NEWS

The set pressure (also known as opening pressure or calibration pressure) of marine safety valves is not a fixed value. It strictly depends on the design working pressure of the specific protected equipment and applicable ship regulations/standards.

 

Core Principles:

 

Set Pressure ≤ Equipment's Maximum Allowable Working Pressure (MAWP):

This is the fundamental requirement. The safety valve must open before equipment pressure exceeds its safety limit.

 

Equal to or Slightly Below MAWP:

 

Typically, set pressure equals the Maximum Allowable Working Pressure (MAWP) under operating conditions.

 

According to specific codes/standards (e.g., ASME, PED, Class Society rules), set pressure may approach but must not exceed MAWP. Examples:

 

ASME Code may permit 100%–103% of MAWP (under specific conditions).

 

EU Pressure Equipment Directive (PED) usually requires set pressure ≤ MAWP.

 

Critical point: The safety valve must reliably open and achieve full discharge capacity before pressure reaches or exceeds MAWP.

 

Determining Factors:

 

Type and Design Parameters of Protected Equipment:

 

Boilers: Based on boiler design pressure. Typically includes main/auxiliary safety valves with slightly different settings (e.g., main valve at MAWP, auxiliary valve marginally higher). Superheater safety valves usually have lower settings than main valves.

 

Pressure Vessels (air receivers, purifiers, hot wells, etc.): Directly based on the vessel’s MAWP.

 

Compressed Air Systems: Based on compressor outlet or air receiver design pressure.

 

Steam Piping: Based on piping design pressure.

 

Hydraulic Systems: Based on pump max. output pressure or system design pressure.

 

Fuel/Lubricating Oil Systems: Based on pump pressure or relevant vessel design pressure.

 

Applicable Codes & Standards (Most Critical):

 

International Conventions: SOLAS (International Convention for Safety of Life at Sea) mandates general requirements for critical systems (e.g., boilers, pressure vessels).

 

Class Society Rules: The most authoritative design/construction/inspection basis. Major societies (DNV, LR, ABS, BV, CCS, KR, NK, RINA, etc.) specify detailed requirements, calculation methods, and tolerances (typically ±1% or ±3%).

 

National Regulations: Flag state laws.

 

International/National Standards: e.g., ISO 4126 series (safety valves), ASME BPVC (boilers), EN ISO. Often referenced in Class rules.

 

Key Summary:

 

Core Requirement: Set Pressure ≤ MAWP, ensuring full opening before MAWP is reached.

 

Code Dependency: Values must follow equipment design parameters and the vessel’s Class Society rules. No universal "marine safety valve set pressure" exists.

 

Equipment Specificity: Settings vary by equipment type (boiler, air receiver, piping, etc.).

 

Precision Setting & Verification:

 

Must be set/verified by certified personnel using calibrated equipment (via cold test bench).

 

Set pressure is marked on the valve body/nameplate.

 

Terminology Clarification:

 

Set Pressure: Theoretical value at which lifting/continuous discharge begins.

 

Opening Pressure: Measured pressure at which discharge becomes detectable (may slightly deviate from set pressure).

 

Reseating Pressure: Pressure at which valve closes (typically < set pressure).