Middleby Marshall PS500 - Manual (Page 12)

12
ENGLISH
B. Preparation for Use with Various Gases
Before proceeding to set up the oven for a specific gas, check
that the main gas supply valve and the circuit breaker/fused
disconnect are in the OFF ("O") position.
The main and pilot orifices must match the sizes shown in Table
1-5. If necessary, replace the orifices. Refer to Part C, Replacing
the Gas Orifices.
The orifice (manifold) pressure should be adjusted to the value
shown in Table 1-5 (in the Description section) for the specific
gas type and location.
1. For Use with Natural Gas
The actual heat input to the oven must match the rated heat
input. The input to the burner can be determined using the
orifice (manifold) pressure data or by the volume supplied
using the gas meter. Both of these procedures are
described in Part E, Checking the Heat Input.
If the measured input does not correspond with the rated
input (shown in Table 1-5 in the Description section of this
Manual), check first that the correct orifices are installed. If
the orifices are correct, check and correct the supply and
orifice pressures to obtain the correct input based on the
gas meter reading.
2. For Use with Liquid Propane (LP) Gas
When using liquid gas with an oven equipped with a Type
2 gas control valve (see Figure 2-16), the converter in the
multifunction gas valve must be removed, and then replaced
INVERTED from its former position. Inverting the converter
will disable the governor. This step is only required if the
supply pressure is below 50mbar.
C. Replacing the Gas Orifices (if so required)
1. Replacing the Main Orifice
a. Check that the main gas supply valve and the circuit
breaker/fused disconnect are in the OFF ("O") position.
b. Open the 1/2" union in the gas supply line. The union
is located between the oven's manual shutoff valve
and the multifunction gas valve. See Figure 2-16.
c. Refer to Figure 2-17. Unscrew the four hex screws that
hold the venturi mounting plate to the front of the
burner. Remove the gas train/venturi assembly from
the oven.
d. Remove the two 1/2" nuts that secure the gas train to
the venturi mounting plate.
e. Remove the main orifice using an 11/16" wrench.
f.
Install the new orifice by following the above procedure
in reverse order.
Figure 2-17 - Replacing the Main and Pilot Orifices
Main
orifice
Pilot
orifice
Pilot tube
Compression
nut
Main orifice
holder (attached
to gas train)
1/2" hex nuts
Venturi
assembly
Venturi
mounting
plate
Ignition
sensor
wire
Modulating
gas valve
Pilot
pressure
tap
Gas Control
Valve
(see inset)
Gas Burner
Burner
Blower
Supply (inlet)
pressure tap
Manual
shutoff
valve
Gas line for
other oven
cavities
Cap for
top oven
cavity
Elbow, 90°,
1-1/4” dia.
Orifice (manifold)
pressure tap
Nipple, 1-1/4"
dia. X 3"
(76mm) L, NPT
1/2" union
Figure 2-16 - Gas Burner
and Piping Assembly
SECTION 2 - INSTALLATION
Gas
pressure
switch
Governor
enabled for
natural gas
operation
Governor
disabled for
liquid
propane
operation
Manifold pressure
adjustment (under
cap screw)
Manifold pressure
adjustment
Type 1 Gas Control Valve Type 2 Gas Control Valve