Figure 5-23.Ring thermostat control.
The automatic damper should be kept in proper
adjustment to ensure a proper supply of air to the
The burner manifold (fig. 5-24) requires
cleaning and adjusting at times to keep it in good
shape. Remove the manifold. Scrape carbon
deposits from the manifold and ignition
electrodes. Clean the burner nozzles and
When cleaning, you should NOT use a
sharp instrument that can scratch or
disfigure the tip orifice or slots in the
distributor. A slight scratch on these
parts can seriously impair nozzle
Adjust the ignition electrodes to conform with
the dimensions shown in figure 5-24. The gap
must be positioned as accurately as possible, so
it is at the immediate edge of the nozzle spray.
Be careful when bending and adjusting the
electrodes to avoid cracking the insulators. The
insulators may develop an invisible short due to
such a fracture, resulting in ignition failure.
The fuel pressure to the burner must be properly
maintained. Excessive fuel pressure causes the
burner to smoke and results in sooting of the
heating coil. However, if fuel pressure is too
low, the plant comes up to pressure slowly and
does not maintain adequate steam pressure
during periods of maximum steam demand.
Adjust the pressure as needed.
Figure 5-25 shows a drawing of a fuel pressure
switch. To adjust the switch, close the light and
fuel indicator pilot when fuel pressure rises to
about 70 psi by turning the adjusting screw (1)
clockwise to increase or counterclockwise to
decrease pressure at which the switch closes.
This step allows enough pressure to induce
proper atomization when fuel is admitted to the
burner. Secure the adjusting screw with the
locknut after adjustment.
The steam pressure switch (SPS) can be adjusted
to open and stop the burner at any maximum
pressure between 65 and 195 psi. The switch
closes and restarts the burner when steam
pressure drops about 8 psi below that point.
The modulating pressure switch (MPS) is
normally adjusted to modulate the burner to
"low-fire" operation when steam pressure
reaches 10 psi below maximum and to return the
burner to "high-fire" operation when steam
pressure drops about 8 psi below that point. The
recommended setting of 10 psi below the
maximum, in most cases, provides both stable
operation and stable steam pressure during