It is recommended to divide the engines into several circuits in multi-engine installations. One reason is of
course redundancy, but it is also easier to tune the individual flows in a smaller system. Malfunction due
to entrained gases, or loss of cooling water in case of large leaks can also be limited. In some installations
it can be desirable to separate the HT circuit from the LT circuit with a heat exchanger.
The external system shall be designed so that flows, pressures and temperatures are close to the nominal
values in Technical data and the cooling water is properly de-aerated.
Pipes with galvanized inner surfaces are not allowed in the fresh water cooling system. Some cooling water
additives react with zinc, forming harmful sludge. Zinc also becomes nobler than iron at elevated temperat-
ures, which causes severe corrosion of engine components.
Ships (with ice class) designed for cold sea-water should have provisions for recirculation back to the sea
chest from the central cooler:
•
For melting of ice and slush, to avoid clogging of the sea water strainer
•
To enhance the temperature control of the LT water, by increasing the seawater temperature
9.3.1 Stand-by circulation pumps (4P03, 4P05)
Stand-by pumps should be of centrifugal type and electrically driven. Required capacities and delivery
pressures are stated in Technical data.
NOTE!
Some classification societies require that spare pumps are carried onboard even though the
ship has multiple engines. Stand-by pumps can in such case be worth considering also for this
type of application.
9.3.2 Sea water pump (4P11)
The sea water pumps are always separate from the engine and electrically driven.
The capacity of the pumps is determined by the type of coolers and the amount of heat to be dissipated.
Significant energy savings can be achieved in most installations with frequency control of the sea water
pumps. Minimum flow velocity (fouling) and maximum sea water temperature (salt deposits) are however
issues to consider.
9.3.3 Temperature control valve, HT-system (4V01)
External HT temperature control valve is an option for V-engines.
The temperature control valve is installed directly after the engine. It controls the temperature of the water
out from the engine, by circulating some water back to the HT pump. The control valve can be either self-
actuated or electrically actuated. Each engine must have a dedicated temperature control valve.
96°C
Set point
9.3.4 Temperature control valve for central cooler (4V08)
When it is desired to utilize the engine driven LT-pump for cooling of external equipment, e.g. a reduction
or a generator, there must be a common LT temperature control valve in the external system, instead of
an individual valve for each engine. The common LT temperature control valve is installed after the central
cooler and controls the temperature of the water before the engine and the external equipment, by partly
bypassing the central cooler. The valve can be either direct acting or electrically actuated.
The set-point of the temperature control valve 4V08 is 38 ºC in the type of system described above.
Engines operating on HFO must have individual LT temperature control valves. A separate pump is required
for the external equipment in such case, and the set-point of 4V08 can be lower than 38 ºC if necessary.
9.3.5 Charge air temperature control valve (4V09)
The temperature of the charge air is maintained on desired level with an electrically actuated temperature
control valve in the external LT circuit. The control valve regulates the water flow through the LT-stage of
the charge air cooler according to the measured temperature in the charge air receiver.
The charge air temperature is controlled according to engine load.
92
Product Guide Wärtsilä 34DF - 3/2012
Product Guide
9. Cooling Water System
