Tractor Repair: IH 1566 fuel system priming, check valves, priming pump

Question
1566 with 2040 hrs. We thought it was running out of fuel so shut it down and fueled up. Would not start and have been trying to prime it ever since. Fuel is getting to and through the primary filter, but it will not go to the priming pump; cannot get the hand pump to prime. Have loosened connections, cranked the engine, pressurized the tank, even removed the line from the primary filter and pressurized it, trying to get fuel through the system. Stumped! Am now thinking the pump was failing, not that it was running out of fuel. Would be very pleased to have your input.

Answer
  The fuel goes from the tank to the primary filter, then through the transfer and priming pump, then through the final filter before going to the injection pump.  It sounds like you have already verified that enough fuel is coming from the tank and through the primary filter.  If fuel will flow through the primary filter but not through the primer pump, then maybe there is something wrong with the primer pump.  There are check valves inside it that could be stuck.