Safety Valve-Basic Type - China Donjoy

Application

&#;The safety valve is used to protect the flow pressure safety through pipes, pumps, accessories, pools, etc.
&#;With sanitary and safe design, it's avoid operation danger and equipment failure caused by exceed pressure.
&#;With sanitary design and completely material of stainless steel, the valves is the best choice for protection of equipments in diary, food, beverage, pharmaceutical and fine chemical industries.

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Operating Principles

Manual fast row safety valve features: you can open the valve manually, the spot cleaning (used together with the pump channel) can allow the fluid to pass through
&#;Under normal operating conditions, the valve remains closed.
&#;The specific pressure is set by adjusting the spring pressure nut.
&#;When the pressure in the pipes is exceed the specific pressure, the valve will open automatically to make the liquid pass over,so that pressure in the pipeline is reduced.
&#;The valve can be operated with handle . When the handle remains open on the operation spot, the detergent can flow though the flow valves.

 Technical Specifications

&#;Size&#;1"-4",DN25-DN100
&#;KV Value&#;8.5-180m3/h
&#;Max. temperature&#;130&#;(EPDM)/266&#;
&#;Set pressure&#;(0-3bar/0-6bar/6-10bar&#;
&#;Material&#;304/316L
&#;Certification: safety valve manufacturing license for special

Introduction to Safet&#;y Valves

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

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

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

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

The primary function of a safety valve is therefore to protect life and property.

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

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

• An imbalance of fluid flowrate caused by inadvertently closed or opened isolation valves on a process vessel.
• Failure of a cooling system, which allows vapour or fluid to expand.
• Compressed air or electrical power failure to control instrumentation.
• Transient pressure surges.
• Exposure to plant fires.
• Heat exchanger tube failure.
• Uncontrollable exothermic reactions in chemical plants.
• Ambient temperature changes.

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.

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

A listing of the relevant national standards can be found at the end of this module.

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.

The ASME/ANSI PTC25.3 standards applicable to the USA define the following generic terms:

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

This is a general term, which includes safety valves, relief valves and safety relief valves.

• Safety valve - A pressure relief valve actuated by inlet static pressure and characterised by rapid opening or pop action.

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

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

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

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

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

The European standard EN ISO -1 provides the following definition:

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

Typical examples of safety valves used on steam systems are shown in Figure 9.1.1.

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