Wed Nov 13, 2013 8:37 pm
I have not posted here for a while but still come back time to time for some info when I need it.
I have been wanting to add a hyd angle cylinder to the cub grading blade for a whilre now but just have not done it.
Well I aquired a cylinder the other day and already had the cub cadet valve so now I really had no excuse.
Instead of a pressure relief valve I added a cushion valve inline to the cylinder. It serves both purposes as a relief valve and if I were to catch something with the edge of the plow hidden in the snow, it will pop open and the fluid will flow to the other side of the cylinder. It came preset at 1000 psi and that is where I left it. If I take the plow off i will have to use a jumper hose from the work ports of the valve as it has no pressure relief.
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Wed Nov 13, 2013 9:00 pm
Looks good. I would have never thought of mounting the cylinder sideways like that. That should offer some protection to the cylinder when pushing. It seems that the angle to the rotation of the blade would require more power, but with a cylinder that size, rotating force shouldn't be a problem. I used much smaller cylinders, and while there is enough power, both functions are way too fast. I will have to add flow limiting valves to slow them down. A larger cylinder would accomplish the same thing.
I would look at adding a relief valve before your spool valve for the following reason. When using the blade, moving the TC lever in the down direction after the blade has touched the ground will cause pressure in the TC unit. The cushion valve that you installed inline to the cylinder acts on differential pressure across the cylinder. So, if you had the TC lever lower than what is required to put the blade on the ground and you operated the cylinder to the end of it's stroke, the differential pressure across the cushion valve would be equal to the pressure on the side of the cylinder being applied minus the pressure on the touch control unit. That could easily exceed the maximum pressure capacity of the pump, effectively dead heading the pump, which apparently is a very bad thing.
I hope that makes sense. Maybe someone can explain it a little better, or maybe I'm way off base. Either way, I wouldn't want all your work to end with a broken hydraulic pump. Does anyone see a flaw in my reasoning? Anyway, your modification looks good, and it should be a lot more fun to use.
Wed Nov 13, 2013 10:42 pm
Well I had considered that scenerio but was under the impression that the fluid at that point would open the cross flow in the cushion valve and flow not to the other side of the cylinder but back to the valve and into the return. Because at that instant the return on the spool valve on the empting side of the cylinder would be open.
Am I wrong in my thinking? Maybe I am not understanding the cushion valve operation correctly.
Thanks for the input.
Wed Nov 13, 2013 10:53 pm
Ok, I thought a little more about it. What you are saying is that when the blade touches the ground and compresses the spring, there is equal pressure on both the supply side and the return side of the touch control because the rotation of the rock shaft is unable to reach the setting you are trying to send it to. Being unable to reach this position the pressure inside the touch control unit does not equalize. I was thinking there was no real amount of pressure on the return line.
Anyone else with there thoughts on this please chime in.
Thu Nov 14, 2013 11:48 am
Remember that the "return" line from your aux valve does not return to the tank (no back pressure). It is actually the pressure side of the TC unit. The way I understand it, the TC will build pressure until it reaches the relief setpoint when it is unable to move to the position requested by the TC control. This would effectively create backpressure on the return side of your aux valve, and cause the cushion valve to open at a higher absolute pressure. My concern is that this pressure could exceed the capacity of the pump. A relief valve works against spring pressure which I think is independent of downstream pressure. Hopefully someone will correct me because I like the clean installation that you've done, and another valve would just be a little more complicated.
Thu Nov 14, 2013 7:00 pm
I was thinking this morning about just what you said in your last post before I read it. The return side of the aux valve is not the return line. It is just extending the pressure side of the pump to the touch control unit. Kinda like it takes the scenic route to get to the TC. I put the blade all the way down on the concrete floor and compressed the spring as far as the travel of the rock shaft would take it. I pulled the aux valve lever and it rotated the blde all the way to the stop. It struggled but it moved it. When it hit the stop, I held the lever for a second and It did not stall the tractor. I did this at low idle just in case it did deadhead the circiut. The cushion valve had to open now sending fluid back to the aux valve and back to the TC I wish i knew more about the TC innards. I think with the cushion valve set at 1000psi I should be ok. When it opens i am still only getting what the pump makes as far as pressure. If I were to hit something and the valve pop to the other side of the cylinder, most likely the aux would be closed. Maybe not always.
The only problem i am having is when you try to ease the aux lever back or forward slowly. It will drag the tractor down and stall it. If you just pull it open all the way quickly it works fine. Pressure relief ahead of the aux valve would help this I believe.
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