240utility fastitch hydraulic problems

[glennster]

been having fasthitch problems with this new to me 240 utility. when raising the hitch, bush hog or back blade, the hydraulics strain a few times and then finally lift. i switched hoses to the cylinder from the check valve, hitch worked better but hitch would slowly drop. pulled the check valve out and took it apart. it has the 278 hydraulic check valve, single acting. looks like it is missing the o ring on the check valve actuator piston. what is the difference between the double acting check valve and the single acting? tractor has a two way cylinder in the fast hitch. does this tractor have the wrong valve on it? i kind of think the cylinder is hooked up wrong, pushing down on the hitch control lowers the hitch, pulling up raises the hitch. with the new o-ring and changing the hoses back, this should work correct...?? here is a picture of the valve disassembled

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[PaulW_NJ]

Glennster

You’re correct that the O-ring for the moveable piston is missing. It should be part # 350667R1. Without the O-ring there is no seal, so the check valve won’t hold pressure. The purpose of the check valve is to prevent the hitch from dropping due to pressure bleed down back in the control valve due to normal wear. It's essentially a safety valve.

I have a single acting check valve on my 340U and a double acting one on the 240U. I rebuilt both valves because the O-rings were badly deteriorated. Your photo looks just like mine did except the O-ring isn’t there. Apparently the earlier models used the single check valve.

The single check valve is supposed to prevent the raised hitch (up pressured)from dropping under load. The double check valve works in both up and down directions. In other words, what it adds is holding the hitch when it is used for down pressure, such as using the hitch to raise the rear wheels off of the ground.

Here’s the blowup of the double acting check valve. I'll see if I can find a schematic of the single valve hookup

 

[PaulW_NJ]

According to the schematic, hose #20 goes to the check valve, and #17 goes to the junction block.

 

[glennster]

thanks paul, that helps a bunch!! i"ll get my parts and get er buttoned back up!! thanks again, glenn

 

[PaulW_NJ]

Glennster

I scanned this diagram from the Blue Ribbon Service Manual (GSS 1278 - Hydraulics), which is invaluable if you start going into these hydraulics systems. They show the control valves, check valves, power steering, etc for the 240. They're on eBay all the time and well worth the $$.

It shows that high pressure thru line P flows to the hitch piston, which at the same time moves the check valve, closing off any passage to the return low pressure side. Therefore the hitch cylinder can't drop, even when you let off the control valve. When you reverse the lift control valve, high pressure goes to line Q instead, which breaks the check valve's hold, and also pushes the lift cylinder back down. If the O-ring on that check valve piston is gone, the high pressure will flow around the leaky piston no matter what position the control valve is in, and who knows what it will do?

 

[bc]

Thanks Paul. I learned a lot from that flow chart. I also figured out that when the flow is reversed and going in through Q, the piston moves up and the rod on the piston also opens the check ball which allows flow back out through P. It took me a little bit to figure that out cause I thought the check ball would still keep the fluid from coming back through P.

A missing oring on any of those check valve actuator pistons on about any valve setup could account for fluid bypass problems on other things such as power steering.