Safety Valves / Relief valves
Safety Valves are a failsafe valve for equipment and media pipelines. They can be used on compressors and steam lines for example to relieve any dangerous or excess pressure build up. They have been around since the early 1800’s and operate in principle by weight on a valve disc pressing down on a seat. In early designs this “deadweight” was literally just that, various weighted components gave a “set” pressure to valve. These weights were eventually replaced by springs which have a given pressure range of which can be adjusted within those parameters.
They are available in threaded or flanged ends from 10nb to 400nb in various designs and up to 15,000psi pressure rating. Some Cryogenic / Hydrogen service Safety valves can go down as far as minus 240 Degrees C (refer Hydrogen industry page). Materials are brass, iron, steel and stainless. Safety valves can also be protected from certain aggressive medias by the use of Bursting Discs which are also available from Valve and Flow Control Specialists. Safety valves can comply with ASME, BS or API standards. In Australia, Safety and Relief valve compliance to AS 1271 has been a minimum requirement for valves fitted to Boiler and other Pressure vessels. ASME is by far a better option as it maintains a higher standard across the board for every certified valve no matter who the manufacturer is. With non compliance to local Codes now a criminal offence in many countries and litigation there after if any industrial issues occur it is very important to know the application and fit the correct valve.
What are the differences between AS 1271 and ASME Section 1 Safety Relief Valves for Boilers and which to use?
This is a bit of a shady area when it comes to any discussion in the market, decision making and purchasing. One would have to ask why? It is almost like an “ostrich policy” prevails. Some may take the most commercially upfront attractive option whilst others will take the total cost of ownership into consideration selecting what we believe to be the best practice engineered decision. To find out more read below the document that will assist you in your research.
We tag AS 1271 compliant valves accordingly with test dates and compliant certificates. This is due to the legal requirement of ongoing annual testing. These valves are not a fit and forget valve as other types of valves tend to be. The same applies for ASME compliant valves. READ MORE ABOUT ASME AND AS options below on this page.
What do I need to know to select a Safety Relief Valve?
There are 10 very basic things you have to know before you can even consider selecting a general service Relief Valve / Safety Relief Valve. If on critical service like Boiler or pressure vessel applications we will supply you with a form that has to be completed with some 28 prefill data questions. In many cases design consultants will supply a specification design sheet for each valve required.
1. What is the service? Liquid or Gas? Gas valves can have a larger outlet while liquid service valves will usually be the same inlet and outlet size.
2. What is the application? Boiler? Pressure Vessel? Pipeline?
3. What is the design pressure of the system the valve is installed in?
4. What is the set pressure the valve has to relieve at?
5. Is there any back pressure? Some systems can vent back into a closed system which causes a back pressure while some vent to atmosphere..
6. What temperature is the system design / operating at applicable to the relief valve?
7. What material is required? Body materials trim materials can be varied to suit specific applications.
8. What design is required? Standard Spring / Bellows / Pilot operated etc.
9. What capacity does the valve have to cope with at the set pressure?
10. What connections does the valve? NPT, BSP, Flanged and if flanged to what “table”?
Once the basics are known allow us to assist you from our diverse range of valves.
Marine Industry / NAVAL Safety valves 1/2″ to 8″ (DN15 to DN200) in ASTM B62 and ASTM B148 Bronze and NI Bronze materials are available.
Valve Data
General Purpose Industrial Valves
Starting at ½” to 1” is the ‘workhorse” of the Broady Safety Relief Valve Range the 2600 series. This conventional direct acting full lift valve is designed for rapid opening and controlled re-seating. Essential in the power generation and petro-chemical sectors. For Vapour, Liquid or Gas, threaded or flanged connections in various body materials. Designed API520.
ASME rated valves for Boilers are ASME 1 and Pressure Vessels ASME V111
The Broady 3500 series Flanged Safety relief Valve is a direct acting conventional full lift valve is designed for rapid opening and controlled re-seating. Essential in the power generation and petro-chemical sectors. For Steam, Liquid or Gas, with flanged connections in various body materials in sizes from 1″ through to 8″. As Broady still operate their own foundry (as a back-up to their global sourcing) in the UK exotic alloy materials can also be offered. Options such as Micro-Switches, Test gags, Bellows and lifting gear are easily fitted. Designed API 520 / 526/ 527 and ASME VIII (but not ASME 1).
Most maintenance staff will be familiar with the Direct Acting Conventional Relief Valves like the 3500 Series however a versatile design that can be adapted to many functions is the Pilot Operated Valve. These can be from 1” up to 10” and pressure class from ANSI150 to ANSI 2500. For Gas / 2 Phase or Liquid with flanged connections in various body materials.
For Boiler applications ASME 1 certified or AS1271 certified are required. Due to limited Australian manufacture and ASME becoming the go to standard ASME has eclipsed the older Australian Standard. ASME is also a far more stringent INDEPENDANT documented standard required by many insurance agencies globally. ASME Sec 1 valves overpressure requirements at 3% are far more befitting than 10% for vessels (boilers) that generate pressure. A 10% overpressure is normal for static pressure vessels (tanks) that just hold pressure. AS 1271 uses the latter.
For small bore screwed bronze body valves up to 2″ the Fig 560 Bronze body and trim valves (up to 250psi) and the Fig 563 bronze body with Stainless steel trim valves (up to 300psi) are available in BSP or NPT M x F from 1/2″ (15nb) through to 21/2″ (65nb). If opting for soft seats you will have to refer the saturated steam pressure temperatures (Technical Section) to ensure the elastomer selected is suitable for the application. If you are using this valve on a chemical service also refer the chemical compatibility chart there as a guide.
For ASME 1 flanged valves these are available in sizes from 3/4″ (DN20) through to 24″ (DN600) in Steel and Stainless up to pressure class ANSI 2500 contact our sales office for further information.
A word of advice do not be tricked into thinking that a safety valve is CERTIFIED to ASME 1 or ASME VIII with unethical marketing by those that reference their valves with “made in accordance to or tested to or complying to”. They have to be ASME certified and carry the UV or V stamping, failing that could leave the unknowing customers to potential litigation if a failure occurs. ASME is strictly regulated globally so report any issues. AS1271 is self governed there is no licensing authority for it in Australia and many clauses therein are guides. Any manufacturer can claim compliance so there is an element of trust from the supplier. With ASME there is no doubts, the factories/testing centers and valves themselves are vetted and documented regularly and individually authorized certified for compliances.
Why use a Pilot Operated Relief Valve like the Broady Type 4000?
A consideration for using this style of valve is the initial lower cost. By using a small pilot valve separate from the main valve also makes maintenance simpler, cheaper and gives reliability of functionality. A small movement on the pilot valve gives a large result from the main valve. These valves can be set to pop or modulate, the variable is the pilot valve. Options you can have are remote sensing, manual blowdown, surge snubbers, test gags or field test connectors. Designed API 520 / 526/ 527 and ASME VIII
Instrumentation (small bore) high pressure relief valves up to 6000psi
Safety Valve Vent Silencers
Safety Valve Vent Silencers also known as noise diffusers are very necessary in most high-pressure gas and steam services. Each is sized to suit an individual application. Safety valve design and trim in many instances will have a large influence in noise output. With EPA surveillance particularly in the city environment it makes these units ideal as their output noise levels range from 15db to 60db.
Pressure, temperature and output capacities have to be taken into consideration minimise any adverse effect to the safety valve operation.
Whilst many SVVS’s will be direct mounted to one safety valve some applications allow consideration to be given to the use of a discharge collector allowing one SVVS to service more than one safety valve.
The multi-stage system via diffuser, absorbent noise plenum and disruptive stage makes highly effective noise reduction. Larger silencers may require additional support. Connections are flanged for rigidity. The flanges can be to AS / PN or ANSI.
As these are made to order non-standard each to suit an individual application, please contact us to find out more.
Pressure Reducing Valves
Pressure Reducing Valves give a constant flow of media when “set” reduce to the set pressure downstream of the valve. They can be spring and or diaphragm and pilot operated for use on liquids and gas. Not to be confused with pressure sustaining valves. Sizes range from 6nb to 350nb in various designs up to 5000psi pressure ratings. Materials are of brass, iron, steel and stainless. In addition to standard PRV’s we distribute the Broady DH61i Hydrant Pressure Reducing valves. Broady Valves UK are well known for these valves globally in the oil and gas firefighting industry.
Valve Data
Note for pressure reducing valves above 150nb inlet size and above PN40 / Class 300 please consult us for product to be indented from overseas. For non Steam applications such as Water, Gas, Oil and Chemicals VCS offer AUSTRALIAN made product in threaded and flanged connections in Bronze, Steel and Stainless up to 725psi inlet pressures.
Pressure Sustaining Valves
Pressure Sustaining or Back Pressure Regulating Valves regulate upstream pressures by relieving the surplus pressure downstream or via a return line (when installed in a tee). Sizes range from 6nb to 350nb in various designs up to 5000psi pressure ratings. Materials are of brass, iron, steel and stainless.
Wherever possible Valve and Flow Control Specialists support Australian manufactured valve products and part of this Safety and PRV range is fully Australian made.
Broady Valves UK are also distributed in Safety Valves, Pressure reducing and pressure sustaining valves. (Broady also manufacture Hydrant Valves and Specialist Naval Defense Valving). When enquiring on any of these valve types you must know the system requirements and set pressures.
Boiler Blowdown Valves
Traditional Boiler Blowdown valves are of the engineered parallel slide valve configuration. Available in Bronze or steel PN25 and PN40 rated flanged and drilled as required, usually Table F or H although threaded ends are available. Life expectance of these valves is in excess of 20 years, they are built for purpose.
For pressure ratings in excess of PN40 we have to change patterns offering a steel valve rated to ANSI class 600. For pressure ratings above that we have to offer made to measure valves on indent ie from overseas.
An option to the traditional blow down valves are specially designed ball valves for below PN 25 pressures. These usually have to be re-kitted on annual boiler service works ie requiring ongoing maintenance unlike the parallel slide types, These can be cheaper to purchase initially.
Remember that all boiler valves usually have to comply with local boiler codes they are not standard valves.
Rupture Discs
Rupture Discs are also known as a pressure safety disc, bursting discs, or burst diaphragm. They are a non-reclosing pressure relief safety device that, in most uses, protects a pressure vessel, equipment or system from over-pressurization or potentially damaging vacuum conditions. They are like a fuse in functionality, a sacrificial part because it has a one-time-use membrane that fails at a predetermined pressure or vacuum condition. There come in various styles and materials (mostly stainless) to suit different applications. With our sector most are used in conjunction with Safety / Relief valves. There is the disc itself and then the holding assembly which is mated to the Safety valve. Once used a new disc is inserted into the holder and re-assembled.