Mack LEU, Operator'S Handbook Manual

Page: 27 / 59

OPERATION 23
LNG Tank Pressure Relief Valves
Periodically pressure will be harmlessly released through the primary relief valve as
the fuel heats up and expands due to ambient outside temperature. Liquid LNG in
the tanks can be as low as -260°F (-177°C). Because small amounts of LNG are
converted into large amounts of natural gas, pressures may rapidly increase if a means
of relief is not provided.
The primary and secondary pressure vents are located inside the fuel tank door. The
primary vent is connected to piping which should be attached to the body of the
truck facing toward the rear of the vehicle, away from the passenger compartment.
Only the primary relief valve is piped away. The secondary relief valve should be
left with the factory installed plastic cap in place. Refer to the tank manufacturer’s
manual for more details.
From the factory, the vent piping from the primary LNG tank vent is attached to the
intake stack by disposable plastic straps. The piping should be removed from the
intake stack and plumbed up and over the body by the body installers as shown in the
illustration at the end of the SAFETY section in this handbook.
CAUTION
It is important to keep the primary pressure vent free of blockage due to ice, snow
or debris.
LNG Fueling
Normal procedure is to refuel the tanks on a daily basis or each time the vehicle is
taken into active service. The normal operating pressure in each tank is approximately
120 psi or higher. If the pressure is low, say 90 psi, the vehicle is probably low on
fuel. As a result, it will be low in power and may eventually run out of fuel.
Note: Complete and safe instructions on LNG fueling should be obtained from the
tank manufacturer’s manual and from the assistance of personnel who are experienced
in LNG fueling.
WARNING
COVER EYES AND EXPOSED SKIN.
Accidental contact with the eyes or skin
may cause a freezing injury similar to
a burn. Protect the eyes and cover the
skin whenever possible contact with
supercooled metals, liquids or gases
exists.