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This sub-system is still under development. The intention is that when water supply approaches exhaustion, ARMAC can inject Barricade fire retardant gel into the water stream, creating a protective coating that adheres to surfaces and provides continued fire resistance even after water evaporates. The gel injection system represents one of ARMAC's more sophisticated subsystems, employing hydraulic and chemical engineering principles to achieve precise dosing under varying pressure conditions.
Dosatron for precise concentrations: The foundation component is a Huiji DN009 Dosatron proportional dosing pump, a hydraulically-driven device that uses water flow as its power source to inject a secondary liquid at a preset concentration ratio. The Dosatron operates across 0.2-6 bar pressure differential (inlet pressure above system ambient) and accommodates flow rates of 50-2500 L/hour (0.8-42 L/min). Crucially, the Dosatron maintains its set injection ratio across varying flow rates and pressures, unlike venturi injectors which exhibit pressure-dependent performance.
Electric pump to power the Dosatron inlet: The gel injection implementation employs a two-branch architecture to overcome a key challenge: the Dosatron requires positive inlet pressure (0.2-6 bar above system pressure) to function, but the system's nominal 4.5 bar operating pressure during sprinkler operation leaves insufficient differential for direct connection. The solution diverts a controlled portion of flow through a Bringsmart JT-1000A3-24 DC 12V inline booster pump before the Dosatron.
The Bringsmart pump specifications (1800-2600 L/hour flow, 4.2-6m head at 0.42-0.6 bar, drawing 3.0 amperes at 12V with dialable speed control) provide adequate boost pressure to the Dosatron inlet. At 2% gel dilution with the Dosatron set to 10% concentration (its maximum), the required flow through the Dosatron branch is approximately 36 L/min. The booster pump, operating against 4.5 bar system pressure and adding approximately 0.2-0.4 bar differential, delivers this flow while remaining within its performance envelope when dialed to approximately two-thirds maximum speed.
Fail safe design: Since the Dosatron is made of polymer the system has a normally closed solenoid valve on its inlet side, and a check valve asserting one-way flow on the outlet side. Thus if the Dosatron itself fails no water pressure is lost in the main sprinkler system.
Dilution calculations proceed as follows: System total flow F_total = 180 L/min at reduced flow. Desired final gel concentration C_final = 2%. Dosatron setting C_dosatron = 10% (1 part gel per 10 parts water through Dosatron). Required Dosatron branch flow F_dosatron = (C_final × F_total) / 0.10 = 0.02 × 180 / 0.10 = 36 L/min. This yields gel flow rate F_gel = 0.10 × 36 = 3.6 L/min, which, when mixed with the remaining 144 L/min of undosed flow in the main branch, produces 3.6 / 180 = 2% final concentration.
The gel reservoir is a 15.2-liter supply of Barricade gel (four 3.8L containers) intended to coat approximately 400 square meters at 2% concentration. The gel is to be consolidated into a sealed container with an agitator mechanism (a 24V electric paint mixer with 10cm impeller) to maintain gel suspension, as Barricade requires periodic stirring to prevent component separation. The Dosatron's suction port draws from this reservoir, with a check valve and manual shutoff on the suction line providing isolation when the system is not in gel mode.
Control sequencing for gel injection follows this logic: When water level falls below 0.30 meters but remains above 0.05 meters (the gel priority band), or when explicitly commanded in emergency conditions, the control system energizes both RV4 (the gel solenoid valve) and the Bringsmart booster pump simultaneously. Flow begins through the branch containing the booster pump and Dosatron, with the Dosatron drawing gel from the reservoir at the 10% internal ratio. After the gel branch flow rejoins the main flow downstream of the tee junction, the combined stream at 2% dilution proceeds to the sprinklers. Gel application continues until either the water level falls below the 0.05m dry cutoff threshold (triggering complete system shutdown) or the gel reservoir empties, whichever occurs first.
Safety interlocks address potential gel system failures: If flow suddenly drops between the gel system inlet and outlet (detected by comparing upstream and downstream flow sensors), indicating booster pump or Dosatron failure, the system closes RV4 and deactivates the booster pump, allowing continued water-only operation. The Dosatron's 40°C maximum operating temperature, lower than other system components, is mitigated by shed cooling and by the system's gel deployment only during final water exhaustion when fire conditions are likely moderating (post-fire-front phase). Future enhancements under consideration include insulating wrap for the Dosatron housing.
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