Abstract: A bypass valve 30 for a fuel supply system 10 of an aircraft. The bypass valve 30 has a housing 32 with a chamber 38 having an entrance port 34 connected to a pump 16 and an exit port 36 connected to a regulator 14. An end cap 44 which is screwed into the housing 32 to seal the chamber 38. A sleeve 46 which extends from the end cap 44 into chamber 38 has a series of radial openings 48 and 50 to communicate the exit port with the interior of the sleeve 46. A piston 58 is retained in the sleeve 46 by a retainer stop 68. A spring 64 acts on the piston 58 to move a face 66 against retainer stop 68 to separate the entrance port 34 from the exit port 36. When a predetermined pressure drop occurs across a filter 26, piston 58 moves and allows fuel to directly flow to regulator 14 without passing through filter 26. At the same time, the fluid pressure acts on the cylindrical body 76 of indicator 74 to move face 75 away from housing 32 and provide a visual indication that unfiltered fuel has entered the fuel system.