Why would it relieve in only one direction? That makes no sense. I thought the purpose of that relief valve was to allow oil to pass from one side to another in the event you hit something hard (a rock or tree for example), with one side of the plow, creating a pressure spike. It should work when the control valve is not even open. Am I missing something?
How do I slow down side to side motion of HLA2000 angle plow
- Thread starter rfc143
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Why would it relieve in only one direction? That makes no sense. I thought the purpose of that relief valve was to allow oil to pass from one side to another in the event you hit something hard (a rock or tree for example), with one side of the plow, creating a pressure spike. It should work when the control valve is not even open. Am I missing something?
LD1
Epic Contributor
Yes.
Base side of cylinder holds more oil than rod side.
So when you try to compress cylinder, you are trying to move MORE oil out of the base end of the cylinder than there is room for on the rod side.
With the control valve centered so no oil can pass, there is a closed system. You CANNOT shove a cylinder rod into that closed system without oil leaving somehow.
Crossover valves we're intended to be used on a PAIR of cylinders, a double rod cylinder, or a hydraulic motor with high inertial load.
They were never mentioned to work on a single double acting cylinder. So I cannot answer why people and manufactures continue to mis-apply it's use.....oh wait, yes I can. They don't understand hydraulics
The manufacturer recognizes that it is not the most effective solution, but better than nothing. Furthermore, if one typically plows pushing snow to the right (as if driving on the right side of the road...I always do), the likelihood of hitting something is far greater on that side, hitting something in the ditch, a guard rail, sign or whatever. Because the base end of the cylinder is on the right side of the tractor and the rod end is on the left, when hitting such an object, the crossover should work fine, as it's dumping less oil from the rod end of the cylinder to the base end.
You are most correct though that if you hit something on the left side of the plow, not much oil is going to pass, (unless the piston seals are shot, lol).
You are most correct though that if you hit something on the left side of the plow, not much oil is going to pass, (unless the piston seals are shot, lol).
LD1
Epic Contributor
Nope. That's wrong. Even if Piston seals are shot, no oil is gonna transfer. Simply not enough room. You could remove the Piston and seals all together.... You are NOT gonna shove a cylinder rod down into the cylinder (retract) without oil LEAVING the cylinder.
kennyd
Advertiser
They both are, at one time or another. When the rod is extending, the rod port will "meter out" through the flow control valve. When the rod retracts, there will be full flow the other way through that port, and metered flow out the other port. All I have to do is end for end the flow controls.
LD1
Epic Contributor
Thats typical of a pneumatic flow control, not typical of a hydraulic flow control.
Well, I'm not using pneumatic flow controls; I'm using Parker hydraulic flows. These work exactly as described; they have a ball check and needle valve built into the block. I'll let you know how well it works once I reverse them.