Stainless Steel Threaded Safety Valve: Features, Selection and Installation

Pressure vessels, boilers and pipelines can be seriously damaged if the operating pressure exceeds its permitted limit, which also endangers personnel. A stainless steel threaded safety valve is a safety device that opens automatically against its spring when the system pressure reaches the set pressure, relieves the excess pressure and recloses once the pressure returns to normal. Its stainless steel body and internals make it suitable for corrosive media and hygienic applications.

“Threaded” means the valve is screwed into the installation; this type is generally used in small and medium-size applications.

How Does It Work?

The valve disc is pressed onto its seat by an adjustable spring. When the force of the system pressure on the disc exceeds the spring force, the disc lifts and the fluid is discharged through the outlet. When the pressure falls somewhat below the set pressure (reseating pressure), the spring pushes the disc back onto the seat. A lifting lever allows the valve to be tested manually.

Why Is It Important?

• Equipment protection: Protects pressure vessels, boilers, heat exchangers and pipelines from overpressure damage.
• Personnel safety: Prevents dangerous situations such as bursts and sudden leaks.
• Last line of defence: It is the final mechanical safety element that acts when control devices such as pressure reducers or pressure switches fail.

Technical Data

The values below apply to the Ayvaz L9-LSP stainless steel safety valve series supplied by ORFA:

Because the set range depends on the spring, the required set pressure and its spring range should be specified when ordering.

Applications

• Steam boilers and hot water systems
• Compressed air and gas lines
• Chemical and petrochemical process plants
• Food and pharmaceutical equipment
• Heating and cooling systems

Selection Criteria

• Set pressure: Must not exceed the maximum allowable working pressure of the protected equipment.
• Relieving capacity: The valve must be able to discharge the worst-case flow (e.g. the steam output of the boiler); do not select by pipe size alone.
• Fluid and temperature: Check material and sealing compatibility with the fluid and temperature.
• Back pressure: Back pressure in the discharge line can affect the opening behaviour.

Installation and Maintenance

1. Install the valve vertically, as close as possible to the protected equipment.
2. Never fit an isolating valve between the equipment and the safety valve.
3. The inlet pipe must not be smaller than the valve inlet; route the discharge line to a safe point where it cannot injure people.
4. Test the valve periodically with the lifting lever and have it inspected by competent persons.

Frequently Asked Questions

Conclusion

With corrosion-resistant construction and a wide temperature range, stainless steel threaded safety valves provide reliable overpressure protection in steam, water, air and gas systems. Correct set pressure, sufficient relieving capacity and proper installation are the basis of safety. For other models, see our Safety Valves page.