Issued September 2017
Compressed Natural Gas (CNG) Option
Copyright 2017, Heil Environmental
Printed in U.S.A.
172
TRANSFER FUELING (DEFUELING) MODES,
COMPONENTS AND PROCEDURES
(CONTINUED)
3. Compressor Inlet Method (Continued)
c. BOTH the vehicle AND the fuel system should be
grounded. Use a minimum 14-gauge multi-
stranded wire. Contact the CNG system
manufacturer for attachment points for the ground
wire.
F. Purging with an Inert Gas Prior to Welding or Major
Repairs
If welding or major repairs is required, you must remove
all of the fuel from the vehicle including the residual fuel
and replace it with an inert gas such as nitrogen. The
objective is to completely purge the system of all
combustible gas. In order to complete the operation, the
entire system should be purged with the inert gas 3
times to a pressure of at least 689kPa (100 psig).
Approximately 70kPa (10 psig) of residual inert gas
pressure should be left on the system during the major
repair.
WARNING
Never weld on a compressed natural gas vehicle unless
the compressed natural gas fuel system has been purged
with inert gas.
NOTICE
Avoid exposing CNG system parts to molten metal from
weld, torch, cutting, or grinding splatter. The CNG system
and/or the CNG system components can be damaged.
G.Recharging the Fuel System after Purging and
after Major Repairs
After repairs, the inert gas must be removed from the
system in a similar manner as the inert gas was
introduced. Specifically, the entire system should be
charged 3 times with approximately 689kPa (100 psig)
of natural gas. Between each natural gas charging
session, the system should be vented or extracted to
remove the remaining inert gas from the system. See
the Notices below and the atmospheric venting method
instructions on the previous page.
NOTICE
It is critical when venting between gas charging sessions
to make sure the tank pressure never goes below 34kPa
(5 psig). 69-138kPa (10-20 psig) is the recommended
cutoff for this procedure. This will ensure that outside air
does not re-enter the tank due to the pressure dropping
too low in the tank.
NOTICE
If venting to atmosphere, you must first check to see if this
method is legal in your area as some natural gas will be
vented along with the inert gas.
Summary of Contents for PT 1000
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