94221 Emergency Vent & Manhole Cover (Pressure & Vacuum)

The Shand & Jurs 94221 Emergency Vent and Manhole Cover provides emergency relief of excessive internal pressure and vacuum beyond that provided by tank conservation vent requirements.

This weight loaded vent utilizes Expanda-Seal diaphragms which provide tight seals between pallets and seats. Special diaphragm materials are available for vents subjected to severe low temperatures or used on tanks storing heated stock. Corrosion resistant pressure/vacuum seat is standard.

The 94221 is available in 20″ and 24″ sizes to fit a standard API or ANSI flange. Special Flanges are available including EN1092-1.

The pallet starts to lift when set pressure is approached. Flow efficiency rises rapidly to approximately 60% of a perfect orifice at 40% excess of the set pressure.

At a higher overpressure, the pallet completely clears the manhole and the efficiency approximates 75%. For a standard setting the capacity at 1.4 oz/in2 (40% overpressure) is approximately 500,000 SCFH for the 20” size.

Pallet construction permits settings from 1.0 oz/in2 for aluminum pallet & 1.3 oz/in2 for S.S. pallet standard to 8 oz/in2 maximum pressure. Vacuum settings are from 1.1 oz/in2 standard to 4.0 oz/in2 maximum. If specifying other than standard vacuum setting, it must be recognized that increased vacuum setting automatically increases the set point of pressure relief.

Shand & Jurs “Expanda-Seal” option is available on all pressure pallet assemblies. This feature significantly reduces leakage. The ballooning effect of the Teflon diaphragm effectively seals the valve.


  • Design incorporates pressure and vacuum relief
  • 20″ and 24″ roof manhole
  • “Self-energizing” Expanda-Seal diaphragm assures a tight seal
  • Reduced maintenance costs
  • No unbolting of vent for gasket replacement or tank examination

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94225 Emergency Vent And Manhole Cover (Pressure And Vacuum)