Emission Control
Figure 4 : Tank pressure / vacuum vents open to relieve pressure to the atmosphere , or to pull in air to break the tank vacuum ( Emerson ’ s Enardo™ Series ES-950 Pressure / Vacuum Relief Valve shown ). These devices should only activate rarely , but they must operate reliably when called into service , with zero leakage at all other times .
The key design features for this equipment are very reliable operation despite remaining inactive for months and even years , and near zero leakage when not in operation . Higher-tier products have leakage rates of less than 0.1 SCFH at 90 % of the set point .
Emergency vents
Ideally , an emergency tank vent ( Figure 5 ) should never come into service , but if an abnormal fire or pressure event occurs , the vent will relieve the vapour load to protect the tank . Typically , these devices incorporate a large , weighted disk that only opens under high over-pressure conditions . The key design feature for these devices is a weighted lever assembly that opens within a tight tolerance of the set pressure , while maintaining a leak-proof seal . Given the narrow operating range of the tank pressure controls , this device is usually required to provide a sealing performance of less than one SCFH of leakage at 90 % of the pressure setpoint .
Conclusions
Sizing these devices and coordinating their operation takes knowledge and expertise . Design professionals who are unfamiliar with these processes and equipment specifications should consult with their tank pressure equipment vendor . This will help them better understand their options so they can
Figure 5 : Emergency tank vents ( Emerson ’ s Enardo™ Model 2000 Emergency Relief Vent shown ) typically only actuate under extreme pressure events , which require very high flow capacities . When not in use , these vents must maintain minimal leakage at 90 % of setpoint .
select the right combination of devices for a particular application . A welldesigned system will provide years of reliable service , while minimising nitrogen usage and environmental emissions , but a poorly designed system can place a tank and the surrounding environment at considerable risk .
Figures all courtesy of Emerson
48 Valve World March 2025 www . valve-world . net