I have done some work on the hydraulics of my new major today. With no success.
There has been some topics about this subject over the years on all three boards but none was salved as far as I could remember.
In an attempt to get things straighten for me and other folks that are having the same problem I will describe what I have done so far and post some pictures. Maybe together we can solve this one.
Two years ago my lift was lowering slowly. It was bothering me because of my fertilizer that was dropping. My guess was that it was the piston gland (seal). I removed it and it looked fine, but I renewed the gland. Nothing changed.
Then I removed the valve body again and checked the two valves inside it. They seem ok to me.
After I have used a cultivator for some time the problem went worse. I could not hold up the plow.
I have put a washer on top of the unloading (relief) valve and the plow was now going down very slowly. That gave me the idea it was the unloading valve.
I plugged in a pressure gauge and with the first setting the pump gave 200 bar pressure but it dropped right after I stopped pumping. I placed the washer again and the pressure went up to 225 bar and dropped also but very slowly. The pressure should be 150 bar.
I removed the valve body again and removed both valves again. I could not find anything wrong with them.
Nevertheless I honed them both on each other with some grinding pasta. (400). I renewed the o-ring on the unloading valve seat. The book say it should be a 0.375” x 0.07” o-ring. That would mean 9.5 mm x 1.75 mm. I have used before a 10 mm x 1.75 mm one. Now I have replaced it by a 10 mm x 2 mm because the grove is 2.5 mm width.
I rebuild everything and placed it back on the lift cover.
Pressure was now 200 bar and going down fast. With the washer on it pressure was 225 bar and going down just as fast. Seemed the problem was worse.
I know how the unloading valve works, but how does the non return (check) valve work?
Could the piston valve have anything to do with it?
Now some pictures.
Relief valve seat with the 1.75 mm o-ring
Relief valve top
Grinding the relief valve
Non return valve seat
Non return valve complete
Non return valve top