Fixed inductor system
The simplest and cheapest method of making foam is with a foam inductor unit. The foam inductor creates a suction to draw foam concentrate from a storage tank, and then mix it with the firewater at the correct ratio.
Pros
- Low cost
- Simple to install
Cons
- High pressure loss through inductor (typically 30-35%)
- Requires fixed flow conditions where inductor is specifically calibrated to match the installation duty
Balance valve foam proportioning system
In the next progression from the simple foam inductor system, Pressure Balancing Valves are used in conjunction with a Balanced Pressure Foam Proportioner and foam concentrate pump. This ensures the foam concentrate fed from an atmospheric storage tank is mixed accurately with the firewater over a range of flows and pressures.
The Pressure Balancing Valve uses a diaphragm to sense and balance the pressures of the incoming foam concentrate and firewater sensing lines, before delivering the regulated foam concentrate pressure to the Balanced Pressure Foam Proportioner.
Pros
- Can be used with an atmospheric foam tank which can be replenished during use, extending operating time of the system
- Variable flow installations are possible
Cons
- Greater physical space required for installation compared to other systems
- Additional maintenance / service costs
Foam bladder tank units
This system uses an outer steel pressure vessel enclosing an internal bladder or polymer bag that contains foam concentrate. During operation, the fire water supply is partially diverted and fills the tank, exerting pressure on the external surface of the bladder and causing compression. This forces the foam concentrate out of the bladder and delivers foam to the proportioning device installed in the water piping. Older existing bladder tanks can also be upgraded to a water driven foam proportioner.
Pros
- Variable flow installations are possible
- No external power supply required
Cons
- Greater physical space required for installation compared to other systems
- Additional maintenance / service costs
Pumped foam proportioning skids (water-driven)
This system uses a pelton-wheel, water-driven pump to deliver accurately metered foam concentrate into a balanced pressure foam proportioner. The whole system includes: a foam tank, a pump, inter-connecting pipework, a proportioner and other accessories – all of which can be skid mounted.
Pros
- Can be used with an atmospheric foam tank which can be replenished during use, extending operating time of the system
- Variable flow installations are possible
Cons
- Water-driven pumps create waste water
- Reliable / sufficient water supply required
Pumped foam proportioning skids (electrically-powered)
With this system accurately metered foam concentrate is delivered via an electrically-driven pump into a balanced pressure foam proportioner. The whole system includes: a foam tank, a pump, inter-connecting pipework, a proportioner and other accessories – all of which can be skid mounted.
Pros
- Can be used with an atmospheric foam tank which can be replenished during use, extending operating time of the system
- Variable flow installations are possible
Cons
- Electric Pump requires external power supply
- Capital cost of related system components / logic
Turbinator - foam dosing machine (water-driven)
The Knowsley “Turbinator” is an inline, positive displacement, foam dosing machine. It’s an advancement from the previously mentioned pump and balanced pressure proportioner system.
Made up of a water powered motor and foam concentrate pump – which are close coupled and integrated within a single compact body – the Turbinator is available for 1% or 3% foam mixing ratios.
Pros
- No external power source required
- Easy Set-up and operation: plug and play
- Integrated foam pump and motor
Cons
- Fixed foam mixing rate 1% or 3%
- Consumes water pressure to drive the foam pump
- 12,000 L/min max flow per single unit
Electronic foam mixing system
The Knowsley electronic foam mixing system that very accurately mixes foam concentrate and water based on the actual firewater demand of the system.
It does this by continually monitoring the firewater and foam concentrate flows using electromagnetic flowmeters and real-time adjustment of the concentrate control valve.
The accuracy and stability of the system is based on the combination of specially selected components and a unique control system with state-of-the-art logic – developed specifically for this system.
Pros
- Variable proportioning rates 0,5% – 6%
- Very wide proportioning flow range up to 150,000 l/m
- Consumes no water pressure
- Environmentally friendly testing
Cons
- Requires external power source
- Requires foam pumping system
- Requires skilled technicians for maintenance