through the pipe depends on the number of vent pipes to the tank and the size of the orifices in the vent
pipes. The table below can be used for guidance.
Table 9.1 Minimum diameter of balance pipe
Max. number of vent pipes
with ø 5 mm orifice
Max. flow velocity
(m/s)
Nominal pipe size
3
1.1
DN 32
6
1.2
DN 40
10
1.3
DN 50
17
1.4
DN 65
9.3.12
Drain tank (4T04)
It is recommended to collect the cooling water with additives in a drain tank, when the system has to be
drained for maintenance work. A pump should be provided so that the cooling water can be pumped back
into the system and reused.
Concerning the water volume in the engine, see chapter Technical data. The water volume in the LT circuit
of the engine is small.
9.3.13
Preheating
The cooling water circulating through the cylinders must be preheated to at least 60 ºC, preferably 70 ºC.
This is an absolute requirement for installations that are designed to operate on heavy fuel, but strongly
recommended also for engines that operate exclusively on marine diesel fuel.
The energy required for preheating of the HT cooling water can be supplied by a separate source or by a
running engine, often a combination of both. In all cases a separate circulating pump must be used. It is
common to use the heat from running auxiliary engines for preheating of main engines. In installations with
several main engines the capacity of the separate heat source can be dimensioned for preheating of two
engines, provided that this is acceptable for the operation of the ship. If the cooling water circuits are sep-
arated from each other, the energy is transferred over a heat exchanger.
Heater (4E05)
The energy source of the heater can be electric power, steam or thermal oil.
It is recommended to heat the HT water to a temperature near the normal operating temperature. The
heating power determines the required time to heat up the engine from cold condition.
The minimum required heating power is 5 kW/cyl, which makes it possible to warm up the engine from 20
ºC to 60...70 ºC in 10-15 hours. The required heating power for shorter heating time can be estimated with
the formula below. About 2 kW/cyl is required to keep a hot engine warm.
Design data:
min. 60°C
Preheating temperature
5 kW/cyl
Required heating power
2 kW/cyl
Heating power to keep hot engine warm
Required heating power to heat up the engine, see formula below:
where:
Preheater output [kW]
P =
Preheating temperature = 60...70 °C
T
1 =
Ambient temperature [°C]
T
0 =
Engine weight [ton]
m
eng
=
Lubricating oil volume [m
3
] (wet sump engines only)
V
LO
=
HT water volume [m
3
]
V
FW
=
Product Guide Wärtsilä 34DF - 3/2012
95
Product Guide
9. Cooling Water System
