yes that is the filter i replaced and it came from nh dealer. i was running on asphalt maybe you have a point about the pump getting warm as temp for the day was quite hot at the time. i also checked the hyd oil with the fel and backhoe on the ground and it was at the proper level. i don"t know how to put pictures on computer unfortunately i know about as much about the computer as i do hydraulics although i am learning a lot from you, thank you. i was also suprised to hear the smaller pipe is the discharge pipe from the pump. on a dump truck the largest hose is the return line. the smaller line is the one i was referring to as having a banjo fitting (round fitting on far end of small steel line with bolt thru the middle of it.) so the other line is the suction line? if i remember right it has a short rubber hose on it right close to the pump. by the way you have a point when i checked the oil when it wouldn"t work the oil looked clear not foamy or full of air thanks again for all your help. also checked oil by dipstick don"t have sight glass.
you are welcome. No issues with the pictures. i went to NH website and other than replaceable filter media in lieu of screen the rest is almost identical between 1700 and 1300. In general piping going to inlet of a pump hyd or otherwise is a bit larger. Th reason for it is to have pump volute flooded and have less change of pump cavitation specially in a open circuit pump (non-recirculating). This is true both for gear type pumps and variety of others that are not used in a tractor hyd system. There is always a lot of energy added to the fluid on the discharge side of the pump so pressure drop on smaller pipe is okay as the pipe is sized both for pressure drop and flow volume. You said on trucks the larger pipe is " return"... well that is also true in tractor. The larger inlet pipe to the suction side is actually return from reservoir to the pump. So in other words
supply side of the pump in discharge and return side is inlet to the pump. I'll add a few pics below here that in concept is almost identical with your rig.
#38 is discharge, outlet or supply pipe from the pump on the left side and on the right side banjo fitting it ties to a pressure regulating device and then to lift spool (aka , valve) for 3 point.
#25 id the larger dia pipe which can be called inlet, suction or return as you call it. banjo #26 is on the diffy and rubber hose #24 is the rubber hose to pump inlet.
Pump connection on top next to the filter is the inlet and outlet in on the bottom with smaller dia pipe.
Below I have a few pictures of my 1700 which conceptually is the same as yours.
Fords 1700: Larger dia pipe=suction, smaller dia= discharge.
Ford 1700: discharge pipe going to pressure regulator/relief device.
Ford 1700: suction banjo and fitting in diffy.
Keep watching it and take notes so we might get to the bottom of it.
JC,