Henro
Super Member
- Joined
- Jul 4, 2003
- Messages
- 5,005
- Location
- Few miles north of Pgh, PA
- Tractor
- Kubota B2910, BX2200, KX41-2V mini EX
Sorry, but “Question about a grapple” was already taken as a thread title by PineRidge! /forums/images/graemlins/blush.gif
Anyway, in This Thread we tenderized the meat, so to speak, with respect to Junkman’s grapple hook up. No need to relive that here, but that thread does lead to my question.
I remember reports in the past of home built grapples being bent up (twisted, pretzeled) because the hydraulic cylinder that operated them pushed harder than the design could handle. I am almost certain the controls for those grapples were normal open-center control valves, plumbed up just like any auxiliary output would be.
We also have had some recent examples where electrically operated valves have been used to switch one of the spools of the loader valve, to operate the grapple when a button is pushed. Full hydraulic pressure would be applied to the grapple cylinder in this case also, and it would push quite hard, squeezing things between the grapple and the bucket pretty hard, until the control valve was centered, at which time the cylinder would lock in place.
The thread mentioned above gives an alternative-operating scheme for a grapple. At first it seems contrary to normal practice on a tractor’s open center hydraulic circuit, but once one takes a second look, it really is an alternative that could offer grapple movement, close and open, without having to worry about great pressure being developed by the grapple itself. The grapple would close and hold, and open and hold, and hold at any point between the two limits of travel, but would not damage itself, because the cylinder operating it could not in most cases develop enough force to do so.
So my question is, would it make a practical difference in operation, if the grapple were not able to squeeze real hard? If it could close down on something, then stay locked in that position, without being able to apply crushing force, would it matter much in a practical sense?
<font color="green"> [Quick summary of the how/why follows…]</font>
<font color="red"> (Background information, not part of the original question) </font>
The tractor in question has a closed center control valve hooked between the hydraulic line feeding the loader control valve, and the return to tank line. This control valve operates a cylinder which moves the grapple. Being closed center it has no effect on the system until it is operated.
It looks to me like the unless one of the open circuit loop valves are operated, the system pressure felt by the closed center valve would be quite low, maybe 100 PSI or less. Enough to operate the grapple, but not enough to apply crushing force.
The pressure available to the grapple cylinder would increase if one of the normal open-center-loop valves were operated, of course. And the grapple would squeeze harder if it were operated in conjunction with one of the open center loop valves.
Anyway, in This Thread we tenderized the meat, so to speak, with respect to Junkman’s grapple hook up. No need to relive that here, but that thread does lead to my question.
I remember reports in the past of home built grapples being bent up (twisted, pretzeled) because the hydraulic cylinder that operated them pushed harder than the design could handle. I am almost certain the controls for those grapples were normal open-center control valves, plumbed up just like any auxiliary output would be.
We also have had some recent examples where electrically operated valves have been used to switch one of the spools of the loader valve, to operate the grapple when a button is pushed. Full hydraulic pressure would be applied to the grapple cylinder in this case also, and it would push quite hard, squeezing things between the grapple and the bucket pretty hard, until the control valve was centered, at which time the cylinder would lock in place.
The thread mentioned above gives an alternative-operating scheme for a grapple. At first it seems contrary to normal practice on a tractor’s open center hydraulic circuit, but once one takes a second look, it really is an alternative that could offer grapple movement, close and open, without having to worry about great pressure being developed by the grapple itself. The grapple would close and hold, and open and hold, and hold at any point between the two limits of travel, but would not damage itself, because the cylinder operating it could not in most cases develop enough force to do so.
So my question is, would it make a practical difference in operation, if the grapple were not able to squeeze real hard? If it could close down on something, then stay locked in that position, without being able to apply crushing force, would it matter much in a practical sense?
<font color="green"> [Quick summary of the how/why follows…]</font>
<font color="red"> (Background information, not part of the original question) </font>
The tractor in question has a closed center control valve hooked between the hydraulic line feeding the loader control valve, and the return to tank line. This control valve operates a cylinder which moves the grapple. Being closed center it has no effect on the system until it is operated.
It looks to me like the unless one of the open circuit loop valves are operated, the system pressure felt by the closed center valve would be quite low, maybe 100 PSI or less. Enough to operate the grapple, but not enough to apply crushing force.
The pressure available to the grapple cylinder would increase if one of the normal open-center-loop valves were operated, of course. And the grapple would squeeze harder if it were operated in conjunction with one of the open center loop valves.
