Page 11 - Webster Service Manual

On installations where the oil tank is below the fuel unit,
the gauge reading should show t he amount of vacuum
approximately 1" vacuum per 16" of vertical lift, plus
the tube loss of total run).
The viscosity chosen for the above figures is 50 SSU.
The above losses will be reduced at lower viscosities.
The gravity chosen is 40° API (60°F) at 68°F, which
gives a specific gravity of 0.822. Gravity of No. 2 oils
varies from 30° to 45° API.
Even though a fuel unit is capable of a very high vac-
uum, this has very little to do with the maximum advis-
able lift because of the volatility of the oil under vacuum,
which varies with dif ferent oils. Under certain condi-
tions, installations as high as 28 feet have operatedsat-
isfactorily with a two-stage unit, but generally high lifts
should be avoided on any liquid having volatile frac-
tions. When the combined vertical lift and the equivalent
losses through the tubing add up to 10” vacuum or more
for single-stage pumps, 15” vacuum or more for two-
stage pumps, use of a W ebster supply pump unit is
If the vacuum gauge reads higher than the calculated
vacuum, look for restriction in the suction line ... a
closed tank valve, kink ed copper tubing, plugged filter ,
sticking foot or check valve, frozen oil line, undersized
oil line, or excessive oil lift. On the other hand, if the
gauge reading is below the calculated vacuum, look for
air leaks in the lines, valve, fittings, or fuel unit.
On gravity fed jobs where the oil tank is above the fuel
unit, vacuum should read zero except when restrictions
are apparent such as closed shut-of f valve, clogged fil-
ter, kinked line, etc. Any of these restrictions should be
Relation between vacuum and vertical lift
° API all at 68° F
Ins. of
Ins. of
Ins. of
Vacuum Lift
Vacuum Lift
Vacuum Lift
1 1'4”
8 11'0”
15 20'7”
2 2'9”
9 12'4”
16 22'0”
3 4'1”
10 13'9”
17 23'4”
4 5'6”
11 15'1”
18 24'9”
5 6'10”
12 16'6”
19 26'1”
6 8'3”
13 17'10”
20 27'6”
7 9'7”
14 19'3”