15
There will be air in the gas supply line after testing for leaks
on a new installation. Therefore, the air must be bled from
the line by loosening the ground joint union until pure gas
is expelled. Tighten union and wait for ve minutes until all
gas has been dissipated in the air. Be certain there is no
open ame in the vicinity during air bleeding procedure.
The unit is placed in operation by closing the main
electrical disconnect switch for the unit.
All propane gas equipment must conform to the safety
standards of NFPA 58 - Liqueed Petroleum Gas Code.
For satisfactory operation, propane gas pressure must be
within 9.7 - 10.3 inches w.c. for high re at the manifold
with all gas appliances in operation. Maintaining proper
gas pressure depends on three main factors:
1. Vaporization rate, which depends on (a) temperature
of the liquid, and (b) wetted surface area of the
container or containers.
2. Proper pressure regulation.
3. Pressure drop in lines between regulators, and
between second stage regulator and the appliance.
Pipe size required will depend on length of pipe run
and total load of all appliances.
Complete information regarding tank sizing for
vaporization, recommended regulator settings and pipe
sizing is available from most regulator manufacturers and
propane gas suppliers.
Since propane gas will quickly dissolve white lead or most
standard com mercial compounds, special pipe dope must
be used. Shellac base compounds resistant to the actions
of liqueed petroleum gases such as Gasolac
®
, Stalactic
®
,
Clyde’s
®
or John Crane
®
are satisfactory.
See the following gure for typical propane gas piping.
The gas supply piping location and installation for roof
top units must be in accordance with local codes or, in
the absence of locals codes, with ordinances of the latest
edition of the National Fuel Gas Code ANSI Z223.1/NFPA
54.
A manual gas shut o valve must be eld installed external
to the roof top unit. In addition, a drip leg must be installed
near the inlet connection. A ground joint union connection
is required between the external shut o valve and the unit
connection to the gas valve to permit removal of the burner
assembly for servicing.
1. Route gas piping to unit so that it does not interfere
with the removal of access panels. Support and
align piping to prevent strains or misalignment of the
manifold assembly.
2. All units are furnished with standard female 1/2" NPT
pipe connections. The size of the gas supply piping
to the unit must be based on length of run, number
of units on the system, gas characteristics, BTU
requirement and available supply pressure. All piping
must be done in accordance with local codes or, in the
absence of local codes, with the latest edition of the
National Fuel Gas Code
ANSI Z223.1/NFPA 54.
To Next Page
Loading...