In order to achieve full opening from this small overpressure, the disc arrangement has to be specially designed to provide rapid opening. This is usually done by placing a shroud, skirt or hood around the disc. The volume contained within this shroud is known as the control or huddling chamber.

Our controllers can be used simply as an on-demand controller for your recirculation pump or, once configured using either an iPhone, iPad, or Android smart device; it can be configured via timers to keep the recirculation loop hot between specific times of day and on specific days of the week (up to 10 timers can be set).

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The design of the shroud must be such that it offers both rapid opening and relatively small blowdown, so that as soon as a potentially hazardous situation is reached, any overpressure is relieved, but excessive quantities of the fluid are prevented from being discharged. At the same time, it is necessary to ensure that the system pressure is reduced sufficiently to prevent immediate reopening.

For most countries, there are independent bodies who will examine the design and performance of a product range to confirm conformity with the relevant code or standard. This system of third party approval is very common for any safety related products and is often a customer requirement before purchase, or a requirement of their insurance company.

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This incremental increase in opening force overcompensates for the increase in spring force, causing rapid opening. At the same time, the shroud reverses the direction of the flow, which provides a reaction force, further enhancing the lift.

Safety valves used in Europe are also subject to the standards associated with the Pressure Equipment Directive (PED). Being classified as ‘Safety accessories’, safety valves are considered as ‘Category 4’ equipment, which require the most demanding level of assessment within the PED regime. This can usually be met by the manufacturer having an ISO 9000 quality system and the safety valve design and performance certified by an officially recognised approval authority referred to as a ‘Notified Body’.

These combined effects allow the valve to achieve its designed lift within a relatively small percentage overpressure. For compressible fluids, an additional contributory factor is the rapid expansion as the fluid volume increases from a higher to a lower pressure area. This plays a major role in ensuring that the valve opens fully within the small overpressure limit. For liquids, this effect is more proportional and subsequently, the overpressure is typically greater; 25% is common.

The additional pressure rise required before the safety valve will discharge at its rated capacity is called the overpressure. The allowable overpressure depends on the standards being followed and the particular application. For compressible fluids, this is normally between 3% and 10%, and for liquids between 10% and 25%.

Standards relevant to safety valves vary quite considerably in format around the world, and many are sections within codes relevant to Boilers or Pressure Containing Vessels. Some will only outline performance requirements, tolerances and essential constructional detail, but give no guidance on dimensions, orifice sizes etc. Others will be related to installation and application.

The actual requirements for approval will vary depending on the particular code or standard. In some cases, revalidation is necessary every few years, in others approval is indefinite as long as no significant design changes are made, in which case the approval authority must be notified, and re-approval sought. In the USA, the National Board of Boiler and Pressure Vessel Inspectors represents the US and Canadian government agencies empowered to assure adherence to code construction and repair of boilers and pressure vessels.

When the inlet static pressure rises above the set pressure of the safety valve, the disc will begin to lift off its seat. However, as soon as the spring starts to compress, the spring force will increase; this means that the pressure would have to continue to rise before any further lift can occur, and for there to be any significant flow through the valve.

If you have a circulation pump installed, you don’t need to replace it – we have controllers to turn your system into a smart hot water recirculating pump. With a combination of smart timer technology, you’ll never have to worry about high water or energy bills from your hot water system again.

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

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Many cities provide rebates and incentives for installing a recirculating pump because they save water, however, your hot water recirculation system is working nonstop, ultimately driving up your energy bill, so it ends up being a costly luxury.

We’ve all had those moments when we let the water run for 30 seconds or sometimes even a few minutes before any hot water came out of the faucet. With a hot water recirculation system, this will no longer be an issue.

Any pressurised system requires safety devices to protect people, processes and property. This tutorial details situations when overpressure may occur, the wide and often confusing types of device on offer, how such devices operate and the many codes, standards and approval authorities to note.

When water sits in a pipe, it begins to drop in temperature from heat loss, quickly matching the temperature of the pipes. Therefore, typical recirculation systems constantly run water through the pipes to keep them heated. When the water is recirculated through the system, it doesn’t get a chance to cool down, offering a constant flow of hot water. However, there are some drawbacks to this.

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

The basic elements of the design consist of a right angle pattern valve body with the valve inlet connection, or nozzle, mounted on the pressure-containing system. The outlet connection may be screwed or flanged for connection to a piped discharge system. However, in some applications, such as compressed air systems, the safety valve will not have an outlet connection, and the fluid is vented directly to the atmosphere.

* designed and manufactured in the U.S.A with U.S. and foreign made components (most semiconductor manufacturing is done overseas)

minimising the overpressure value but correspondingly requiring a greater blowdown before the valve re-seats. When the lower blowdown ring is adjusted to its lower position there is minimal restriction in the huddling chamber and a greater overpressure will be required before the valve is fully open but the blowdown value will be reduced.

The valve inlet (or approach channel) design can be either a full-nozzle or a semi-nozzle type. A full-nozzle design has the entire ‘wetted’ inlet tract formed from one piece. The approach channel is the only part of the safety valve that is exposed to the process fluid during normal operation, other than the disc, unless the valve is discharging.

The on-demand controller is contained within the utility closet and activates hot water delivery from any plumbing fixture on-demand and/or with the use of Smart Timers. Owners control the settings of the Smart Recirculation Control units via a smartphone app to ensure your system only runs when you need it.

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

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For steam boiler applications there are very specific requirements for safety valve performance, demanded by national standards and often, insurance companies. Approval by an independent authority is often necessary, such as British Engine, TÜV or Lloyd’s Register.

Once normal operating conditions have been restored, the valve is required to close again, but since the larger area of the disc is still exposed to the fluid, the valve will not close until the pressure has dropped below the original set pressure. The difference between the set pressure and this reseating pressure is known as the ‘blowdown’, and it is usually specified as a percentage of the set pressure. For compressible fluids, the blowdown is usually less than 10%, and for liquids, it can be up to 20%.

The disc is held against the nozzle seat (under normal operating conditions) by the spring, which is housed in an open or closed spring housing arrangement (or bonnet) mounted on top of the body. The discs used in rapid opening (pop type) safety valves are surrounded by a shroud, disc holder or huddling chamber which helps to produce the rapid opening characteristic.

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As lift begins (Figure 9.1.6b), and fluid enters the chamber, a larger area of the shroud is exposed to the fluid pressure. Since the magnitude of the lifting force (F) is proportional to the product of the pressure (P) and the area exposed to the fluid (A); (F = P x A), the opening force is increased.

The closing force on the disc is provided by a spring, typically made from carbon steel. The amount of compression on the spring is usually adjustable, using the spring adjuster, to alter the pressure at which the disc is lifted off its seat. Standards that govern the design and use of safety valves generally only define the three dimensions that relate to the discharge capacity of the safety valve, namely the flow (or bore) area, the curtain area and the discharge (or orifice) area (see Figure 9.1.4).

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

Furthermore, different designs are required to meet the numerous national standards that govern the use of safety valves.

Full-nozzles are usually incorporated in safety valves designed for process and high pressure applications, especially when the fluid is corrosive.

When you want hot water, simply turn the faucet on then off, wait a few seconds and the system sends the hot water to your faucet.

Conversely, the semi-nozzle design consists of a seating ring fitted into the body, the top of which forms the seat of the valve. The advantage of this arrangement is that the seat can easily be replaced, without replacing the whole inlet.

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The lower blowdown ring is also factory set to achieve the appropriate code performance requirements but under certain circumstances can be altered. When the lower blowdown ring is adjusted to its top position the huddling chamber volume is such that the valve will pop rapidly,

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

Constantly running hot water can also cause copper pipes to erode. This can lead to pinhole leaks in your pipes, which will then need replacement, as well as cause water damage to your home.

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

The basic spring loaded safety valve, referred to as ‘standard’ or ‘conventional’ is a simple, reliable self-acting device that provides overpressure protection.

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

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2. Curtain area - The area of the cylindrical or conical discharge opening between the seating surfaces created by the lift of the disk above the seat. The diameter of the curtain area is represented by dimension ‘d1’ in Figure 9.1.4.

The blowdown rings found on most ASME type safety valves are used to make fine adjustments to the overpressure and blowdown values of the valves (see Figure 9.1.8). The lower blowdown (nozzle) ring is a common feature on many valves where the tighter overpressure and blowdown requirements require a more sophisticated designed solution. The upper blowdown ring is usually factory set and essentially takes out the manufacturing tolerances which affect the geometry of the huddling chamber.

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1. Flow area - The minimum cross-sectional area between the inlet and the seat, at its narrowest point. The diameter of the flow area is represented by dimension ‘d’ in Figure 9.1.4.

Basically saved my wallet! Gas bill went from over $100 to $32.00 in the first month. No more worrying about the pump running all the time and what damage maybe occurring to plumbing and fixtures, not to mention just wasting energy like crazy. Best investment I’ve made and hot water on demand. Love it!

On-demand recirculating systems can help you save money on your electric bill and water bill, and you also have the added benefit of not having to wait for hot water.

Leridian Dynamics sells the 2006SN10 three speed pump that works great with our on demand controls. It is offered as an option when purchasing our controller.

This is an amazing product that helps you save water and energy while providing the luxury of immediate hot water at your fingertips. The design is elegantly simple and genius. I would not consider a hot water recirculation loop system without the Leridian control system.

On-demand systems only pull hot water when necessary; smart recirculation pumps typically run less than 30 minutes a day.

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

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

On-demand hot water recirculating pumps work with one key difference: your water isn’t constantly recirculating, and you save energy and money.

If you’re not sure which pump is right for your home or business, please read our article “Hot Water Recirculation Pump Recommendations: What’s Best for Your Situation” to help you ensure you’re installing the best pump to deliver hot water with the speed and volume you expect from your new or existing plumbing.

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

This product is simply genius. It revolutionizes the hot water on demand market. Circulating pumps have been sold for years bragging instant hot water and little water waist while waiting for hot water. When we bought this house that had one installed, I was very happy to save water and have instant hot water. That was until I did some research that revealed I am using massive energy by running the pump 24-7 and energy to keep that water hot in the line.  All that waist for the convivence having instant hot water a few times a day. Sure, it did save some water but a very high cost to me and the environment. So, I added a timer to my pump to turn it on morning and evenings when I was more likely to use hot water. Better, but still not that efficient.  I have searched for remote on demand systems that I could add to be more efficient, but they all had issues like hard to install, hard to remember if it was left on or off, WIFI or Bluetooth issues, need to use apps or find a good location(s) for control(s).  Then I ran across this product. Are you kidding me! No fumbling with buttons or apps – just turn the hot water on for a second to get the pump pumping. Brilliant!! Only pumps when you ask for it and need it.  This checks all of the environmental boxes. Absolutely saves water. Use the absolute minimum energy to deliver the hot water – ONLY when needed. The Smart control 32 should be required with every recirculating pump sold.

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