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Discussion Starter #1 (Edited)
I want to be able to control my rear 8 ft heavy duty blade from my 4044M tractor seat. I know they sell a expensive hydraulic control kit for this but it has to wait for other PTO Operated Stuff in line first. My Idea is to get the dual action ram now to angle the blade with and plumb in a tempory hydraulic closed loop line with a valve to control the flow. I have high presser valves and fittings I could use to place one near the seat. My thought is to open the valve, set the blade and close it again for a Hydraulic Fluid Lock. I would first purge all the air from the hydraulic cylinder and hose then put the valve on to control fluid flow. Now with the valve open at the seat it would be easy to re/angle the blade using the tractor movement then lock the valve. Seems when I am plowing snow or grading it is a real hassle to get off and move it so I just work around it and waste fuel in the process. Locking the fluid should lock the blade rigid at least I think it should work that way? Anyone try this before? Just thought about it more nope each side is different in fluid capacity and it won't move till fluid can flow at different rates in the single loop hose at the same time . Won't happen.
 

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Discussion Starter #2 (Edited)
Guess it is not a dumb idea(except the locking loop one) cause it is being sold on this site exactly how I was thinking it could work. Heck the 3rd SCV was even bolted where I thought it would be a good place to put it. Did not need to re/invent the wheel just read the SCV Thread.
 

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The problem you would run into is volume of oil differences.

E.g. If the cylinder is fully retracted, the cylinder will be full of oil around the rod. The volume of the cylinder here is volume of the cylinder barrel minus the volume of the cylinder rod. When the cylinder extends, the oil will be pushed out of the rod port into the piston side port. The issue is, the barrel side has more volume than the rod side port.

See below diagram to explain.

If a cylinder is extended, and the piston seals are completely shot, if both ports are closed the cylinder will not retract because the piston side volume is larger than the rod side volume. Essentially, there isn't enough space for the oil to go so the cylinder will stay extended. The reverse is turn if the cylinder is retracted and the rod is pulled out by some external force. The oil will be forced out of the rod side port but the space left on the piston side is larger than the oil volume pushed out of the rod side, this will result in a vacuum build up in the cylinder or air will be sucked in around the rod seals.
 

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Discussion Starter #4
Your right on trying to move different volumes in the same cylinder and in the same hose it won't work. Looking at I think Ken's 3rd SCV set up it appears to be a nice package for the money. By the time you figure out all the fittings, angles hose lengths, people who sell the right stuff you need to buy that is a good price to me for what you get. I know I have designed things many times only to find out it is all ready made and cheaper to buy out right if your time is also valuable to you for other things.
 

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The Hydraulink folks use a small air reservoir to compensate for the fluid volume differences. Take a peek at the patent https://encrypted.google.com/patents/US8464802 with the cylinder image:
US08464802-20130618-D00000.png

If you want to go this route, I have one I'd part with...
 

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Discussion Starter #6 (Edited)
The Hydraulink folks use a small air reservoir to compensate for the fluid volume differences. Take a peek at the patent https://encrypted.google.com/patents/US8464802 with the cylinder image:
View attachment 563569

If you want to go this route, I have one I'd part with...
Wow that gave me a idea to try once for fun just to see if I could make it work on a cylinder. I like how the guy moved the tractor to set the blade cause that was part of what I was saying. The air chamber part might be the ticket. I was thinking later about how a small reservoir open to both hoses could do it and a valve to close both hoses on the cylinder. The pump part is just the movement of the ram before shutting the valve for a hydraulic lock. If I am thinking right you could lock the cylinder with one side full and the other larger side empty to be used as a reservoir and the air to compress/vacuum as needed when the piston moved open or closed. Here I go again just thinking out loud. Using a dual action cylinder as a single action and the other end as the reservoir. Hard part is sucking the fluid in the large end and not getting the air which should work if the threaded hydraulic fluid hole is down and your not bouncing around while changing the angle of the blade may just work?
 

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I am thinking "T" an accumulator into the system. Put a "T" on each side of the valve, so two lines to the accumulator. It would also act as a "shock absorber" if you hit something non moveable with your blade. You might have to experiment with the nitrogen charge in the accumulator.
 

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The Hydraulink folks use a small air reservoir to compensate for the fluid volume differences. Take a peek at the patent https://encrypted.google.com/patents/US8464802 with the cylinder image:
View attachment 563569

If you want to go this route, I have one I'd part with...
From what I can tell by the description, they are using air to displace the volume difference. The issue is, air is compressible so the cylinder cannot be locked so that the cylinder rod is locked from moving in and out with this set up. It can be locked in one direction only. Using this to hold a blade from moving in either direction will most likely not work. I would agree it could work on the top link of a 3 point if you do not need to adjust the top link under load with power. :dunno:
 
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