how pressure cooker safety valve works factory

Pressure cooking is a wonderful way to prepare food that cooks thoroughly and quickly at a high temperature. Some are worried about the dangers of using a pressure cooker, so it is helpful to find out how to check your pressure cooker safety valve for safe operation.

For those worried that a pressure cooker might explode, the safety valve is the design feature that prevents this from happening. If the cooker has a safety valve, you can see it installed on the cooker’s lid.

A pressure cooker is designed to trap the steam inside to increase the pressure. However, too much pressure is not safe. The valve must release pressure if it gets too high.

The blog of pressure cooking today has many recipes that are delicious. There are 25 recipes for pasta so you can try a new one every day for nearly a month.

There is a weight inside many of the safety valves that is lifted by the internal steam pressure when it reaches a certain amount. When the pressure lifts the weight inside the valve, this allows some steam to escape.

Jeffrey Eisner who says “he is a nice Jewish boy from Long Island.” He started with pressure cooking by making a simple mac and cheese dish with a recipe that he shared on YouTube. The video was an immediate success and led to his making new recipes for pressure cooking.

In a sealed cooker, as the pressure builds up, the boiling point of water rises. This phenomenon is the cause of the increased heat that cooks the food more thoroughly and faster.

The science that explains this is fascinating. The normal boiling point of water under standard atmospheric pressure of 15 pounds per square inch (psi) is 212°F (100°C). In a pressure cooker, the atmospheric pressure doubles from 15 psi to 30 psi. This added pressure raises the boiling point of water from 212°F (100°C) to 250°F (121°C).

If you see steam escaping from the safely valve do not worry. The steam escaping from the safety valve is its normal function, which means the valve is working properly.

If the internal pressure within the cooker gets high enough, this lifts a weight in the safety valve that allows steam to escape. The escaping vapor lowers the pressure. You can hear the steam escaping, making a whistling sound, or rattling the valve.

The first pressure cooking devices were used in the 17th century. They were useful to remove fat and collagen from bones so that the bones could then be ground down to make a pure bone meal.

The inventor of the device, Denis Papin, called it a “steam digester” or “bone digester.” His invention was the precursor to both pressure cookers and the steam engine. Surprisingly, the early designs did not have any safety features, and this caused some of the first ones to explode while being used.

The legacy of those early pressure-cooking devices may be why some still fear this problem even today. Papin, to his credit, came up with a design improvement that is what we call a safety valve to avoid the dangers of these explosions.

By the 1930s, the modern pressure cooker design became useful in a home kitchen. The Flex-Seal Speed Cooker, invented by Alfred Vischer, came out in 1938.

These home cookers became even more popular in 1939 with the release of the design by the National Pressure Cooker Company (now called National Presto Industries), which is still manufacturing these cookers today.

The first-generation cookers had a safety valve that worked with a weight. When the internal pressure rises high enough to lift the weight, some steam escapes, and the valve makes a distinctive rattling sound.

Second-generation cookers use a spring-loaded valve that makes less noise and is adjustable for pressure sensitivity by using a dial, which is on the cooker.

Third-generation models are the most recent versions. They use an electric heating source that is regulated by the internal pressure. These devices do not need a safety valve because the heat source automatically shuts off before the pressure gets too high.

Suppose you are thinking about getting a new cooker. In that case, there is another device that you might consider called a food dehydrator, which I describe in the article entitled, “How Much Electricity Does a Dehydrator Use?” here.

For the styles of cookers with a safety valve, it may not be obvious when the valve is not working if it is blocked. You may notice the lack of steam while the cooker is heated. The valve could rarely be blocked, but if not cleaned properly, it is possible.

Alternatively, the valve may be broken, missing, or the pot may not seal properly. These problems might allow too much steam to escape. This leakage may cause the cooker not to heat up properly and not allow the internal pressure to build up to the proper level.

One of the signs of a problem with a lack of pressure is that the food takes much longer to cook than you normally expect when using a cooker of this type.

One tip in the video is not to open the cooker after finishing cooking and take the lid to run it under cold water. This sudden temperature change can make the safety valve work less well and may cause the need to change the valve more frequently.

If you use a cooker that needs a valve to work properly and the valve is broken or missing, you can replace it with a new valve. Be sure to get the manufacturer’s specifications to ensure you use the correct replacement part.

Some of these problems include the ventilation knob being open or not enough liquid is in the cooker (requires at least one cup). Another cause is the sealing ring is missing, damaged, covered with food particles, or not in the proper position.

The video narrator shows how she cleans her float valve for her instant pot that she uses as a cooker. If you use too little liquid or too much, the cooker may not pressurize.

For the type with screws, hold the valve from the bottom of the lid with the pliers and use the screwdriver to remove the screws from the top to remove the broken part. Replace it with the new one and tighten the screws that hold it in place by holding it with the pliers from the bottom of the lid again and tightening the screws from the top.

For the type with a nut, use the wrench to loosen it for removal and perhaps a socket when you put on the new valve to tighten it with enough torque to hold it securely in the proper position.

Modern pressure cookers that are in good repair are quite safe. The one caution to remember is not to overfill the cooker so that the food might block the safety valve. This overfilling with food would be very difficult to do and not something to worry about for normal use.

Be careful where you keep your cooker on the countertop because it is important to know how hot a stovetop can get. Even when turned off, a stovetop may still be very hot, which I discuss in this article.

Now you know everything you need to know about a pressure cooker safety valve. You know what they do, how they work, and how to replace one if it needs repair. Enjoy your pressure-cooking recipes without worrying about the safety valve.

If having a safety valve on your cooker still bothers you, consider buying an electric cooker without a valve that instead has a built-in safety feature that automatically shuts off power if the pressure gets too high.

Pressure cookers have become an essential part of everyday cooking. As they don’t have any complicated functionalities, they are quite easy to prepare.

However, in technological aspects, a pressure cooker is a bit complicated. In order ensure user-safety, they have been equipped with different safety features – among them safety valve is a crucial one.

Pressure cookers have to deal with a lot of steam pressure in the cooking process. At some point, it has to release the excess steam to prevent the cooker from blowing up or exploding.

This release happens through the safety valve that holds weight. When the pressure is too high, it lifts the weight and steam escapes through making a buzz sound.

One of them is a classic whistle with pressure regulating valve and another is pressure regular valve present a little away from the first one. It is fixed onto the cooker lid and made from synthetic rubber like hardened viton or neoprene which helps in maintaining the pressure and good seal.

When the pressure inside the cooker increases, the inner part of safety valve will sense the elevation. And when it exceeds the normal levels, the rubber will start to melt and disc will lift.

Once the excess pressure is released, the disk goes back into its position. And the safety valve will open only when other means of steam release have failed as a last resort to prevent any explosion.

Pressure or steam release doesn’t always mean danger. It mostly indicates some dysfunctions that need attention. We have mentioned some of the possibilities below for your reference.

Damaged gasket – Usually, a rubber ring is present to seal the cooker. When there is a damage to it or if placed unevenly, it can compromise the cooker seal and let the pressure escape through the safety valve.

Overfilled pressure cooker – If the appliance is filled up with food ingredients without any space left for the steam, then this can block the regulating valve due to food expansion or foaming.

If the pressure cooker is made from cheap quality and from on an unknown brand, then they are a safety hazard as they compromise on the protection and health of a consumer. They often have low-quality safety valve which malfunctions easily and lead the steam to escape.

When the food and water quantity is little and water boils away, this can result in burnt and empty cooker. And the temperature gets too hot very quickly, leading to break down of the safety valve.

If the pressure cooker is placed over a larger burner and on a high flame, then the flame starts licking the sides of the appliances, leading to high temperature build up and damaging the safety valve.

Not cleaning the pressure cooker regularly can lead to clogs in the pressure regulating valve and this lets the safety valve to emit the steam from the cooker.

Some of the models come with a manual setting sealing feature. In such case, never forget to turn them on or else the steam takes safety valve for escape.

If you suspect the pressure cooker is not because of the safety valve, then the first thing is to take the appliance to the nearest service centre. You can use the cooker without the lid on but it is better to avoid using it with the lid until you get it repaired.

Yes, it is possible to replace safety valve of a pressure cooker. And moreover, it is recommended to replace it if the valve is out of friction or damaged.

Replacing the safety valve can be done in two methods – one includes changing it from inside and another from the outside. Below are the clear instructions for the same.

Make sure the pressure cooker is filled up to only 2/3 full and the rest of 1/3 part has to be empty so that the foods have enough space to swell and foam.

It is important to add adequate amount of liquid into the pressure pot. If not, the water runs out quickly, cause rapid heat increase and lead to explosion. Not to say that burns caused food burns as well.

To maintain the pressure cooker longevity and prevent any disasters, it is important to check the safety valve and gasket on a regular basis. If there is any damage, getting it repaired or replacing is very important. Safety valve in a pressure cooker plays a very significant role.

We believe any questions and doubts about the safety valve has been clarified by the information present in this article. If it hasn’t then, write them to us in the comment section below.

The modern pressure cooker can be found in so many homes today. It offers convenience and quick results; these are some of the reasons many homeowners have pressure cookers. These cookers rely on hot steam to cook foods under high pressure. Manufacturers of pressure cookers have found ways to incorporate safety systems on these cookers to protect all users.

In this post, I will be discussing some of the safety systems that have been added to the design of modern pressure cookers. These features are easy to understand and use, what’s more, the manufacturers encourage everyone to use these features to ensure pressure cookers serve their purpose.

The newer models of pressure cookers stand out from the types that were used many years ago. Over the years pressure cookers have evolved, there are more features and remarkable improvements regarding durability and value. One of the outstanding improvements in pressure cookers is the introduction of a valve mechanism. It has helped to make the pressure cooker safer and easier to use.

In the past, many homeowners avoided pressure cookers because they were known to explode. As scary as this may sound, there were cases of explosion, but these accidents happened with the very old models. The explosions happened due to poor designs and the use of substandard materials to make the pressure cooker. These anomalies have been corrected in the new models we have today.

During the Second World War, pressure cookers were in high demand; it was a big business for the manufacturers. Unfortunately, many entrepreneurs who didn’t know much about these cookers produced bad products that failed to work as expected. The defects were apparent, and there were no safety features to protect users at that time.

Over the years, the pressure cooker gained popularity again all around the world. The acceptance of this cooker was mainly due to how convenient it was to cook different types of foods quickly. The rise in demand naturally encouraged more manufacturers to enter the business industry. The demand and competition in the markets made it necessary for all manufacturers of pressure cookers to ensure their products were of high-quality to retain their customers. Also, research studies were done to find solutions to address some of the problems the users of pressure cookers reported. Moreover, that marked the beginning of the pressure cooker’s evolution.

The second generation pressure cookers have been a huge hit in the market. They stand out from the older models we used many years ago, and the safety features make them function better. While these features can be generalised, we know about certain brands that have strived to add more innovative features in a bid to get ahead of the competition in the market.

The safety features for pressure cookers can be found on the stove top models and electric pressure cookers. While more people tend to buy the electric pressure cookers because of their peculiar functions and easy management, the modern versions of both devices are excellent and safe for use. It can be noted that the inclusion of more safety features in the design of pressure cookers has caused an increase in their prices. This is expected, after all, there can be no price too high for safety and value. You can get the proper guidance when deciding to buy a pressure cooker by studying the user’s manual to know more about the brand and value you will get while using the pressure cooker.

The modern designs for pressure cookers now have features such as the precision spring valves, sturdy handles, and different safety mechanisms that do not need any special training to understand or use. It is apparent that these pressure cookers have been carefully redesigned to meet the needs of the consumers. There are still some older models in the market, these pressure cookers are cheaper, but you wouldn’t want to compromise value and safety.

Modern designs of pressure cookers feature special locking devices that keep the cooker sealed until the pressure has been released and it is safe to open the vessel. These cookers come with dual pressure valves which give the user more control over the pressure generated inside the cooker. The dual pressure valves have been designed for the management of pressure during and after use. The steam pressure in the cooker is released through a small opening in the gasket.

The flat base of a pressure cooker supports the generation of pressure when the cooker has been placed on a source of heat. The flat base also ensures the cooker is well balanced for safety purposes. There are flanges on the lid of pressure cookers; these features prevent the build-up of pressure except the cooker has been properly positioned over a source of heat.

As earlier mentioned, the pressure release valves have helped to make the cookers safer for everyone. They are used to release the steam pressure from the cooker; modern pressure cookers have pressure release valves that do not make the characteristic hissing sounds many people find disturbing.

When excess pressure is generated inside the cooker, you will hear a hissing sound; this is excess steam escaping through the vent. In a situation where the primary vent is clogged, the steam will be forced to escape through the secondary vent, and if the secondary valve is not sufficient to allow the excess steam pressure escape, the gasket will be dislodged to allow more steam escape, so there is no fear of an explosion while the pressure cooker is in use.

It is essential to ensure the lid of a pressure cooker has been firmly closed before it is used. The lid in a pressure cooker works with a spring mechanism that prevents the gasket from touching the rim until the lid has been properly closed. This is a safety measure that prevents spills and escape of steam pressure. If the lid is not properly closed, you will end up wasting too much energy because the cooker will work longer, and there won’t be sufficient pressure to cook the food.

Some pressure cookers have been fitted with indicators that show the user how much steam pressure has been generated inside the cooker while it is in use. The pressure indicators are also helpful when you need to achieve a particular pressure based on the recipe you are following to cook the meal.

In some cases, you may notice the lid will not close properly no matter how hard you try. You need to troubleshoot and find out why the lid won’t close. First, you should check for dirt under the lid; you may find food particles or other obstacles that have prevented the lid from closing. Next, check the gasket; it may be burnt or damaged by the heat; you can change the gasket in your pressure cooker. Next, look out for dents; this damage will prevent the lid of your pressure cooker from closing properly.

The pressure cookers have a uniquely long handle to enable you to carry the cooker from one spot to another. You can also find models that have handled on opposite sides to help you lift and move the pressure cooker easily.

The handles of pressure cookers are long enough to keep your hands away from the steam pressure; however, you should consider using kitchen gloves for additional protection. They are also sturdy enough to withstand the heat; materials used to make the handles of pressure cookers are poor heat conductors, so you don’t have to worry.

Stainless steel is chosen as the preferred material for manufacturing pressure cookers because it is safe for all types of foods even items that have a high acidic content.

Stainless steel can also be used for all types of cookers and sources of heat without the appearance of the cooker becoming ruined. Pressure cookers made from stainless steel are also easy to clean and maintain. The durability makes it possible to use stainless steel for many years and to cook different types of recipes.

Pressure cookers are designed with an encapsulated base that performs a significant function, but many people don’t realize they are extremely useful. If you go shopping for a pressure cooker ensure it has this type of base. One of the major issues users of the older models of pressure cookers experienced was scorched food. It was easy to ruin meals when they become scorched. This led to the invention and addition of the encapsulated base in pressure cookers. The base has a layer of aluminium which has been placed in between stainless steel. This arrangement of metals is a perfect solution to improve the distribution of heat energy. This is how the issue of scorching has been resolved.

Thankfully, many brands of pressure cookers feature these safety systems. More people can use these cookers satisfactorily without the fear of injury. Overall, always ensure you read the user’s manual carefully to know more about the pressure cooker you have bought.

Say the words “pressure cooker” to someone who’s never used one, and they’ll probably think “danger.” It isn’t hard to imagine what’s going through their heads—visions of flying lids, exploding kettles, or much, much worse. Even people who have used a pressure cooker will sometimes get a little leery around one.

But while such hazards may have been possible in the past, they’re practically fiction today. Pressure cookers are safe to use. More than that, they’re incredibly useful. In this age of speed, efficiency, and optimization, there are few tools in the kitchen more suited to cooks who demand good food quickly. If you’re on the fence about buying a pressure cooker—or if you’re an especially obstinate hater, this article is for you.

The origins of the pressure cooker can be traced to a 17th-century French physicist and mathematician named Denis Papin. Papin, who shared notes with such legendary brainiacs as Christiaan Huygens, Gottfried Leibniz, and Robert Boyle, is best known for his 1679 invention of the “steam digester,” the precursor to both the pressure cooker and the steam engine. Also known as the “bone digester” (such a hardcore name!) or “Papin’s digester,” the device was designed to extract fats and collagen from bones; after extraction, the rendered bones could be ground into bone meal, to be used as a dietary supplement or fertilizer.

The steam digester consisted of a closed pot with a tight-fitting lid. As food and water heated up, the vessel trapped steam, raising the pot"s internal pressure. Papin’s initial designs didn’t include any pressure-release mechanism, which resulted in various explosions early on. Fortunately, Papin subsequently invented a steam-release valve to keep such accidents from happening.

Over the next 200 years, intrepid minds refined the concept. But it wasn’t until the 1930s that the pressure cooker finally made its way into the home kitchen, with the introduction of Alfred Vischer’s “Flex-Seal Speed Cooker” in 1938, and later a model from the National Pressure Cooker Company (which is now named National Presto Industries and is still very much in the pressure cooker game) in 1939.

Since then, not much has changed, and pressure cooker designs can be classified by generations. The first and simplest “old type” pressure cookers feature a weighted “jiggler” valve that releases and regulates pressure, causing a rattling noise as steam escapes. Today, most pressure cookers you can find are first-generation designs, with small safety improvements like pressure-sensitive locking mechanisms, as well as the ability to adjust pressure by changing the weight of the valve.

Second-generation pressure cookers are quieter, have a hidden, spring-loaded valve, and allow you to choose at least two different pressure settings by adjusting a dial. Some cookers don’t even release any steam while cooking; instead, they have an indicator that displays the pressure level. Overall, second-generation models offer more precision when cooking than do first-generation models.

Third-generation models are a relatively recent innovation. Unlike models belonging to the first two generations, these models all have an electric heat source that maintains proper pressure while cooking. They typically have a timer, and more elaborate models include digital controllers, delayed cooking functionality, and smart programming for cooking certain foods.

Legends of exploding pressure cookers aren"t entirely unfounded. As the US entered World War II, the government promoted self-sufficiency programs, which encouraged canning home-grown produce. Steel was allocated for the production of pressure canners, and the popularity of pressure cookers rose as well. After the war, demand for pressure cookers was at an all-time high, precipitating a boom in production. Manufacturers began pumping out pressure cookers, but at the expense of materials, construction, and overall safety. For instance, models from the "50s had a single, poorly constructed weighted valve that easily clogged with debris. As pressure built to an extreme, the gasket would blow, and water or steam would spew from the top; in some cases, the lid would just fly right off.

Fortunately, manufacturing and design practices have improved considerably, and today’s pressure cookers feature several fail-safe mechanisms to ensure safety, such as multiple valves, dual pressure regulators, and spring-loaded lid locks. No more sketchy deathtraps.

A pressure cooker is a sealed chamber that traps the steam generated as its contents are heated. As steam builds, pressure increases, driving the boiling point of water past 212°F. In general, this higher temperature shortens cooking times and, due to a lack of evaporation, extracts flavor more efficiently from foods.

Time for a quick high school chemistry refresher: The pressure cooker can be best explained by the “ideal gas law” (or “general gas equation”), which describes the behavior of most gases under most conditions. It is commonly given as: PV = nRT

P stands for pressure; Vstands for volume; Tstands for temperature; nrepresents the amount of a given gas (expressed as a number of particles);andRrepresents a constant (the ideal gas constant, but, for the sake of simplicity, let’s say that’s not too important here).

In the closed chamber of a pressure cooker, we can make a few assumptions. For one, the volume (V) of the chamber doesn’t change. Second, R (being a constant) doesn’t change either. Third, there is a maximum pressure that the chamber can reach, regulated by a valve system. As the pressure cooker heats food up (i.e., heats water in the food), T goes up. And as T increases, something else must increase to balance the equation. Since we assume that V is constant, it is more than likely that pressure (P) increases as well.

We can explain this increase in pressure another way, too: As the system heats up, there is more energy supplied to molecules of water vapor, which causes them to bounce around and collide randomly both with each other and against the walls of the container. The force of these collisions against the walls is one definition of pressure, based on the “kinetic model of gases.”

But what happens when P maxes out? Consider, for a moment, a pressure cooker containing water and chicken bones for making stock. As the container reaches maximum pressure, the temperature (T) plateaus. If we continue to supply heat (energy) to the system, then we’re still providing energy for more random collisions between water molecules. In the absence of a valve, the water would continue to heat up, building pressure indefinitely. But something has to give. In this case, n (the amount of gas) decreases. We see this in the form of steam escaping slightly, making the pressure-regulating valve rattle as our chicken stock cooks. This is the case for first-generation stove-top cookers. For newer, third-generation electric models, the cooker detects both pressure and temperature and regulates the amount of heat supplied by the heating element, so you don’t see much steam escaping or hear much rattling.

Practically speaking, what all that science amounts to is this: In a sealed pressure cooker, the boiling point of water goes up as pressure increases.

At standard atmospheric pressure, the boiling point of water is 212°F. But in a standard American pressure cooker, the pressure reaches 1 atm or 15 psi (pounds per square inch) above standard atmospheric pressure*, or 2 atm, which is typically the maximum pressure limit on most cookers. At 30 psi, the boiling point of water is about 250°F.

*The reading on the gauge for nearly every pressure cooker indicates the pressure above atmospheric pressure. At sea level, atmospheric pressure is about 1 atm, or 15 psi. If a dial reads 15 psi, then that means the pressure inside the sealed chamber is 15 psi above atmospheric 15 psi (30 psi total, referred to as “absolute pressure”). This dial reading is technically referred to as “gauge pressure.”

The higher cooking temperature in a sealed pressure cooker means, in general, faster cooking without burning food. And, because the vessel is sealed, it also limits evaporation of critical volatile flavor and aroma compounds. An added plus: the contents of a pressure cooker go relatively undisturbed, since the liquid never effectively boils.

What about pressure cooking above sea level? You might be aware that general cooking times and temperatures for certain recipes differ in places like Denver, CO, or high up in the Andes. At high altitudes, the atmospheric pressure is lower**. For example, in Denver, the ambient pressure is around 12.2 psi.

** Pressure is lower at higher elevations because most of the air molecules in the atmosphere are held close to the earth’s surface by gravity, which means there are fewer air molecules above a higher altitude surface than there are above a surface at a lower altitude.

In general, a pressure cooker adds pressure above the given atmospheric pressure. That means the force that closes the valve as pressure builds in the chamber includes the force of atmospheric pressure. For example, if the atmospheric pressure in Denver is 12.2 psi, then the absolute pressure of the chamber at full pressure is 27.2 (12.2 psi + 15 psi)—nearly 3 psi less than at sea level. Looking at our trusty ideal gas equation, we know that lowering pressure will lower the temperature in a system. In this case, the boiling point of water in a sealed chamber cooking at high pressure will be 244.8°F, almost 6 degrees lower than the same system at sea level.

Of course, a lower boiling point means slower cooking. What does that mean for you? It means you have to increase cooking time to accommodate lower pressure and lower cooking temperature in order to get the same results. A good rule of thumb is to increase cooking time by about five percent for every 1000 feet above 2000 feet elevation.

Here in America, you have a greater choice to make when it comes to pressure cookers: electric or stovetop? There are several advantages and disadvantages to using either design. But the single biggest difference is this: Electric pressure cookers operate at lower pressure (12 psi) than their stovetop counterparts (15 psi). Once again, lower pressure means lower temperature, so cooking times will be longer when using an electric model.

Why would you want to cook at lower pressure, and cook slower? The tradeoff is convenience and safety. Electric pressure cookers build pressure up to 15 psi, but maintain a lower pressure during cooking, removing any need to monitor heat. Just like the Ronco Showtime Rotisserie 4000, you can just “set it and forget it.”

Natural release involves taking the cooker off heat and allowing the temperature to gradually decrease until the spring-loaded lock disengages. Keep in mind that there could be significant carryover cooking with a natural release technique, depending on how much food you’re cooking.

Quick release, as the name implies, involves removing the weighted jiggler or pressing a button to allow steam inside the cooker to escape. Doing so allows you to stop the cooking immediately, but it also means that the contents of the pressure cooker will boil vigorously. Kenji takes advantage of that boiling to effectively blend his pressure cooker split pea soup without using a blender.

Lastly, there’s the cold water release, which requires running the entire apparatus under cold running water until the cooker depressurizes and the lock disengages. Like the quick release method, the cold water release allows you to access your food effectively immediately. On the other hand, this method doesn’t cause the contents to vigorously boil, which might be desirable for a given recipe. Be aware that the cold water release can’t be used on electric models.

As the writer Andrew Smith once said, “People fear what they don’t understand (and anything that might blow up in their faces)."*** Hopefully this article has convinced you a pressure cooker won’t blow up in your face, and given you some useful information about how they operate and why they deserve a place in your kitchen.

When you get right down to it, using a modern pressure cooker is about as safe as boiling a pot of water. And when used with care and attention, they can elevate your cooking to greater and tastier heights. But that’s best left for another article, so stay tuned.

Pressure relief valves (safety relief valves) are designed to open at a preset pressure and discharge fluid until pressure drops to acceptable levels. The development of the safety relief valve has an interesting history.

Denis Papin is credited by many sources as the originator of the first pressure relief valve (circa 1679) to prevent overpressure of his steam powered “digester”. His pressure relief design consisted of a weight suspended on a lever arm. When the force of the steam pressure acting on the valve exceeded the force of the weight acting through the lever arm the valve opened. Designs requiring a higher relief pressure setting required a longer lever arm and/or larger weights. This simple system worked however more space was needed and it coud be easily tampered with leading to a possible overpressure and explosion. Another disadvantage was premature opening of the valve if the device was subjected to bouncing movement.

Direct-acting deadweight pressure relief valves: Later to avoid the disadvantages of the lever arrangement, direct-acting deadweight pressure relief valves were installed on early steam locomotives. In this design, weights were applied directly to the top of the valve mechanism. To keep the size of the weights in a reasonable range, the valve size was often undersized resulting in a smaller vent opening than required. Often an explosion would occur as the steam pressure rose faster than the vent could release excess pressure. Bouncing movements also prematurely released pressure.

Direct acting spring valves: Timothy Hackworth is believed to be the first to use direct acting spring valves (circa 1828) on his locomotive engine called the Royal George. Timothy utilized an accordion arrangement of leaf springs, which would later be replaced with coil springs, to apply force to the valve. The spring force could be fine tuned by adjusting the nuts retaining the leaf springs.

Refinements to the direct acting spring relief valve design continued in subsequent years in response to the widespread use of steam boilers to provide heat and to power locomotives, river boats, and pumps. Steam boilers are less common today but the safety relief valve continues to be a critical component, in systems with pressure vessels, to protect against damage or catastrophic failure.

Each application has its own unique requirements but before we get into the selection process, let’s have a look at the operating principles of a typical direct acting pressure relief valve.

In operation, the pressure relief valve remains normally closed until pressures upstream reaches the desired set pressure. The valve will crack open when the set pressure is reached, and continue to open further, allowing more flow as over pressure increases. When upstream pressure falls a few psi below the set pressure, the valve will close again.

Most commonly, pressure relief valves employ a spring loaded “poppet” valve as a valve element. The poppet includes an elastomeric seal or, in some high pressure designs a thermoplastic seal, which is configured to make a seal on a valve seat. In operation, the spring and upstream pressure apply opposing forces on the valve. When the force of the upstream pressure exerts a greater force than the spring force, then the poppet moves away from the valve seat which allows fluid to pass through the outlet port. As the upstream pressure drops below the set point the valve then closes.

Piston style designs are often used when higher relief pressures are required, when ruggedness is a concern or when the relief pressure does not have to be held to a tight tolerance. Piston designs tend to be more sluggish, compared to diaphragm designs due to friction from the piston seal. In low pressure applications, or when high accuracy is required, the diaphragm style is preferred. Diaphragm relief valves employ a thin disc shaped element which is used to sense pressure changes. They are usually made of an elastomer, however, thin convoluted metal is used in special applications. Diaphragms essentially eliminate the friction inherent with piston style designs. Additionally, for a particular relief valve size, it is often possible to provide a greater sensing area with a diaphragm design than would be feasible with a piston style design.

The reference force element is usually a mechanical spring. This spring exerts a force on the sensing element and acts to close the valve. Many pressure relief valves are designed with an adjustment which allows the user to adjust the relief pressure set-point by changing the force exerted by the reference spring.

What is the maximum flow rate that the application requires? How much does the flow rate vary? Porting configuration and effective orifices are also important considerations.

The chemical properties of the fluid should be considered before determining the best materials for your application. Each fluid will have its own unique characteristics so care must be taken to select the appropriate body and seal materials that will come in contact with the fluid. The parts of the pressure relief valve in contact with the fluid are known as the “wetted” components. If the fluid is flammable or hazardous in nature the pressure relief valve must be capable of discharging it safely.

In many high technology applications space is limited and weight is a factor. Some manufactures specialize in miniature components and should be consulted. Material selection, particularly the relief valve body components, will impact weight. Also carefully consider the port (thread) sizes, adjustment styles, and mounting options as these will influence size and weight.

In many high technology applications space is limited and weight is a factor. Some manufactures specialize in miniature components and should be consulted. Material selection, particularly the relief valve body components, will impact weight. Also carefully consider the port (thread) sizes, adjustment styles, and mounting options as these will influence size and weight.

A wide range of materials are available to handle various fluids and operating environments. Common pressure relief valve component materials include brass, plastic, and aluminum. Various grades of stainless steel (such as 303, 304, and 316) are available too. Springs used inside the relief valve are typically made of music wire (carbon steel) or stainless steel.

The materials selected for the pressure relief valve not only need to be compatible with the fluid but also must be able to function properly at the expected operating temperature. The primary concern is whether or not the elastomer chosen will function properly throughout the expected temperature range. Additionally, the operating temperature may affect flow capacity and/or the spring rate in extreme applications.

Beswick Engineering manufactures four styles of pressure relief valves to best suit your application. The RVD and RVD8 are diaphragm based pressure relief valves which are suited to lower relief pressures. The RV2 and BPR valves are piston based designs.

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 are cooking pots with a pressure-proof lid. Cooking at pressure allows the temperature to rise above the normal boiling point of water (100 degrees Celsius at sea level), which speeds up the cooking and makes it more thorough.

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).

"Trial of HMS Rattler and Alecto". April 1845. The very lowest pressure exhibited "when the screw was out of the water" (as the opponents of the principle term it) was 34 lb, ranging up to 60 lb., on Salter"s balance.

Be it known that L-WALTON C. Fmnus, a citizen of the United States, residing at Lin- "co"ln. in the county of Lancaster and State of Nebraska, have invented a new and Improved Safety-Valve for Pressure-Cookers,

" Mypresent invention has for its purpose to provide an improved safety valve, which, while adapter for uses for which blow-ofi" valve devices are usually employed, is more particularly designed for use in connection with high pressure steam cooking utensils.

In the use of safety or blow-off valve devices on high steam pressure cookers, it is essential that the construction of the valve and the adjustments thereof be so simple that any housewife may quickly and conveniently handle the same.

Among other objects my invention has for its purpose to provide a safety valve device of the general character stated, that can be remo-vably applied to a pot or kettle cover and which includes an improved and easily manipulated means for determining the pressure",within thecooker and which takes the place of a pressure gage.

In its more subordinate features, my improved safety valve devices embody the peculiar combination and novel arrangement of .parts hereinafter fully explained, specifically pointed out in the appended claims and illustrated in the accompanying drawings, in which Figure 1 is a perspective view of a high pressure steam cooker with my improv safety valve operatively applied thereon.

Fig. 2 is a vertical section of the valve device and a portion of the cooker cover, the shiftable needle valve being at the normal or closed position.

Fig. 4 is a side elevation of a portion of the valve body and illustrates the adj ustable" cap, as set for holding the needle valveclosed against steam pressure Within the kettle up to 20 lbs.

In the drawings I have illustrated a high pressure cooker of that type for which my safety valve is particularly designed and which includes a kettle or pot 11 and a cover 22 that has a rim for fitting steam tight down onto the pot ledge 33.

view of the said valve readily adapted for The cover 22 includes a central posted wlnch constitutes an abutment for receiving Patented Jan. 20, 1920. v

the lower end of a clamp screw 55 that H passes through a threaded bore in a hub portion 66 which forms apart of a bail-like handle 77 the arms of which straddle the post. 44 and engage stud pintles 88 formed orotherwise fixcdlyattached to the kettle, as shown.

is especially designed for use with a cooker of the type shown and described, it is to be understood that the use, is not limited to such specific type of cooker, since it may be use in connection with the top or covers of. other. types of high pressure coo-king utensils.

My improved safety valve, the construction of which is clearly shown in Figs. 2 and 4, comprises a"bowl-shaped body 4; in the bot-v tom of which is located a raised valve seat 8, which hassquared and knife like edges to prevent the formation of a water cushion that causes a slight leak.

and they are so located around the valve seat as to drain all condensation away from the valve"seat 8 as well as allow the escape of the steam from the valve seat and enters the bowl 4.

3 desi that snugly adjustable along the that screws through the spiral thread 40 Cap 3 has a knurled head portion 31 and is formed with a tubular vertical extension or tower 35 that has an aperture 36 in the upper end thereof which constitutes a passage for the needle valve 2 that ex ends beyond the said apertured end of the tower 35 and terminates ina finger piece 25.

Finger piece 25 constitutes a handy means for lifting the valve 2 to relieve the vacuum created in the pressure cooker. when the same has been allowed to cool with the cover on tight.

" shown and described, it will be noted that the same is outside and away from the steam and possible discharge and it is protected against possible blows by the tapered projection of the cap 3.

The lower end of the spring 1 is attached to the cap 3 by passing the same through a small hole 37 in the cap top and bending said tofp, to which it is over the inside of the secured by puttinga drop 0 older thereon. The body 4 has a pendent threaded extension 41 for screwing into a threaded aperture provided therefor in the cooker cover.

Valve 2 has a pin-likeextension 6" at the lower end, which serves as a guide for placing the valve on the seat 8 and also for clearing the intake hole of bits of food, it being understood that by slipping the upper end 10 of the spring 1 from the shouldered por- .tion- 21 of the valve stem, the valve? may be readily withdrawn when-it is to be used for clearmg the escape holes 7-7, as above l mentioned.

When the cap 3 is screwed down 11 on the bowl 4 in which the valve seat "8 is ocated, the pressure of the tension spring 1 on the valve "2. is increased and, when the said cap 3 is screwed off, the pressure on the said spring is decreased.

TlllS arrangement of parts makes it posslble to determine the steam pressure within the cooker, at any time, by simpl turning the cap 3 back until the steamgins to escape, which operation constitutes a substitute fora pressure age. An advanta e of t 1s located an works-concentrically about the needle valve 2, causing little friction and therefore. sensitive opening and closing of the safety valve. I

mg a tension spring, through use or accident, it can only become weaker, thereby causing the valve to blow-0E at a lower pressure and making the possibility of. accumulation of a dangerous amount of steam pressure within the cooker i n ossible.

It will be noticed that the va ve 2 has but one guide, that at the upper end of the pro- JeCtlOfl 35 and that guide a loose fitting one and located at a considerable distance from I indicate the popping ofi" pressure at-dilferent pomts in one revolution e0,-

P pp 1 valve stem guide, e sprlng 1 is that it the valve seat "8, such arrangement making the chance of gumming up and" possible slu gish action of the valve, improbable.

l he pin 9 in the cap 3 and the quick act in spiral thread 40 cut, in the bowl are provided for economy in manufacture and also keeps the pressure exerted against the cap, at times, from blowing the-cap oil and, as but a single pin 9, at one side is used, 1t causes the cap 3 to bind slightly.

1. In a device of the character described, a bowl having a valve seat passage adapted to communicate with the cooker chamber, a cap fitted over the bowl and having a valve stem guide, a valve mounted with its stem in the said guide and adapted to close said valve seat passage, and a tension device c0nnectin said valve with thesaid"cap, said bowl having provision for the escape of steam, when the valve seat passage is open,

bowl having provision for the escape of steam, when the valve seat passage is open, means for holding said cap on said bowl in different positions, or diminish the effect of said tension device according to the position of the said cap, said cap and said bowl having provision for 1 indicating the degree of said tension, where by to gage the steam pressure in the cooker.

3. A safety valve forsteam cookers comprising a, bowl-shaped body having a valve seat passage adapted to communlcate with the cooker chamber and an external splral thread,a cap fitted on the bowl and having a pin connection for engaging the splral thread in the bowl, the said cap having a a valve m