Pressure relief valves are essential safety devices used to counter an overpressure event in a pressure vessel or piping system. They are fail-safe devices; when the pressure reaches the designated limit known as maximum allowable working pressure (MAWP), the valve releases pressure to avoid over-pressurization. Robust safety protocols are imperative for running pressure vessels efficiently and hazard-free.
Therefore, paying attention to the pressure relief valves with an adequate safety assessment is vital. It is equally important to ensure the pressure relief valves are compatible in terms of size, material, and quality for optimal operation.
Introduction to Pressure Relief Valves
Initially developed in the industrial revolution to mitigate explosions in steam boilers, pressure safety relief valves are widely used in an array of areas like water treatment systems, chemical plants, and others.
Typically, a pressure relief device discharges excessive developed system pressure through an outlet into a relief discharge area to maintain normal operating conditions. This entails a discharge system that allows for the pressure relief valve to allow a rated flow capacity through the valve and for the valve to then close once pressure has reduced back to normal.
It’s worth noting that safety valves and relief valves are not synonymous; they differ in their reaction time. Safety valves respond rapidly to open at the required set pressure, while relief valves open gradually.
For proper operations and under normal circumstances, the valves open at or below the maximum allowable working pressure (MAWP) of the pressure vessel or system. The system’s MAWP ought to be at a minimum level of 10% higher than the highest expected operating pressure.
How to Choose the Correct Pressure Relief Valve
Choosing the right pressure safety relief valve can be a challenging task. However, there are several aspects to consider that will ease the process.
The function of the valve
The intended function of a safety valve will determine the requirements for the size and type. The size will include the connection size to the piping system and the variation of the inlet connection. A correctly sized valve must be at least as big as the inlet and discharge piping.
The material of the valve
The material of the valve is important to ensure compatibility with the process fluid in the system as well as ensuring the suitability for the pressure and temperature conditions. This plays an essential part in the safety and durability of the valve. A poor choice could lead to unnecessary wear and tear and even safety concerns. For instance, non-ferrous materials are better suited for corrosive media compared to carbon steels. Valves in stainless steel and bronze material are available to suit possible corrosion issues.
Specific system conditions
In choosing a safety relief valve, it is vital to consider the system conditions in the pressurised vessel. This is the ‘how’ and ‘what’ involved in the system’s operation. It entails the degree of pressure and temperature the valve is expected to experience should an overpressure event occur.
It is critical to determine the temperature and pressure at the valve’s location. This will be helpful to avoid a mismatch of valve types and possible adverse repercussions. Different valve materials can withstand varying conditions. In metal valves, steel can withstand higher temperatures than bronze.
Types of Safety Relief Valves
The standard design safety relief valve incorporates a spring-loaded disc that is held closed against a seat or nozzle fitted to the valve body. The spring is adjustable through a screw mechanism to control the load that the spring exerts on the disc which subsequently ‘sets’ the pressure at which the valve will open.
For corrosive fluids or applications where back pressure from the discharge piping will affect the pressure that the valve will open at, a bellows design safety relief valve should be used. In a bellows safety relief valve, a flexible corrosion resistant element protects the bonnet, spring and stem of the valve from the process fluid.
Pilot-operated safety relief valves are also available where the set pressure for the valve is controlled by a separate pilot valve. This type of safety relief valve uses the line pressure through the pilot valve to hold the disc or piston in the main relief valve closed. Pilot operated safety relief valves offer a high degree of seat tightness, especially as the set pressure is being approached.
Vacuum safety valves
A vacuum safety valve is an air pressure safety valve designed as a preventive safety measure to stop the collapse of a vessel or container during the emptying process. These pressure safety valves also counter the danger of containers collapsing during a cleaning procedure known as hot SIP (sterilisation-in-place) or CIP (clean-in-place). This happens when cold water is used for rinsing after sterilisation in hot temperatures.
Related: The Reasons Why Air Valves are Needed in Water Application: Read in under 5 minutes.
Safety protocol for maintenance
Pressure relief valves are used for maintaining safety measures in a pressure vessel or pressurised system. Regular scheduled maintenance with adequate safety protocol is, therefore, a priority.
It is essential to consider:
- Compliance of the valve with the safety protocols for the system
- Estimated durability or longevity of material required
- Convenience and system stability
As a leading provider for pressure safety relief valves, John Valves prides itself on providing an array of certified, premium quality products. We also provide technical assistance to help you make the right choice of safety valve from our extensive selection. Contact our friendly team here for inquiries.