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Venturi Eductors

Jacobs Process Analytics Inc. manufactures four different types of Venturi eductors or vacuum pumps. Please select from the options below to see more details about each one.

What is a Venturi Vacuum Pump

Basically the Venturi vacuum pump, originally named a Bernoulli vacuum pump, is a simple device that converts pressure (potential energy) to velocity (kinetic energy) when a fluid (liquid or gas) is forced through a restriction in an enclosed line, which creates a partial vacuum in the process.  It uses fluid mechanics to obtain work from energy stored in the motive fluid.  Because the reduced pressure at the restriction creates a partial vacuum, this device can be used, among other applications, to extract samples from pipes, vent stacks, or ambient air or even to mix samples.  This effect was first described in 1738 by the Swiss scientist Daniel Bernoulli in his publication Hydrodynamica 1.

1 “Hydrodynamica”. Britannica Online Encyclopedia. Retrieved 2008-10-30

How does a Venturi vacuum pump work?

A Venturi vacuum pump is based on the principle of the Conservation of Energy which states that, in a steady flow, the sum of all forms of mechanical energy in a fluid along a line is the same at all points. That is, the sum of the kinetic energy (reflected in the form of velocity) and potential energy (pressure) must remain constant. When a restriction is introduced in a line the velocity through that restriction must be greater than the velocity in the larger line.  This only makes sense since the same mass of fluid is flowing through a smaller cross sectional area.  Therefore, when an increase in the speed of the fluid occurs through the restricted section (see figure 1 below) there is a proportionate decrease in pressure in order to maintain the same total mechanical energy.  The reverse occurs when the fluid expands into the downstream section.

principle-conservation-energy

Figure 1: The pressure in the first measuring tube (P1) is higher than at the second (P2), and the fluid speed V1 is lower than V2, because the cross-sectional area at “1” is greater than at “2”.

How do we use the Bernoulli principal to make a sample pump?

By modifying the geometry of the flowing tube to include a precision machined orifice, fluid discharge and mixing chamber, a high velocity jet produces a vacuum which can pull in another fluid through a side or suction port. Compressed air flows through the nozzle which causes a Venturi effect.  As the air expands and flows into the exhaust tube, the pressure drops below atmospheric pressure. This causes entrainment of the surrounding air or sample which is mixed with the motive fluid and subsequently discharged downstream.  This device is an efficient and inexpensive method to create a vacuum for sampling, mixing, vacuum generation and aspirating. Jacobs Process Analytics makes a line of mini-eductors or mini-aspirators to suit your specific application.

Where are Venturi eductors used?

There are innumerable applications for this simple technology, from environmental sampling to gas cooking stoves to large scale dredging operations.  The small mini eductors (or mini aspirators) that Jacobs Process Analytics offers are routinely used for:

  • Sampling: In process analytics for sampling process gases or aspirating stack gases for continuous analysis or for discrete sampling for lab analysis.
  • Mixing or dilution:  The mini-eductor can be used to mix samples in a specific controlled ratio.  Any pressurized gas (air, nitrogen, argon, natural gas, … ) can be used as the motive force that creates the vacuum flow.  Our standard off-the-shelf eductors meet the majority of applications.  However, we also make customized eductors to suit your specific flow requirements.
  • Vacuum: Create a vacuum for evacuating vessels or lines.
  • Venting: Remove noxious vapors from a chemical process or vessel.

Why use a Venturi eductor instead of a mechanical pump?

A Venturi pump or eductor is a simple device that has many advantages over a mechanical pump.

  • Capital cost:  The mini-eductor is an inexpensive device to purchase and install.  Compare this to the cost of a mechanical pump, especially if it must be explosion proof or made of an exotic material.  An eductor is a fraction of the cost.
  • Installation cost: Installation requires only an air line and a regulator.  Mechanical pumps necessitate installation of conduit, wiring and dedicated circuitry.  Mechanical pumps also occupy much more space, which can be a serious consideration for sample conditioning system enclosures.
  • Compact:  Our educator is built into a tubing Tee with compression fittings and/or threaded ends as integral part of the device.  The mini-eductor (or mini-aspirator, Venturi pump) is easily integrated into any sample system.  No additional fittings are required.
  • Safety:  The Venturi vacuum pump or mini-eductor is an intrinsically safe device.
  • Reliability:  Eductors or aspirators are virtually maintenance-free. Installation of a mechanical pump automatically reduces the reliability of any system.  Moving parts wear, reducing efficiency and capability, and must be serviced periodically.

Compatibility

  • Materials of construction
    • The standard materials of construction for off-the-shelf eductors are 316 SS and Teflon.  See our teflon eductor.
    • Several other metals are also offered (hastalloy, titanium, 316 L, monel, …) depending on process make-up and conditions. See our eductors.
    • For certain low flow requirements ruby or sapphire is utilized in our educator orifices.
  • Sizes
    • Off-the-shelf metal eductors are made from ¼” compression fitting union Tees. See our tee-type eductors.
    • Many other fittings are also available including a combination of compression fittings and NPT threadings, e.g. ¼” NPT male run Tee, male NPT branch ( 1/8” & ¼” NPT), 3/8” union Tee, …  Give us your requirements.
  • Sub-assemblies