A-1
Appendix A: Check Valve/Air Purge Screw Operation
This appendix discusses the theory of operation of the Red Jacket STP’s check valve and air purge screw.
Check Valve Operation
Pump On
As shown in the check valve cutaway diagram in Figure A-1, when the pump is On, the check valve is opened by
fuel flow.
Figure A-1. Pump On condition
Pump Off
When the pump shuts off, the check valve reseats isolating the line. As pressure in the line builds due to thermal
expansion, the excess pressure vents through the relief valve back into the tank as shown in Figure A-2.
Figure A-2. Relief valve vents excess line pressure
From pump
To line
Check valve
Spring
rjpumps\ckvlv1
r
um
s\ckvlv2
Excess line
pressure
To Ta n k
Relief valve
Check valve
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