prestige safety valve free sample

Pressure cookers of the domestic type generally have an escape port, usually in the removable cover of the cooker, and the pressure within the cooker is regulated by a relief valve controlling the port. Relief valves are well known and a common type comprises a valve member and a valve seating, one of which acts against the other under pressure of a predetermined weight. When it is desired to vent the cooker, for example, when cooking is finished, the valve has to be opened. This can cause a rapid escape of steam and hence the operator has to take care to avoid being scalded.

According to the invention there is provided a pressure cooker relief valve assembly comprising a valve member and a valve seating one of which acts against the other under the pressure of a predetermined weight to close a valve port, the assembly including a skirt portion surrounding the valve port to form a chamber, the chamber having an opening in the skirt portion so that gas entering the chamber through the valve port can escape from the chamber to the atmosphere in substantially a sinqle predetermined direction and the skirt portion forms part of the mass of the predetermined weight.

The opening in the chamber enables escaping gases (e.g. steam) to be directed away from the user and escaping steam may also entrain air which can help to provide cooler conditions for the user in the vicinity of the valve. The skirt portion forms part of the mass of the predetermined weight and thus the valve member including the chamber can form a compact design which may be easily removed as a unit in order to gain access to the valve seating, e.g. for cleaning purposes.

Preferably the valve member includes a hand grip portion to enable the valve to be manually manipulated (e.g. to open the valve) and the opening in the skirt is arranged to direct escaping gases away from the hand grip portion.

In a preferred embodiment the chamber has an inner wall surrounding the valve port, the inner wall having an opening therethrough such that gas from the valve port can pass into the chamber through the opening in the inner wall and from the chamber to the atmosphere through the opening in the skirt portion.

With many existing types of pressure cookers it is necessary to manually lift the weight off the valve seating when it is desired to open the valve. This operation requires the weight to be firmly grasped and this can be a disadvantage if escaping steam is issuing from the valve. Alternative methods of venting the cooker include lifting the weight by means of, for example, a pivoted lever or a sliding wedge. These mechanical methods for lifting the weight are complicated and hence expensive to produce.

Accordingly the pressure cooker relief valve assembly may include means for relieving the pressure of the weight by axially rotating the weight and a cam surface relative to each other, the rotation causing the weight to be tilted relative to the valve seating. The valve assembly can be opened by simple rotation of the weight relative to the cam surface. Either the weight or the cam surface or both can be rotated. Preferably the cooker is vented by manual rotation of the weight in which case the weight need only be handled momentarily to turn it through a small angle. In an alternative embodiment the rotation may be achieved by, for example, a clockwork timer acting through a linking mechanism. The tilt of the weight caused by the rotation, whether manual or mechanical, can aid in directing the escaping steam in a predetermined direction, e.g. away from the user, especially if the underside of the weight is in close proximity to another surface. The direction of the escaping steam is further controlled by the opening in the surrounding chamber as explained above, through which any gas (e.g. steam) entering the chamber through the valve port can escape.

As shown in the FIGS. 1 to 6 of the drawings, the first embodiment of a pressure relief valve assembly is indicated generally by reference numeral 1 and is mounted on the lid 2 of a pressure cooker. The assembly includes a valve of known type including a valve seating 3, incorporating a valve support 4, held in position by a wing nut 5 within the lid 2. A port 6 extends through the seating 3 and this can be closed by a valve pin 7. A weight 8 is attached to the upper end of the pin 7.

The weight 8 is retained by the valve support 4 by means of a snap ring 9 and locking ring 10 such that the pin 7 can rotate in the seating 3 and be tilted and lifted by the mechanism described hereinafter or the weight 8 with its attachments can be removed from the seating 3 for cleaning purposes.

Mounted on the lid 2 below the weight 8 is a valve seat collar 13, the structure of which is shown specifically in FIG. 5. The upper face of the collar comprises a cam surface consisting of a flat surface 14 and a recess 15.

Attached to the weight 8, and covering its upper surface, is a cover 16. The cover 16 includes a hand grip portion 17 and an opening 18 (shown most clearly in FIG. 4) in a side wall opposite to the hand grip portion. Extending from the cover 16 are side walls 19 forming an outer skirt which together with the cover 16 forms a chamber surrounding the valve.

In the position shown in FIG. 1 the valve is in the closed or sealed position. The prong member 12 of the weight 8 is within the recess 15 of the collar 13 and the pin 7 is firmly seated on the valve seating 6.

When it is desired to open the valve the cover 16 is rotated through a small angle thus rotating the weight 8. The prong member 12 is thus cammed out of the recess 15 on to the top face 14 of the collar 13. This causes the weight 8 to be tilted and raised, lifting the pin 7 off the seat 3. The valve is thus opened. Any steam within the pressure cooker is released into the chamber formed by the cover 16 and side walls 19 and out through the opening 18, in a direction away from the hand grip 17. The dimensions and shape of the chamber and the opening are chosen so as to minimise the noise level of the escaping steam.

The modified valve seat collar 13" shown in FIG. 6 is similar to that shown in FIG. 5 in having a recess portion 15" and a flat surface 14" forming a cam surface for the prong member 12. The collar 13", however, has two horizontal extensions 20 and 21. A downward extension of the weight 8 can fall between extensions 20 and 21, so that the extensions act as stop members only allowing rotation of the weight through a small angle.

The modified pressure relief valve assembly will now be described with reference to FIGS. 7 to 11. The modified assembly is indicated generally by reference numeral 21 and is mounted on the lid 22 of a pressure cooker. The assembly includes a valve of known type including a valve seating 23, incorporating a valve support 24, held in position by a nut 25 within the lid 22. A port 26 extends through the seating 23 and this can be closed by a valve pin 27. A weight indicated generally by reference numeral 28 is attached to the upper end of the pin 27. The weight 28 comprises a plastic moulding 29 and an annular metal weight ring 30. The moulding 29 has an inner depending skirt portion 31 and an outer depending skirt portion 32. The inner skirt portion 31 has a slot 33 in one face. The outer skirt portion 32 has slits 34 in a corresponding face.

The valve assembly 21 is detachably mounted on the valve support 24 by means of a snap ring 36, held in position by means of a washer 37, such that the pin 27 can rotate in the seating 23 and be tilted and lifted by the mechanism described hereinafter or the assembly 21 cah be removed from the seating 23 for cleaning purposes.

A metal plate 40 extends substantially perpendicular to the outer skirt portion 32 and forms a bottom wall of the chamber. The metal plate 40 is provided with two cam lobes 41 which co-operate with the cam surface of the valve seat collar 42, described hereinbelow.

The valve seat collar 42 is mounted on the lid 22 below the weight 28. An O-ring 43 is retained between the collar 42 and the lid 22. The collar 42 has two recesses 44, 45 to receive the lobes 41. The recess 44 has a cammingsurface comprising a ramp 46. A stop 47 is provided by the vertical end wall of the recess 44. The collar 42 has an upstanding skirt portion 48, which in use, is situated within the inner skirt 31 of the weight 28. A cut-away portion 49 is provided in one face of the skirt portion 48.

In the position shown in FIGS. 7 and 9 the valve is in the closed or sealed position. The lobes 41 are situated within the recesses 44 and 45 of the collar 42 and the pin 27 is firmly seated on the valve seating 23.

When it is desired to open the valve the assembly 21 is rotated through a small angle by means of the handle 39. The lobe 41 within the recess 44 is cammed up the ramp 46 until further rotation is prevented by stop 47. The camming action causes the weight to be tilted and raised, as shown in FIGS. 8 and 10, lifting the pin 27 off the seat 23. The valve is thus opened. Any steam within the pressure cooker is released through the port 26, through holes in the valve support 24, out through the cut-away portion 49 in the skirt 48, through the slot 33 in the inner skirt portion 31 into the chamber between the inner and outer skirt portions 31, 32. The steam escapes from the chamber, in a direction away from the handle 39, via the slits 34 in the outer skirt portion 32, the slits being designed to deflect the steam in a partial upwards direction so as to control its forward projection. The dimensions and shape of the chamber and the various openings are chosen so as to minimise the noise level of the escaping steam.

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Comes with a first time 2-in-1 safety device called PI (Pressure Indicator). The device will rise while there is pressure inside the cooker and will come down when there is no pressure thus indicating that it is now safe to open the vessel. It also fuses at high pressure thereby serving the dual purpose of a Metallic Safety Plug.

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Even in the old days, most pressure cooker disasters could usually be attributed to user error, much like my mother and the beans. Nonetheless, today"s pressure cookers offer a much higher safety level than their predecessors. For one thing, you can"t open them until the pressure is released to 0 PSI.

Today"s pressure cookers have at least three valves for safety and will automatically release pressure should it build too high. Different types of pressure cookers have different styles of valves (refer to the instructions that came with yours), but if you hear hissing or noise coming from the cooker, it"s the valve telling you to check the pressure.

Prestige Pressure Cooker Nutritional Boost - Due to the shorter cooking time and the fact that food is cooked in less liquid that gets boiled away, more vitamins and minerals are retained than with conventional cooking methods.

Prestige Pressure Cooker Saves Time - Food cooks up to 70% faster in a pressure cooker, making it a wonderful tool for when you come home after work and have to get dinner on the table in a hurry. You can put ingredients in the pressure cooker and by the time you"re finished tidying up the kitchen you can have a wholesome, hearty home cooked meal.

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Different models have different valves and locking systems, but all work in much the same way. It"s so simple, I use it as often to quickly steam veggies for quick side dishes at dinner as I do for cooking soups and entrees. They are simple and absolutely foolproof.

You cannot open today"s pressure cookers until you completely release the pressure from the pot - a huge safety improvement over the pressure cookers of yesteryear. Depending on what you"re making, you will release steam, and therefore pressure, from your pressure cooker via the natural release or quick release methods. The recipe will tell you which is the preferred method.

• Too much pressure is created in one of three ways: the heat is too high; the pressure cooker is overfilled, the pressure regulator valve is obstructed or malfunctioning.

• Never fill your pressure cooker more than half full with foods or two thirds full of liquid. As steam builds up it needs space. Over filling your pressure cooker can result in food particles getting lodged in the valves, which can result in pressure not being released.

• Inspect the valves to make sure they are free of debris and food residue. The instructions that came with your pressure cooker can tell you more thoroughly what to look for and how to maintain the valves.

A gasket forms an airtight seal which does not allow air or steam to escape between the pan and the lid; the only way the steam can escape is through a regulator on the lid when the pressure has built up (or if the regulator is blocked, through a safety valve). Sometimes the gasket is referred to as a sealing ring.

The food to be made is placed in the pressure cooker, along with some amount of water. The vessel is then sealed and placed on a heat source (e.g. a stove). When the water reaches the boiling point at atmospheric pressure it begins to boil, but since the produced steam in the pressure cooker cannot escape the pressure rises, consequently raising the internal boiling point. Once the pressure increases to the designed amount above air pressure a relief valve opens, releasing steam and preventing the pressure from rising any further.

Pressure cookers have a reputation as a dangerous method of cooking with the risk of explosion. Early pressure cookers equipped with only a primary safety valve were at risk of explosion if poorly maintained, allowing food residues to contaminate the release valve. Modern pressure cookers typically have two or three independent safety mechanisms, as well as some additional safety features required for UL approval or the equivalent in other countries, such as an interlock to prevent opening the lid while internal pressure exceeds atmospheric pressure.

Modern pressure cookers employ several safety features, such as a lid interlock and a gauge to indicate when the cooker is pressurized. The pressure cannot build up unless the lid is properly closed and locked in place.

There is usually a backup pressure release mechanism (a safety valve of sorts) that may employ any of a number of different techniques to release pressure quickly if the primary pressure release mechanism fails (for example, if food jams the steam discharge path). One such method is in the form of a hole in the lid blocked by a plug of low melting-point alloy. If the internal temperature (and hence pressure) gets too high, the metal plug will melt, resulting in release of pressure.

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Hy Cite warrants that your Royal Prestige® cookware and related pieces will be free from defects in material and workmanship and will not permanently stain, rust, chip, melt, break or crack for 50 years from the date of purchase; except that coverage for the Royal Prestige® silicone cover gasket (where available) is limited to 1 year from the date of purchase.

Hy Cite warrants that your Royal Prestige RoyalCore Electric Skillet (except electrical parts) will be free from defects in material, and workmanship, and will not permanently stain, rust, chip, melt, break or crack for 50 years from the date of purchase. Electrical parts are warranted to be free from defects in material and workmanship for 1 year from the date of purchase.

Hy Cite warrants that your Royal Prestige® ge® Deluxe Easy Release cookware (except silicone gasket) will be free from defects in material and workmanship for 5 years from the date of purchase. Damages, including nonstick deterioration, discoloration, warping, metal separation, stains, discoloration, scratches or broken glass resulting from failure to follow use and care instructions relating to overheating, thermal shock, drops, use of abrasive cleaning utensils or agents and dishwasher use are excluded. Minor imperfections and color variations do not affect performance and are excluded.

Hy Cite warrants that your Royal Prestige Induction Cooktop will be free from defects in material and workmanship for 1 year from the date of purchase.

Hy Cite warrants that your Royal Prestige Pressure Cooker and related pieces (except, plastic parts, and silicone gasket) will be free from defects in material and workmanship for 50 years from the date of purchase. Plastic parts, and silicone gaskets are warranted to be free from defects in materials and workmanship for 1 year from the date of purchase.

Hy Cite warrants that your Royal Prestige Precision Series™ Cutlery and Food Cutter will be free from defects in materials and workmanship, and will not permanently stain, chip, melt or break for 50 years from the date of purchase. Silicone parts, such as the spatula heads, have a warranty of 2 years from the date of purchase. Note: The Precision Series™ and Damascus Series™ cutting knives should be able to maintain a keen cutting edge provided they are used properly and periodically sharpened professionally or using the Royal Prestige Precision Series Sharpener.

Hy Cite warrants that your Royal Prestige Cutlery and Gadgets and Food Cutter will be free from defects in materials and workmanship, and will not permanently stain, chip, melt or break for 50 years from the date of purchase. Silicone parts, such as the spatula heads, have a warranty of 2 years from the date of purchase.

Hy Cite warrants that your Royal Prestige Flatware will be free from defects in material and workmanship, and will not permanently stain, chip, break or melt for 50 years from the date of purchase.

Note: Maintenance parts for your Water Treatment Systems (including diverter valve and hose assembly, and rubber o-rings) may need replacement, not because of defects, but because hard-water minerals may clog valves; and harsh chemicals in tap water can cause rubber o-rings and hoses to become brittle. Maintenance parts may be replaced at one-half (50%) of the current retail price.

Hy Cite warrants that the motor of your Royal Prestige® Juice Extractor will be free from defects in material and workmanship for a period of 10 years from the date of purchase. All other components are warranted to be free from defects in material and workmanship for 2 years from the date of purchase.

Hy Cite warrants that your Royal Prestige Bakeware Set will be free from defects in material and workmanship, and will not permanently stain, rust, chip, melt, break or crack for 50 years from the date of purchase.

Hy Cite warrants that your Royal Prestige Kitchen Tool Set will be free from defects in material and workmanship for a period of 1 year from the date of purchase.

Hy Cite warrants that your Royal Prestige Air Filtration System will be free from defects in material and workmanship for 1 year from date of purchase.

Hy Cite will replace any covered product damaged in shipment free of charge if you notify Hy Cite within 30 days after your receipt of the product. Simply contact the Royal Prestige Service Center. As a condition to replacement, Hy Cite may require you to make the damaged product available for pick-up at Hy Cite’s expense.

This warranty gives you specific legal rights, and you may also have other rights which vary from State to State. For more information on our products please visit www.royalprestige.com.

Your pressure cooker and dinner can be ruined with too much food or too little liquid.  Too much food could block the pressure valve while too little liquid can permanently damage the cooker’s metal, bakelite and silicone fittings.  Here’s everything you need to know to keep your pressure cooker on the level and dinner coming.

Max 1/2 Full for Beans, Rice, Grains, Dehydrated Foods and Fruit – These foods either expand during cooking or generate lots of foam (or both). Beans can swell to twice their size during cooking and some grains, even more.  They also generate lots of foam and bubbles – which climb up the sides of the cooker to spray out of the valves – plugging them up.  This class of ingredients should also be opened using Natural Release method – which avoids the foamy starchy, bubbly, goo from spraying out of the valve during the pressure release, too.

A pressure cooker’s maximum capacity is, in fact, a safety feature. In order for a pressure cooker to receive UL rating, their manual must contain text to this effect.

Pressure cooker maximum capacities apply to all pressure cookers types (electric, jiggler, weight-modified and spring valves), shapes (pressure pans, stock pot- and braiser-type cookers), sizes (from 1 to 12L) and origins (Europe, Asia, America). That’s because all pressure cookers have valves and safety mechanisms placed in the lid.

The maximum capacity recommendations are in place to ensure neither food nor cooking liquid interfere with, or trigger, the safety systems located in the lid. The NUMBER ONE REASON for pressure cooker mishaps usually involves someone not familiar with pressure cooking filling the cooker beyond the cooker’s recommended maximum capacity – ultimately blocking the pressure release valve.

A larger pressure cooker will need more steam to pressurize and will also need more liquid to boil and generate that steam.  Some pressure valves vent by function or design. While a spring valve releases little or no steam to keep a cooker at pressure, instead, a weight-modified or jiggler-type valvemust release pressure and steam rhythmically to maintain a set pressure. The extra venting means that a longer cooking time will evaporate more liquid, and the cooker will require more to keep it from running dry.

You can reach your pressure cooker’s minimum liquid requirement with stock, fruit juice,  a little wine or beer –  but not hard liquor (large quantities of alcohol will evaporate through the valve and the vapor will ignite).

A common sight in a hydronic boiler room is water dripping from the discharge pipe of the boiler relief valve. While it may appear to be inconsequential, it could cause extensive damage to the heating system.

Some boiler rooms have a bucket under the relief valve discharge pipe to mask the problem. The following are some suggestions if you would like to resolve the problem.

The solids can affect the efficiency and safety of the system. Solids form scale on the hottest surfaces in the boiler lowering the heat transfer ability and efficiency of the system. A leaking relief valve can allow solids to form on the seat of the relief valve increasing the rate of the leak.

A worse situation occurs when the solids form on the spring side of the relief valve as it could alter the opening pressure. A relief valve was a contributing factor in a fatal boiler accident as scale formed on the relief valve, prohibiting it from opening properly.

The relief valve, rated for 30 psig, was tested after the accident and did not open until the pressure reached 1,500 psig. Diagnosing the cause of the leaking relief valve is time-consuming and sometimes frustrating. I like to explain this to the customer to prepare them when the diagnosis and repair may take more than one visit.

The next step is to verify the pressure rating of the relief valve. The pressure rating of the relief valve should be at least 10 psig higher than the operating pressure of the system but less than the maximum allowable working pressure (MAWP) of the boiler. Many hydronic boilers are shipped with a 30 psig relief valve from the factory. In this example, the relief valve should be at 40 psig or higher. If the system pressure is 30 psig and the relief valve, rated for 40 psig, is leaking, the relief valve is most likely defective.

In some instances, it may take several days for the pressure to build and open the relief valve and these are the most difficult to troubleshoot. The first place I would look is the compression tank. If the tank is flooded, there are a couple of reasons.

A pinhole leak on top of the tank may be impossible to find and one of the ways to test the integrity of the tank is to valve off the water feeder to the system and check the tank in a few days to see if it flooded. If the tank is flooded, you might have to replace the tank.

Another culprit that can cause the pressure to rise and open the relief valve is if the boiler has an indirect water which uses the boiler water to heat the domestic water using a water to water heat exchanger. A leaking heat exchanger could allow the higher city water pressure to enter the space heating side and increase the system pressure. To test this idea, shut the valves from the domestic water side and see if the pressure still rises.

The last item to check is the pressure-reducing valve (PRV). This is a brass valve with an adjustment screw. Some models have a quick-fill feature, which allows you to pull a lever and quickly fill the system. A stethoscope is sometimes used to trouble shoot the PRV to detect if water is leaking through the valve.

Another way to test for leaking is to feel the downstream pipe and see if it is cold. In many instances, the water is fed slowly and difficult to detect. Another way to test to see if the PRV is leaking through is to shut off the valves on the feed water pipe and see if the pressure still rises. If it does, I will suspect the piping to the compression tank is restricted or the tank is flooded. If the pressure does not rise, it could be the pressure reducing valve.

A safety valve is a valve that acts as a fail-safe. An example of safety valve is a pressure relief valve (PRV), which automatically releases a substance from a boiler, pressure vessel, or other system, when the pressure or temperature exceeds preset limits. Pilot-operated relief valves are a specialized type of pressure safety valve. A leak tight, lower cost, single emergency use option would be a rupture disk.

Safety valves were first developed for use on steam boilers during the Industrial Revolution. Early boilers operating without them were prone to explosion unless carefully operated.

Vacuum safety valves (or combined pressure/vacuum safety valves) are used to prevent a tank from collapsing while it is being emptied, or when cold rinse water is used after hot CIP (clean-in-place) or SIP (sterilization-in-place) procedures. When sizing a vacuum safety valve, the calculation method is not defined in any norm, particularly in the hot CIP / cold water scenario, but some manufacturers

The earliest and simplest safety valve was used on a 1679 steam digester and utilized a weight to retain the steam pressure (this design is still commonly used on pressure cookers); however, these were easily tampered with or accidentally released. On the Stockton and Darlington Railway, the safety valve tended to go off when the engine hit a bump in the track. A valve less sensitive to sudden accelerations used a spring to contain the steam pressure, but these (based on a Salter spring balance) could still be screwed down to increase the pressure beyond design limits. This dangerous practice was sometimes used to marginally increase the performance of a steam engine. In 1856, John Ramsbottom invented a tamper-proof spring safety valve that became universal on railways. The Ramsbottom valve consisted of two plug-type valves connected to each other by a spring-laden pivoting arm, with one valve element on either side of the pivot. Any adjustment made to one of valves in an attempt to increase its operating pressure would cause the other valve to be lifted off its seat, regardless of how the adjustment was attempted. The pivot point on the arm was not symmetrically between the valves, so any tightening of the spring would cause one of the valves to lift. Only by removing and disassembling the entire valve assembly could its operating pressure be adjusted, making impromptu "tying down" of the valve by locomotive crews in search of more power impossible. The pivoting arm was commonly extended into a handle shape and fed back into the locomotive cab, allowing crews to "rock" both valves off their seats to confirm they were set and operating correctly.

Safety valves also evolved to protect equipment such as pressure vessels (fired or not) and heat exchangers. The term safety valve should be limited to compressible fluid applications (gas, vapour, or steam).

For liquid-packed vessels, thermal relief valves are generally characterized by the relatively small size of the valve necessary to provide protection from excess pressure caused by thermal expansion. In this case a small valve is adequate because most liquids are nearly incompressible, and so a relatively small amount of fluid discharged through the relief valve will produce a substantial reduction in pressure.

Flow protection is characterized by safety valves that are considerably larger than those mounted for thermal protection. They are generally sized for use in situations where significant quantities of gas or high volumes of liquid must be quickly discharged in order to protect the integrity of the vessel or pipeline. This protection can alternatively be achieved by installing a high integrity pressure protection system (HIPPS).

In the petroleum refining, petrochemical, chemical manufacturing, natural gas processing, power generation, food, drinks, cosmetics and pharmaceuticals industries, the term safety valve is associated with the terms pressure relief valve (PRV), pressure safety valve (PSV) and relief valve.

The generic term is Pressure relief valve (PRV) or pressure safety valve (PSV). PRVs and PSVs are not the same thing, despite what many people think; the difference is that PSVs have a manual lever to open the valve in case of emergency.

Relief valve (RV): an automatic system that is actuated by the static pressure in a liquid-filled vessel. It specifically opens proportionally with increasing pressure

Pilot-operated safety relief valve (POSRV): an automatic system that relieves on remote command from a pilot, to which the static pressure (from equipment to protect) is connected

Low pressure safety valve (LPSV): an automatic system that relieves static pressure on a gas. Used when the difference between the vessel pressure and the ambient atmospheric pressure is small.

Vacuum pressure safety valve (VPSV): an automatic system that relieves static pressure on a gas. Used when the pressure difference between the vessel pressure and the ambient pressure is small, negative and near to atmospheric pressure.

Low and vacuum pressure safety valve (LVPSV): an automatic system that relieves static pressure on a gas. Used when the pressure difference is small, negative or positive and near to atmospheric pressure.

In most countries, industries are legally required to protect pressure vessels and other equipment by using relief valves. Also, in most countries, equipment design codes such as those provided by the ASME, API and other organizations like ISO (ISO 4126) must be complied with. These codes include design standards for relief valves and schedules for periodic inspection and testing after valves have been removed by the company engineer.

Today, the food, drinks, cosmetics, pharmaceuticals and fine chemicals industries call for hygienic safety valves, fully drainable and Cleanable-In-Place. Most are made of stainless steel; the hygienic norms are mainly 3A in the USA and EHEDG in Europe.

The first safety valve was invented by Denis Papin for his steam digester, an early pressure cooker rather than an engine.steelyard" lever a smaller weight was required, also the pressure could easily be regulated by sliding the same weight back and forth along the lever arm. Papin retained the same design for his 1707 steam pump.Greenwich in 1803, one of Trevithick"s high-pressure stationary engines exploded when the boy trained to operate the engine left it to catch eels in the river, without first releasing the safety valve from its working load.

Although the lever safety valve was convenient, it was too sensitive to the motion of a steam locomotive. Early steam locomotives therefore used a simpler arrangement of weights stacked directly upon the valve. This required a smaller valve area, so as to keep the weight manageable, which sometimes proved inadequate to vent the pressure of an unattended boiler, leading to explosions. An even greater hazard was the ease with which such a valve could be tied down, so as to increase the pressure and thus power of the engine, at further risk of explosion.

Although deadweight safety valves had a short lifetime on steam locomotives, they remained in use on stationary boilers for as long as steam power remained.

Weighted valves were sensitive to bouncing from the rough riding of early locomotives. One solution was to use a lightweight spring rather than a weight. This was the invention of Timothy Hackworth on his leaf springs.

These direct-acting spring valves could be adjusted by tightening the nuts retaining the spring. To avoid tampering, they were often shrouded in tall brass casings which also vented the steam away from the locomotive crew.

The Salter coil spring spring balance for weighing, was first made in Britain by around 1770.spring steels to make a powerful but compact spring in one piece. Once again by using the lever mechanism, such a spring balance could be applied to the considerable force of a boiler safety valve.

The spring balance valve also acted as a pressure gauge. This was useful as previous pressure gauges were unwieldy mercury manometers and the Bourdon gauge had yet to be invented.

Paired valves were often adjusted to slightly different pressures too, a small valve as a control measure and the lockable valve made larger and permanently set to a higher pressure, as a safeguard.Sinclair for the Eastern Counties Railway in 1859, had the valve spring with pressure scale behind the dome, facing the cab, and the locked valve ahead of the dome, out of reach of interference.

In 1855, John Ramsbottom, later locomotive superintendent of the LNWR, described a new form of safety valve intended to improve reliability and especially to be tamper-resistant. A pair of plug valves were used, held down by a common spring-loaded lever between them with a single central spring. This lever was characteristically extended rearwards, often reaching into the cab on early locomotives. Rather than discouraging the use of the spring lever by the fireman, Ramsbottom"s valve encouraged this. Rocking the lever freed up the valves alternately and checked that neither was sticking in its seat.

A drawback to the Ramsbottom type was its complexity. Poor maintenance or mis-assembly of the linkage between the spring and the valves could lead to a valve that no longer opened correctly under pressure. The valves could be held against their seats and fail to open or, even worse, to allow the valve to open but insufficiently to vent steam at an adequate rate and so not being an obvious and noticeable fault.Rhymney Railway, even though the boiler was almost new, at only eight months old.

Naylor valves were introduced around 1866. A bellcrank arrangement reduced the strain (percentage extension) of the spring, thus maintaining a more constant force.L&Y & NER.

All of the preceding safety valve designs opened gradually and had a tendency to leak a "feather" of steam as they approached "blowing-off", even though this was below the pressure. When they opened they also did so partially at first and didn"t vent steam quickly until the boiler was well over pressure.

The quick-opening "pop" valve was a solution to this. Their construction was simple: the existing circular plug valve was changed to an inverted "top hat" shape, with an enlarged upper diameter. They fitted into a stepped seat of two matching diameters. When closed, the steam pressure acted only on the crown of the top hat, and was balanced by the spring force. Once the valve opened a little, steam could pass the lower seat and began to act on the larger brim. This greater area overwhelmed the spring force and the valve flew completely open with a "pop". Escaping steam on this larger diameter also held the valve open until pressure had dropped below that at which it originally opened, providing hysteresis.

These valves coincided with a change in firing behaviour. Rather than demonstrating their virility by always showing a feather at the valve, firemen now tried to avoid noisy blowing off, especially around stations or under the large roof of a major station. This was mostly at the behest of stationmasters, but firemen also realised that any blowing off through a pop valve wasted several pounds of boiler pressure; estimated at 20 psi lost and 16 lbs or more of shovelled coal.

Pop valves derived from Adams"s patent design of 1873, with an extended lip. R. L. Ross"s valves were patented in 1902 and 1904. They were more popular in America at first, but widespread from the 1920s on.

Although showy polished brass covers over safety valves had been a feature of steam locomotives since Stephenson"s day, the only railway to maintain this tradition into the era of pop valves was the GWR, with their distinctive tapered brass safety valve bonnets and copper-capped chimneys.

Developments in high-pressure water-tube boilers for marine use placed more demands on safety valves. Valves of greater capacity were required, to vent safely the high steam-generating capacity of these large boilers.Naylor valve) became more critical.distilled feedwater and also a scouring of the valve seats, leading to wear.

High-lift safety valves are direct-loaded spring types, although the spring does not bear directly on the valve, but on a guide-rod valve stem. The valve is beneath the base of the stem, the spring rests on a flange some height above this. The increased space between the valve itself and the spring seat allows the valve to lift higher, further clear of the seat. This gives a steam flow through the valve equivalent to a valve one and a half or twice as large (depending on detail design).

The Cockburn Improved High Lift design has similar features to the Ross pop type. The exhaust steam is partially trapped on its way out and acts on the base of the spring seat, increasing the lift force on the valve and holding the valve further open.

To optimise the flow through a given diameter of valve, the full-bore design is used. This has a servo action, where steam through a narrow control passage is allowed through if it passes a small control valve. This steam is then not exhausted, but is passed to a piston that is used to open the main valve.

There are safety valves known as PSV"s and can be connected to pressure gauges (usually with a 1/2" BSP fitting). These allow a resistance of pressure to be applied to limit the pressure forced on the gauge tube, resulting in prevention of over pressurisation. the matter that has been injected into the gauge, if over pressurised, will be diverted through a pipe in the safety valve, and shall be driven away from the gauge.

There is a wide range of safety valves having many different applications and performance criteria in different areas. In addition, national standards are set for many kinds of safety valves.

Safety valves are required on water heaters, where they prevent disaster in certain configurations in the event that a thermostat should fail. Such a valve is sometimes referred to as a "T&P valve" (Temperature and Pressure valve). There are still occasional, spectacular failures of older water heaters that lack this equipment. Houses can be leveled by the force of the blast.

Pressure cookers usually have two safety valves to prevent explosions. On older designs, one is a nozzle upon which a weight sits. The other is a sealed rubber grommet which is ejected in a controlled explosion if the first valve gets blocked. On newer generation pressure cookers, if the steam vent gets blocked, a safety spring will eject excess pressure and if that fails, the gasket will expand and release excess pressure downwards between the lid and the pan. Also, newer generation pressure cookers have a safety interlock which locks the lid when internal pressure exceeds atmospheric pressure, to prevent accidents from a sudden release of very hot steam, food and liquid, which would happen if the lid were to be removed when the pan is still slightly pressurised inside (however, the lid will be very hard or impossible to open when the pot is still pressurised).