The standard water ejector produces the vacuum required to pull air from the chamber through the use of a simple three-port device. One port is attached to the chamber drain, the second port is routed to the facility drain, and the third port is connected to the facility water supply.

The sterilizer control system signals the facility water “ON” during periods requiring vacuum which produces a Venturi effect within the water ejector. Thus, a vacuum is drawn on the port connected to the chamber.

The most redeeming feature of a water ejector is its simplicity. It is generally capable of producing 25+ inches of mercury vacuum from a 50 psig water supply but does require in some cases minutes, not seconds, to produce a deep vacuum.

The downside of a water ejector is it uses a fair amount of facility water which is discharged directly to the drain unless the Water Conservation system option was purchased with the sterilizer.

Venturi Effect (How Ejectors Create Vacuum)

The Venturi Effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe.

The fluid velocity must increase through the constriction to satisfy the equation of continuity, while its pressure must decrease due to the conservation of energy. The gain in kinetic energy is balanced by a drop in pressure.

An equation for the drop in pressure due to the Venturi effect may be derived from a combination of Bernoulli’s Principle and the equation of continuity.

Have a question or having difficulties? Talk to Dave Schall, our PRIMUS sterilizer expert who is here to assist you anytime at 877.679.7800 extension 1212 or email at

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