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HEI 125 7th Edition

Standards for Steam Jet Vacuum Systems, 7th Edition
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The HEI Standards for Steam Jet Vacuum Systems (7th Edition) is the primary global authority for the design, calculation, and testing of steam jet ejectors. These systems are the "workhorses" of the power and process industries, using high-pressure motive steam to create a vacuum without any moving parts.

Because ejectors are deceptively simple in appearance but complex in fluid dynamics (involving supersonic flow and shock waves), the HEI standards are critical for ensuring they are sized correctly for the specific non-condensable gas loads of a plant.

Technical Scope & Content

The 7th Edition covers the entire "ejector package," which typically includes the ejectors themselves, the inter-condensers, and the after-condensers. Key sections include:

  • Ejector Design & Performance: Formulas for calculating the "Motive Steam" required to entrain a specific "Suction Load." It defines how to handle mixtures of air, water vapor, and other gases.
  • Standard Air Ratings: Similar to the liquid ring standards, this defines "Dry Air Equivalent" (DAE) to allow engineers to compare different designs on a leveled playing field.
  • Multi-Stage Systems: Guidance on designing 2-stage or 3-stage systems (with inter-condensers) to achieve the deep vacuums required for high-efficiency steam turbines.
  • Critical Flow & Velocity: Standards for the "diffuser" and "nozzle" geometries to ensure the steam reaches the supersonic velocities necessary to create a vacuum.

Key Features of the 7th Edition

This edition modernized several aspects of ejector technology to align with current environmental and efficiency goals:

  • Performance Testing (Section 5): Provides the most rigorous procedures in the industry for "Shop Tests." It outlines exactly how to measure steam flow and suction pressure to prove the unit meets its guarantee.
  • Condenser Integration: Detailed standards for the shell-and-tube condensers that sit between ejector stages to "knock out" the motive steam, reducing the load on the next stage.
  • Materials & Erosion: Updated recommendations for nozzle materials (like 316 Stainless Steel or Monel) that can withstand the high-velocity "sandblasting" effect of wet motive steam.
SDO HEI: Heat Exchange Institute
Document Number 125
Publication Date Jan. 1, 2012
Language en - English
Page Count 142
Revision Level 7
Supercedes
Committee
Publish Date Document Id Type View
Jan. 1, 2012 HEI 125 7th Edition Revision