Middleby Marshall PS500 - Manual (Page 13)

13
ENGLISH
2. Replacing the Pilot Orifice
NOTE: All natural gases use the same size pilot orifice
(0.635mm), as do all liquid propane (LP) gases (0.381mm).
Because of this, it is not normally necessary to replace the
pilot orifice unless converting the oven from natural to
propane, or from propane to natural, operation.
a. Follow Steps a-d in Replacing the Main Orifice, above.
b. Refer to Figure 2-17. Unscrew the pilot tube
compression nut and slide it out of the way. Pull the
tube from the fitting to expose the pilot orifice.
c. Remove the pilot orifice.
d. Slip the new pilot orifice into the pilot tube.
e. Push the pilot tube back into place until it bottoms, and
hold it in place. Slide the compression nut back into
place and engage the threads. Tighten the nut to a
snug fit with your fingers.
f. Gently tighten the nut one complete turn with a wrench.
DO NOT OVERTIGHTEN THE COMPRESSION NUT.
g. Replace the gas train and venturi by following Steps a-
d in Replacing the Main Orifice, above, in reverse order.
WARNING
After completing these procedures, perform a gas
leak test before operating the oven.
D. Checking the Gas Supply (Inlet) Pressure
1. Attach a manometer to record the supply (inlet) pressure.
For a Type 1 gas control valve (see Figure 2-16), you will
need to check the supply pressure at the gas connection
to the oven. For a Type 2 gas control valve, remove the
supply (inlet) pressure cap screw and attach a manometer
to the stud.
2. Depress the two machinery compartment safety switches
to allow the oven to operate.
3. Open the main gas supply valve. Switch the circuit breaker/
fused disconnect to the ON ("I") position.
4. Start the oven according the directions in the Operation
section of this Manual. Adjust the temperature controller to
the maximum setting (288°C).
5. Measure the supply (inlet) pressure.
6. Switch the oven off. Close the main gas supply valve, and
switch the circuit breaker/fused disconnect to the OFF ("O")
position. Remove the manometer. For a Type 2 gas control
valve, replace the cap screw.
7. Compare the measured supply (inlet) pressure to the
nominal pressures shown in Table 1-5 (in the Description
section of this Manual).
If the supply pressure is lower or higher than the nominal
pressure, the reason should be investigated and the gas
supplier contacted.
For natural gas ovens, if the measured supply pressure is lower
than 17mbar, or higher than 25mbar, contact the gas supplier.
DO NOT OPERATE THE OVEN or adjust the oven controls.
E. Adjusting the Orifice (Manifold) Pressure and Heat Input
To use the orifice pressure method, you must know the specific
gas type and quality used. If using the orifice pressure method,
you should double-check the input using the volumetric method.
To use the volumetric method, you must know the heat value
(HuB) of the gas used. This information is available from your
gas supplier.
During these measurements, do not operate any other
appliances that use the same gas meter as the oven.
Consumption (m 3 /hr.) =
NB (Rated input in kW)
HuB (Heat [Calorific] value
of gas in kW/m3)
=
Time (in minutes) of
0.1m3 of gas usage
1. Orifice (Manifold) Pressure Method
a. Check that the main gas supply valve and the circuit
breaker/fused disconnect are in the OFF ("O") position.
b. Attach a manometer to record the regulated (manifold)
pressure. For a Type 1 gas control valve, you will need
to remove the cap from the open end of the gas line tee
as the line enters the burner. For a Type 2 valve, you
can connect the manometer to this location, or to the
stud on the valve, shown in Figure 2-16 (underneath
the cap screw).
c. For a Type 2 gas control valve, remove the cap screw
from the pressure adjustment screw (governor). The
Type 1 valve does not have a cap screw.
d. Depress the two machinery compartment safety
switches to allow the oven to operate.
e. Open the main gas supply valve. Switch the circuit
breaker/fused disconnect to the ON ("I") position.
f. Start the oven according the directions in the Operation
section of this Manual. Adjust the temperature controller
to the maximum setting (288°C).
g. Adjust the pressure adjustment screw as necessary
to match the correct pressure for the oven's specific
gas type. Refer to Table 1-5 in the Description section
of this Manual. Turning the adjustment screw clockwise
increases the flow, while turning it counterclockwise
reduces the flow.
h. Switch the oven off. Close the main gas supply valve,
and switch the circuit breaker/fused disconnect to the
OFF ("O") position. Remove the manometer, and
replace all cap screws and gas line caps.
2. Volumetric Method
a. Determine the time of 0.1m 3 (100 liters) of gas usage
as follows.
6
Consumption
b. Check that the main gas supply valve and the circuit
breaker/fused disconnect are in the OFF ("O") position.
c. For a Type 2 gas control valve, remove the cap screw
from the pressure adjustment screw (governor). The
Type 1 valve does not have a cap screw.
d. Depress the two machinery compartment safety
switches to allow the oven to operate.
e. Open the main gas supply valve. Switch the circuit
breaker/fused disconnect to the ON ("I") position.
f. Start the oven according the directions in the Operation
section of this Manual. Adjust the temperature controller
to the maximum setting (288°C).
g. Adjust the pressure adjustment screw as necessary
to match the calculated volume using the time (in
minutes) of 0.1m 3 of gas usage. Turning the
adjustment screw clockwise increases the flow, while
turning it counterclockwise reduces the flow.
h. Record the reading obtained from the gas meter and
calculate the obtained gas flow. Compare this value
to the information in Table 1-4 in the Description
section of this Manual.
i. Switch the oven off. Close the main gas supply valve,
and switch the circuit breaker/fused disconnect to the
OFF ("O") position. For a Type 2 gas valve, replace the
cap screw.
SECTION 2 - INSTALLATION