Page 127 - Webster Service Manual

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The OSV
®
operates as a pressure reducer, with supply
line pressure on the valve inlet side and fuel pump vac-
uum on the valve outlet side.
In systems with burners connected for one-pipe opera-
tion, GPH flow through the valve is the same as the
burner nozzle firing rate. In two pipe operation, GPH
flow through the valve is the same as the fuel unit suc-
tion capacity. Refer to fuel unit manufacturer's specifi-
cation for inlet suction capacity . Operation of OSV
®
valves in parallel is not recommended.
Recommended Maximum Flow Rates and Pressure
Tbl.1
OSV
®
38
and OSV
®
50
PSI
PSI
PSI
PSI
PSI
PSI
5
15 30 40 50 60
1
gph 2.5 2.7 3.5 4.5 5.0 5.5
15
gph 2.7 3.0 4.0 5 0 5.5 6.0
32
gph 3.7 4.0 4.7 5.2 6.0 7.0
45
gph 4.0 4.5 5.0 6.0 7.0
55
gph 4.5 5.0 5.7
60
gph 5.0 5.2 6.0 Do not operate
70
gph 5.5 6.0
in this region
Vacuum (inches Hg) to operate valve is shown for vari-
ous flow and pressure conditions.
Values given are averages of test results and may vary
slightly.
Entrapment Caution
In supply systems having a check valve on the supply
pump discharge, an entrapment condition may exist
between the supply pump and OSV
®
.
In the burner OFF
condition, cold oil in the line expands when heating to
room temperature, causing a line pressure increase that
may prevent the OSV
®
from operating, or may cause
leakage at the threaded joints. The condition may be
observed by use of a pressure gauge at the inlet side of
the OSV
®
,
or on the discharge side of the supply pump
check valve. Correction requires use of a pressure relief
valve as shown in Figure 3, set to insure a maximum 60
PSI at any OSV
®
inlet under all conditions.
Figure 3. Supply Pump Systems — Multi Level
Inlet Pressure
Flow
thru
Valve