Why Diesel Engines on Fire
Pumps Fail Prematurely
By Gene Allen, Allianz Energy, Houston
Allianz Global Corporate & Specialty www.agcs.allianz.com
Large diesel engines that are used to power fixed fire
protection water pumps appear to have a pattern of
premature failure due to “overheating.” When diesel
engines are used in over-the-road trucks, they normally
operate over 6,000 hours before major repairs are
needed. However, many of these engines on fixed fire
protection water pumps are failing with less than 500
hours of operation.
In large flammable and combustible liquids handling
complexes, the total area of process units can be as large
as a small town. Because of the facility size and
quantities of flammable liquids, multiple large (2,500 to
5,000 gpm) fire protection water pumps are needed.
These pumps are almost always powered by diesel
engines and not electric motors because if the facility
has a large incident, such as a Vapor Cloud Explosion
(VCE), the electrical supply could be impaired. Thus, the
diesel engine is the driver of choice for these large fire
protection water pumps.
All Photos and drawings
by author except
Engine on upper left only had 150 hours of
operation before the top end
overhaul / new head
Two ways to cool a water jacketed diesel engine
There are two methods of removing/rejecting heat from water jacketed internal combustion diesel engines:
1. The method used in trucks and cars is circulation of the heated water from the engine through a water to air heat
exchanger, called a radiator. Older engine driven firewater pumps, as well as newer, very large diesel firewater
pumps, use radiators for cooling.
In cold weather climates, firewater pumps installed outside would have to be freeze protected.
For current installations, most fire pumps are enclosed in buildings. If equipped with a radiator, the building can be
very expensive because it would require specially designed ventilation systems that allow fresh air into the building
and hot air exiting the radiator out of the building. See figure below.
Fig A.11.3.2(b) from NFPA 20, Installation of Stationary Pumps for Fire Protection, 2013 Edition
Two ways to cool a water jacketed diesel engine (continued)
2. When a diesel engine is used to power something in an enclosed area, like a boat or other marine application (e.g.
engine room), a liquid to liquid heat exchanger is used to cool the engine by exchanging the generated internal
heat with the cool “sea water” or “fresh water” from outside the boat. For decades, many diesel engine drivers on
fire pumps could be provided with these liquid to liquid heat exchangers instead of radiators. These exchanger
equipped engines get raw cooling water from the discharge side of the fire pump. Traditionally, a “shell and tube”
type heat exchanger is used. See the yellow exchanger mounted in front of the engine photo below.
The idea of using water to water heat exchangers has
been around in very expensive pleasure boats since the
1920’s. During World War II, between 1938 and 1945,
they were produced by the thousands to be used in
small to medium sized watercraft, landing craft, service
boats, and even fighting craft like the Patrol Torpedo
All those boats used one or more water to water heat
exchangers, not only to cool the engine, but also to cool
the engine intake combustion air from the supercharger.
Additionally, the engine room was kept cooler by using
the outside water to cool the engine exhaust manifold.
The limited space is more than evident when looking at
the photo below of a PT boat and its three giant 12
cylinder Packard engines.
These water to water heat exchangers typically were a
standard shell and tube exchanger with the hot engine
water on one side and the cool raw water on the other.
For corrosion resistance, the choice of metal depended
on whether the raw water was “salty” sea water or
“fresh” lake or river water. Also, the exchangers were
bolted together so they could be disassembled for
cleaning at regular intervals. This was done in order to
remove foreign material and scaling accumulation before
the exchanger plugged and the engine overheated.
PT boat Engine Room with three Packard V 12 engines
Photo with permission of T. Garth Connelly
The death of the radiator on engine driven fixed firewater pumps
When the economic pressures to reduce costs and
expenses came to the energy industry in the early
1980’s, many energy, petrochemical, and chemical
companies started outsourcing things like maintenance
and engineering. The design of fire protection water
systems slowly became one of the items that was
outsourced. Instead of an in-plant engineer designing
fire pumps and systems, outside vendors took on more
and more of the water system projects including new
firewater pump design.
These vendor contractors turned to public standards like
the National Fire Protection Agency’s Code for Stationary
Pumps (NFPA 20) for design information. Because NFPA
20 allowed the water to water exchangers, and fire
pump sets with these exchangers are less expensive to
manufacture and install, the contractors influenced the
firewater pump manufacturers to offer more pumps
with water to water exchangers. Industry quickly moved
in that direction. Without the experienced in-plant
engineer to be the gate keeper on the decision, the
radiator equipped diesel engine began to disappear.
While NFPA 20 provides good information on the design of the emergency bypass piping, (see above), almost all of the rest
of the raw water cooling loop, including the heat exchanger design, is left to the discretion of the manufacturer or vendor.
Premature overheating engine failure is from insufficient heat exchanger cooling
The “non-mechanical related” premature diesel engine
failures that have been reviewed had one thing in
common: they all had water to water heat exchanger
Why are these water to water heat exchanger
equipped engines failing?
1. The raw cooling water flow may be reduced below
the minimum recommended rate before the heat
• In some cases, the raw water line is reduced
in size at the supply connection to the source
water piping, as can be seen in the photos to
the right. These small connections may have
produced enough cooling flow when the
pump was installed, but over time, these
smaller orifices can be restricted by rust or
Raw water Normal and Bypass piping NFPA 20, Installation of Stationary Pumps for Fire Protection, 2013 Edition
Premature overheating engine failure is from insufficient heat exchanger cooling (continued)
• The inlet water strainers and/or regulator may be
too small for the larger diesel engines or may be
clogged with debris. It is recommended by some
engine manufacturers that the inlet strainers be
disassembled and cleaned before each weekly
engine churn test, not just blown down.
During a recent flow test of a new 3,500 gpm
firewater pump, when the pump was at rated
capacity with 150 psi discharge pressure, the raw
cooling water regulated pressure was 35 psi, as
expected. When the discharge was increased to
150% of rated capacity, the discharge pressure was
97 psi, also as expected. However, the raw cooling
water regulated pressure surprisingly dropped to
26 psi! Closing the primary supply side valve and
opening the emergency bypass side also resulted in
26 psi. But with both the primary and bypass valves
open the pressure returned to 35 psi.
The strainers were clean, so the strainers and/or
the regulators on this “new installation” unit were
simply too small to allow the correct amount of raw
cooling water to flow through the exchanger at the
lower inlet water pressure.
2. Even if the cooling water is flowing at the correct rate,
the diesel engine may still overheat if the heat
exchanger loses its thermal transfer efficiency due to
some plugging and/or internal parts “fouling” (coated
with silt or sludge) – see below. Neither the NFPA nor
the manufacturers suggest a schedule for internal
inspection of the heat exchanger.
The raw water going to the heat exchanger is
expected to be “clean”, maybe even potable water.
The strainers on the supply line and even the screen in
the regulator (a well-kept secret ) are designed to
remove small particles like sand and gravel. Typically,
the raw water source for fire protection water pumps
(at most of the large flammable/combustible liquids
processing complexes) is from rivers, ponds, or utility
water. These are certainly not potable water sources.
These water sources have materials, silt, mud flakes,
small shells, biological growth, organics, and slime
which can slide through the strainers, but collect in
the exchanger due to velocity changes or turbulence.
Any time the fire protection water is supplied by these
non-potable sources, the inspection of the internal
parts of any heat exchanger should be conducted on a
regularly scheduled basis.
FM (Factory Mutual) Approval, a third-party certification
organization, has recognized the low flow problem in
the raw water cooling loop by requiring an automatic
low flow alarm if the raw water flow is reduced more
than 75% of the required cooling water requirement.
This is a requirement of the FM approval standard for
diesel engine fire pump drivers, section 3.6.1.A May