Introduction to Air and Gas Jet Venturi Ejectors

What are Fox Air Ejectors?

Fox Venturi Jet Ejectors (also called eductors, venturi jets, aspirators, jet mixers, jet pumps) use compressed gas (1 to 1500 psig) to exhaust, vent, compress, or mix another gas stream; or create moderate to deep vacuum (to below 1 psia.)

No Moving Parts – for Handling Corrosive, High-Temperature or Cryogenic, Explosive, Toxic, or Dust-Laden Gasses, Fumes, or Exhaust

Fox Venturi Jet Ejectors have no moving parts, no seals, no shafts, no packing, no maintenance. Their rugged construction and simplicity enables their reliable maintenance-free use with caustic, high-temperature, or explosive gasses – such as hydrocarbons. An ejector replaces the need for XP motors on fans or blowers.

Vacuum-Generation, Exhausting or Venting Vapors, Fumes, and Exhaust; Gas Sampling, and Compressing Gases

  • Line Sizes: 1/4 to 42 inch diameter (6mm to ~1m)
  • Temps: -350° to 2000° F (to 1090° C)
  • Materials:
    • Metals: Stainless, Monel, Hastelloy, Titanium, Alloy 20, Aluminum, or Any Machinable Metal
    • Plastics: PVC, CPVC, TFE-Lined, PVDF-Lined
  • Off-The-Shelf Gas Ejectors in cs/ss: 1/4″ to 8″
  • Off-The-Shelf PVC: 1/2″ to 3″; CPVC 1/2″ to 2″
  • Custom built ejectors: 1/4″ to 42″
  • MAWP available to 10,000 psig (700 barg)
  • End Connections:
    • Threads: NPT, BSP, SAE 45° Flare, AN 37° Flare
    • Flanges: 150# to 3000# ANSI, DIN Flanges, or any custom-built flange to mate to any equipment
    • Tubing: Stub ends of any specified tubing, inch or mm
    • Food-Grade: Tri-clamp or other sanitary/hygienic ferrules
    • Weld: Butt weld prep ends
  • Available Processes: Electropolish, oxygen cleaning, passivation, anodizing, etc.

Common Applications

  • Venting methane and sewer gasses from landfills, WTP’s, natural gas processing
  • Blending gasses in precise mixture ratios (Argon + chlorine in a recent application)
  • Evacuating Sulfur fumes (H2S) from sulfur pits, trucks and tanks with steam jacketed ejectors, maintaining internal gas temps above 280° F to prevent solidification
  • Venting Engine exhaust, fumes, and CO2, etc – including creating deep vacuum on jet and rocket engines for high altitude simulation
  • Evacuating pipelines, vessels and tubing of explosive or toxic fumes before maintenance
  • Exhausting explosive or radioactive gasses
  • Creating vacuum in evaporators, crystalizers, deodorizers and other chemical and food processing applications
  • Blowdown: Pass gasses through venturi ejector from a vessel or pipeline at up to 5000 psig during initial purging, then venturi ejector completes evacuation down to 1 to 2 psia
  • Blending gasses (optional with Fox sonic choke on suction) to blend to precise mixture ratio
  • Exhausting air at 700° F containing cement kiln dust from cement kilns
  • Pump Priming

For detailed technical information about these specific applications, please visit the following pages:

Natural Gas, Methane, Vapor Recovery, Flare Gas Ejectors

Hydrogen/Natural Gas Ejectors in fuel cells

Gas sampling mini-eductors for analyzers, instrumentation

Where are the Fox venturi gas ejector capacity charts? How can I get a quick estimate of ejector capacity, motive gas consumption, size, and cost?

Only a small portion of the gas ejector inquiries we receive are for air-air at ambient temps, so published tables for air at 70° F are usually not useful for quick preliminary sizing of applications with different gasses at higher or lower gas temperatures. Our proprietary computer models enable us to size the required ejector very quickly, for any gas at any temperature. The fastest way to get the right answer regarding what a Fox venturi ejector can do in your application is to complete our Application Data Sheet (choose either Imperial or Metric units) and email to us at We aim for a same-day reply, although not always a quote, during normal working hours, EST in New Jersey.

What do we mean by “off-the-shelf” gas ejectors?

Fox maintains a large inventory of assembled and unassembled 1/4″ to 8″ Fox venturi ejectors in carbon steel and stainless, manufactured in Dover, NJ, USA. This large inventory of unassembled ejector components enables Fox to quickly make modifications to ejector internals to suit application requirements—and still often ship in 1 to 1.5 weeks or less. This includes remachining motive nozzle orifice to define required motive gas consumption, welding nozzle in place if required, and welding on flanges or other end connections or adapters—all in our building.

This process of reworking existing ejector components enables Fox to supply, sometimes in days, what we call B+ ‘proof of concept’ prototypes for OEM applications, leading later to optimized, highly customized A+ production ejectors for integration into our customer’s OEM equipment.

Frequently Asked Questions

For more detailed information regarding operation, performance, turndown, and technical limitations, please download Bulletin 251 from our Download Literature page, or request that we email you this bulletin using the Ask a Question Button.

The first three FAQ’s from Bulletin 251 are below

1. What’s the deepest vacuum I can pull with an air ejector?

Using air at 80 to 100 psig, our off-the-shelf ejectors can pull down to about 10 psia. Custom engineered ejectors can use air at 100 to 150 psig pull down to about 2 psia. Two stage ejectors can reach 1 psia.

2. Can I use an air ejector to handle dusty or corrosive gasses?

Yes, to eliminate the expensive fans or blowers, with exotic metal internals and/or XP motors, which, despite their high cost, will eventually fail.

3. Is air at 60 to 100 psig (4 to 7 barg) necessary? Our plant’s compressors are already maxed out.

Using plant air is convenient for small ejectors or those that run intermittently, like once or twice a day. However, for continuous gas venting of low pressure gasses, a matched blower/ejector combination from Fox can be provided. Blower pressure to the ejector of only 2 to 3 psig is often adequate for many gas venting applications.

Do you have a specific question about your application? Please use the ASK AN ENGINEER button.

Gas Sampling for Analyzers and Instrumentation with Fox Mini-Eductors

Fox Air-Driven Mini-Eductors have been installed on thousands of analyzer systems for gas sampling since the 1960’s. Please visit the Mini-Eductor section of our website for more information.

Schematics of Typical Applications

Venting, Evacuating, and Exhausting from Vessels, Tanks, and Chemical or Refining Processes

 Fox Air and Gas Ejectors
Fox Air and Gas Ejectors are frequently used as exhausters to vent gases from a tank or vessel.

Pump Priming with Air Jet Ejectors

Fox Air Ejector
A Fox Air Ejector pulls a vacuum on a pump housing to evacuate the suction line and draw water up into the pump.

Purging or Evacuating Piplines or Tubing

Fox Ejectors are frequently used to purge or evacuate pipelines or tubing.

Creating Deep Vacuum to 1 psia with a Two-Stage Air Ejector

 Two-Stage Ejector System
Two-Stage Ejector System installed on the roof of the hypersonic wind tunnel at Princeton University

Venting Hydrocarbon Vapors to Flare Header in Oil and Gas Applications (Ref. EPA 40 CFR Quad O)

For information about Fox Gas Ejectors used in the oil and gas industries, please visit our Natural Gas Ejectors page.