boiler safety valve discharge piping manufacturer

Safety valves are precision items of safety equipment; they are set to close tolerances and have accurately machined internal parts. They are susceptible to misalignment and damage if mishandled or incorrectly installed.

Valves should be transported upright if possible and they should never be carried or lifted by the easing lever. In addition, the protective plugs and flange protectors should not be removed until actual installation. Care should also be taken during movement of the valve to avoid subjecting it to excessive shock as this can result in considerable internal damage or misalignment.

When designing the inlet pipework, one of the main considerations is to ensure that the pressure drop in this pipework is minimised. EN ISO 4126 recommends that the pressure drop be kept below 3% of the set pressure when discharging. Where safety valves are connected using short ‘stub’ connections, inlet pipework must be at least the same size as the safety valve inlet connection. For larger lines or any line incorporating bends or elbows, the branch connection should be at least two pipe sizes larger than the safety valve inlet connection, at which point it is reduced in size to the safety valve inlet size (see Figure 9.5.5a). Excessive pressure loss can lead to ‘chatter’, which may result in reduced capacity and damage to the seating faces and other parts of the valve. In order to reduce the pressure loss in the inlet, the following methods can be adopted:

Safety valves should always be installed with the bonnet vertically upwards. Installing the valve in any other orientation can affect the performance characteristics.

The API Recommended Practice 520 guidelines also state that the safety valve should not be installed at the end of a long horizontal pipe that does not normally have flow through it. This can lead to the accumulation of foreign material or condensate in the pipe, which may cause unnecessary damage to the valve, or interfere with its operation.

There are two possible types of discharge system – open and closed. An open system discharges directly into the atmosphere whereas a closed system discharges into a manifold along with other safety valves.

It is recommended that discharge pipework should rise for steam and gas systems, whereas for liquids, it should fall. Horizontal pipework should have a downward gradient of at least 1 in 100 away from the valve ensuring that any discharge will be self-draining. It is important to drain any rising discharge pipework. Vertical rises will require separate drainage. Note: all points of system drainage are subject to the same precautions, notably that valve performance must not be affected, and any fluid must be discharged to a safe location.

It is essential to ensure that fluid cannot collect on the downstream side of a safety valve, as this will impair its performance and cause corrosion of the spring and internal parts. Many safety valves are provided with a body drain connection, if this is not used or not provided, then a small bore drain should be fitted in close proximity to the valve outlet (see Figure 9.5.3).

One of the main concerns in closed systems is the pressure drop or built-up backpressure in the discharge system. As mentioned in Module 9.2, this can drastically affect the performance of a safety valve. The EN ISO 4126: Part 1 standard states that the pressure drop should be maintained below 10% of the set pressure. In order to achieve this, the discharge pipe can be sized using Equation 9.5.1.

Calculate the nominal diameter of the discharge pipework for a safety valve required to discharge 1 000 kg/h of saturated steam; given that the steam is to be discharged into a vented tank via the pipework, which has an equivalent length of 25 m. The set pressure of the safety valve is 10 bar g and the acceptable backpressure is 10% of the set pressure. (Assume zero pressure drop along the tank vent).

Therefore, the pipework connected to the outlet of the safety valve should have an internal diameter of at least 54 mm. With schedule 40 pipe, this would require a DN65 pipe.

Balanced safety valves require that their bonnets be vented to atmosphere. In the case of the balanced bellows type, there will be no discharge of the process fluid, so they can be vented directly to the atmosphere. The main design consideration is to ensure that this vent will not become blocked, for example, by foreign material or ice. With the balanced piston type, consideration must be given to the fact that process fluid may be discharged through the bonnet vent. If discharging to a pressurised system, the vent has to be suitably sized, so that no backpressure exists above the piston.

Safety valves that are installed outside of a building for discharge directly into the atmosphere should be covered using a hood. The hood allows the discharge of the fluid, but prevents the build up of dirt and other debris in the discharge pipework, which could affect the backpressure. The hood should also be designed so that it too does not affect the backpressure.

Manifolds must be sized so that in the worst case (i.e. when all the manifold valves are discharging), the pipework is large enough to cope without generating unacceptable levels of backpressure. The volume of the manifold should ideally be increased as each valve outlet enters it, and these connections should enter the manifold at an angle of no greater than 45° to the direction of flow (see Figure 9.5.6). The manifold must also be properly secured and drained where necessary.

In open systems, careful consideration must be given to the effects of the reaction forces generated in the discharge system when the valve lifts. In these systems, there will be significant resultant force acting in the opposite direction to that of discharge. It is important to prevent excessive loads being imposed on the valve or the inlet connection by these reaction forces, as they can cause damage to the inlet pipework. The magnitude of the reaction forces can be calculated using the formula in Equation 9.5.2:

The reaction forces are typically small for safety valves with a nominal diameter of less than 75 mm, but safety valves larger than this usually have mounting flanges for a reaction bar on the body to allow the valve to be secured.

Regardless of the magnitude of the reaction forces, the safety valve itself should never be relied upon to support the discharge pipework itself and a support should be provided to resist the weight of the discharge pipework. This support should be located as close as possible to the centreline of the vent pipe (see Figure 9.5.7).

Changeover valves (see Figure 9.5.10) permit two valves to be mounted side by side, with one in service and one isolated. This means regular maintenance can be carried out without interruption of service or the vessel being protected. Changeover valves are designed in such a way that when they are operated, the pass area is never restricted.

Changeover valves can also be used to connect safety valve outlets so that the discharge pipework does not have to be duplicated. The action of both inlet and outlet changeover valves has to be limited and synchronised for safety reasons. This is usually by means of a chain drive system linking both handwheels.

Consideration must be made to pressure loss caused by the changeover valve when establishing the safety valve inlet pressure drop, which should be limited to 3% of the set pressure.

Pressure relief devices are used to provide a means of venting excess pressure which could rupture a boiler or pressure vessel. A pressure relief device is the last line of defense for safety. If all other safety devices or operating controls fail, the pressure relief device must be capable of venting excess pressure.

There are many types of pressure relief devices available for use in the boiler and pressure vessel industry. This inspector guide will address the most common devices found on boilers and pressure vessels. Virtually all jurisdictions require a pressure relief device to be manufactured and certified in accordance with the ASME BPV Code in addition to being capacity-certified by the National Board.

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 typically 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°F.

The inlet piping connected to the device must not be smaller in diameter than the inlet opening of the device. An inlet pipe that is smaller than the device inlet opening could alter the operating characteristics for which the device was designed.

The discharge piping connected to the device must be no smaller than the discharge opening of the device. A discharge pipe that is smaller than the device discharge opening could cause pressure to develop on the discharge side of the device while operating.

Multiple devices discharging into a discharge manifold or header is a common practice. The discharge manifold or header must be sized so the cross-sectional area is equal to or greater than the sum of the discharge cross-sectional areas of all the devices connected to the discharge manifold or header. Failing this requirement, the devices would be subjected to pressure on the discharge side of the device while operating. Even a small amount of pressure here could adversely affect the operation of the device.

Constant leakage of the device can cause a build-up of scale or other solids around the discharge opening. This build-up can prevent the device from operating as designed.

Discharge piping connected to the device must be supported so as not to impart any loadings on the body of the device. These loadings could affect or prevent the proper operation of the device including proper reclosure after operating.

Some devices, especially on larger boilers, may have a discharge pipe arrangement which incorporates provisions for expansion as the boiler heats up or cools down. These expansion provisions must allow the full range of movement required to prevent loads being applied to the device body.

Drain holes in the device body and discharge piping, when applicable, must be open to allow drainage of liquids from over the device disk on spring loaded valves. Any liquid allowed to remain on top of the device disk can adversely affect the operating characteristics of the device.

Most jurisdictional requirements state the device must be "piped to a point of safe discharge." This must be accomplished while keeping the run of discharge piping as short as possible. Most jurisdictions also limit the number of 90 degree elbows that may be installed in the discharge piping. Too long of a run and multiple elbows can adversely affect the operation of the device.

While inspecting a boiler or pressure vessel, the inspector will also be evaluating the pressure relief device(s) installed on, or associated with, the equipment. The inspector should:

Compare the device nameplate set pressure with the boiler or pressure vessel maximum allowable working pressure (MAWP) and ensure the device set pressure does not exceed the MAWP. A device with a set pressure less than MAWP is acceptable. If multiple devices are used, at least one must have a set pressure equal to or less than the MAWP. The ASME Code should be reviewed for other conditions relating to the use of multiple devices.

Instruct the owner or owner"s representative to lift the test lever, if so equipped, on spring-loaded devices. ASME BPV Code Section IV devices can have the test levers lifted without pressure in the boiler. All other devices must have at least 75% of the device set pressure under the device disk prior to lifting the test lever. If the device is found to be stuck in a closed position, the equipment should be immediately removed from service until such time the device can be replaced or repaired.

The small pressure relief devices found on many air compressor vessels have a ring inserted through a drilled hole on the end of the device stem. These are tested by pulling the stem straight out and then releasing. The discharge openings in this type of device are holes drilled around the periphery of the device. These holes often get filled with oily dust and grit which can cause eye damage when the device is tested. A rag, loosely wrapped around the device when testing, can help prevent personal injury from the dust and grit.

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.

Discharge pipe shall discharge independently by gravity through an air gap into the drainage system or outside of the building with the end of the pipe not exceeding 2 feet (610 mm) and not less than 6 inches (152 mm) above the ground and pointing downwards.

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.

ASME Section IV Safety Relief Valve for protection of small hot water heating boilers and hydronic heating systems. Made from proven ASTM grade Brass and Bronze materials with decorative chrome finish.

ASME Section IV capacity certified bronze safety relief valve for protection of hot water heating boilers, systems and similar equipment. It can be Pre-set to any pressure ranging between 20 to 80 psig (1.4 to 5.5 bar) at 250�F (121�C) max

ASME Section IV capacity certified bronze safety relief valve for protection of hot water heating boilers, systems and similar equipment. It can be pre-set to any pressure ranging from 15 to 160 psig (1 to 11 bar) at 250�F (121�C) max.

ASME Section VIII design certified Safety Valve to protect portable steam vessel applications such as autoclaves, sterilizers and pressure cookers against excess pressure build-up. Made from proven ASTMgrade Brass with optional decorative chrome finish.

ASME Section I & VIII air and steam capacity certified safety valve for overpressure protection of steam power boilers, deaerators, accumulators, pressure reducing stations and pressure piping systems.

Medium capacity safety valves protect ASME Section IV low pressure steam heatingboilers. Cast bronze, full nozzle design features PTFE faced elastomer soft seatingfor dependable operation.

The Apollo� 13 Series bronze low pressure steam safety valve is designed to meet ASME Section IV code requirements for protection of steam heating boilers, systems and similar equipment.

The Apollo� 13 Series bronze low pressure steam safety valve is designed to meet ASME Section IV code requirements for protection of steam heating boilers, systems and similar equipment.

The Apollo� 14 Series is a 100% American Made Bronze Safety Relief Valve for protection of steam boilers, low pressure, high volume blowers, compressors and vacuum systems.

ASME Section I and VIII capacity certified safety valve for overpressure protection of steam power boilers, systems, pressure vessels, piping and similar equipment. Suitable for steam, air and non-hazardous gases.

ASME Section I/Section VIII capacity certified safety valve for overpressure protection of steam power boilers, steam and air systems, pressure vessels, piping and similar equipment. Compact and economic design ideal for OEM applications.

ASME Section VIII capacity certified safety relief valve for overpressure protection of steam, air/gas and liquid systems, pressure vessels, piping and similar equipment.

Drip Pan Elbows connect to the safety valveoutlet and direct steam discharge into the discharge piping, allowing condensate to drain away. Isolates the valve from piping stresses.Highly recommended in steam service.

ASME Section I & VIII air and steam capacity certified safety valve for overpressure protection of steam power boilers, deaerators, accumulators, pressure reducing stations and pressure piping systems.

High volume air relief valves designed for low pressure air and gas service. Ruggedbronze construction features elastomer soft seating and TFE coated discs fordependable operation.

ASME Section VIII capacity certified relief valve foroverpressure protection of compressors, intercoolers,dryers, receivers, control and instrument air lines andsimilar equipment.

ASME Section I and VIII capacity certified safety valve for overpressure protection of steam power boilers, systems, pressure vessels, piping and similar equipment. Suitable for steam, air and non-hazardous gases.

ASME Section I/Section VIII capacity certified safety valve for overpressure protection of steam power boilers, steam and air systems, pressure vessels, piping and similar equipment. Compact and economic design ideal for OEM applications.

ASME Section VIII capacity certified safety relief valve for overpressure protection of steam, air/gas and liquid systems, pressure vessels, piping and similar equipment.

High flow vacuum relief valves feature one piece cast bronze bodies, Teflon coated discs and elastomer soft seating provide accurate and dependable operation. Ideal for use with high volume vacuum systems, bulk hauling tanks and trailers, powdered solids/bulk handling and pneumatic conveying equipment.

The Apollo� Model VR Vacuum Relief valve is designed to automatically vent a system should avacuum occur. It prevents siphoning of water from the system and/or tank collapse.

farishta - Based on your profile info, you"re located in The Netherlands so I assume this is for a European facility. If so, you need to get a copy of the ISO standard that applies to this type of steam boiler. I don"t work with steam boiler very often so I don"t remember the specific differences between the requirements in that ISO standard and ASME Sec I. I recall that they are similar, but there are some differences.

If this boiler was in an ASME jurisdiction, then you wouldn"t be allowed to install a muffler (ref: ASME Sec I, PG-71.4). Be aware that the rules for steam boilers are different from those for pressure vessels - that"s true in EU countries and in ASME jurisdictions. For example, the pressure drop rules don"t apply to steam boiler applications. Instead, the ASME Sec I rules prescriptively state that there must be as little as possible piping on the inlet and outlet side. ASME Sec I allows a muffler on boilers that operate at low T & P, but not for "high-temperature water boilers" which operate at a pressure greater than 160 psi or a temperature over 250F.

Boilers in EU countries and those in ASME jurisdictions must be inspected and approved by an independent boiler inspector. Even without the muffler, I don"t think any boiler inspector would approve a line pocket like the one shown in this installation. That pocket creates the dangerous possibility of the line being plugged in the wintertime due to ice, and/or the possibility of a "steam explosion" caused by high temperature steam mixing with water trapped in the pocket.

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.

Temperature/pressure-relief or TPR valves are safety devices installed on water heating appliances, such as boilers and domestic water supply heaters. TPRs are designed to automatically release water in the event that pressure or temperature in the water tank exceeds safe levels.

If temperature sensors and safety devices such as TPRs malfunction, water in the system may become superheated (exceed the boiling point). Once the tank ruptures and water is exposed to the atmosphere, it will expand into steam almost instantly and occupy approximately 1,600 times its original volume. This process can propel a heating tank like a rocket through multiple floors, causing personal injury and extensive property damage.

Water-heating appliance explosions are rare due to the fact that they require a simultaneous combination of unusual conditions and failure of redundant safety components. These conditions only result from extreme negligence and the use of outdated or malfunctioning equipment.

The TPR valve will activate if either water temperature (measured in degrees Fahrenheit) or pressure (measured in pounds per square inch [PSI]) exceed safe levels. The valve should be connected to a discharge pipe (also called a drain line) that runs down the length of the water heater tank. This pipe is responsible for routing hot water released from the TPR to a proper discharge location.

It is critical that discharge pipes meet the following requirements, which can be found in InterNACHI’s Water Heater Discharge Piping mini-course, at www.nachi.org/education. A discharge pipe should:

discharge to a termination point that is readily observable by occupants, because discharge indicates that something is wrong, and to prevent unobserved termination capping.

A properly functioning TPR valve will eject a powerful jet of hot water from the discharge pipe when fully activated, not a gentle leak. A leaky TPR valve is an indication that it needs to be replaced. In the rare case that the TPR valve does activate, the homeowner should immediately shut off the water and contact a qualified plumber for assistance and repair.

Inspectors should recommend that homeowners test TPR valves monthly, although inspectors should never do this themselves. The inspector should demonstrate to the homeowner how the main water supply can be shut off, and explain that it can be located at the home"s main water supply valve, or at the water supply shut-off for the appliance on which the TPR is mounted.

The pressure at which a TPR valve will activate is printed on a data plate located beneath the test lever. This amount should not exceed the working pressure limit marked on the data plate of the water-heating appliance it serves.

TPR valves with missing data plates should be replaced.Although a TPR valve might never become activated, it is an essential safety component on boilers and domestic water heaters. Guidelines concerning these valves and their discharge pipes reflect real hazards that every homeowner and home inspector should take seriously. More information about this subject can be found in InterNACHI"s Water Heater Discharge Piping mini-course, InterNACHI"s Plumbing Inspection course or by contacting a qualified plumber.

In a previous article, we explored some common causes of industrial valve leakage, such as incomplete closure, damage, and valve design. These causes are properties of the valve itself, and they can result in significant leakage. However, the most common causes of safety valve leakage we see at job sites are not related to the valves themselves, but rather to improper installation and operating practices.

Most safety valves are designed, manufactured, and tested to be used vertically, meaning in the upright position with the spindle vertical. Mounting a valve horizontally can have a number of significant adverse effects:

A safety valve mounted in a non-vertical orientation may not perform as expected: the seat tightness, operation, and set pressure of the valve may be affected.

Improperly installed valves can both cause leakage and pose safety risks. To guarantee that your valves are installed correctly, and prevent damage to both the valve and the system, ensure that the installation company you use is adequately trained.

Discharge piping must be installed so that it supports its own weight and does not put any weight or strain on the valve itself. According to the National Board of Boiler and Pressure Vessel Inspectors, improperly supported discharge piping is one of the top problems that can prevent valves from operating normally. They write:

“Discharge piping connected to the device must be supported so as not to impart any loadings on the body of the device. These loadings could affect or prevent the proper operation of the device including proper reclosure after operating.”

Piping that does not allow for the full range of motion.When a boiler heats up, it moves up and down, and the installation must allow both the valve and the piping to move along with it. Otherwise, there can be too much stress placed on the valve body.

Piping that is too long or has too many 90° elbows.Most jurisdictions specify the maximum length of discharge piping and the maximum number of 90° elbows permitted.

Drain holes that are closed. The drain holes on spring-loaded safety valves and their discharge piping must be open when required to drain liquid from the top of the valve.

We see more problems caused by improper safety valve installation than by safety valve operation. That said, the most common operating problems we encounter are those caused by operating the valve too close to its set pressure.

For most safety valves, it is recommended that you maintain a 10% differential between the system operating pressure and the nameplate set pressure. However, seat tightness, and thus valve performance, will be better at a differential of 20%.

If you are experiencing problems with your safety valves, Allied Valve can help you identify and fix the problem so you can get back up and running as quickly and efficiently as possible.

This article describes the requirements for a discharge tube or drain line on temperature & pressure relief valves used on any appliance that heats water. These include hydronic heating boilers (hot water boilers), steam boilers, and all types of water heaters, both those that use a water storage tank or cylinder and those that heat water on demand such as tankless water heaters.

Here we describe the installation specifications for TPR valve drain line piping and we include an extensive list of discharge tube installation or condition defects, most of which are unsafe. All of them are improper.

The Temperature & Pressure Relief Valve or TPR Valve on any heated appliance that contains water, such as a heating boiler, hot water tank, water heater, water cylinder, must have a drain line or discharge tube properly installed, routed, and made of proper materials. The purpose of this drain line is to discharge potentially hot scalding water to a safe location so that a bystander is not scalded.

At left we see a typical TPR valve installation (by the author) including the vertical 3/4" copper drain piping that will discharge any T&P valve spillage to the floor.

An unsafe TPR drain line installation is shown at the top of this page. Only a complete fool would do what we found on this boiler. To "stop" an annoying boiler drip at the pressure temperature relief valve, the mechanic installed a short length of pipe capped by a drain valve which he could simply shut. This might have been installed on a system for other reasons, such as connecting a hose to permit easy draining of pressure off of the boiler through the TP valve.

But it is in all events dangerous, illegal, and plain stupid to ever install a shutoff valve or any other sort of "cap" on a pressure/temperature relief valve.

But how dangerous is it to omit a discharge drain tube on a TPR valve? The possibility of a scalding burn is obvious but do these accidents actually happen?

Noticing that a TPR discharge tube was missing on a heating boiler during a home inspection I [DF] pointed out this safety hazard to my client while the real estate agent nearby frowned at my "old maid" trouble-making personality.

My client burst into tears. Sobbing she told me that she was grateful that inspectors would routinely point-out this hazard. Her son, playing with friends in the basement, lost an eye when he and a pal opened the discharge lever on a heating boiler, scalding his face and ruining his left eye forever.

Less dramatic but scary, at a different inspection I found that a string tied through a small hole in the end of the TPR valve"s test lever. The string was routed up towards the ceiling, over a horizontal plumbing line and back down to a termination in a nice knot a few feet above the floor.

This interesting TPR test lever addition was explained by the building owner. His son and friends liked to play steam boat. It was fun to pull the string, pretending it was a steam boat whistle, and to see the burst of steamy hot water emerge from the end of the discharge line.

TPR Valve Discharge tube is installed: Check that the Temperature/Pressure relief valve has a discharge tube properly installed. The drain line must be connected to the discharge outlet of the T&P valve to "avoid water damage and scalding injury." (Watts 2011)

Our photo (left) shows an oil fired water heater with a T&P valve that has no discharge tube installed. There are of course other operating problems with this water heater as the photo makes clear.

TPR Valve Discharge tube blocked: Check that the discharge is not blocked by anything whatsoever. Our page top photo shows a shutoff drain valve installed at the end of a short T&P valve discharge line.

The risk is that the valve is no longer leaking not because a proper repair has been made, but because the valve has become clogged and blocked by mineral salts left behind by the evaporating hot water - leaving the installation dangerous and risking a BLEVE - explosion.

This is an unsafe condition as the operation of the temperature or pressure relief valve may be interfered with by the insulation and also because the valve cannot be inspected for evidence of leaks or failure.

Similarly, discharging a relief valve leakage or drip to a location where the leak or drip cannot be observed is a dangerous practice because the leak can go unnoticed, causing failure to recognize an unsafe condition.

TPR Valve Discharge Tube Piped "UP": the drain line must never be piped upwards in any of its course. The hazard is that the drain can become blocked or that a small drip, representing an unsafe condition at the T&P valve, may be hidden as the water simply accumulates in the bend of the trap or upwards piped section.

TPR Valve Discharge Tube Crimped, Plugged, or Reduced: the drain line may not be bent, crimped, nor plugged by any material. The diameter of the drain line may not be reduced to a size smaller than the opening of the T&P valve that it serves. Some jurisdictions may limit the number of elbows or bends permitted in the piping.

The photos above illustrates this unsafe installation practice: a 1/2" copper tube has been installed through a reducing fitting into the mouth or piping of a 3/4" diameter TPR valve.

Below the reducer from 3/4" to 1/2" was installed at the TPR valve opening. At above right a reducing elbow was used to shrink the 3/4" horizontal T&P drain line (from the TPR valve mouth) to 1/2" for the vertical run to the floor. Both of these installations are improper and unsafe.

TPR Valve Discharge Tube Active Leaking: above we show a wet floor area as well as the corroded end of the T&P discharge tube in our first photo: this relief valve is actively leaking. In this case investigation showed that the valve itself had failed - we replaced it.

TPR Valve Drain line Drip Marks: any drip stains on the floor below the valve discharge tube (second photo above ) also indicate a history of leaks at the T&P valve. Without further investigation we don"t know if this problem has been repaired or if it is simply intermittent.

TPR Valve Discharge Tube Opening is Wet: If there is corrosion on the end of the discharge tube or if you see drip stains on the floor below the drain pipe, even if the floor is dry you should always test for active or recent spillage at the relief valve. It"s possible that water on the floor has dried (on its own or with some help before a building inspection).

But if there has been recent spillage at the TPR valve the interior of the end of the discharge tube can confirm that. Using your finger, feel the inside of the tip of the discharge tube and check for water - it should be dry.

As the two photos show below, even though the floor was dry below this T&P drain line, the interior of the drain was wet - there was active leaking (or someone had recently opened the valve).

TPR Valve Discharge Tube Materials: the drain line material requirements vary by jurisdiction; some areas permit both plastic as well as copper or galvanized steel piping. But where plastic drain line materials are used, the temperature rating of the plastic must be above the highest temperature that might be produced by the heating appliance to which the T&P valve is connected.

TPR Valve Discharge Tube Termination Fittings: the end of the discharge or drain line tube should not be threaded nor fitted with any device that would permit attachment of a cap, plug, or valve that could close off the line.

TPR Valve Discharge Tube Termination Location: The water that may be discharged from a T&P valve must be conducted to a safe place of disposal. This may be a floor drain (recommended by Watts) or in some jurisdictions another location may be permitted.

Some jurisdictions do not permit the discharge drain destination to be hidden from view, on the theory that you won"t see a drip or leak and won"t thus detect an unsafe condition.

Other jurisdictions, such as in the U.K., permit the TPR valve drain line to be piped to a hidden location but require the installation of a tundish in the drain line at a suitable visible location.

The Tundish will allow the occupants to see that the TPR valve is leaking, and its air gap provides other plumbing sanitation and blockage protection features.

Outdoor terminations of a T&P valve drain line may be permitted in some jurisdictions, even required, to avoid water damage inside the building. However unless a tundish device is properly included such installations are unsafe. And piping a T&P drain line outside in freezing climates is unsafe because a dripping line may freeze and become blocked.

TPR Valve Mounting Leaks: Check for leaks around the valve where it is mounted on the boiler or boiler piping. This is a TPR valve defect, not a TPR discharge tube defect, but depending on the valve position and location, a leak around the TRP valve mount may send water (or corrosion or mineral salts) down the outside of the discharge tube, offering a valuable visual clue and possibly being mistaken for a defect in the tube itself

I am ... in the process of selling a condo I own. I got this request for repairs for the hot water heater with a picture of the heater. On the picture it shows the that the discharge line is above the TPR valve, and that this is a problem (see description on attachment). This doesn"t make any sense to me. Can you help me decide what the best action would be? thanks. - R.N. 7/11/2013

The photo is a bit difficult to read but if you look closely where the two flexible copper lines enter the wall behind the water heater, you"ll see that the smaller leftmost flexible tube, connected back to the water heater TP valve, enters the wall at a height above the valve outlet opening. What the home inspector said was perfectly correct and represents a safety hazard.

The temperature/pressure relief valve on a water heater is connected to a drain line so that if the valve  opens someone nearby is not shot in the face with hot water. The discharge drain extension is typically taken to just a few inches above the floor or in some jurisdictions it may be directed outdoors - a solution that I think is risky because IF the valve should be leaking, dripping, etc., one wants to notice that and fix it to keep the system safe.

The inspector"s report makes a valid point: we should never route the discharge tube "up" from the actual outlet opening of the TP valve. That"s because if the valve should develop a small leak or be discharged on occasion, the up-routed discharge tube will keep water and debris remaining in the tube at the valve outlet where debris or mineral accumulation clog the valve or interfere with its operating spring.

The result over time could be that the valve becomes clogged and would then fail to open in a true emergency - risking, ultimately a dangerous BLEVE or water heater explosion.

Watch out: ALSO, I suspect from the photo that your water heater has a discharge tube that directs the valve outlet into a wall and going to who knows where. If the other end of that line is not already readily visible and in a location where it would be noticed, that too would be unsafe and improper.

The FIX for this unsafe condition is usually trivial: the discharge tube must be routed only "downwards" from the TP valve outlet opening, and the end of the discharge tube must be in a readily accessible, visible, and safe location. You"d probably find these same instructions in the installation manual for the water heater.

The COST for this repair should be no more than a simple plumbing service call and perhaps a few piping connections. What would make sense to me and what would be most economical would be to combine this repair with any other plumbing repairs that are needed at the home.

10. Terminate not more than 6 inches (152 mm) and not less than two times the discharge pipe diameter above the floor or waste receptor flood level rim.

14. Be one nominal size larger than the size of the relief-valve outlet, where the relief-valve discharge piping is constructed of PEX or PE-RT tubing. The outlet end of such tubing shall be fastened in place.

10. Terminate not more than 6 inches (152 mm) above and not less than two times the discharge pipe diameter above the floor or flood level rim of the waste receptor.

Some model and adopted building and plumbing codes expressly prohibit discharging the TPR valve out of the room containing the heating appliance that it is intended to protect.

1. All pressurized storage-type water heaters and unfired hot water storage tanks shall be equipped with one or more combination temperature and pressure relief valves. The temperature steam rating of a combination temperature and pressure relief valve or valves shall equal or exceed the energy input rating in BTU per hour of the water heater. No shut off valve or other restricting device may be installed between the water heater or storage tank and the combination temperature and pressure relief valve.

2. All pressurized non-storage type water heaters shall be provided with a pressure relief valve installed at the hot water outlet with no shut off valve between the heater and the relief valve.

3. Temperature and pressure relief valves shall be installed so that the sensing element of the valve extends into the heater tank and monitors the temperature in the top 6 inches of the heater or tank.

5 (e) The discharge pipe shall be installed to drain by gravity flow to a floor served by a floor drain or to a receptor in accordance with s. Comm 82.33 (8).

The outlet of the discharge pipe shall terminate within 6 inches over the floor or receptor, but not less than a distance equal to twice the diameter of the outlet pipe. The discharge pipe may not be threaded.

5 (f) The discharge pipe for a water heater shall terminate within the same room or enclosure within which the water heater or hot water storage tank is located.

WISCONSIN PLUMBING CODE, Chapter SPS 382, DESIGN, CONSTRUCTION, INSTALLATION, SUPERVISION, MAINTENANCE AND INSPECTION OF PLUMBING [PDF] (2016) retrieved 2019/11/13 original source: https://docs.legis.wisconsin.gov/code/admin_code/sps/safety_and_buildings_and_environment/380_387/382.pdf

Illustrated here in a photo and sketch you can see that the relief valve drain line can, where local codes approve, be routed "up" to carry discharge across a ceiling and then down to an approved drain discharge location provided that a special draining device, shown as a spiral-wound small-diameter copper tube is attached to drain the residue water in the vertical section of the drain line after a discharge.

Later explanation from Mr. Nesbitt clarified that the copper pigtail is a small diameter "drain" intended to remove water from the vertical portion of the relief valve up-piped drain line after the valve has discharged water during an over-pressure or over-temperature or test condition.

It"s not a control nor thermocouple, it"s simply a small diameter drain. The small diameter and flow resistance of the coiled tubing causes any significant volume of TPR valve discharge to be routed up through the vertical TPR valve drain line from the tee, and the combination of tee and short copper nipple connected to the wound copper tubing are probably intended to prevent standing water or debris accumulation at the mouth of the TPR valve itself.

The pigtail drain may appear to work perfectly to drain the residing water in the vertical section of the discharge line for the relief valve at initial installation and testing, experience suggests to us that debris, especially mineral scale, is epidemic at water heater relief valves, especially if the leak at the valve is a slow drip.

Some details including the design, the pigtail connection (presumably to a shutoff control) and research supporting this up-draining valve would be helpful.

It would be useful to know what research was done to support accepting this up-draining TPR design, presumably using a temperature sensor that shuts down the boiler if hot water is found at the bottom of that tee at the TPR valve outlet.

In our OPINION that is an unsafe and questionable relief valve design in that any TPR that drains "up" is at risk of ultimately depositing mineral salts that can lead to the valve refusing to open in response to an over-temperature or over-pressure condition in the boiler, risking a catastrophic BLEVE explosion.

worse, draining the valve "up" as shown, means that a slow drip or leak won"t be discovered by visual inspection until it has leaked so long as to fill that up-sloping TPR drain that, we hope, ultimately empties at a visible location.

In our OPINION the design you show violates CA §608.5 Discharge Piping 608.5 Discharge Piping - The discharge piping serving a temperature relief valve, pre