boiler safety valve regulations supplier

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 documents are meant to be used as a guide for developing local laws and regulations and also may be used to update a jurisdiction’s existing requirements. As such, they’re intended to be modifiable to meet any jurisdiction’s local conditions.

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.

Cast-iron boilers may be used in steam heating or hot water heating applications within the scope and service restrictions of ASME BPV Code Section IV. ASME BPV Code Section IV service restrictions limit steam boilers to pressures not exceeding 15 psi and hot water boilers to pressures not exceeding 160 psi and/or temperatures not exceeding 250°F.

One Piece – a single casting with no assembly joints. Another term used to describe this design is monobloc. This type of cast-iron boiler is usually small in size.

Sectional boilers are typically assembled with tapered connections called push nipples or elastomeric-type gaskets between the sections to seal the water-containing chambers. Another type of assembly uses external headers to connect the water containing chambers.

Cast-iron boilers can be found in almost any application where heating boilers are used. They are popular replacements for large welded steel boilers which may have been installed as the building was being constructed. Cast-iron sectional boilers can usually be installed in existing boiler rooms by moving the individual sections through doors or window openings. A very large boiler can be assembled in this manner without modifications to the building structure.

There will be two pieces of information missing from a cast-iron boiler nameplate: a National Board registration number and the year built. Cast-iron boilers are not registered with the National Board, and ASME BPV Code Section IV makes no provisions for a year of construction to appear on the nameplate. Since most inspection forms ask for a year of construction, the inspector will have to estimate. If the boiler is original to the building, the age of the building would directly correspond to the age of the boiler. If the boiler is a replacement, the inspector will have to question the owner to determine its age.

Cast-iron boilers may be used in steam heating or hot water heating applications within the scope and service restrictions of ASME BPV CodeSection IV. ASME BPV CodeSection IV service restrictions limit steam boilers to pressures not exceeding 15 psi and hot water boilers to pressures not exceeding 160 psi and/or temperatures not exceeding 250°F.

Steam boilers must have at least one safety valve with a set pressure not to exceed 15 psi. The safety valve inlet must not be smaller than NPS 1/2 nor larger than NPS 4-1/2.

Hot-water boilers must have at least one safety relief valve with a set pressure at or below the maximum allowable working pressure (MAWP) marked on the boiler. The safety relief valve inlet must not be smaller than NPS 3/4 nor larger than NPS 4-1/2. The minimum relieving capacity of safety or safety relief valves must equal or exceed the maximum output of the boiler. Cast-iron boilers constructed since 1943 will have information on the nameplate indicating the minimum required safety or safety relief valve capacity. Cast-iron boilers constructed prior to 1943 may not have that information. In those circumstances, the inspector must estimate the maximum output of the boiler. Gas or oil burners generally have a rating plate or label containing the Btu output of the burner. A generally applied guideline for older boilers is to use 80% of the maximum burner output as the maximum boiler output. Boilers fired with solid fuel such as coal or wood will be extremely difficult to estimate, since there is no way for the inspector to calculate the cast-iron boiler heating surface. In those cases, the inspector should request the boiler owner/user perform an accumulation test in accordance with HG-512(a), or a maximum burned fuel evaluation in accordance with HG-512(b) and Appendix B. These procedures should only be used if the safety or safety relief valve capacity is in doubt.

two pressure controls (if the boiler is automatically fired); one is considered the operating control and the other is considered the high-limit control (Note: some jurisdictions require the high-limit control be equipped with a manual reset switch) (HG-605);

an automatic low-water fuel cutoff – if the boiler is automatically fired (Note: some jurisdictions require an additional low-water fuel cutoff with a manual reset switch) (HG-606).

two temperature controls (if the boiler is automatically fired); one is considered the operating control and the other is considered the high-limit control (Note: some jurisdictions require the high limit control be equipped with a manual reset switch) (HG-613);

an automatic low-water fuel cutoff – if the boiler is automatically fired and has a heat input greater than 400,000 Btu/hr (Note: some jurisdictions require an additional low water fuel cutoff with a manual reset switch)(HG-614)

Clearances on the front, rear, sides, and top of all cast-iron boilers for operation, maintenance, and inspection shall meet jurisdictional requirements. If no jurisdictional requirements exist, then the boiler manufacturer"s requirements shall be met.

All cast-iron boilers should be installed on foundations or supports suitable for the weight of the boiler and its contents. The foundation or support must also be unaffected by the heat of the operating boiler.

Although most jurisdictions do not require inspection of the piping associated with an ASME BPV CodeSection IV boiler, there are some installation requirements in ASME BPV Code Section IV the inspector should review. Please see HG-703 and HG-705.

Steam boilers must have at least one safety valve with a set pressure not to exceed 15 psi. The safety valve inlet must not be smaller than NPS 1/2 nor larger than NPS 4-1/2.

Cast-iron boilers typically have a few inherent problems. The inspector should always look for water leaks at the connecting joints of sectional boilers. The inspector should request the removal of the sheet metal casing any time there is evidence of leakage and the leakage cannot be traced to an external source.

The most common problem associated with cast-iron boilers is cracking due to overheating or thermal shock. Overheating occurs when the boiler is allowed to operate with low-water conditions or poor circulation caused by sludge concentrated in the lower water passages of the boiler. Thermal shock can occur when a boiler is overheated and cold water is added in an attempt to raise the water level. Under those circumstances, cracking is usually the least that can happen. The worst that can happen is an explosion which shatters the cast-iron boiler into many pieces and cause destruction and injury.

Sectional cast-iron boilers use long rods, threaded on both ends, called draw bolts. It is not unusual for these draw bolts to appear loose when the boiler is cold. When the boiler is operating, the heat will cause the boiler to expand which tightens the draw bolts. A loose draw bolt on a hot boiler should be investigated by a competent cast-iron boiler service/repair company.

Cast-iron boilers typically have a few inherent problems. The inspector should always look for water leaks at the connecting joints of sectional boilers. The inspector should request the removal of the sheet metal casing any time there is evidence of leakage and the leakage cannot be traced to an external source.

Upon entering the boiler room, the inspector should perform a general assessment of the boiler, piping, controls, fuel system, and combustion air supply. The inspector should then:

compare the safety or safety relief valve nameplate data (set pressure and relieving capacity) with the boiler nameplate to ensure the safety or safety relief valve is adequate for this installation;

check the thermometer reading on hot water boilers (if there is a reason to question the accuracy of the thermometer, it should be replaced or recalibrated);

check the water gage glass to ensure it provides a clear indication of the water level in a steam boiler. (Please see the National Board Inspector Guide for Water Level Controls and Devices);

look for evidence of overheating (this may be difficult to detect on a cast-iron boiler; warped external sheet metal casings with scorched paint is usually a reliable indicator);

inspect the fuel-burning apparatus as required by the jurisdiction (for example, some jurisdictions mandate compliance with ASME Standard CSD-1, Controls & Safety Devices for Automatically Fired Boilers).

Internal inspections of cast-iron boilers can prove to be difficult or almost impossible. Threaded plugs on the cast iron boiler could be removed, but the inspector will see very little past the immediate vicinity of the opening on many cast iron boiler designs. In addition, the threaded plugs are sometimes heavily corroded which virtually "welds" them to the cast iron. Removal of threaded plugs in this condition may damage the cast iron irreparably. Some boilers may have valves installed in the lowest threaded openings of the boiler to facilitate draining and/or flushing of the boiler. If valves are present, the inspector can ask for them to be opened briefly to observe the condition of the water. If no water is present when the valves are opened, this could be an indication the lowest portion of the boiler is filled with sludge. The inspector is advised to follow the jurisdiction"s requirements for internal inspections of cast-iron boilers.

Threaded plugs in the piping connecting a water gage glass, water column, and low-water fuel cutoff to a steam boiler must be removed to allow inspection of the piping to ensure there is no blockage.

As a design engineer responsible for developing and specifying boilers, dryers, furnaces, heaters, ovens and other industrial heating equipment, you face a daunting labyrinth of standards and industry regulations. Regulatory bodies sound a bit like alphabet soup, with acronyms like UL, FM, CSA, UR, AGA, ASME, ANSI, IRI, CE and NFPA tossed about. This article will help explain a common task for many thermal processing equipment specifiers: meeting the requirements of key codes — including Underwriters Laboratories (UL), Factory Mutual Insurers (FM) and the National Fire Protection Association (NFPA) — for safety valve equipment used in process heating applications.

Key to designing safety into your fuel train configurations are familiar technologies such as safety shutoff valves and vent valves as well as visual-indication mechanisms and proof-of-closure switches.

Your design skills come into play with how you take advantage of the wide range of products available. You can mix and match solenoid and safety shutoff valves — within designs from catalytic reactors to multi-zone furnaces — to create easily installed, cost-effective solutions that comply with all necessary standards. (See table.)

Make sure, however, that you start with a good grasp of valve element fundamentals. For example, examining a proof-of-closure (POC) switch underlines how reliably modern valves can ensure combustion safety. The POC unit provides an electrical contact interlocked with the controller safety circuit. In a typical design, the switch is located at the bottom of the valve, positioned to trace the stroke of the valve disc. When the disc seal reaches the fully closed position, it triggers the mechanism to push down on the contact, closing it and triggering the unit’s visual indicator to show open or closed status. As a result, the operator can act with full confidence in situations where it is critical that a safety valve be safely closed.

To provide ease of installation, many users prefer valves with modular capabilities. For example, to reduce mounting complexity, you can choose modular gas safety shut-off valves — combining a solenoid valve with an electrohydraulic motorized valve for a compact double-valve footprint, a slow-open feature and high flow rates. An accompanying actuator can provide on/off or high/low/off firing rates as well as visual indication and proof of closure for compliance with most industry standards.

Also, you may want to look for valves that include useful features such as pipe taps, which can facilitate accurate pressure readings and leakage testing.

Knowing your valve choices — and how they meet given codes and standards — can reduce the time required for design and production while facilitating compliance. This results in safer, more efficient and cost-effective heating process installations.

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.

The S100 Safety Shut Off valve is mainly used to avoid any damage to components as well as to avoid too high or too low pressure in the gas train. This could cause high financial losses and/or injured ...

130 Series Safety valves are also available as Relief valves. Relief valves, identified by the letter R after the type number, are devices with an operational function, ...

Parker"s cartridge safety relief valves (CSRV) are designed to offer the highest level of protection while maintaining easy serviceability. The CSRV was designed from the existing Parker ...

H. When two or more boilers, operating at different pressures and safety valve settings, are interconnected, the lower pressure boilers or interconnected piping shall have safety valves of sufficient capacity to prevent over-pressure, considering the maximum generating capacity of all boilers.

I. A boiler supplied with feedwater directly from a water main without the use of feeding apparatus other than a return trap, may not have a safety valve set at a pressure greater than 94 percent of the lowest pressure obtained in the supply main feeding the boiler.

(a) An accumulation test (unless the valve is located on a boiler having a superheater or reheater), performed by shutting off all other steam-discharge outlets from the boiler and forcing fires to the maximum. The safety valve relief capacity shall be sufficient to prevent increased pressure in excess of 6 percent of the maximum allowable working pressure.

(2) When either method in §J(1)(b) or (c) is used, the sum of the safety valve capacities shall equal or exceed the maximum evaporative capacity of the boiler.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

A. Standard boilers. The maximum allowable working pressure of standard boilers shall in no case exceed the pressure indicated by the manufacturer"s identification stamped or cast on the boiler or on a plate secured to it.

B. Nonstandard riveted boilers. The maximum allowable working pressure on the shell of a nonstandard riveted heating boiler shall be determined in accordance with 16VAC25-50-360 C covering existing installations, power boilers, except that in no case shall the maximum allowable working pressure of a steam heating boiler exceed 15 psig, or a hot water boiler exceed 160 psig or 250°F temperature.

C. Nonstandard welded boilers. The maximum allowable working pressure of a nonstandard steel or wrought iron heating boiler of welded construction shall not exceed 15 psig for steam. For other than steam service, the maximum allowable working pressure shall be calculated in accordance with the ASME Code, Section IV.

1. The maximum allowable working pressure of a nonstandard boiler composed principally of cast iron shall not exceed 15 psig for steam service or 30 psig for hot water service.

2. The maximum allowable working pressure of a nonstandard boiler having cast iron shell or heads and steel or wrought iron tubes shall not exceed 15 psig for steam service or 30 psig for hot water service.

1. Each steam boiler must have one or more officially rated (ASME Code stamped and National Board rated) safety valves of the spring pop type adjusted to discharge at a pressure not to exceed 15 psig. Seals shall be attached in a manner to prevent the valve from being taken apart without breaking the seal. The safety valves shall be arranged so that they cannot be reset to relieve at a higher pressure than the maximum allowable working pressure of the boiler. A body drain connection below seat level shall be provided by the manufacturer, and this drain shall not be plugged during or after field installation. For valves exceeding two inch pipe size, the drain hole or holes shall be tapped not less than 3/8 inch pipe size. For valves less than two inches, the drain hole shall not be less than 1/4 inch in diameter.

2. No safety valve for a steam boiler shall be smaller than 3/4 inch unless the boiler and radiating surfaces consist of a self-contained unit. No safety valve shall be larger than 4-1/2 inches. The inlet opening shall have an inside diameter equal to, or greater than, the seat diameter.

4. The minimum valve capacity in pounds per hour shall be the greater of that determined by dividing the maximum BTU output at the boiler nozzle obtained by the firing of any fuel for which the unit is installed by 1,000 or shall be determined on the basis of the pounds of steam generated per hour per square foot of boiler heating surface as given in Table 2. When operating conditions require it a greater relieving capacity shall be provided. In every case, the requirements of subdivision 5 of this subsection shall be met. TABLE 2

NOTES: When a boiler is fired only by a gas giving a heat value of not in excess of 200 BTU per cubic foot, the minimum safety valve or safety relief valve relieving capacity may be based on the value given for handfired boilers in Table 2.

5. The safety valve capacity for each steam boiler shall be such that with the fuel burning equipment operating at maximum capacity, the pressure cannot rise more than five psig above the maximum allowable working pressure.

6. When operating conditions are changed, or additional boiler surface is installed, the valve capacity shall be increased, if necessary, to meet the new conditions and be in accordance with subdivisions 4 and 5 of this subsection. When additional valves are required, they may be installed on the outlet piping provided there is no intervening valve.

7. If there is any doubt as to the capacity of the safety valve, an accumulation test shall be run (see the current edition of the ASME Code, Section VI).

8. No valve of any description shall be placed between the safety valve and the boiler, nor on the discharge pipe between the safety valve and the atmosphere. The discharge pipe shall be at least full size and be fitted with an open drain to prevent water lodging in the upper part of the safety valve or in the discharge pipe. When an elbow is placed on the safety valve discharge pipe, it shall be located close to the safety valve outlet, or the discharge pipe shall be securely anchored and supported. All safety valve discharges shall be so located or piped as not to endanger persons working in the area.

1. Each hot water boiler shall have one or more officially rated (ASME Code stamped and National Board rated) safety relief valves set to relieve at or below the maximum allowable working pressure of the boiler. Safety relief valves officially rated as to capacity shall have pop action when tested by steam. When more than one safety relief valve is used on hot water boilers, the additional valve or valves shall be officially rated and shall be set within a range not to exceed six psig above the maximum allowable working pressure of the boiler up to and including 60 psig and 5.0% for those having a maximum allowable working pressure exceeding 60 psig. Safety relief valves shall be spring loaded. Safety relief valves shall be so arranged that they cannot be reset at a higher pressure than the maximum permitted by this paragraph.

3. No safety relief valve shall be smaller than 3/4 inch nor larger than 4-1/2 inches standard pipe size, except that boilers having a heat input not greater than 15,000 BTU per hour may be equipped with a safety relief valve of 1/2 inch standard pipe size. The inlet opening shall have an inside diameter approximately equal to, or greater than, the seat diameter. In no case shall the minimum opening through any part of the valve be less than 1/2 inch diameter or its equivalent area.

4. The required steam relieving capacity, in pounds per hour, of the pressure relieving device or devices on a boiler shall be the greater of that determined by dividing the maximum output in BTU at the boiler outlet obtained by the firing of any fuel for which the unit is installed by 1,000, or on the basis of pounds of steam generated per hour per square foot of boiler heating surface as given in Table 2. When necessary a greater relieving capacity of valves shall be provided. In every case, the requirements of subdivision F 6 of this section shall be met.

5. When operating conditions are changed, or additional boiler heating surface is installed, the valve capacity shall be increased, if necessary, to meet the new conditions and shall be in accordance with subdivision F 6 of this section. The additional valves required, on account of changed conditions, may be installed on the outlet piping provided there is no intervening valve.

6. Safety relief valve capacity for each boiler shall be so that, with the fuel burning equipment installed and operated at maximum capacity the pressure cannot rise more than six psig above the maximum allowable working pressure for pressure up to and including 60 psig and 5.0% of maximum allowable working pressures over 60 psig.

7. If there is any doubt as to the capacity of the safety relief valve, an accumulation test shall be run (see the current edition of the ASME Code, Section VI).

8. No valve of any description shall be placed between the safety relief valve and the boiler, nor on the discharge pipe between the safety relief valve and the atmosphere. The discharge pipe shall be at least full size and fitted with an open drain to prevent water lodging in the upper part of the safety relief valve or in the discharge pipe. When an elbow is placed on the safety relief valve discharge pipe, it shall be located close to the safety relief valve outlet or the discharge pipe shall be securely anchored and supported. All safety relief valve discharges shall be so located or piped as not to endanger persons working in the area.

G. Valve replacement and repair. Safety valves and safety relief valves requiring repair shall be replaced with a new valve or repaired by the original manufacturer, its authorized representative, or the holder of a "VR" Stamp.

H. Pressure relieving devices. Boilers and fired storage water heaters except those exempted by the Act shall be equipped with pressure relieving devices in accordance with the requirements of the current edition of the of the ASME Code, Section IV.

I. Instruments, fittings and control requirements. Instruments, fittings and controls for each boiler installation shall comply with the requirements of the current edition of the ASME Code, Section IV.

1. Each automatically fired hot water heating boiler with heat input greater than 400,000 BTUs per hour shall have an automatic low water fuel cutoff that has been designed for hot water service, located so as to stop the fuel supply automatically when the surface of the water falls to the level established in subdivision 2 of this subsection (also see ASME Code, Section IV).

2. As there is no normal waterline to be maintained in a hot water heating boiler, any location of the low water fuel cutoff above the lowest safe permissible water level established by the boiler manufacturer is satisfactory.

3. A coil type boiler or a water tube boiler with heat input greater than 400,000 BTUs per hour requiring forced circulation, to prevent overheating of the coils or tubes, shall have a flow sensing device installed in the outlet piping, instead of the low water fuel cutoff required in subdivision 1 of this subsection to stop the fuel supply automatically when the circulating flow is interrupted.

1. Each steam boiler shall have a steam gauge connected to its steam space, its water column, or its steam connection, by means of a siphon or equivalent device exterior to the boiler. The siphon shall be of sufficient capacity to keep the gauge tube filled with water and arranged so that the gauge cannot be shut off from the boiler except by a cock.

2. The range of the scale on the dial of a steam boiler pressure gauge shall be not less than 30 psig nor more than 60 psig. The gauge shall be provided with effective stops for the indicating pointer at the zero point and at the maximum pressure point. The travel of the pointer from zero to full scale 30 psig shall be at least three inches.

1. Each hot water boiler shall have a pressure or altitude gauge connected to it or to its flow connection in a manner so that it cannot be shut off from the boiler except by a cock with tee or lever handle placed on the pipe near the gauge. The handle of the cock shall be parallel to the pipe in which it is located when the cock is open.

M. Thermometers. Each hot water boiler shall have a thermometer located and connected so that it shall be easily readable when observing the water pressure or altitude gauge. The thermometer shall be located so that it will at all times indicate the temperature in degrees Fahrenheit of the water in the boiler at or near the outlet.

1. Each steam boiler shall have one or more water gauge glasses attached to the water column or boiler by means of valved fittings. The lower fitting shall be provided with a drain valve of the straightaway type with opening not less than 1/4 inch diameter to facilitate cleaning. Gauge glass replacement shall be possible while the boiler is under pressure.

1. If a boiler can be closed off from the heating system by closing a steam stop valve, there shall be a check valve in the condensate return line between the boiler and the system.

2. If any part of a heating system can be closed off from the remainder of the system by closing a steam stop valve, there shall be a check valve in the condensate return pipe from that part of the system.

1. Feedwater, make-up water, or water treatment shall be introduced into a boiler through the return piping system or through an independent feedwater connection that does not discharge against parts of the boiler exposed to direct radiant heat from the fire. Feedwater, make-up water, or water treatment shall not be introduced through openings or connections provided for inspection or cleaning, safety valve, safety relief valve, surface blowoff, water column, water gauge glass, pressure gauge or temperature gauge.

2. Feedwater piping shall be provided with a check valve near the boiler and a stop valve or cock between the check valve and the boiler or return pipe system.

Q. Return pump. Each boiler equipped with a condensate return pump, where practicable, shall be provided with a water level control arranged to maintain the water level in the boiler automatically within the range of the gauge glass.

R. Repairs and renewals of boiler fittings and appliances. Whenever repairs are made to fittings or appliances, or it becomes necessary to replace them, the repairs or replacements shall comply with the requirements for new installations.

S. Conditions not covered by this chapter. Any case not specifically covered by this chapter shall be treated as a new boiler or pressure vessel installation pursuant to 16VAC25-50-280 or may be referred to the chief inspector for instructions concerning the requirements.

(a) Each power boiler, nuclear boiler, and high temperature water boiler shall have safety valves or pressure relieving devices constructed, stamped and installed in accordance with the applicable section of the Code, except:

(2) Upon written request by the employer, the Division may permit three-way two-port valves to be installed under two safety valves, each with the required relieving capacity, provided they are so installed that both safety valves cannot be closed off from the boiler at the same time and provided the three-way valve will permit at least full flow to the safety valve in service at all time.

(b) The user shall maintain all pressure relieving devices in good operating condition. Where the valves cannot be tested in service, the user shall maintain and make available to the inspector records showing the test dates and set pressure for such valves.

3. Change without regulatory effect inserting "(a)" immediately preceding the first paragraph and "(b)" immediately preceding the fourth paragraph, filed 1-24-91 pursuant to section 100, Title 1, California Code of Regulations (Register 91, No. 7).