- No moving parts
- Minimal maintenance
- Simple operation
- Variable metering
- 65% Allowable back pressures
- Available in four different flows
- Operates with inlet pressure of 200 PSI (13.8 Bar)
National Foam Handline Proportioners are venturi devices that introduce Foam Concentrate into a flowing stream of water at a controlled rate of either 1%, 3% or 6%. As water flows through the venturi (water orifice) at a high veloc- ity, a negative pressure area develops at the discharge of the venturi. This negative pressure creates a pressure differential across the foam concentrate metering orifice, thereby allowing atmospheric pressure to push foam con- centrate in to the proportioner at the correct percentage. As the water pressure at the inlet to the proportionier in- creases or decreases the solution flow from the device will increase or decrease correspondingly. Because the amount of foam concentrate to be injected into the water stream is controlled by the relationship between the negative pres- sure area and atmospheric pressure the range over which proper injection occurs is limited. The Handline Proportioners are available in four sizes and are matched to specific nozzles (See chart). They are designed to op- erate with an inlet pressure of 200 psi. (13.8 Bar).
Higher than design pressure will result in a leaner (lower percent- age) mixture; lower than design pressure will result in a richer (higher percentage) mixture. In addition to water pressure, Handline Proportioners are sensitive to back pres- sure. Back pressure is the amount of pressure required down stream of the proportioner to discharge the total foam solution flow. This will include the pressure required at the inlet to the nozzle, elevation head and hose losses. The total allowable back pressure on the discharge side of the Handline Proportioner can not exceed 65% of the water inlet pressure. If back pressure exceeds 65%, the Handline Proportioner may not pick-up foam concentrate or the solution may be lean.