Northeast Controls Inc. · Eductors – Jet Pumps
Gas Eductors — Models ML, SG & HG
Exhausting · Evacuation · Scrubbing · Vacuum Generation · Thermocompression
Gas eductors use the kinetic energy of one fluid to pump, compress, or move a gas stream — with no moving parts, no electrical connections, and no mechanical wear. Two distinct motive configurations are available: liquid-powered (Models ML & MLE) for applications where a liquid motive is available, and gas/steam-powered (Models SG & HG) for applications where a gas or steam motive is preferred.
Gas motive eductors use a converging-diverging nozzle that allows the motive gas to reach sonic velocity, maximizing the energy available for entraining the suction gas. The two gas streams mix in the throat and are discharged together through a diverging diffuser that recovers pressure. Because there are no moving parts, gas eductors are inherently safe for hazardous areas and require essentially zero maintenance.
Bronze Inline Eductor — B62 Alloy, NPT
Gas Eductor Model Series
Three model series cover liquid-motive and gas/steam-motive configurations across a wide range of pressures and flow rates.
Performance
Description
Liquid-powered gas eductors. A liquid motive stream (water, oil, or process fluid) drives the pumping of a gas suction stream. The MLE variant includes an extended mixing tube for improved gas entrainment at lower motive pressures.
Typical Applications
- →Scrubbing and absorbing toxic or odorous gases
- →Injecting oxygen or air into liquid streams
- →Removing dissolved gases from process liquids
- →Vacuum generation using plant water
Performance
Description
Standard gas-powered gas eductor. A gas or steam motive stream drives the pumping of a gas suction stream through a converging-diverging nozzle. The motive gas can reach sonic velocity, maximizing entrainment of the suction gas.
Typical Applications
- →Exhausting reaction vessels of inert or hazardous gases
- →Removing steam from vessels before opening
- →Vacuum generation using compressed air or steam
- →Purging pipelines and equipment
Performance
Description
High-performance gas-powered gas eductor with enhanced pressure recovery. Higher entrainment ratio than the SG series, suited for demanding gas compression and multi-stage vacuum applications.
Typical Applications
- →Multi-stage vacuum systems
- →High-volume gas exhausting
- →Thermocompressor service
- →Steam-jet ejector systems
Model Performance Comparison
| Description | Model ML / MLE | Model SG | Model HG |
|---|---|---|---|
| Motive Media | Liquid | Gas / Steam | Gas / Steam |
| Suction Media | Gas | Gas | Gas |
| Motive Pressure (PSIG) | 15–250 | 30–150 | 20–150 |
| Suction Pressure | Vacuum–10 PSIG | Vacuum–15 PSIG | Vacuum–20 PSIG |
| Pressure Recovery % | 30–35 | 15–20 | 30–35 |
| Nozzle Type | Converging | Converging-Diverging | Converging-Diverging |
| Sonic Velocity Capable | No | Yes | Yes |
Exhausting vs. Evacuation
Exhausting
Pulling gases from a defined volume by pumping the vessel down from a starting pressure to a final lower pressure. Sized by determining the time required to reduce pressure to the desired final level.
Examples
- →Reducing pressure in a reaction vessel to purge detrimental gases
- →Removing steam from a vessel before opening
- →Evacuating a tank before filling with a new product
- →Degassing a liquid-filled vessel
Sizing input: vessel volume, starting pressure, final pressure, time allowed
Evacuation (Continuous)
Removing gases at a continuous rate while maintaining pressure at a stable level. Used where gases or fumes are continuously recurring and must be removed at the rate they are generated.
Examples
- →Removing smoke or fumes from a welding or machining area
- →Maintaining vacuum in a continuous distillation process
- →Exhausting off-gases from a chemical reactor
- →Injecting oxygen into a liquid stream for aeration
Sizing input: continuous gas flow rate (SCFM), suction pressure, discharge pressure
Gas Eductor Applications
Gas eductors serve a broad range of industries including chemical processing, petrochemical, pharmaceutical, power generation, water treatment, food & beverage, and environmental control.
Exhausting
Pulling gases from a defined volume by pumping a vessel down from a starting pressure to a lower final pressure. Sized by the time required to reduce pressure to the desired level. Examples: reducing pressure in a reaction vessel to purge detrimental gases, or removing steam from a vessel before opening it.
Evacuation
Removing gases at a continuous rate from an area while maintaining pressure at a stable level. Used where gases or fumes are continuously recurring. Examples: removing smoke from a welding or machining area, or maintaining vacuum in a continuous process.
Gas Scrubbing
Using a liquid motive (Model ML/MLE) to simultaneously pump and contact a gas stream with a reactive scrubbing liquid. The gas and liquid mix intimately in the eductor throat, enabling absorption, neutralization, or odor control in a single compact device.
Gas Injection
Injecting a gas (oxygen, air, ozone, CO₂) into a liquid stream using a liquid motive eductor. The venturi action draws in and disperses the gas as fine bubbles, providing efficient mass transfer for aeration, oxidation, or carbonation.
Vacuum Generation
Creating and maintaining vacuum for distillation, filtration, drying, degassing, and impregnation processes. Steam or compressed gas motive. No moving parts, no oil contamination, no mechanical wear.
Thermocompression
Using high-pressure steam as the motive to compress low-pressure steam (suction) to an intermediate pressure. Recovers energy from low-pressure steam that would otherwise be wasted, reducing overall steam consumption.
Purging & Inerting
Purging pipelines, vessels, and equipment of hazardous or reactive gases using an inert motive gas. No electrical components at the purge location — inherently safe for hazardous areas.
Reactive Motive Neutralization
When the gases being removed have undesirable characteristics, a reactive motive fluid can neutralize them directly in the eductor. Combines pumping and chemical treatment in a single step.
How a Gas Eductor Works
Motive Connection
High-pressure motive fluid (gas, steam, or liquid) enters the nozzle. For gas/steam motives, the converging-diverging nozzle accelerates the flow to sonic or supersonic velocity, creating a high-velocity jet.
Suction Chamber
The high-velocity motive jet creates a low-pressure zone in the suction chamber. This draws in the suction gas through the suction connection. The two gas streams begin to mix.
Discharge Diffuser
The mixed gas stream passes through a diverging diffuser that converts kinetic energy back to pressure. Discharge pressure is always between motive pressure and suction pressure.
Key Operating Principle — Gas Motives
Gas motives are compressible fluids. When passed through a converging-diverging (de Laval) nozzle, the gas can exceed the speed of sound. This supersonic jet creates a very low-pressure zone in the suction chamber, enabling the entrainment of large volumes of suction gas at low or sub-atmospheric pressures. The entrainment ratio (suction flow / motive flow) for gas-powered gas eductors typically ranges from 0.5:1 to 3:1 depending on the pressure ratio and model series.
Selecting the Right Model — Motive Fluid Guide
The choice between liquid-motive and gas/steam-motive eductors depends on what motive fluid is available, whether a dry discharge is required, and the vacuum depth needed.
Why
Liquid motive provides higher entrainment ratios and better pressure recovery than gas motive. Ideal when plant water or process liquid is available at adequate pressure.
Best For
Gas scrubbing, aeration, odor control, vacuum generation with water seal
Why
Gas motive with converging-diverging nozzle reaches sonic velocity for efficient gas entrainment. No liquid in the discharge stream — keeps the process dry.
Best For
Vessel purging, inerting, dry vacuum generation, gas transfer
Why
High-performance gas/steam motive with enhanced pressure recovery. Higher entrainment ratio than SG. Steam motive also provides heating effect at discharge.
Best For
Thermocompression, multi-stage vacuum, steam-jet ejectors, high-volume gas exhausting
Why
Single-stage eductors cannot achieve very deep vacuum. Two or three stages in series, each handling a progressively lower pressure, can reach 1–5 torr absolute.
Best For
Vacuum distillation, freeze drying, high-vacuum process vessels
Vacuum Level Reference
Vacuum is expressed in multiple units depending on industry and application. Provide the required vacuum level in any unit — we will convert for sizing purposes.
| Vacuum Level | in. Hg Abs | Torr | mbar | PSIA |
|---|---|---|---|---|
| Atmospheric | 29.92 | 760 | 1013 | 14.7 |
| Mild vacuum (typical single-stage) | 20 | 508 | 677 | 9.8 |
| Moderate vacuum | 10 | 254 | 339 | 4.9 |
| High vacuum (single-stage limit) | 2 | 51 | 68 | 0.98 |
| Deep vacuum (2-stage) | 0.5 | 12.7 | 17 | 0.25 |
| Very deep vacuum (3-stage) | 0.1 | 2.5 | 3.4 | 0.05 |
Note: Single-stage gas eductors typically achieve down to ~2 in. Hg abs. Multi-stage configurations required for deeper vacuum.
Applications by Industry
Gas eductors serve virtually every process industry where gases, vapors, or fumes must be moved, compressed, scrubbed, or injected.
| Industry | Typical Uses |
|---|---|
| Chemical Processing | Reactor off-gas exhausting, solvent vapor recovery, acid fume scrubbing, vacuum distillation, inerting with nitrogen |
| Petrochemical & Refining | Hydrocarbon vapor recovery, vacuum stripping, flare gas recovery, vessel purging, steam-jet ejector systems |
| Pharmaceutical | Vacuum drying, solvent vapor removal, sterile gas injection, vessel evacuation before filling, CIP off-gas handling |
| Power Generation | Condenser air removal, steam-jet ejectors, thermocompression of low-pressure steam, boiler off-gas handling |
| Water & Wastewater Treatment | Aeration (oxygen/air injection), ozone injection, chlorine gas scrubbing, digester gas handling, odor control |
| Food & Beverage | Vacuum cooking, vacuum packaging, CO₂ injection, steam stripping, aroma recovery |
| Pulp & Paper | Non-condensable gas removal, vacuum forming, black liquor off-gas handling, steam-jet ejectors |
| Environmental & Industrial Hygiene | Fume and smoke extraction, welding fume removal, dust suppression, hazardous gas scrubbing |
Special Considerations for Gas Eductor Sizing
Gas eductor sizing is more complex than liquid eductor sizing because gas properties (density, compressibility, condensability) vary significantly with temperature and pressure. The following factors must be addressed for accurate sizing.
Condensable Vapors in Suction Stream
When the suction gas contains condensable components (steam, solvent vapors), condensation can occur in the mixing tube and diffuser. This releases latent heat and changes the effective molecular weight of the mixture. Sizing must account for the condensation load — provide vapor composition and dew point data.
Superheated vs. Saturated Steam Motive
Saturated steam is the standard motive for steam-powered gas eductors. Superheated steam reduces entrainment efficiency because the superheat must be removed before condensation can occur. If superheated steam is the only available motive, provide superheat temperature so the nozzle can be sized accordingly.
Non-Condensable Gas Accumulation
In steam surface condenser service, non-condensable gases (air, CO₂) accumulate and must be continuously removed to maintain condenser vacuum. Gas eductors are the standard solution — sized for the non-condensable gas load at the condenser operating pressure.
Corrosive or Toxic Gas Streams
Material selection is critical for corrosive gas service. Provide full gas composition including trace components. For toxic gases, consider the discharge destination — the motive and suction streams mix at discharge, so the discharge stream will contain the suction gas. Scrubbing the discharge may be required.
Temperature Effects on Gas Density
Gas density varies significantly with temperature. All flow rates must be specified at actual conditions (ACFM) or at standard conditions (SCFM at 60°F, 14.7 PSIA). Provide actual gas temperature at the suction connection for accurate sizing.
Back-Pressure Sensitivity
Gas eductors are sensitive to discharge back-pressure. If the discharge pressure exceeds the design value, the eductor will lose suction and cease to pump. Ensure the discharge line is sized for low pressure drop and that no downstream valves can be inadvertently closed during operation.
Materials of Construction
Available in a wide range of materials to match your gas stream, temperature, and pressure requirements. All metallic units are full ANSI rated and meet ASME/ANSI B16.5.
Bronze
Standard for steam, air, and general gas service.
Cast Iron
For larger sizes and non-corrosive gas streams.
Carbon Steel
For higher pressures and temperatures.
316 Stainless Steel
For corrosive gases, acids, and chemical service.
304 Stainless Steel
General corrosion resistance at lower cost.
Alloy 20
For sulfuric acid fumes and highly corrosive gas streams.
Hastelloy C
For extremely aggressive chemical gas environments.
PVC / CPVC
For corrosive chemical fumes and scrubbing applications.
Polypropylene
For aggressive acid and alkali gas scrubbing.
Titanium
For chlorine, seawater, and highly oxidizing gas streams.
Construction & Quality Features
Sizing a Gas Eductor — What We Need
Gas eductor sizing requires accurate process data. Provide the following on the Jet Pump Application Sheet for a detailed sizing calculation:
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