boiler safety valve sizing for sale

After a boiler has been engineered, built and tested for a given operating pressure there is only one reliable way to prevent operation of the boiler above this design pressure.  This is a safety valve.  The safety valve should be sized so that a single valve can handle the maximum steam production rate of the boiler and once open prevent boiler pressure to continue to rise.  Standard operating procedure for the last century has been to install two safety valves on the boiler, one set 3-5 lbs below the design pressure and one valve set at the design pressure.

The 1st valve listed below is a true adjustable differential pop valve.  The differential is adjured through the differential rings lock screw hole, from 3 PSI to whatever the operator desires.  The pressure of the valve can be adjusted from 40 to 200 PSI.

The other valves listed are adjustable for release pressure and have a "pop" action:  The pressure differential is not adjustable on these valves.  If the valves are operated above their nominal pressure, the set-reset differential increases.  If operated at lower pressure, the differential decreases to the point of disappearing about 10-15% below nominal pressure.

Safety valves and pressure relief valves are crucial for one main reason: safety. This means safety for the plant and equipment as well as safety for plant personnel and the surrounding environment.

Safety valves and pressure relief valves protect vessels, piping systems, and equipment from overpressure, which, if unchecked, can not only damage a system but potentially cause an explosion. Because these valves play such an important role, it’s absolutely essential that the right valve is used every time.

The valve size must correspond to the size of the inlet and discharge piping. The National Board specifies that the both the inlet piping and the discharge piping connected to the valve must be at least as large as the inlet/discharge opening on the valve itself.

The connection types are also important. For example, is the connection male or female? Flanged? All of these factors help determine which valve to use.

The set pressure of the valve must not exceed the maximum allowable working pressure (MAWP) of the boiler or other vessel. What this means is that the valve must open at or below the MAWP of the equipment. In turn, the MAWP of the equipment should be at least 10% greater than the highest expected operating pressure under normal circumstances.

Temperature affects the volume and viscosity of the gas or liquid flowing through the system. Temperature also helps determine the ideal material of construction for the valve. For example, steel valves can handle higher operating temperatures than valves made of either bronze or iron. Both the operating and the relieving temperature must be taken into account.

Back pressure, which may be constant or variable, is pressure on the outlet side of the pressure relief valve as a result of the pressure in the discharge system. It can affect the set pressure of the upstream valve and cause it to pop open repeatedly, which can damage the valve.

For installations with variable back pressure, valves should be selected so that the back pressure doesn’t exceed 10% of the valve set pressure. For installations with high levels of constant back pressure, a bellows-sealed valve or pilot-operated valve may be required.

Different types of service (steam, air, gas, etc.) require different valves. In addition, the valve material of construction needs to be appropriate for the service. For example, valves made of stainless steel are preferable for corrosive media.

Safety valves and relief valves must be able to relieve pressure at a certain capacity. The required capacity is determined by several factors including the geometry of the valve, the temperature of the media, and the relief discharge area.

These are just the basic factors that must be considered when selecting and sizing safety valves and relief valves. You must also consider the physical dimensions of the equipment and the plant, as well as other factors related to the environment in which the valve will operate.

A safety valve must always be sized and able to vent any source of steam so that the pressure within the protected apparatus cannot exceed the maximum allowable accumulated pressure (MAAP). This not only means that the valve has to be positioned correctly, but that it is also correctly set. The safety valve must then also be sized correctly, enabling it to pass the required amount of steam at the required pressure under all possible fault conditions.

Once the type of safety valve has been established, along with its set pressure and its position in the system, it is necessary to calculate the required discharge capacity of the valve. Once this is known, the required orifice area and nominal size can be determined using the manufacturer’s specifications.

In order to establish the maximum capacity required, the potential flow through all the relevant branches, upstream of the valve, need to be considered.

In applications where there is more than one possible flow path, the sizing of the safety valve becomes more complicated, as there may be a number of alternative methods of determining its size. Where more than one potential flow path exists, the following alternatives should be considered:

This choice is determined by the risk of two or more devices failing simultaneously. If there is the slightest chance that this may occur, the valve must be sized to allow the combined flows of the failed devices to be discharged. However, where the risk is negligible, cost advantages may dictate that the valve should only be sized on the highest fault flow. The choice of method ultimately lies with the company responsible for insuring the plant.

For example, consider the pressure vessel and automatic pump-trap (APT) system as shown in Figure 9.4.1. The unlikely situation is that both the APT and pressure reducing valve (PRV ‘A’) could fail simultaneously. The discharge capacity of safety valve ‘A’ would either be the fault load of the largest PRV, or alternatively, the combined fault load of both the APT and PRV ‘A’.

This document recommends that where multiple flow paths exist, any relevant safety valve should, at all times, be sized on the possibility that relevant upstream pressure control valves may fail simultaneously.

The supply pressure of this system (Figure 9.4.2) is limited by an upstream safety valve with a set pressure of 11.6 bar g. The fault flow through the PRV can be determined using the steam mass flow equation (Equation 3.21.2):

Once the fault load has been determined, it is usually sufficient to size the safety valve using the manufacturer’s capacity charts. A typical example of a capacity chart is shown in Figure 9.4.3. By knowing the required set pressure and discharge capacity, it is possible to select a suitable nominal size. In this example, the set pressure is 4 bar g and the fault flow is 953 kg/h. A DN32/50 safety valve is required with a capacity of 1 284 kg/h.

Where sizing charts are not available or do not cater for particular fluids or conditions, such as backpressure, high viscosity or two-phase flow, it may be necessary to calculate the minimum required orifice area. Methods for doing this are outlined in the appropriate governing standards, such as:

Coefficients of discharge are specific to any particular safety valve range and will be approved by the manufacturer. If the valve is independently approved, it is given a ‘certified coefficient of discharge’.

This figure is often derated by further multiplying it by a safety factor 0.9, to give a derated coefficient of discharge. Derated coefficient of discharge is termed Kdr= Kd x 0.9

Critical and sub-critical flow - the flow of gas or vapour through an orifice, such as the flow area of a safety valve, increases as the downstream pressure is decreased. This holds true until the critical pressure is reached, and critical flow is achieved. At this point, any further decrease in the downstream pressure will not result in any further increase in flow.

A relationship (called the critical pressure ratio) exists between the critical pressure and the actual relieving pressure, and, for gases flowing through safety valves, is shown by Equation 9.4.2.

Overpressure - Before sizing, the design overpressure of the valve must be established. It is not permitted to calculate the capacity of the valve at a lower overpressure than that at which the coefficient of discharge was established. It is however, permitted to use a higher overpressure (see Table 9.2.1, Module 9.2, for typical overpressure values). For DIN type full lift (Vollhub) valves, the design lift must be achieved at 5% overpressure, but for sizing purposes, an overpressure value of 10% may be used.

For liquid applications, the overpressure is 10% according to AD-Merkblatt A2, DIN 3320, TRD 421 and ASME, but for non-certified ASME valves, it is quite common for a figure of 25% to be used.

Backpressure - The sizing calculations in the AD-Merkblatt A2, DIN 3320 and TRD 421 standards account for backpressure in the outflow function,(Ψ), which includes a backpressure correction.

Two-phase flow - When sizing safety valves for boiling liquids (e.g. hot water) consideration must be given to vaporisation (flashing) during discharge. It is assumed that the medium is in liquid state when the safety valve is closed and that, when the safety valve opens, part of the liquid vaporises due to the drop in pressure through the safety valve. The resulting flow is referred to as two-phase flow.

The required flow area has to be calculated for the liquid and vapour components of the discharged fluid. The sum of these two areas is then used to select the appropriate orifice size from the chosen valve range. (see Example 9.4.3)

Many standards do not actually specify sizing formula for two-phase flow and recommend that the manufacturer be contacted directly for advice in these instances.

Relief valves are designed to open at a preset pressure (or temperature) level and relieve the system when it has exceeded the desired level. The valve"s relief of elevated liquid, gas, or steam pressures prevents damage to the system. We offer a wide selection of relief valves for any application.

The SMS-7100 direct spring operated pressure relief valves has been designed to protect against excess pressure steam boilers and to provide superior performance.

Flanged, Butt weld spring loaded, direct acting, full nozzle safety relief valves for steam service (ASME Sect.I). Media: steam (suitable also for gas).

Boiler explosions have been responsible for widespread damage to companies throughout the years, and that’s why today’s boilers are equipped with safety valves and/or relief valves. Boiler safety valves are designed to prevent excess pressure, which is usually responsible for those devastating explosions. That said, to ensure that boiler safety valves are working properly and providing adequate protection, they must meet regulatory specifications and require ongoing maintenance and periodic testing. Without these precautions, malfunctioning safety valves may fail, resulting in potentially disastrous consequences.

Boiler safety valves are activated by upstream pressure. If the pressure exceeds a defined threshold, the valve activates and automatically releases pressure. Typically used for gas or vapor service, boiler safety valves pop fully open once a pressure threshold is reached and remain open until the boiler pressure reaches a pre-defined, safe lower pressure.

Boiler relief valves serve the same purpose – automatically lowering boiler pressure – but they function a bit differently than safety valves. A relief valve doesn’t open fully when pressure exceeds a defined threshold; instead, it opens gradually when the pressure threshold is exceeded and closes gradually until the lower, safe threshold is reached. Boiler relief valves are typically used for liquid service.

There are also devices known as “safety relief valves” which have the characteristics of both types discussed above. Safety relief valves can be used for either liquid or gas or vapor service.

Nameplates must be fastened securely and permanently to the safety valve and remain readable throughout the lifespan of the valve, so durability is key.

The National Board of Boiler and Pressure Vessel Inspectors offers guidance and recommendations on boiler and pressure vessel safety rules and regulations. However, most individual states set forth their own rules and regulations, and while they may be similar across states, it’s important to ensure that your boiler safety valves meet all state and local regulatory requirements.

The National Board published NB-131, Recommended Boiler and Pressure Vessel Safety Legislation, and NB-132, Recommended Administrative Boiler and Pressure Vessel Safety Rules and Regulationsin order to provide guidance and encourage the development of crucial safety laws in jurisdictions that currently have no laws in place for the “proper construction, installation, inspection, operation, maintenance, alterations, and repairs” necessary to protect workers and the public from dangerous boiler and pressure vessel explosions that may occur without these safeguards in place.

The American Society of Mechanical Engineers (ASME) governs the code that establishes guidelines and requirements for safety valves. Note that it’s up to plant personnel to familiarize themselves with the requirements and understand which parts of the code apply to specific parts of the plant’s steam systems.

High steam capacity requirements, physical or economic constraints may make the use of a single safety valve impossible. In these cases, using multiple safety valves on the same system is considered an acceptable practice, provided that proper sizing and installation requirements are met – including an appropriately sized vent pipe that accounts for the total steam venting capacity of all valves when open at the same time.

The lowest rating (MAWP or maximum allowable working pressure) should always be used among all safety devices within a system, including boilers, pressure vessels, and equipment piping systems, to determine the safety valve set pressure.

Avoid isolating safety valves from the system, such as by installing intervening shut-off valves located between the steam component or system and the inlet.

Contact the valve supplier immediately for any safety valve with a broken wire seal, as this indicates that the valve is unsafe for use. Safety valves are sealed and certified in order to prevent tampering that can prevent proper function.

Avoid attaching vent discharge piping directly to a safety valve, which may place unnecessary weight and additional stress on the valve, altering the set pressure.

A little product education can make you look super smart to customers, which usually means more orders for everything you sell. Here’s a few things to keep in mind about safety valves, so your customers will think you’re a genius.

A safety valve is required on anything that has pressure on it. It can be a boiler (high- or low-pressure), a compressor, heat exchanger, economizer, any pressure vessel, deaerator tank, sterilizer, after a reducing valve, etc.

There are four main types of safety valves: conventional, bellows, pilot-operated, and temperature and pressure. For this column, we will deal with conventional valves.

A safety valve is a simple but delicate device. It’s just two pieces of metal squeezed together by a spring. It is passive because it just sits there waiting for system pressure to rise. If everything else in the system works correctly, then the safety valve will never go off.

A safety valve is NOT 100% tight up to the set pressure. This is VERY important. A safety valve functions a little like a tea kettle. As the temperature rises in the kettle, it starts to hiss and spit when the water is almost at a boil. A safety valve functions the same way but with pressure not temperature. The set pressure must be at least 10% above the operating pressure or 5 psig, whichever is greater. So, if a system is operating at 25 psig, then the minimum set pressure of the safety valve would be 30 psig.

Most valve manufacturers prefer a 10 psig differential just so the customer has fewer problems. If a valve is positioned after a reducing valve, find out the max pressure that the equipment downstream can handle. If it can handle 40 psig, then set the valve at 40. If the customer is operating at 100 psig, then 110 would be the minimum. If the max pressure in this case is 150, then set it at 150. The equipment is still protected and they won’t have as many problems with the safety valve.

Here’s another reason the safety valve is set higher than the operating pressure: When it relieves, it needs room to shut off. This is called BLOWDOWN. In a steam and air valve there is at least one if not two adjusting rings to help control blowdown. They are adjusted to shut the valve off when the pressure subsides to 6% below the set pressure. There are variations to 6% but for our purposes it is good enough. So, if you operate a boiler at 100 psig and you set the safety valve at 105, it will probably leak. But if it didn’t, the blowdown would be set at 99, and the valve would never shut off because the operating pressure would be greater than the blowdown.

All safety valves that are on steam or air are required by code to have a test lever. It can be a plain open lever or a completely enclosed packed lever.

Safety valves are sized by flow rate not by pipe size. If a customer wants a 12″ safety valve, ask them the flow rate and the pressure setting. It will probably turn out that they need an 8×10 instead of a 12×16. Safety valves are not like gate valves. If you have a 12″ line, you put in a 12″ gate valve. If safety valves are sized too large, they will not function correctly. They will chatter and beat themselves to death.

Safety valves need to be selected for the worst possible scenario. If you are sizing a pressure reducing station that has 150 psig steam being reduced to 10 psig, you need a safety valve that is rated for 150 psig even though it is set at 15. You can’t put a 15 psig low-pressure boiler valve after the reducing valve because the body of the valve must to be able to handle the 150 psig of steam in case the reducing valve fails.

The seating surface in a safety valve is surprisingly small. In a 3×4 valve, the seating surface is 1/8″ wide and 5″ around. All it takes is one pop with a piece of debris going through and it can leak. Here’s an example: Folgers had a plant in downtown Kansas City that had a 6×8 DISCONTINUED Consolidated 1411Q set at 15 psig. The valve was probably 70 years old. We repaired it, but it leaked when plant maintenance put it back on. It was after a reducing valve, and I asked him if he played with the reducing valve and brought the pressure up to pop the safety valve. He said no, but I didn’t believe him. I told him the valve didn’t leak when it left our shop and to send it back.

If there is a problem with a safety valve, 99% of the time it is not the safety valve or the company that set it. There may be other reasons that the pressure is rising in the system before the safety valve. Some ethanol plants have a problem on starting up their boilers. The valves are set at 150 and they operate at 120 but at startup the pressure gets away from them and there is a spike, which creates enough pressure to cause a leak until things get under control.

If your customer is complaining that the valve is leaking, ask questions before a replacement is sent out. What is the operating pressure below the safety valve? If it is too close to the set pressure then they have to lower their operating pressure or raise the set pressure on the safety valve.

Is the valve installed in a vertical position? If it is on a 45-degree angle, horizontal, or upside down then it needs to be corrected. I have heard of two valves that were upside down in my 47 years. One was on a steam tractor and the other one was on a high-pressure compressor station in the New Mexico desert. He bought a 1/4″ valve set at 5,000 psig. On the outlet side, he left the end cap in the outlet and put a pin hole in it so he could hear if it was leaking or not. He hit the switch and when it got up to 3,500 psig the end cap came flying out like a missile past his nose. I told him to turn that sucker in the right direction and he shouldn’t have any problems. I never heard from him so I guess it worked.

If the set pressure is correct, and the valve is vertical, ask if the outlet piping is supported by something other than the safety valve. If they don’t have pipe hangers or a wall or something to keep the stress off the safety valve, it will leak.

There was a plant in Springfield, Mo. that couldn’t start up because a 2″ valve was leaking on a tank. It was set at 750 psig, and the factory replaced it 5 times. We are not going to replace any valves until certain questions are answered. I was called to solve the problem. The operating pressure was 450 so that wasn’t the problem. It was in a vertical position so we moved on to the piping. You could tell the guy was on his cell phone when I asked if there was any piping on the outlet. He said while looking at the installation that he had a 2″ line coming out into a 2×3 connection going up a story into a 3×4 connection and going up another story. I asked him if there was any support for this mess, and he hung up the phone. He didn’t say thank you, goodbye, or send me a Christmas present.

Safety valves are an arrangement or mechanism to release a substance from the concerned system in the event of pressure or temperature exceeding a particular preset limit. The systems in the context may be boilers, steam boilers, pressure vessels or other related systems. As per the mechanical arrangement, this one get fitted into the bigger picture (part of the bigger arrangement) called as PSV or PRV that is pressure safety or pressure relief valves.

This type of safety mechanism was largely implemented to counter the problem of accidental explosion of steam boilers. Initiated in the working of a steam digester, there were many methodologies that were then accommodated during the phase of the industrial revolution. And since then this safety mechanism has come a long way and now accommodates various other aspects.

These aspects like applications, performance criteria, ranges, nation based standards (countries like United States, European Union, Japan, South Korea provide different standards) etc. manage to differentiate or categorize this safety valve segment. So, there can be many different ways in which these safety valves get differentiated but a common range of bifurcation is as follows:

The American Society of Mechanical Engineers (ASME) I tap is a type of safety valve which opens with respect to 3% and 4% of pressure (ASME code for pressure vessel applications) while ASME VIII valve opens at 10% over pressure and closes at 7%. Lift safety valves get further classified as low-lift and full lift. The flow control valves regulate the pressure or flow of a fluid whereas a balanced valve is used to minimize the effects induced by pressure on operating characteristics of the valve in context.

A power operated valve is a type of pressure relief valve is which an external power source is also used to relieve the pressure. A proportional-relief valve gets opened in a relatively stable manner as compared to increasing pressure. There are 2 types of direct-loaded safety valves, first being diaphragms and second: bellows. diaphragms are valves which spring for the protection of effects of the liquid membrane while bellows provide an arrangement where the parts of rotating elements and sources get protected from the effects of the liquid via bellows.

In a master valve, the operation and even the initiation is controlled by the fluid which gets discharged via a pilot valve. Now coming to the bigger picture, the pressure safety valves based segment gets classified as follows:

So all in all, pressure safety valves, pressure relief valves, relief valves, pilot-operated relief valves, low pressure safety valves, vacuum pressure safety valves etc. complete the range of safety measures in boilers and related devices.

Safety valves have different discharge capacities. These capacities are based on the geometrical area of the body seat upstream and downstream of the valve. Flow diameter is the minimum geometrical diameter upstream and downstream of the body seat.

The nominal size designation refers to the inlet orifice diameter. A safety Valve"s theoretical flowing capacity is the mass flow through an orifice with the same cross-sectional area as the valve"s flow area. This capacity does not account for the flow losses caused by the valve. The actual capacity is measured, and the certified flow capacity is the actual flow capacity reduced by 10%.

A safety valve"s discharge capacity is dependent on the set pressure and position in a system. Once the set pressure is calculated, the discharge capacity must be determined. Safety valves may be oversized or undersized depending on the flow throughput and/or the valve"s set pressure.

The actual discharge capacity of a safety valve depends on the type of discharge system used. In liquid service, safety valves are generally automatic and direct-pressure actuated.

A safety valve is used to protect against overpressure in a fluid system. Its design allows for a lift in the disc, indicating that the valve is about to open. When the inlet pressure rises above the set pressure, the guide moves to the open position, and media flows to the outlet via the pilot tube. Once the inlet pressure falls below the set pressure, the main valve closes and prevents overpressure. There are five criteria for selecting a safety valve.

The first and most basic requirement of a safety valve is its ability to safely control the flow of gas. Hence, the valve must be able to control the flow of gas and water. The valve should be able to withstand the high pressures of the system. This is because the gas or steam coming from the boiler will be condensed and fill the pipe. The steam will then wet the safety valve seat.

The other major requirement for safety valves is their ability to prevent pressure buildup. They prevent overpressure conditions by allowing liquid or gas to escape. Safety valves are used in many different applications. Gas and steam lines, for example, can prevent catastrophic damage to the plant. They are also known as safety relief valves. During an emergency, a safety valve will open automatically and discharge gas or liquid pressure from a pressurized system, preventing it from reaching dangerous levels.

The discharge capacity of a safety valve is based on its orifice area, set pressure, and position in the system. A safety valve"s discharge capacity should be calculated based on the maximum flow through its inlet and outlet orifice areas. Its nominal size is often determined by manufacturer specifications.

Its discharge capacity is the maximum flow through the valve that it can relieve, based on the maximum flow through each individual flow path or combined flow path. The discharge pressure of the safety valve should be more than the operating pressure of the system. As a thumb rule, the relief pressure should be 10% above the working pressure of the system.

It is important to choose the discharge capacity of a safety valve based on the inlet and output piping sizes. Ideally, the discharge capacity should be equal to or greater than the maximum output of the system. A safety valve should also be installed vertically and into a clean fitting. While installing a valve, it is important to use a proper wrench for installation. The discharge piping should slope downward to drain any condensate.

The discharge capacity of a safety valve is measured in a few different ways. The first is the test pressure. This gauge pressure is the pressure at which the valve opens, while the second is the pressure at which it re-closes. Both are measured in a test stand under controlled conditions. A safety valve with a test pressure of 10,000 psi is rated at 10,000 psi (as per ASME PTC25.3).

The discharge capacity of a safety valve should be large enough to dissipate a large volume of pressure. A small valve may be adequate for a smaller system, but a larger one could cause an explosion. In a large-scale manufacturing plant, safety valves are critical for the safety of personnel and equipment. Choosing the right valve size for a particular system is essential to its efficiency.

Before you use a safety valve, you need to know its discharge capacity. Here are some steps you need to follow to calculate the discharge capacity of a safety valve.

To check the discharge capacity of a safety valve, the safety valve should be installed in the appropriate location. Its inlet and outlet pipework should be thoroughly cleaned before installation. It is important to avoid excessive use of PTFE tape and to ensure that the installation is solid. The safety valve should not be exposed to vibration or undue stress. When mounting a safety valve, it should be installed vertically and with the test lever at the top. The inlet connection of the safety valve should be attached to the vessel or pipeline with the shortest length of pipe. It must not be interrupted by any isolation valve. The pressure loss at the inlet of a safety valve should not exceed 3% of the set pressure.

The sizing of a safety valve depends on the amount of fluid it is required to control. The rated discharge capacity is a function of the safety valve"s orifice area, set pressure, and position in the system. Using the manufacturer"s specifications for orifice area and nominal size of the valve, the capacity of a safety valve can be determined. The discharge flow can be calculated using the maximum flow through the valve or the combined flows of several paths. When sizing a safety valve, it"s necessary to consider both its theoretical and actual discharge capacity. Ideally, the discharge capacity will be equal to the minimum area.

To determine the correct set pressure for a safety valve, consider the following criteria. It must be less than the MAAP of the system. Set pressure of 5% greater than the MAAP will result in an overpressure of 10%. If the set pressure is higher than the MAAP, the safety valve will not close. The MAAP must never exceed the set pressure. A set pressure that is too high will result in a poor shutoff after discharge. Depending on the type of valve, a backpressure variation of 10% to 15% of the set pressure cannot be handled by a conventional valve.

Years ago, it was not uncommon to read news about tragic boiler explosions, sometimes resulting in mass destruction. Today, boilers are equipped with important safety devises to help protect against these types of catastrophes. Let’s take a look at the most critical of these devices: the safety valve.

The safety valve is one of the most important safety devices in a steam system. Safety valves provide a measure of security for plant operators and equipment from over pressure conditions. The main function of a safety valve is to relieve pressure. It is located on the boiler steam drum, and will automatically open when the pressure of the inlet side of the valve increases past the preset pressure. All boilers are required by ASME code to have at least one safety valve, dependent upon the maximum flow capacity (MFC) of the boiler. The total capacity of the safety valve at the set point must exceed the steam control valve’s MFC if the steam valve were to fail to open. In most cases, two safety valves per boiler are required, and a third may be needed if they do not exceed the MFC.

There are three main parts to the safety valve: nozzle, disc, and spring. Pressurized steam enters the valve through the nozzle and is then threaded to the boiler. The disc is the lid to the nozzle, which opens or closes depending on the pressure coming from the boiler. The spring is the pressure controller.

As a boiler starts to over pressure, the nozzle will start to receive a higher pressure coming from the inlet side of the valve, and will start to sound like it is simmering. When the pressure becomes higher than the predetermined pressure of the spring, the disc will start to lift and release the steam, creating a “pop” sound. After it has released and the steam and pressure drops below the set pressure of the valve, the spring will close the disc. Once the safety valve has popped, it is important to check the valve to make sure it is not damaged and is working properly.

A safety valve is usually referred to as the last line of safety defense. Without safety valves, the boiler can exceed it’s maximum allowable working pressure (MAWP) and not only damage equipment, but also injure or kill plant operators that are close by. Many variables can cause a safety valve on a boiler to lift, such as a compressed air or electrical power failure to control instrumentation, or an imbalance of feedwater rate caused by an inadvertently shut or open isolation valve.

Once a safety valve has lifted, it is important to do a complete boiler inspection and confirm that there are no other boiler servicing issues. A safety valve should only do its job once; safety valves should not lift continuously. Lastly, it is important to have the safety valves fully repaired, cleaned and recertified with a National Board valve repair (VR) stamp as required by local code or jurisdiction. Safety valves are a critical component in a steam system, and must be maintained.

All of Nationwide Boiler’s rental boilers include on to two safety valves depending on the size; one set at design pressure and the other set slightly higher than design. By request, we can reset the safeties to a lower pressure if the application requires it. In addition, the valves are thoroughly checked after every rental and before going out to a new customer, and they are replaced and re-certified as needed.

Unfortunately, because of the lack of knowledge and disappearing expertise worldwide, the quality of selection and operation of pressure relief valves is often insufficient. This possibly jeopardizes the safety of each of us living or working in the neighborhood of a process plant.

Proper sizing, selection, manufacture, assembly, testing, installation, and maintenance of a pressure relief valve are all critical to obtaining maximum protection.

Designed around a series of practical examples which we work through to a solution, this valuable course is an essential guide to a complete understanding of construction details and the functioning of relief and safety valves. This understanding is a pre-requisite for the proper sizing, selection, assembly, test, installation, and maintenance of pressure relief valves.

The course presents reference data, technical recommendations, and field observations based on our many years of experience in sizing, selecting, testing, installing, and operating pressure relief valves. This course"s basic formulae and capacity correction factors reflect current state-of-the-art pressure relief valve sizing technology.

Typical valve sizing examples have been included to assist in understanding how specific formulae are applied. Useful technical data covering terminology, standards, codes, basic design, sizing, and selection information, are presented in an easy-to-use format.

This course also cautions the piping designer, the process engineer, and any user of safety valves that the performance of a properly sized and selected pressure relief valve can be severely compromised when used in conjunction with improper companion piping or incorrect handling and installation.

IMPORTANT SAFETY NOTES It is important to always remember that a pressure relief valve is a safety device employed to protect pressure vessels or systems from catastrophic failure. With this in mind, the application of pressure relief valves should be assigned only to fully trained personnel and be in strict compliance with rules provided by the governing Codes and Standards.

Pressure relief valves must be sized, selected, and installed by those who have complete knowledge of: The pressure relieving requirements of the system to be protected and The environmental conditions particular to that installation.

Sizing and selecting pressure relief valves should not be based on arbitrarily assumed conditions or incomplete information. Merely having a mandatory safety valve installation does not make a system safe.

Understand how the ASME Boiler and Pressure Vessel Code, Section VIII affects sizing, selection, assembling, testing and installation of pressure relief valves