability. In order to solve the problem of pressure-relieving under the high-pressure drop, a kind of second-grade throttling balanced sleeve type pressure relief valve was designed.

What are the types of pressure relief valves?

According to the structural form, pressure relief valves can be divided into direct-acting film type, direct-acting bellows type, pilot film type, pilot bellows type, and pilot piston type. Regardless of the structural form, they all use elastic components to automatically balance the pressure of the medium to regulate the opening of the valve flap to throttle and reduce pressure.

The valve flap is the essential part of the pressure relief valve. Whether it is reasonably designed or not directly affects the performance of the pressure relief valve.

Second-grade throttling balanced sleeve type pressure relief valve has a lot of advantages:

1. It can achieve second-grade throttling, thus solving the problem of pressure-relieving under high-pressure drop conditions, slowing down the hydraulic shock, avoiding cavitation, reducing the noise. It can also be used for pressure relieving under low-pressure drop conditions.

2. Through a simple structural design, the valve flap is kept balanced in the horizontal direction while also being kept balanced in the vertical direction. This reduces the cost of design and manufacturing.

3. The lateral thrust of the valve flap is balanced. The piloting is smooth. The service life of the joint surface of the valve seat is improved, and the structural optimization is reasonable.

4. The valve flap can be quickly disassembled in whole, which is easy for maintenance.

5. The elastic components only correspond to the outlet pressure of second-grade throttling, which can improve the stability of the outlet pressure of the pressure relief valve.

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A pressure relief valve is a specialized device that automatically reduces the operating pressure in various pipeline systems. It can also provide a special function to reduce the relatively high water pressure of the pre-valve pipeline to the level required for the post-valve pipeline.

Types of Pressure Relief Valves

There are many types of pressure relief valves with slightly different structures. The two most common types of pressure relief valves are: 

• Thin Film Type
• Inner Spring Piston Type

The basic application of pressure relief valves is that the flow channel inside the valve has a local resistance to the water flow to reduce water pressure. The range of water pressure drop is automatically regulated by the thin film connecting the valve flaps or inlet and outlet water pressure difference on both sides of the piston.

Fixed-Type Pressure Relief Valves

In recent years, engineers have developed new types of pressure relief valves, such as the fixed-type pressure relief valve. The principle of fixed-type pressure relieving is to use the water pressure ratio control of the floating piston in the valve body. The pressure relieving ratio at the inlet and outlet ends is inversely proportional to the piston area on the inlet and outlet sides. This kind of pressure relief valve works smoothly without vibration. Since there’s no spring in the valve body, we don’t need to worry about spring corrosion and metal fatigue or failure. The sealing performance is good and there’s no leakage, so both dynamic pressure and static pressure can be reduced. When the pressure is reduced, the water flow is not affected.

Pressure relief valves usually have DN50~DN100 and other specifications. The operating pressure of pre-valve and post-valve is <1MPa and 0.1~0.5MPa, respectively. The error of the range of pressure regulating is ±5%~10%.

It should be noted that although there’s a large water head loss when the water flows through the pressure relief valve, it’s still energy efficient on the whole due to the fact that the waste of water is reduced, the distribution of system flow is reasonable, and the system layout and working conditions are improved.

Applications of Pressure Relief Valves

Sanitary pressure relief valves are widely used in high-rise buildings, areas with overly high water pressure in urban water supply networks, mines and other conveyance systems to ensure that various points in the water supply obtain the appropriate service water pressure and flow. In light of the fact that the water leakage and degree of waste are almost proportional to the water pressure of the water supply system, pressure relief valves have the role of improving the running working conditions of the system and can potentially save water. According to recent statistics, some pressure relief valves have water-saving effects of about 30%.

6 Precautions to Take When Using Pressure Relief Valves

1. Before the pressure relief valve leaves the factory, its opening pressure should be adjusted one by one to the set value required by the user. If the user proposes the working pressure level of the spring, it should generally be adjusted according to the lower limit of the pressure level.
2. Before installing the pressure relief valve on the protected equipment or before installation, the user must re-adjust at the installation site to ensure that the set pressure value of the pressure relief valve meets the requirements.
3. You can adjust the opening pressure by changing the spring’s compression level. Simply rotate the adjusting screw within the spring’s working pressure level range, usually indicated on the nameplate.
4. Before rotating the adjustment screw, the valve inlet pressure should be reduced to below 90% of the opening pressure. This prevents the valve disc from rotating when the adjustment screw is rotated, which may damage the sealing surface.
5. In order to ensure the accuracy of the opening pressure value, the media conditions during adjustment, such as the type of media and temperature, should be as close as possible to the actual operating conditions.
6. The conventional pressure relief valve is used to mitigate excess back pressure. When the opening pressure is adjusted after inspection (the back pressure is atmospheric pressure at this time), its setting value should be the required opening pressure minus the additional back pressure.

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Why Is My Pressure Relief Valve Making Noise?

There are many reasons why your pressure relief valve is making noises. In some cases, these noises can be a sign your pressure valve is bad. In order to help you diagnose the problem, let’s divide the causes into the following three categories of valve noises: mechanical vibration noise, fluid dynamics noise, and aerodynamics noise. Now, let’s take a closer look at each of these causes of noises from sanitary pressure relief valves.

1. Water Pressure Regulator Valve – Mechanical Vibration Noise

Various parts of pressure relief valves produce mechanical vibrations when fluid flows through them. Usually, this vibration is not noticeable, but it can become a nuisance when maintenance is required. These mechanical vibrations can be divided into two types:

1) Low-frequency vibration

Low-frequency vibrations are caused by jets and pulsations in the fluid medium brought on by fast flow rates at the valve outlet, unreasonable or inefficient pipeline layouts, and insufficient stiffness of the active parts of the valve.

2) High-frequency vibration

High-frequency vibrations create resonance when the natural frequency of the valve coincides with the excitation frequency caused by the fluid flow. This phenomenon occurs within a certain range of pressure-reducing sanitary pressure relief valves. And the changes in noise can be very large once there’s even the slightest change in conditions. This kind of mechanical vibration noise has nothing to do with the flow rate of the medium but is primarily due to the unreasonable design of the pressure relief valve.

There are a few methods to consider when learning how to reduce a valve’s mechanical vibration noise:

1. Re-design the clearance between the sleeve and stem of the valve
2. Check the valve for any imperfections or defects. Some valve manufacturers don’t practice high machining precision.
3. Check the valve’s natural frequency and the stiffness of the active parts.
4. If you suspect the valve material may not be compatible with the medium, replace it immediately.

Causes of Noise from Pressure Relief Valves

2. Water Pressure Regulator Valve – Fluid Dynamics Noise

Fluid dynamics can generate noise from turbulence and eddy currents after the fluid passes through the valve’s pressure-reducing port. The process can be divided into two stages:

1) Turbulence noise

Turbulence noise is generated by the interactions between the turbulent fluid and the pressure relief valve or pipe surface. Its frequency and noise level are relatively low, which generally does not constitute a noise problem. If it does become a noise issue, you may need to rearrange the pipeline more efficiently.

2) Cavitation noise

During the valve’s pressure-reducing process, the fluid (liquid) will begin to vaporize once the fluid flow rate reaches a particular value. When the pressure on the bubble inside the liquid reaches a specific level, the bubble will explode, leading to very high pressure and shock waves in some parts. The instant pressure of the impact can be up to 196MPa. The pressure will sharply decline in locations far away from the center of the explosion. Shock waves can be a major factor in cavitation noises coming from the pressure relief valve.

3. Water Pressure Regulator Valve – Aerodynamic Noise

When vapor and other compressible fluid pass through the pressure-reducing portion of the pressure relief valve, the fluid’s mechanical energy is converted into sound energy, and the water regulator produces an audible nuisance.

How Do I Know If My Pressure Relief Valve Is Bad?

While these are the most common causes of noisy valves, there are several more possibilities. In rare cases, a failed expansion tank, quick closing pressure relief valves on new appliances, bad vacuum breakers, faulty valves with loose washers, or even improperly strapped pipes can be the cause of those noises coming from your pressure relief valve. In addition to the noises, also check for the signs that your pressure valve is bad.

Five symptoms that can indicate your pressure relief valve is going bad:

• Diminishing water pressure
• No water pressure
• Hammering or vibrating noises in your walls
• High water pressure
• A leak in your flower bed or landscaping close to the house could be a leaking PRV.

How Often Should Pressure Relief Valves Be Replaced?

First, check for a specified replacement cycle on the valve itself. If there is no date listed, you can also check the manufacturer’s website or contact them directly. If you still can’t find the specified replacement life cycle, you should replace most pressure relief valves five years after the manufacture date. Many industries recommend replacing relief valves on a five-year schedule.

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The sanitary pressure relief valve is an essential component of pneumatic sanitary regulating valves. Its main use is to reduce the pressure of the gas source and to stabilize it to a fixed value so that the regulating valve can get a stable gas source force for regulating.

According to structural type, they can be divided into film type, spring film type, piston type, lever type, and bellow type.

According to the number of valve seats, they can be divided into single-seat types and double-seat types.

According to the position of the valve gate, they can be divided into positive-acting type and reaction type.

How does a pressure relief valve work?

When the pressure relief valve’s output pressure is high or the diameter is large, regulating the pressure using a regulator spring will make the stiffness of the spring too big. When flow changes, the output pressure has a big fluctuation, so the structural size of the sanitary valve will increase, too. In order to overcome these shortcomings, pilot-type pressure relief valves can be used.

The mechanism of pilot-type pressure relief valves is basically the same as that of the direct-acting type. The regulating gas that the pilot-type pressure relief valve uses is supplied by a small direct-acting pressure relief valve. If the small direct-acting pressure relief valve is installed inside the valve, then it’s known as the internal pilot-type pressure relief valve. If the small direct-acting pressure relief valve is installed outside the valve, then it’s known as the external pilot-type pressure relief valve.

How do you adjust a pressure relief valve?

With a slotted screwdriver, turn the screw in the center of the knob clockwise, until flow can be heard escaping from the internal valve. Slowly turn the screw counterclockwise until the flow from the relief valve stops. Turn the screw an additional 1/8 to 1/4 turn counter-clockwise. Replace the silver cap in the knob.

Conclusion

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

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1. Control failure, so that the host doesn’t run
Failure of pilot relief valve will cause the host to stop running. Possible reasons include: the valve core spring of pilot valve is broken; damping hole is blocked; poor sealing of valve opening of pilot valve; the main valve core is stuck. The corresponding solutions are: replacement or adding a flattened pad at the broken place for emergency use; cleaning and dredging; grinding or cutting off the oil pipeline for emergency use; grinding and cleaning.

2. Instable limit pressure
Instable limit pressure of pilot relief valve is demonstrated as lower or higher hydraulic system pressure, weakness of hydraulic actuator or burst of oil tube, pump and valve body.

The causes of this failure include: improper pressure regulation; bending or softening of pilot valve core spring; overly dirty oil or unsmooth flow of the oil. The corresponding solutions are: readjustment; recalibrating, pad-adding or replacement; replacement and cleaning.

Limit pressure instability of pilot relief valve is a gradual failure. It mostly occurs in construction machinery with more motorcycle hour reserve. Limit pressure failure of pilot relief valve is a sudden failure. It mostly occurs in construction machinery with less motorcycle hour reserve. After troubleshooting, we should readjust the pressure of pilot relief valve according to the pressure defined by the system.

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There are many kinds of sanitary pressure relief valves, they can be divided into two general categories: direct-action type and indirect-action type. The direct-action type uses the energy of the medium itself to control the required pressure. The Indirect-action type uses external power, such as air pressure, hydraulic pressure, or electric power to control the required pressure. Compare these two types, and it’s easy to conclude that the former has a relatively simple structure while the latter has higher precision.

According to the structure of pressure relief valves, they can be divided into:

Piston-type pressure relief valve:

It uses the piston to balance pressure and drive the movement of the valve flap.

Membrane-type pressure relief valve:

It uses a membrane as a sensing element to drive the movement of the valve flap.
Air bag-type pressure relief valve: It uses the pressure produced by the medium entering the air bag to balance pressure.

The above classification method is based on the structure of the valve.

According to the types of valve seats, they can be divided into single-seat valves and double-seat valves.

On the one hand, a double-seat valve can make the force on upper and lower seats mostly balanced and offset, reducing the resultant effect on the valve stem.

On the other hand, a larger channel area can be achieved, and the overall size of the valve can be reduced. However, the valve seat technology of the pressure relief valve is not good, and machining and grinding of it are difficult. The Assembly size chain should be well controlled in order to ensure assembly accuracy, making the valve normal and stable when working.

Conclusion

Different types of hydraulic pressure valves include relief, reducing, sequence, counterbalance, safety, and unloading. All of them are typically closed valves, except for reducing valves, which are usually open. For most of these valves, a restriction is necessary to produce the required pressure control.

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There are many types of sanitary pressure relief valves. Piston type and spring film type are the main two types. Piston type pressure relief valve is a type of valve that uses a piston for pressure relief. Spring film-type pressure relief valve relies on spring and film for pressure balance.

The use of a pressure relief valve:

A pressure relief valve is a kind of automatic valve that reduces the medium pressure to a certain value. Generally, the pressure after the valve is less than 50% of the pressure before the valve.

Pressure testing method:

The strength test of the pressure relief valve is usually for assembly after the test of a single piece, or for test after assembly. The duration of a strength test: 1 minute for DN<50mm; more than 2 minutes for DN65~150mm; more than 3 minutes for DN>150mm. After the bellows and the components are welded, apply 1.5 times the maximum pressure and use the air to perform a strength test.

When performing the sealing performance test, it should be based on the actual working medium. When tested with air or water, the test is to be carried out at 1.1 times the nominal pressure. When tested with steam, the test is to be carried out under the maximum working pressure allowed in the operating temperature. The difference between inlet pressure and outlet pressure shouldn’t be less than 0.2MPa.

The testing method:

After the inlet pressure is set, gradually adjust the regulating screw of the valve so that the outlet pressure can sensitively and continuously change within the range of maximum and minimum value without stagnation or jamming.

How are pressure relief valves tested?

Pressure relief valves are tested depending on their operating conditions, and the valves are instrumented to verify correct operation at their set point pressure.

Conclusion

The most commonly mandated form of pressure relief valve testing, bench testing is unique in that it requires you completely shut down your facility’s system and remove all pressure relief valves. The valves are then transported to a lab where they are tested and repaired as necessary.

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The high-pressure chamber of the oxygen pressure relief valve is connected to the steel cylinder. The low-pressure chamber is for gas emission and also has access to the system. The indication of the high-pressure gauge is the pressure of the stored gas in the steel cylinder. The outlet pressure of the low-pressure gauge can be controlled by the regulating screw.

How does a pressure relief valve work?

When using sanitary pressure relief valve, open the master switch of the steel cylinder first, and then turn clockwise the pressure regulating screw of the low-pressure gauge to compress the mainspring and drive the film, spring pads, and mandrel to open the shutter. This way, the high-pressure gas at the inlet, after throttling and decompression, goes from the high-pressure chamber into the low-pressure chamber and then through the outlet to the work system. Turn the regulating screw to change the height of the shutter, so that the amount of high-pressure gas can be regulated and the required pressure value can be achieved.

What is a Pressure relief valve?

Pressure relief valves are all equipped with safety valves, which are the devices used to protect and ensure the safe use of pressure relief valves. Also, they are signal devices when the pressure relief valve encounters failure. If the shutter pad or the entire shutter is damaged, causing the outlet pressure to rise on its own and exceed a certain allowed value, the safety valve will automatically open and exhaust.

Conclusion

Pressure relief valves (safety relief valves) are designed to open at a preset pressure and discharge fluid until the pressure drops to acceptable levels. When the force of the steam pressure acting on the valve exceeded the force of the weight acting through the lever arm the valve opened.

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The pressure of a pilot-operated sanitary relief valve is provided on the upstream side (the system being protected) at the dome often by a small pilot tube. The downstream side is the pipe or open-air where the PORV directs its exhaust. The outlet pipe is usually larger than the inlet. 2 in × 3 in (51 mm × 76 mm), 3 in × 4 in (76 mm × 102 mm), 4 in × 6 in (100 mm × 150 mm), 6 in × 8 in (150 mm × 200 mm), and 8 in × 10 in (200 mm × 250 mm) are some common sizes.

What are the pressure and safety relief valves?

The upstream pressure tries to push the piston but it is opposed by this same pressure because the pressure is directed towards the dome above the piston. The zone of the piston on which the force of the fluid acts is greater in the dome than in the upstream direction; the result is a greater force on the dome side than on the upstream side. This produces a net sealing force.

The pressure from the pilot tube to the dome is routed through the actual control pilot valve. There are many designs but the control driver is basically a conventional PRV with the special job of controlling the pressure at the main valve dome. The pressure at which the pilot is released is the functional operating pressure of the PORV. When the pilot-operated sanitary relief valve reaches the set pressure, it opens and releases the dome pressure. The piston is then free to open and the main valve discharges the fluid from the system. The control pilot opens either on the exhaust pipe of the main valve or on the atmosphere.

What is the functioning mode of pilot-operated sanitary relief valves?

When the pilot-operated valve reaches set pressure, it opens and releases the pressure. It is then free to open, and the main valve exhausts the pressure at the bottom of the dome. It opens either to the main exhaust pipe or into the atmosphere. There are typically two functioning modes: snap-acting and modulating.

Conclusion

Thank you for reading our article and we hope it can help you better understand the functioning mode of pilot-operated sanitary relief valves. If you want to learn more about sanitary relief valves, we would like to advise you to visit Adamant Valve homepage for more information.

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