Foam Proportioning System Product

Overview

A foam proportioning system meters firefighting foam concentrate into the water stream of a fire pump at a controlled percentage — typically 0.3 % for Class A wetting agents on vegetation and structure fires, 1–6 % for Class B film-forming foams on flammable liquids. Getting the ratio right matters in both directions: too lean and the foam blanket fails to seal the fuel surface, too rich and the apparatus exhausts its 75–150 L concentrate cell in minutes.

Older apparatus used around-the-pump or eductor proportioning, which depend on fixed pressure differentials and restrict pump operating range. The electronically controlled direct-injection system described here, the architecture used by FoamPro- and Hale-pattern units, instead measures actual water flow and injects concentrate downstream of the pump, so proportioning stays accurate as the operator gates discharges open and closed.

How it works

A Water Flowmeter in the discharge piping reports water flow: the Paddlewheel Rotor spins at a rate proportional to water velocity and its embedded magnets pulse a Hall Sensor, giving the controller a frequency signal it converts to liters per minute. The Controller multiplies that flow by the set percentage to get a target concentrate rate, then drives the Drive Motor by PWM through its Power MOSFET output stage. A second Hall Sensor on the motor closes the loop: the Microcontroller runs a feedback control loop comparing commanded and actual pump speed, holding the ratio within the ±5 % accuracy band NFPA 1901 requires.

The Concentrate Pump is a positive-displacement gear pump — flow per revolution is fixed, so pump speed is an honest proxy for injection rate regardless of discharge pressure. Its Helical Gear Pair runs in a bronze Pump Body with clearances tight enough to self-prime and to push viscous alcohol-resistant concentrates (some exceed 4000 cP) against 17–28 bar of discharge pressure. A Pump Relief Valve bypasses flow if a downstream valve is closed against the pump.

Concentrate enters the water at the Injection Manifold, downstream of the flowmeter so the meter reads plain water. The Injection Check Valve stops pressurized water backflowing into the concentrate plumbing when the system is off — water contamination gels many concentrates — and the Water-side Check Valve keeps foam solution out of plumbing that must stay clean, such as the tank-fill line. A Pressure Sensor at the manifold lets the controller detect a blocked or dead-headed injection point.

Concentrate supply

The Concentrate Tank Interface connects the apparatus foam cell to the pump. A Pickup Tube reaches the tank sump, protected by a cleanable Concentrate Strainer; aged concentrate polymerizes into lumps that would wedge the gear pump. The Tank Level Sensor drives a low-foam warning on the Operator Display, and the Tank Vent lets the cell breathe as it drains. On dual-agent apparatus the Tank Selector Valve switches between Class A and Class B cells — always through an intermediate flush, since mixing concentrate families can gel both.

After any Class B operation the Flush Valve admits clean water through the pump and lines; dried AFFF residue is the leading cause of gear pump seizure. The Calibration Valve supports the periodic accuracy check: output is diverted to a graduated container for a timed draw at a set percentage and flow, and measured volume is compared against theory.

Operator interface

The panel-mounted Controller presents one knob-and-button interface on the pump panel: the Membrane Keypad sets percentage in 0.1 % steps, and the Operator Display cycles between water flow rate, total water, percentage, and total concentrate consumed — the consumption total is what tells an officer whether the remaining cell supports continued attack. A Relay in the controller drops motor power on fault or when the operator presses standby, and the Circuit Breaker in the Wiring Harness protects the 40–80 A motor feed from the apparatus battery bus.

System behavior and limits

Because injection is discharge-side, only plumbing downstream of the Injection Fitting ever sees foam solution; the pump, tank, and relief valving stay wet with plain water, unlike around-the-pump systems that contaminate the whole pump. The limit of a single-point system is that every foam-capable discharge shares one percentage; apparatus needing simultaneous Class A and B streams fit two independent injection systems. Maximum concentrate rate also caps total foam-solution flow: a 19 L/min pump supports roughly 3800 L/min of water at 0.5 %, but only about 630 L/min at 3 %, so high-percentage Class B work on large flows moves to larger multi-pump systems or installed balanced-pressure proportioners.