A safety valve — also called a pressure safety valve — is a critical component in any pressurized piping system. Whether you're working with steam, water, air, or gas, a safety valve automatically releases excess pressure to prevent equipment damage or catastrophic failure. There are two main types commonly used in industrial and mechanical applications: the lever type safety valve (with lever) and the no-lever safety valve (screwed cap type). Understanding the difference is essential for selecting the right valve for your system.

A safety valve serves one primary purpose: to protect pressurized systems from over-pressure conditions. When internal pressure reaches the pre-set level (known as the set pressure), the valve opens automatically to discharge fluid or gas, then closes again once pressure returns to a safe level.

Key properties of a well-functioning safety valve include:

• Set pressure accuracy - Opens precisely at the designated pressure, no earlier or later
• Tight shutoff - Closes completely without leaking once pressure normalizes
• Fast response - Opens and closes rapidly (snap action) to minimize pressure fluctuation
• Environmental compatibility - Resistant to the temperature, pressure, and fluid type of the specific system
• Appropriate material - Brass for general water and low-pressure applications; stainless steel for corrosive or high-temperature environments

Two Main Types of Safety Valves

Safety valves used in industrial and commercial applications are broadly divided into two configurations based on their actuation mechanism:

• Lever Type Safety Valve - Features a protruding lever handle that allows manual operation and testing
• No-Lever Safety Valve  - Uses direct spring force on the valve disc, sealed with a fixed cap; no manual actuation

How Each Type Works

Lever type safety valves transfer force to the valve disc via a mechanical lever arm. This design allows operators to manually lift the lever to test valve function or manually relieve pressure without waiting for system pressure to reach the set point. This is particularly important in steam and compressed air systems where regular operational testing is required by safety standards.

No-lever safety valves rely entirely on calibrated spring tension pressing directly against the valve disc. The screwed cap protects the spring adjustment mechanism and prevents tampering. Because there is no external lever, the valve is more compact and less susceptible to vibration-induced leakage, making it well-suited for liquid systems or space-constrained installations.

How to Choose the Right Safety Valve

• Choose lever type if your system uses steam, compressed air, or gas — or if regulations require periodic manual valve testing
• Choose no-lever type if your system uses water, oil, or other liquids, and manual activation is not required
• Check material compatibility — brass suits most general applications; stainless steel is better for chemicals or high temperatures
• Verify set pressure rating matches your system's maximum allowable working pressure (MAWP)
• Confirm thread standard — most applications in Thailand and Asia use BSP (British Standard Pipe) fittings