Foam Bladder Tank with Ratio Controller

The bladder tank foam proportioning system stores foam concentrate in a flexible elastomeric bladder inside an ASME Section VIII Division 1 carbon steel pressure vessel, and proportions it into the fire water stream through a ratio controller. It uses only the pressure of the fire water supply: no foam pump, no external power and no drive.

It proportions the concentrate automatically over a wide range of flow and pressure, with low pressure loss.

Principle of operation

The concentrate is stored inside the bladder. The space between the bladder and the vessel wall is connected to the fire water supply upstream of the ratio controller.

When fire water flows, water enters the vessel around the bladder and squeezes it, pushing the concentrate out at the same pressure as the incoming water to the concentrate inlet of the ratio controller.

In the ratio controller the water passes through an inlet nozzle (mouth piece) into a diffuser. The jet creates a low-pressure zone at the concentrate inlet, and the concentrate enters through a metering orifice sized for the required proportioning rate. As the water flow changes, the pressure difference across the orifice changes with it, so the concentrate flow follows the water flow and the proportioning stays within limits over the listed flow range.

After operation the bladder is refilled with concentrate once the water side is drained. The vessel and bladder do not need to be removed.

Tested to UL 162

The bladder tank and ratio controller combination is UL Listed under File No. EX29134 (Proportioners, Foam Concentrate). Representative samples were tested to UL 162, Standard for Foam Equipment and Liquid Concentrates, including:

• Hydraulic characteristics (equivalent length)
• Equipment pressurization
• Induction rate
• Salt spray corrosion
• Hydrostatic pressure
• Elastomeric parts (reinforced bladder)

Scope of supply

Standard: the bladder tank — pressure vessel with bladder, legs (vertical) or saddles (horizontal) and name plate — and a ratio controller, DTL-FRC-B or DTL-FRC-SS, with a stainless steel body, sized to suit the design flow.

The pressure vessel is not supplied with an over-pressure relief device unless one is ordered; the owner or system designer decides whether the water supply requires one.

Optional:

• Water spool and foam spool
• Water and foam piping, water charging valve, foam supply valve and non return valve (valves SS 316 standard, SS 304 available)
• Vessel and bladder vent and drain valves
• Pressure gauges, water and foam
• Level indicator with valves
• Relief valve, bronze or SS 316
• Hydraulically operated foam concentrate valve
• Ladder (tanks of 1,000 L and above; smaller tanks on request)
• Foam filling kit
• Radiography of shell and dished ends
• Ratio controller with a carbon steel body
• Seaworthy wooden packing for export

Ratio controller

A venturi-type proportioner installed in the water line downstream of the bladder tank. Model DTL-FRC-B has a bronze (gun metal) inlet nozzle and diffuser cone; model DTL-FRC-SS has them in SS 304 or SS 316, as the client requires. The metering orifice at the concentrate inlet is sized for the proportioning rate the client specifies. Each controller carries an SS 304 nameplate with its size, serial number, rated pressure and the UL mark, and a flow direction arrow.

• Install with the flow arrow on the body in the direction of water flow.
• Provide at least 5 pipe diameters of straight, unobstructed pipe upstream and downstream.
• Support the upstream and downstream pipes so that no strain is put on the controller.
• Make provision in the piping for removing the controller.

Installation

• Install as per the DTL installation manual (DTL/BT/MAN-01), NFPA 11 and the authority having jurisdiction, by qualified personnel.
• On receipt, check the tank, trim and piping for transit damage, and the markings against the order.
• Use lifting gear suitable for the weight of the tank, and anchor the tank to the floor.
• Keep at least 0.9 m (3 ft) clear above and around the tank for piping and maintenance.
• Vertical tank: keep access from the top for future removal of the piping and bladder. Horizontal tank: keep vertical clearance, and a clear area at one end at least twice the length of the tank, for bladder removal.
• Do not weld on the tank shell — welding heat damages the bladder.

Filling, inspection and maintenance

• Fill the bladder with a foam concentrate pump through the fill connection, venting the bladder until concentrate free of air bubbles comes out of the vent. Manual filling is only for small top-ups.
• Release the tank pressure before opening any valve.
• Keep all valves in their normal stand-by positions; check that the bladder is full and that the water supply gives the design pressure and flow.
• The bladder is shipped filled with air to hold its position in the tank.
• After any operation, isolate the tank, flush the ratio controller and system with water, then refill the bladder.
• Inspect the tank, flanges and piping regularly for damage and leakage, and check flange bolts for tightness.
• A bladder that needs replacing is removed and fitted through the manhole by qualified personnel, as described in the manual.