Emergency Fire Pump Systems on Ships

Emergency fire pumps are vital safety equipment on ships, strategically located to ensure operability even if a fire disables the main fire pumps or their power source. Their placement outside the main machinery space is crucial due to the inherent fire risks in a confined environment like a vessel.

Here are three common areas for installing emergency fire pumps and the reasons behind their placement:

• Steering Flat: This location is often chosen because it is relatively remote from the main engine room, providing a good vantage point for accessing the fire main system. This separation helps ensure the pump remains operational even if a major fire erupts in the engine room.
• Shaft Tunnel: Similar to the steering flat, the shaft tunnel offers a degree of separation from the main machinery space. This makes it a viable and protected location for the emergency pump, minimizing its exposure to a machinery space fire.
• Forward Part of the Ship (e.g., Bow Thruster Room): Placing the pump at the ship's fore ensures that a fire in the aft part or engine room does not incapacitate the emergency firefighting capability. This forward placement provides an independent and accessible means of firefighting, crucial for overall ship safety.

Priming using Eductor.

There are 2 solenoid valve which opens during the start of the pump (Check the diagram below). 7 bar air keeps flowing through the air eductor. Eductor creates vacuum and takes out air from our pump casing and water floods into the pump casing. When the pressure transmitter senses the discharge pressure above a certain level, the solenoid valve closes.

Description:

1. Compressed Air Inlet: High-pressure compressed air (from the ship's air system) is supplied to the eductor.
2. Nozzle: Inside the eductor, the compressed air passes through a convergent nozzle, increasing its velocity and creating a low-pressure zone (venturi effect).
3. Suction Port: The low-pressure zone at the nozzle's throat connects to the suction line of the fire pump. As air flows rapidly, it entrains the air from the fire pump's suction line.
4. Discharge: The mixture of compressed air and the air drawn from the suction line is discharged overboard or to an appropriate drain.
5. Priming Action: This continuous removal of air from the suction line creates a partial vacuum. Atmospheric pressure acting on the surface of the sea water then pushes the water up the suction pipe and into the pump casing, "priming" the pump. Once water flows, the primer is shut off, and the fire pump can then take over and build pressure.

Expected Suction Lift from a Single-Stage Pump System:

The theoretical maximum suction lift at sea level is approximately 10.3 meters (33.8 feet) of water, corresponding to atmospheric pressure. However, in practical applications, due to factors such as:

• Vapor Pressure of Water: Water starts to vaporize at lower pressures, especially at higher temperatures.
• Friction Losses: Resistance to flow in the suction piping, valves, and strainers.
• Air Leaks: Even small leaks in the suction line can significantly reduce lift.
• Pump Efficiency: No pump is 100% efficient at creating a perfect vacuum.

Therefore, the practical maximum suction lift for a single-stage centrifugal pump system is typically much lower, around 4 to 7 meters (13 to 23 feet). This is why emergency fire pumps, when placed above the waterline, always require a reliable priming system.

Water Jet Capacity:

The emergency fire pump must be capable of delivering at least two jets of water, each with a minimum pressure of 2.5 bar at any hydrant. The pump's capacity should be at least 40% of the total capacity of all fire pumps, but not less than 25 m³/hr. For cargo ships, the fire main's diameter needs to be sufficient for a discharge of 140 m³/hr.

Precautions in Sub-Zero Temperatures:

In freezing weather conditions, several precautions are crucial to prevent damage and ensure system operability:

• Draining Lines: It is essential to drain the fire and deck wash water lines after use to prevent water from freezing, which can cause pipe damage or blockages.
• Cold Start Capability: If the emergency fire pump is diesel engine-driven, it must be capable of starting easily in cold conditions (0°C).
• Heating Arrangements: If the pump is motor-driven and located in an unheated space, heating arrangements should be provided to ensure its readiness and prevent freezing of any residual water.

Description of Components and Connection:

• Sea Chest: The point of seawater intake for the pump.
• Emergency Fire Pump: The pump unit, typically located outside the main machinery space.
• Isolation Valve (Sea Chest): A valve at the sea chest to isolate the emergency fire pump's suction from the sea.
• Emergency Fire Pump Suction Line: Piping connecting the sea chest to the emergency fire pump.
• Isolation Valve (Emergency Fire Pump Suction): A valve to isolate the suction side of the emergency fire pump.
• Emergency Fire Pump Discharge Line: Piping connecting the pump to the main fire main.
• Isolation Valve (Emergency Fire Pump Discharge): A valve to isolate the emergency fire pump from the fire main.
• Fire Main: The main firefighting water distribution system running throughout the ship.
• Isolation Valves (Fire Main): Valves fitted within the fire main, especially outside machinery spaces, to isolate sections during maintenance or in case of a fire within the engine room. For tankers, these valves are fitted on the poop and tank deck at intervals not exceeding 40 meters.
• International Shore Connection: A standardized flange with nuts, bolts, washers, and a coupling for the ship's fittings. It is used to connect the ship's fire main to a shore-based or another ship's firefighting system.

Reasons for these Connections and Valve Placements:

• Independent Suction: The emergency fire pump must have its own independent suction line. This ensures a continuous water supply even if the main sea chests or primary piping for the main fire pumps are compromised during an emergency.
• Isolation Valves (System Integrity): Isolation valves are critical for maintaining the integrity and functionality of the fire main system. They allow for:
  • Sectional Isolation: Specific sections, such as the machinery space area with the main fire pumps, can be isolated if a fire occurs there, preventing pressure loss throughout the rest of the system.
  • Emergency Supply: This isolation enables the emergency pump to supply water to the unaffected parts of the ship even if the main fire pumps are disabled.
  • Maintenance: Valves facilitate safe maintenance of pump or piping sections.
• International Shore Connection (External Assistance): This connection is vital for receiving external firefighting assistance. If the ship's fire pumps are completely disabled, this standardized interface allows for connection to shore-based or other ship's firefighting resources. The International Shore Connection is usually located in a readily accessible position, such as near the gangway or on both sides of the accommodation area, and its exact location is indicated on the ship's fire control plan.