FUEL SYSTEMS

A fuel system (100) can include a selection and shutoff valve, SSOV, (101) configured to allow a primary flow having a primary flow pressure (P3) to pass therethrough in a first state such that the primary flow can travel to an output line (103). The SSOV can also be configured to shut off the primary flow in a second state to prevent the primary flow from travelling to the output line. In the second state, the SSOV can be configured to allow a secondary flow from a secondary flow source (105) to pass therethrough such that the secondary flow can travel to the output line (103).