It is common for fluid mediums such as compressed gas, liquids, or steam to be damaged or malfunction when overpressure is present. It may be caused by failed controlled systems, faulty parts, human error, or some combination of these. The purpose of a safety valve is to protect critical components from malfunctions or damages, which can lead to human injury or death.
Because of this, safety valves are operated by the fluid media being controlled, and they have only mechanical parts. In other words, the valves even work when pneumatic or electronic control systems fail.
In several industries, safety valves serve a wide range of purposes. Among other things, it is available in a variety of sizes, designs, operating temperatures, and pressures. Let’s first understand how safety valves work and the types that are commonly used before we explore the areas where they are used.
Working Principles of Safety Valves
It is easiest to think of a safety valve as a mechanical, medium-actuating pressure-reducing/removing device. As a safety procedure, it opens up a valve and releases excess pressure to prevent damage to the system. Ports at the inlet and discharge are often designed differently. It is easier and more convenient to reduce excess pressure this way.
Safety valves open fully once the system pressure reaches a given level, and they remain open until the pressure drops back to normal. For optimal performance, the safety valves must be selected, sized, installed, and maintained properly.
Safety valves are fast-acting, unlike relief valves that proportionally release fluid medium to maintain pressure. It takes them only a few seconds to open the valve, resulting in almost an instant reduction in pressure. Additionally, they require no external intervention, unlike a relief valve that must be controlled.
Safety valve types and descriptions
Safety valves come in three main types: spring-load mechanisms, pilot-operated valves, and balanced bellows valves. Listed below are three types of three-valve valves.
1. Mechanisms that are spring-loaded in pumps
An injection system of this type contains a spring, a nozzle, and a popper valve. You can install it for pressures ranging from 1 bar to 1400 bar. Using the spring force, the valve opens and closes. Popper valves are also controlled by the force of the medium on them, also called input force. This is determined by the available surface area of the popper valve and the inlet pressure.
Variations of these valves are also available, each designed to handle a specific type of liquid or gas. In terms of determining the operation of a poppet valve, its shape is crucial. There are also some models that contain a lifting chamber, which helps to lift the excess pressure and saves time and effort. A limitation of this type of valve is its strong susceptibility to backpressure, which may compromise its safety. During the flow of fluid from the safety valve, backpressure builds up at the outlet of the valve.
2. Balanced bellows valves
Safety valves of this type solve the problem of backpressure caused by spring-loaded valves. By incorporating metal bellows into the design, the poppet valve’s top and bottom surfaces are able to exert more pressure, which reduces backpressure.
A spring mechanism may be isolated from the media thereby preventing any effect of the media on the spring force. However, this type of safety valve also has a limit beyond which back pressure cannot be exceeded. As an example, most types don’t operate beyond 15.9 bars, the maximum backpressure.
3. A safety valve that is pilot-operated
Inlet pressure is used to press the poppet valve onto the nozzle with a pilot-operated safety valve. As long as the inlet pressure is below the predetermined/set pressure, this valve will remain closed.
When the inlet pressure exceeds the maximum allowable working pressure (MAWP), the valve opens, allowing the media to flow. In the event that the pressure drops to normal again, the valve will close.
An overview of safety valve applications
A safety valve is most commonly used in industries that deal with compressed gases, steam, and liquids. The following are among them:
- Petroleum companies – for example, oil companies that deal with petroleum products.
- Power plants and heat exchangers use safety valves to prevent fires, explosions, and other safety hazards.
- Industries such as refineries and paper mills.
- Industries involved in food processing.
- A chemical and pharmaceutical industry.
- Both air and water pressure boosters.
- Industrial boilers and steam boilers.
The bottom line
In nearly every industry where compressed air, steam, or liquid can overpressurize equipment, safety valves play a critical role. A safety valve can be classified as one of three types. Despite their wide range of working pressure, spring-loaded valves suffer from backpressure. Backpressure is solved by safety valves with balanced bellows, while pilot-operated safety valves prevent leaks.
Consider the set pressure, discharge capacity, backpressure, lining materials, and operating temperatures when choosing a safety valve. As well as industry certifications, product warranties, and the manufacturer’s reputation, other factors to consider are the manufacturer’s experience and reputation in the industry.