Literature
- Inexpensive.
- No moving parts.
- Minimal maintenance.
- Simple operation.
- 65% Allowable back pressures
- Flows up to 250 GPM (946 LPM) @ 100 PSI (6.9 Bar)
- Operates with pressures from 75 PSI to 200 PSI (5.2 Bar to 13.8 Bar), however optimum performance is with pressures above 125 PSI (8.6 Bar)
National Foam Line Proportioners are venturi devices that introduce Foam Concentrate into a flowing stream of water at a controlled rate of either 3% or 6%. As water flows through the venturi (water orifice) at a high velocity, 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 concentrate in to the proportioner at the correct percentage. As the water pressure at the inlet to the proportioner increases 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 pressure area and atmospheric pressure the range over which proper injection occurs is limited. Therefore, each model of line proportioner has an operating pressure range and to achieve optimum performance, the water inlet pressure must be maintained within this range. Higher than design pressure will result in a leaner (lower percentage) mixture; lower than design pressure will result in a richer (higher percentage) mixture. In addition to water pressure, LP’s are sensitive to back pressure. 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 discharge device(s), elevation head and line losses. The total allowable back pressure on the discharge side of the LP can not exceed 65% of the water inlet pressure. If back pressure exceeds 65%, the LP may not pick-up foam concentrate or the solution may be lean.
