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Jerry, I wish I was sure that a 240U is similar in design to its bigger bro' 460. Again, I think they are--never can be too sure about the million variants IH produced. Assuming the 240 is the same as a 460, I am of the opinion when you are asking about a safety valve screen, you are referring to the ORIFICE PLUG and screen. On a 460, these items are located in what I call the regulator/pressure relief control block. This is the device bolted to the left dash cast support bracket and is where the hydraulic pump's output hose screws into. You mentioned replacing the hose, so you are familiar with where it attaches. The orifice plug and screen are located just behind the regulator block's rear cap. This cap also compresses the relief valve spring so take care in removing the cap--best to remove in stages using progressively longer cap screws. You will see what looks very much like a large carburetor jet staring at you. This is the orifice plug, and it has a slotted body for removal with a screwdriver. The screen is attached to the orifice plug and will come out of the threaded port with the plug. Since the 240 has been sitting awhile, and there is indication of moisture in the system, it sure sounds to me like the regulator piston is stuck holding open a ball check valve. This will allow hydraulic pump output oil to bypass everything and dump back into the sump. The regulator piston is either stuck in its bore--galled bore or wadded-up piston O-ring, AND/OR oil is trapped between the piston's top and a BLOCKED hole in the orifice plug due to crud. Actuation of a remote cylinder or fast hitch will lower hydraulic pressure on the screen side of the orifice. Provided the orifice is not plugged, the lowered pressure allows the ball check spring to push the piston up displacing oil through the orifice plug. If oil is trapped here, the piston will be hydraulic locked holding open the ball check--no pressure for your remotes. You have not complained about the power steering operation so this translates to the suction pipe--common to both the PS pump and hyd pump--being OK.
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