BS ISO 4126-10:2010

This standard BS ISO 4126-10:2010 Safety devices for protection against excessive pressure is classified in these ICS categories:

• 23.060.40 Pressure regulators
• 13.240 Protection against excessive pressure

This part of ISO 4126 specifies the sizing of safety valves for gas/liquid two-phase flow in pressurized systems such as reactors, storage tanks, columns, heat exchangers, piping systems or transportation tanks/containers. The possible fluid states at the safety valve inlet that can result in two-phase flow are given in Table 1.

NOTE The expression “safety valve” is a synonym for valves as described in ISO 4126-1, ISO 4126-4 and ISO 4126-5.

Table 1

Possible fluid state at the inlet of the safety valve that can result in two-phase flow

Fluid state at valve inlet	Cases	Examples
liquid	subcooled (possibly flashing in the safety valve) saturated with dissolved gas	cold water boiling water CO2/water
gas/vapour	near saturated vapour (possibly condensing in the safety valve)	steam
gas/liquid	vapour/liquid non-evaporating liquid and non-condensable gas (constant quality) gas/liquid mixture, when gas is desorbed or produced	steam/water air/water