The fuel gas pressure control valve adjusts the gas feed pressure to the engine according to engine load.
The pressure control valve is controlled by the engine control system. The system is designed to get the
correct fuel gas pressure to the engine common rail pipe at all times.
Readings from sensors on the GVU as well as opening and closing of valves on the gas valve unit are
electronically or electro-pneumatically controlled by the GVU control system.All readings from sensors and
valve statuses can be read from Local Display Unit (LDU). The LDU is mounted on control cabinet of the
GVU.
The two shut-off valves together with gas ventilating valve (between the shut-off valves) form a double-
block-and-bleed function. The block valves in the double-block-and-bleed function effectively close off
gas supply to the engine on request. The solenoid operated venting valve in the double-block-and-bleed
function will relief the pressure trapped between the block valves after closing of the block valves. The
block valves V03 and V05 and inert gas valve V07 are operated as fail-to-close, i.e. they will close on current
failure. Venting valves V02 and V04 are fail-to-open, they will open on current failure. There is connection
for inerting the piping with nitrogen, see figure "Gas valve unit P&I diagram". The inerting of the fuel gas
pipe before double block and bleed valves is done from gas storage system and gas is blown out via vent
valve V02 on the GVU.
During a stop sequence of DF-engine gas operation (i.e. upon gas trip, pilot trip, stop, emergency stop or
shutdown in gas operating mode, or transfer to diesel operating mode) the GVU performs a gas shut-off
and ventilation sequence. Both block valves (V03 and V05) on the gas valve unit are closed and ventilation
valve V04 between block valves is opened. Additionally on emergency stop ventilation valve V02 will open
and on certain alarm situations the V07 will inert the gas pipe between GVU and the engine.
The gas valve unit will perform a leak test procedure before engine starts operating on gas. This is a safety
precaution to ensure the tightness of valves and the proper function of components.
One GVU is required for each engine. The GVU has to be located as close the engine as possible to ensure
engine response to transient conditions. The maximum length of fuel gas pipe between the GVU and the
engine gas inlet is 10 m.
Inert gas and compressed air are to be dry and clean. Inert gas pressure max 1.5 MPa (15 bar). The require-
ments for compressed air quality are presented in chapter "Compressed air system".
Figure 6.4
Gas valve unit P&I diagram (DAAF003882D)
Unit components:
Shut off valve
V08
First block valve
V03
Gas filter
B01
Shut off valve
V09
Vent valve
V04
Control air filter
B02
Pressure regulator
V10
Second block valve
V05
Inert gas filter
B03
46
Product Guide Wärtsilä 34DF - 3/2012
Product Guide
6. Fuel System
