Tractor Repair: International Tractor 684, filter canister, hydraulic filter

Question
The hydraulics were working, I have changed hydraulic filter, put it back together, it worked for approximate. 20 times lifting, but now it has stopped working.   What can I do?

Answer
  Check if the sealing ring on the filter canister could be leaking air into the hydraulic system.  The sealing ring has to be in perfect condition.  If it's full of oil, and if the filter ring is good, about the only thing you can do is flowtest the pump to see if it's good.  Also, the gasket can blow out in the multiple control valve behind the filter.