Marine Fire Pumps: The Ultimate Guide

December 9th, 2020

Everyone knows that the ocean is full of dangers. However, with water everywhere you look, you may not realize that fire is one of the most significant hazards on ships.

Despite being on the water, ships have lots of heavy machinery and flammable fuels. That is why there are always major ship fires that make news headlines every year.

Because of this, it’s essential to have a robust and reliable marine fire pump onboard every ship.

In this article, you’ll get a complete look at marine fire pumps:

  • What marine fire pumps are
  • Types of fire pumps found on ships
  • How to choose the right marine fire pump (including maritime regulations)
  • How to install them
  • Marine fire pump maintenance
  • The best marine fire pumps

By the end of it, you’ll know everything you need to know about marine fire pumps.

marine-fire-pump

Image by Viola ‘ from Pixabay

What are Marine Fire Pumps?

Marine fire pumps provide the water to extinguish any fire in a ship. These pumps carry seawater or foam to put out the fire quickly before it gets out of hand. Most ships are required to have several of these on board.

Having a fire system on board is critical. A fire onboard can put everyone’s life at risk. That’s why there are strict maritime regulations concerning these that you need to know of (more on this later).

When not in use, a marine fire pump can also serve as a general service pump. You can use fire pumps to assist with ballasting, or, in case the ship is sinking, help the emergency bilge pump remove water.

However, a fire pump should never pump any type of oil or flammable liquid.

Large ships should also have an emergency fire pump, which should not assist with anything except fire emergencies. These should be able to run even if the main fire pumps fail.

Types of Marine Fire Pumps

There are two types of fire pumps: centrifugal and positive displacement.

Both of these have their advantages and disadvantages. Let’s have a closer look at each one.

Centrifugal Fire Pumps

Centrifugal fire pumps are the most common type for ships. Of all pump types, these have the highest capacities – something that is essential in fire fighting.

When a fire breaks out, you’ll need as much water or foam as possible to put it out. That’s why centrifugal types are the first choice for marine fires.

Centrifugal types are also the most affordable, simple-designed, and most comfortable to maintain.

The only downside of centrifugal types is that they need priming before they can run. If you run one of them dry, they can get seriously damaged.

However, priming is easy. And there are also several fast ways to prime your centrifugal pump automatically.

How Centrifugal Pumps Work

Centrifugal pumps use a spinning impeller and a volute casing to pump water. As the impeller spins, it uses centrifugal force to push water to the pump’s sides and out the discharge.

Centrifugal types connect to motors that allow them to spin at incredible speeds. Thanks to this design, they have the highest capacities of all.

The impellers of centrifugal types have solid vanes that curve outwards. As the impeller spins, the vanes fling incoming water to the sides with incredible force.

The shape of the volute casing is also essential. It starts narrow and gets wider towards the discharge. This snail-shape forces water out of the discharge instead of spinning the water around the casing.

Once water leaves the discharge, it creates low pressure, which pulls in more water.

Because centrifugal types rely on centrifugal force and water leaving the discharge to pull in more water, they can’t run until they are full of water first. If there is air, it will spin around the casing instead of leaving the discharge.

The way they work is why priming is essential to get centrifugal types up and running.

Advantages and Disadvantages

Advantages:

  • Highest capacity
  • Simple design
  • Easy maintenance
  • Affordable

Disadvantages:

  • Needs priming

Positive Displacement Fire Pumps

The other type of fire pump you find in ships are positive displacement types.

There are several variations of positive displacement pumps, but they all work in similar ways and have the same advantages and disadvantages.

Compared to centrifugal types, positive displacement types can discharge higher pressures of water. They are even capable of releasing mist, which helps put out certain types of fire.

Positive displacement types are also better at handling foam. Since water isn’t very effective at putting out oil fires, having foam to blanket the fire will significantly help.

Positive displacement types’ ability to pump at high-pressures can be a valuable addition to your ship’s safety. However, they aren’t as popular as centrifugal fire types for several reasons.

For one, they can’t pump nearly as much water as centrifugal types can. Positive displacement types are also more expensive and difficult to maintain.

How Positive Displacement Pumps Work

Positive displacement types use cavities with one-way valves on either side to work. As the hole expands, a vacuum is created, which pulls water in through the inlet valve. As the cavity collapses, this forces the trapped water out of the discharge valve.

Both the inlet and outlet valves are one-way valves. Water can flow in one direction, but the valve seals shut when water tries to go the other way.

Because of the way they work, positive displacement types can pump air and highly-viscosity liquids. They are a lot better at pumping at high-pressures than centrifugal types are.

As said above, there are several variations of positive displacement types. While they work the same way, they all use different methods to expand and collapse the cavity.

For firefighting, positive displacement types can be gear, piston, or plunger pumps.

Advantages and Disadvantages

Advantages:

  • Can handle high pressure
  • Better at pumping mist and foam
  • Doesn’t need priming

Disadvantages:

  • Lower capacities
  • Expensive
  • High maintenance

How to Choose a Marine Fire Pump

Choosing the right fire pump mostly depends on the size and type of ship you have. Because of a fire’s hazardous nature in machine spaces, there are strict regulations for selecting a fire pump.

If your ship is heading out to the ocean, you must get a pump that is both ABS and DNV certified, ensuring that you are complying with international maritime standards.

Aside from that, there are several other things you should know before getting a marine fire pump.

What Type of Marine Fire Pump Should You Get?

Because large ships are required to have high GPM fire systems, centrifugal types are the go-to choice.

No other type of pump can move water faster than them. That’s why the main fire pump in ships is almost always centrifugal.

However, having a positive displacement type inject foam into the water stream can help when there is an oil fire.

Positive displacement types may not have enough GPM to be used as the main fire pump, but they can assist in firefighting by supplying foam to the fire line.

Some regulative bodies, such as the USCG, require ships to have a foam system in place.

What Are the SOLAS Capacity Requirements for Marine Fire Pumps?

Main fire pumps’ capacity requirements depend on your bilge pumps’ capacity and the type of ship you have. Your fire pump should have a capacity of not less than ⅔ of the bilge pumps’ capacity for passenger ships. For cargo ships, fire pumps should contain not less than 4/3 of the bilge pumps’ capacity in a passenger ship of the same dimension.

To get an idea of how much GPM that is, SOLAS requires the main bilge pump to pump water through the main pipes at 2m/s minimum.

The GPM of your fire pumps needs to be high enough to deliver a strong stream of water in your fire hose. Keep in mind that in centrifugal types, flow is affected by pressure. The higher the pressure, the less flow your pump will give (more on this later).

How Much Head and Pressure Do You Need From Marine Fire Pumps?

Aside from flow, it’s also important to consider how much head you will need from your marine fire pump. If your pump has an insufficient head, you won’t be able to get enough pressure at your fire jet.

Pressure Requirements for Marine Fire Pumps

The pressure requirements of your main fire pump depend on the gross tonnage and type of ship you have:

Passenger ships:
<4,000 GT = .30 N/mm2(44 psi)
>4,000 GT = .40 N/mm2(58 psi)
Cargo ships:
<6,000 GT = .25 N/mm2(36 psi)
>6,000 GT = .27 N/mm2(39 psi)

How to Calculate Head

You can calculate how much head you need by adding the elevation, friction loss, and pressure of your fire pipes.

Elevation + friction loss + pressure = total head

Elevation refers to the vertical rise from your fire pump to the discharge in feet. You don’t consider the length of your pipes when calculating elevation – just the total vertical height.

Friction loss refers to the amount of flow loss due to friction between the water and the pipes. To determine friction loss, you’ll have to use a complicated equation with many factors to it. That’s why we recommend using a friction loss calculator for this.

Pressure refers to how much pressure is in the pipes. The equation for this is 1 PSI = 2.31 head feet.

Once you add those together, you will get how much total head you need. Keep in mind that when calculating the total head, you also need to factor in the elevation, friction loss, and pressure of the suction pipe.

Do You Need an Emergency Fire Pump?

If there is a fire in the engine room, this may cause the main fire pump to stop working. That is why it is wise for ships to have an emergency fire pump available.

SOLAS requires passenger ships over 1,000 GT and cargo ships over 2,000 GT to have at least one emergency pump outside the engine room. This pump should be independently powered and should not suction from the same sea chest as the primary fire pump (except in special cases).

You may power your emergency fire pump using a diesel engine or an electrical motor from the emergency generator. It must deliver a capacity of at least 110 GPM and a horizontal throw of over 40 ft.

How to Install a Marine Fire Pump in Your Ship

There are also plenty of regulations that govern how and where to install a marine fire pump. Knowing these will ensure that you are as safe as possible from fire and comply with international standards.

Below are some of the most important things to consider when installing a fire pump on your ship.

Marine Fire Pump System Overview

Your marine fire system should connect to a network of pipes that can extinguish fire anywhere on the ship.

The suction comes directly from the sea. It passes through a sea chest, which filters out any large debris that might clog the pipes.

The water flows into the main fire pump and or general service pump. From there, a series of valves determine where the water will ultimately end up. Lines lead up to the machinery platforms, decks, steering room, diesel generator, and any other area that may catch fire.

The emergency pump (if present) also connects to the same series of pipes. However, the inlet should not come from the same sea chest as the main fire pump. On special occasions, it may, but this will require its pipes to penetrate the engine room.

If you have a sprinkler system onboard, the fire pump can also refill the sprinkler tank when it gets used up. Note: the water from the sprinkler system comes from a high-pressure sprinkler tank, not directly from the pump suction.

The primary fire and general service pump also connect to the ballasting and bilge transfer pipe systems. Once again, valves determine where the water comes from and where it goes.

How Many Marine Fire Pumps Do You Need?

Again, the amount of fire pumps you need depends on the type and weight of your ship.

Passenger ships:

>4,000 GT = At least 3

<4,000 GT = At least 2

Cargo ships:

>1,000 GT = At least 2

<1,000 GT = At least 1

Those are the requirements for the main marine fire pumps inside the engine room. They do not include the emergency pump outside the machine spaces.

How Should You Power Marine Fire Pumps?

Marine fire pumps need a powerful motor to spin the impeller at the appropriate speed. They are powered electrically by the main supply of the ship.

The emergency fire pump outside the engine room must be independently powered. Either a diesel engine or the emergency generator must power it. Having an independently-powered emergency pump is crucial since a blackout in the engine room will stop the main fire pump from working.

Marine Fire Pump Controls

You can operate a marine fire pump manually at its location. However, fire pumps should be controllable from several areas. With this, if one control is inaccessible due to the fire, you can still turn on the fire pump.

It should be possible to control the marine fire pump from the engine control room, the bridge, and the fire station.

There are no automatic controls for the primary fire system. You will have to direct the water to the fire manually. However, if you have a sprinkler system on board, this will turn on automatically if it detects fire in the area.

Marine Fire Pump Pipes

As mentioned earlier, a marine fire pump connects to a complex system of pipes. These pipes must handle seawater corrosion, which is why most marine fire pipes use galvanized metal.

The fire pipe size is usually between 50mm-180mm, depending on how big the ship and what type it is.

For centrifugal types, the pipes must have non-return valves. This way, water won’t flow back once the pump switches off.

If you are using a positive displacement pump, you must have pressure-relief valves. If positive displacement types run when the discharge end is closed, this can increase the pipes’ pressure to alarming levels. A pressure-relief valve will let off the building pressure inside the lines.

How to Prime a Marine Fire Pump

Centrifugal marine fire pumps need to priming before they can operate. Because time is a critical factor in fire emergencies, it’s best to prime the marine fire pump ahead to ready it for use anytime (another reason to use non-return valves).

The step-by-step of priming a centrifugal pump will differ from model to model. Read your manufacturer’s instructions to learn how to do it properly. Generally, however, priming a pump takes six steps:

  1. Close discharge valve
  2. Open top vent
  3. Open outside supply line to start filling the pump
  4. Wait for the fluid to reach the top vent
  5. Close top vent
  6. Close supply line

There are also self-priming centrifugal pumps.

These have a priming mode where the pump can fill itself with water. In this mode, centrifugal types work like a positive displacement pump. The air is forced out the discharge instead of turning around the pump like on a regular pump.

As the air leaves, this creates low pressure, which sucks in more air and, eventually, water.

When the pump fills up with water, the pump switches to pump mode – allowing the centrifugal pump to pump at its high capacities once again.

You may also use ejectors or vacuum pumps to prime your centrifugal pump. Connect these to the pump, and they can pull the fluid up into the pump. Once the centrifugal pump fills up, you may turn it on and begin pumping.

It’s best to leave your fire pump primed and ready to go at a moment’s notice. You don’t want to waste time priming as the fire rages.

However, a vessel operating in cold water seas could lead to water freezing, so one should drain the water in the fire pipes.

Marine Fire Pump Maintenance

Centrifugal types are famous for the fact that they are simple-designed and easy to maintain. However, it is still essential to perform checks daily, weekly, monthly, and semi-annually.

These will ensure that your marine fire pump is running correctly and is always ready for disaster strikes.

Daily checks

Visual Inspection: Make sure to inspect for any visible abnormalities when doing the engine room rounds.

Temperature Check: Aside from a visual inspection, you should also take the motor’s temperature driving the pump every day.

If you are using a frame-mounted centrifugal pump, you need to check the bearings’ temperature as well.

Sound Check: Make sure to listen for any unusual noises. The pump may look and feel fine, but listen for any loose parts because that is often the first problem.

Weekly Checks

Vibration Check: If the fire pump vibrates when in use, investigate the cause right away. It may be the bearing, coupling, foundation, or it may be that your pump is misaligned.

Whatever the case, inspect your pump immediately if you find it vibrating.

Discharge Pressure Check: You should check the pressure of your fire pump’s discharge once in a while. A drop in discharge pressure signals that there may be a leak or that the sea chest filter is clogged.

If discharge pressure is not normal, identify and fix the problem immediately.

Power Reading Check: Take a power reading of your pump’s motor every week. Monitoring its amperage is a great way to spot problems before they grow.

Monthly Checks

Coupling Check: Check the alignment of your pump’s coupling with its motor every month. Also, you may use this time to grease the coupling and bearings.

Foundation Bolt Check: Even without vibrations, it’s a good idea to check the bolts and see if they need fastening.

Semi-Annual Checks

Run Standy Pumps: If your emergency fire pump has been on standby for several months, you should run it.

Running Hours Check: Every mechanical part of a pump has a set lifespan. By the time the running hours of a mechanical part is over, you should replace it even if it still works.

You cannot take chances with fire emergencies. All the parts always need to be in ideal condition because lives are at stake.

Best Marine Fire Pump

When things go wrong, you cannot take your chances. That is why when choosing a marine fire pump, you should get one that is excellent in quality.

For your fire pump needs, no company is as reliable as CarverPump.

Their GH end-suction centrifugal pump, which is both ABS and DNV certified, is the perfect pump to put out any fire that breaks out. You can get the GH in stainless steel alloy or nickel-aluminum bronze – which are ideal for handling seawater.

GH

Aside from the GH, CarverPump also offers several other pumps for marine use. If you need a quality pump that you can rely on, get one of these.

Carver Pump is a leading manufacturer of marine fire pumps. With over 80 years of building pumps to the most challenging military and engineering standards, you can trust Carver Pump to meet your demands.

As one of the first American ISO 9001 certified companies, you can expect superior pumps, R&D, and customer service. When you talk with one of our distributors or with us directly, we take the time to understand your needs fully and provide you with the best possible solution.

Based in Muscatine, Iowa, all CarverPump pumps are proudly American made.

The ocean is not the place to find that your marine pumps don’t cut it. Trust your shipboard services to Carver Pump, the industry leader in shipboard centrifugal pumps.

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