What Is a Foam Proportioner on a Fire Truck? PH Series Explained-fire-trucks.com

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The PH series around-the-pump foam proportioner is a professional foam concentrate suction and delivery device designed specifically for foam firefighting systems and fire trucks. It is installed within the supporting fire truck fire pump and water supply system and serves as the core device for achieving automatic proportional mixing of foam concentrate and clean water.

PH series foam proportioner installed on a fire truck

Unlike traditional manual mixing equipment, this proportioner operates on the principle of water pressure differential: according to the selected flow rate setting, it draws a precise amount of foam concentrate from the foam tank, delivers the foam concentrate to the fire pump inlet, and thoroughly mixes it with pressurized water to form a uniform foam solution. The properly mixed solution is then delivered to foam-generating devices or discharge equipment for efficient firefighting operations.

I. Structure of the PH Series Foam Proportioner

1. Adjustment Handle and Indicator Plate

The indicator plate is marked with different values corresponding to the mixed solution flow rates required by the connected foam-generating devices. Rotating the adjustment handle to the required flow rate position sets the operating flow rate of the proportioner.

2. Regulating Valve

The regulating valve controls the amount of foam concentrate passing through the proportioner based on the handle setting. Once the handle position is determined, the valve opening determines the foam concentrate suction flow rate.

3. Narrowed Flow Passage Section (Negative Pressure Generation Section)

This is the core component of the proportioner. As water flows through this narrowed passage, its velocity increases and its pressure drops below atmospheric pressure, creating a negative pressure. This negative pressure is transmitted to the foam concentrate suction port, drawing foam concentrate from the storage tank.

4. Mixing Chamber

The mixing chamber is where foam concentrate enters the water stream. The foam concentrate merges with the water here to form foam solution. An arrow cast on the mixing chamber exterior indicates the flow direction—the arrow tail connects to the pump discharge line, and the arrow head connects to the pump inlet line.

5. Diffuser Tube

The diffuser tube reduces the velocity of the mixed solution as it exits the proportioner, converting kinetic energy back into pressure energy so that the mixed solution enters the pump inlet line at an appropriate pressure.

II. How Does the PH Series Foam Proportioner Work?

The PH series around-the-pump foam proportioner uses the water flow and pressure conditions within the fire pump system to draw foam concentrate from the foam tank, introduce it into the fire pump inlet, and mix it with water to form foam solution. The fire pump then pressurizes the mixed solution again and delivers it to downstream foam discharge equipment.

Step 1: The fire pump pressurizes the water

Water enters the fire pump from the fire truck's water tank or another suitable water source. The fire pump pressurizes the water and delivers it through the discharge line.

Step 2: A portion of pressurized water enters the proportioner

A portion of the pressurized water from the fire pump discharge side is diverted to the foam proportioner. This pressure and flow condition provides the necessary operating conditions for the proportioner to draw foam concentrate from the foam tank. The proportioner is typically installed near the fire pump and connected to the pump inlet and discharge lines according to the system configuration.

Step 3: The proportioner controls foam concentrate flow

As water flows through the proportioner, its internal flow passages and regulating mechanism create the conditions needed to draw foam concentrate. The operator selects the appropriate operating setting using the adjustment handle and indicator plate. Different values on the indicator plate correspond to the mixed solution flow rates required by the connected foam generators or discharge devices. For example, the PH64 proportioner provides different adjustment settings corresponding to 24, 32, 48, and 64 L/s mixed solution flow rates.

Step 4: Foam concentrate is drawn from the foam tank

Foam concentrate flows from the foam tank through the foam inlet line into the proportioner. The proportioner controls the foam concentrate flow rate based on the selected setting and the actual operating conditions of the firefighting system.

Step 5: Mixed solution returns to the fire pump inlet

The foam concentrate enters the system and mixes with the water flow. The resulting foam solution then flows to the fire pump inlet. The fire pump pressurizes the mixed solution again and delivers it through the discharge line to downstream firefighting equipment, such as:

• Foam fire monitors
• Foam nozzles
• Foam generators
• Other compatible foam discharge devices

The entire working process can be simplified as:

Water tank → Fire pump → Foam proportioner → Fire pump inlet → Fire pump → Foam discharge equipment

III. PH Series Performance Parameters

The PH series is available in three main models: PH32, PH48, and PH64, where the number indicates the maximum foam solution flow rate in liters per second.

Common operating parameters:

Parameter	Specification
Inlet working pressure (pump discharge)	0.6–1.4 MPa
Outlet working pressure (pump inlet)	< 0.03 MPa
Mixing ratio	6–7% (typically for 6% foam concentrate)
Mounting position	Near fire pump, connected between discharge and inlet lines

Flow rate and foam concentrate suction for each model:

Model	Handle Setting (L/s)	Foam Concentrate Drawn (L/min)	Example Foam Device
PH32	4	0.24	P
	8	0.48	PC8
	16	0.96	PC16
	24	1.44	PC24
	32	1.92	PL32
PH48	16	0.96	PCL8×2
	24	1.44	PCL8×3
	32	1.92	PCL16×2
	48	2.88	PL48
PH64	24	1.44	PQ4×6
	32	1.92	PQ8×4
	48	2.88	PQ16×3
	64	3.84	PL32×2

IV. How Is the Foam Proportioner Installed on a Fire Truck?

Installation position: The proportioner must be installed near the fire pump, with the inlet connected to the pump discharge line and the outlet connected to the pump inlet line. The foam concentrate suction port connects to the foam tank.

Critical installation requirement: The fire pump inlet pressure must be maintained below 0.03 MPa. This is typically achieved by ensuring adequate suction conditions and avoiding excessive pressure on the inlet side.

Pressure relationship: When the inlet pressure is within the 0.6–1.4 MPa range, the proportioner draws a relatively constant amount of foam concentrate at a given handle setting. However, if the foam-generating devices operate at different pressures, the mixed solution flow rate changes, which in turn affects the actual mixing ratio. Operators should adjust the discharge pressure of the foam-generating devices to keep the mixing ratio within the intended range (typically 6–7% for 6% foam concentrate).

Maintenance: After each use, flush the proportioner with clean water to prevent foam concentrate residue from causing corrosion or blockage. Periodically inspect the adjustment handle and indicator plate for smooth operation.

V. Common Problems with Foam Proportioners

Whether a foam proportioner works properly depends closely on system pressure conditions and the configuration of valves, piping, and equipment.

Problem	Possible Cause	Recommended Check
Foam concentrate not drawn	Fire pump inlet pressure too high	Check fire pump inlet pressure
Unstable foam concentrate output	Incorrect operating conditions	Check fire pump and discharge pressure
Foam mixing ratio changes	Mixed solution flow rate changes	Check downstream equipment flow and pressure
Insufficient foam concentrate flow	Valve or piping problem	Check foam inlet valve and piping
Abnormal proportioner adjustment	Incorrect adjustment setting	Check adjustment handle and indicator plate
Foam system fails to achieve expected performance	Equipment mismatch	Check compatibility between proportioner and discharge devices

VI. FAQ

Q1: How does a fire truck foam proportioner work?

A: The proportioner draws foam concentrate through its internal flow passages and regulating mechanism, delivers it to the fire pump inlet, mixes the foam concentrate with water, and then sends the mixed solution to downstream foam equipment.

Q2: Why can't the fire truck foam proportioner draw foam concentrate?

A: The most common cause is that the pump inlet pressure exceeds 0.03 MPa, or there is a blockage in the piping or a valve not fully open. Check inlet pressure and piping flow first.

Q3: What is the difference between PH32, PH48, and PH64 foam proportioners?

A: The main difference is the supported mixed solution flow rate range. PH32 reaches a maximum of 32 L/s, PH48 reaches 48 L/s, and PH64 reaches 64 L/s.

Q4: What should the fire pump inlet pressure be?

A: The fire pump inlet pressure should be maintained below 0.03 MPa, because excessive inlet pressure can affect the proportioner's ability to draw foam concentrate.

Q5: What is the difference between an around-the-pump proportioner and a balanced-pressure proportioner?

A: The around-the-pump type (PH series) relies on the fire pump's own pressure differential to create negative pressure and draw foam concentrate. It has a simple structure and low cost, but the mixing ratio is more affected by changes in pump inlet pressure and foam-generating device flow rate. A balanced-pressure proportioner uses an independent foam pump to actively inject foam concentrate into the water stream, offering higher mixing accuracy and a wider flow adaptation range, but with a more complex structure and higher cost. Selection should be based on system accuracy requirements and budget.

Q6: After the proportioner handle is set, why does the actual mixing ratio still change?

A: Within the 0.6–1.4 MPa inlet pressure range, the proportioner draws a relatively constant amount of foam concentrate at a given setting. However, when foam-generating devices operate at different pressures, their mixed solution flow rate changes. When the equipment flow rate deviates from the proportioner handle setting, the actual mixing ratio changes accordingly. Operators should adjust the discharge pressure of the foam-generating devices so that their flow rate matches the proportioner handle setting, ensuring the mixing ratio remains within the reasonable range of 6–7%.

VII. Conclusion

As a core component of a foam fire truck's firefighting system, the working performance of the PH series around-the-pump foam proportioner directly determines the overall firefighting capability of the foam fire truck. Mastering its standard operating pressure, model matching parameters, installation specifications, pressure control requirements, and supporting valve functions is essential for fire equipment maintenance, daily commissioning, and on-site firefighting operations.