Fuel Cell Ejectors

Fox Venturi Ejectors for Hydrogen, Natural Gas, Steam Applications in Fuel Cells

Fox venturi ejectors have been used in fuel cells since a Fox venturi ejector was installed in the fuel recirculation system of SpaceLab in 1986 and launched into orbit. Since then, Fox H2 ejectors have been included in hundreds of fuel cell systems, for stationary, vehicle, and military applications installed by dozens of companies in over ten countries. Recirculation of anode gas is critical to fuel cell operation to remove by-product inert gasses, especially nitrogen, that can accumulate in the anode chambers and act as a ‘blanket.’

Many vehicle manufacturers, in the USA and EU, have worked with Fox to develop venturi ejectors for their onboard recirculation systems. With Fox Valve’s 50+ years supplying venturi equipment for spacecraft and flight hardware, Fox understands the technical requirements to reduce weight, shrink envelopes, and meet exacting QA – yet still meet performance specifications.

Quickly Supplied Prototypes Leading to Optimized Production Designs

Prototypes Fast

Fox maintains a large inventory of liquid and gas eductors, stocked as unassembled components. Using our proprietary computer models, we can then quickly size required ejector internals based on gas properties, temperatures, and pressures. We can then assess how existing components can be re-machined with new internal dimensions – and then assemble and weld these components into a first-iteration prototype – often in a in a week or less.

To facilitate easy installation without clunky adaptors, Fox prototype ejectors can be supplied with plain tubing ends in inch or metric OD’s, SAE and AN flared tube fittings, NPT threads and any commercially available fitting. Common materials of construction include stainless steel, aluminum, titanium, Monel, Inconel.

R & D Ejectors with Interchangeable Internals

When operating conditions vary broadly, it has been useful to our fuel cell customers to procure robust R & D ejectors. These have easily removable, interchangeable motive nozzles that allow motive flow rate to be varied while supplied with the same motive pressure. Other R & D ejectors use an actuator to remotely position a needle in the ejector nozzle to regulate/control motive flow with infinite resolution, with highly accurate position feedback.

Optimized Production Designs

Once the prototypes have been evaluated, Fox can then provide the fully optimized, custom-engineered production ejectors.

Cartridge Ejector Sets for Installation in Valve/Manifold Blocks

 Fox Venturi Ejector
Fox Venturi Ejector sets can be designed as cartridge inserts to slide into pre-drilled bores, with tight tolerances sealed by o-rings, within our customer’s manifold block. Cross drilled bores provide the motive flow to multiple ejecotrs installed in parallel, with common suction and discharge ports.
Fox Cartridge insert venturi ejector
A Fox Cartridge insert venturi ejector. The outside diameter is machined to within +/-0.001″ of the machined bore in our customer’s pre-drilled manifold block. Such insert ejectors enable multiple venturi ejectors to be installed in a small assembly, which can also contain check valves and selector on/off valves.


Fox has now supplied thousands of ejector sets that are installed into pre-machined valve or manifold blocks. Fuel cells that operate over a broad range of power output usually require a set of ejectors installed in parallel. Rather than connect individual ejectors with a complex tubing arrangement – Fox ejectors are often provided as precision-machined cartridge inserts. Sealed with o-rings, they slide into precision machined bores, their position established by internal shoulders so that drilled passageways connect the ejectors’ suction and motive ports, and combine the discharge to a common outlet. Fox holds these dimensions to +/-0.001 inch or better.

Fox provided about 100 ejector sets that were installed into a valve block – with integral solenoid and check valves, which were installed on the dozens of CITARO fuel cell busses that operated in Europe.

Turndown And Range of H2 Ejectors

Gas jet ejectors have limited range. A single ejector cannot be operated with the motive flow rate varying in unison with a varying suction gas flow rate. Operation across a broad range of suction gas flow rates typically requires multiple ejectors installed in parallel.

Adjustable Area Ejectors

Fox has many variable-area ejectors that enable the motive flow rate to be throttled while still maintaining critical flow through the nozzle. This has been used extensively during the R&D phase of evaluating ejectors in a fuel cell system. The variable area ejector has proven to be a very useful tool, enabling operation of an ejector over a broad range of operative motive flow rates. Adjusting flow rate by changing the needle position can be made with stepper motors, pneumatic actuators, or manually.

Available Materials of Construction and End Connections

Materials Of Construction:

  • 316 Stainless Steel
  • Aluminum
  • Inconel, Hastelloy, Monel and other high-nickel alloys
  • Plastics: CPVC, PTFE, etc.
  • Brass

End Connections:

  • Stub ends of plain tubing in any size, inch or metric – for use with flareless tube fittings
  • NPT or BSP Threads
  • Butt weld or socker well prep
  • SAE 45° Flare
  • AN 37° Flare