Page 13 - Webster Service Manual

a fuel unit with a pumping capacity of not more than 30
gallons per hour is used, tubing of 1/2” OD can be used
with safety.
The tubing size can vary widely depending upon flow
rate. See the pipe sizing charts for help in determining
which tubing size is best suited for each application.
To Determine Suction Line Size in Installations
Using Webster Fuel Units on Two-Pipe Systems
Check suction gear capacity (see table of pumps).
Measure total tube length (horizontal and vertical).
Refer to “Friction Tube Loss Chart” for desired tubing
size. Read up from line “total feet of copper tube” to
suction capacity” in gph.
Read left to column “inches of vacuum at fuel unit”.
This is vacuum required to draw oil through tube listed
of given length.)
If installation has lift add .75” of vacuum for every foot
of lift.
Rule of Thumb:
A quick rule to check an installation is to figure 1”
of vacuum for every foot of vertical lift, and 1” of
vacuum for every 10' of horizontal run Refer to
Frictional Tube Loss charts for actual installation data.
Total inches of vacuum (frictional tube loss plus lift if
If total is over 10” when single stage is employed on
two-pipe system, check on next larger tube size chart
for proper tube size.
If total is over 15” when two-stage unit is employed
on a two-pipe system, check on next larger tube size
The above does not allow for any added restrictions
such as line filter, elbows, sharp bends, check valves, etc.
On high lifts and long runs, too small tubing will cause
the oil to separate and have a milky appearance.This is
not air, it is actually light, volatile portion of the oil sepa-
rating from the heavy portion. This is likely to occur any
time the vacuum gauge shows a reading of 15” or more,
and may occur at a lower vacuum with some oils. When
vacuums of 20” to 22” are reached, the pressure gauge
will start to bounce and delivery at the nozzle will begin
to fall off. To correct these conditions, check the tubing.
If the tubing size is correct and there are no kinks or
other restrictions, a supply or booster pump may be