Page 12 - Webster Service Manual

7
Pressure Gauge
The pressure gauge, on the other hand, shows whether
the gears are pumping and building up a steady even
pressure to deliver oil to the nozzle. It also shows
whether the shut-off valve in the nozzle line is giving a
positive cut-off of the oil flow.
Pressure Data
A pressure gauge applied to the pressure gauge port
reveals the pressure to which the fuel unit has been reg-
ulated. An adjustment can be made to suit the firing
conditions (usually 100 psi). Also the pressure gauge,
when applied to the pressure gauge port, can be used
to check fuel unit ef ficiency. A unit in satisfactory oper-
ating condition should be able to support a nozzle at full
spray, up to several psi above the rated burner pres-
sure. Fuel unit manufacturers typically rate domestic
units for maximum burning rate at a nominal 100 psi.
Collapse of nozzle spray below specified limits indicates
either excess bypass, missing or damaged valve gas-
ket, worn valve piston or sleeve, worn gear set, or pump
RFS less than nozzle rating. Pumping capacity also
decreases under correspondingly higher lift (or vacuum).
A pressure gauge applied directly to nozzle outlet port
for cut-off check should hold dif ferential pressure on
shutdown. For example, with operating pressure of 100
psi, the cut-of f should be approximately 80 psi. If the
pressure gauge drops below the cut-of point, this would
indicate a leak at cut-of f, therefore the valve assembly
should be disassembled, cleaned or replaced if neces-
sary. Cut-off pressure must never be more than 20%
below set operating pressure.
To determine what pressures should be provided by
each pump, refer to the selection charts in the desired
model sections.
Correct System Tubing Sizing
Many people both in engineering and in service make
the mistake of laying out and installing jobs with tubing
which is too small in diameter and too long in length. If
Return Line
Inlet Line
75-90
psi cut-off point should
hold. If pressure drops back to
zero, indicates leaky cutoff.