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ULTRA HIGH EFFICIENCY POWER VENT/POWER DIRECT VENT - SERVICE MANUAL
Technical Literature Department 14 of 52 Ashland City, TN © 2008
Servicing should only be performed by a Qualified Service Agent
VENTURI
A Venturi is connected to the inlet of the blower. All combustion air flows through the Venturi.
The outlet of the 24 VAC gas valve connects directly to the side of the Venturi. Fuel gas
flows from the outlet of the gas valve into the side of the Venturi directly.
Inside the Venturi there is a cone shaped restrictor that constricts the air passage to the
blower inlet. As air enters the constriction point it’s velocity increases. A pressure drop
occurs at this point and creates a negative pressure in the cavity between the cone shaped
restrictor and the Venturi housing. This negative pressure “pulls” gas from the outlet of the
gas valve into the blower where it is mixed with combustion air and then supplied to the
burner. See the images below.
GAS
VALVE
Velocity Increases
At Constriction Point
Pressure Drops
Negative Pressure
Negative Pressure
Combustion Air
Venturi Inlet
24 VAC Gas Valve
Gas Inlet
Supply Gas
Blower
Blower
Burner
Venturi