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OT: Hydraulic position / stroke control / end of stroke valves

Strostkovy

Titanium
Joined
Oct 29, 2017
Does anyone know where to get reasonably accurate hydraulic position / stroke control / end of stroke valves? I'm looking for the type with a little button that cuts off flow to the cylinder when it is pushed.

I'd like to setup an adjustable stop using one of these on some presses I've built instead of stacking shims to prevent oversqueezing.

Specifically it would be nice to have a valve that is not significantly pressure dependent and is repeatable to the same stroke. I used to run a press brake that had a valve like this in it and it seemed good to a few thousandths.
 
Look for a manual poppet valve. There are screw in and stand alone types. Parker and Sun and just about any major mfg will have them.
Would a manual poppet as a pilot to another spool valve decrease the pressure related inaccuracy?
 
I have no idea but I will look into them
Here's an example - the trip dogs on the table flip the lever back and forth, that changes the oil flow from one cylinder to another, or one end of a single cylinder to the other. They are not thousandths-accurate because it's hydraulics, but better than a sixteenth. Probaly better than that. Landis is not going to be economical but almost every grinder with table traverse uses some version of this, so there should be plenty to choose from, either new or used.

Another nice feature about this method is you can kick the trip lever out of the way to bypass the dogs if you want to move farther away, like for a rapid traverse. Then bring the table back and swing the lever back in and you have recip again.

Should be able to find all the hydraulic circuit schematics pretty easily, maybe on the tony's uk lathe site.

(The other two dials below the trip lever adjust the table speed, so that's readily available also. They are flow control so not too pressure-dependent).

btw, the lever on the right beings the wheelhead in to a solid stop, accurate within tenths (honest, real tenths) so if that's what you need, it's also achievable. But that's what you already have, right ? Good repeatability but done with a mechanical stop and you want to get away from that ? I can verify that the table controls are reliable within less than a grind relief but haven't ever tried running right up to a shoulder. I'd think you'd want ten thou to feel comfy doing that.

table-reverse.jpg
 
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Here's an example - the trip dogs on the table flip the lever back and forth, that changes the oil flow from one cylinder to another, or one end of a single cylinder to the other. They are not thousandths-accurate because it's hydraulics, but better than a sixteenth. Probaly better than that. Landis is not going to be economical but almost every grinder with table traverse uses some version of this, so there should be plenty to choose from, either new or used.

Another nice feature about this method is you can kick the trip lever out of the way to bypass the dogs if you want to move farther away, like for a rapid traverse. Then bring the table back and swing the lever back in and you have recip again.

Should be able to find all the hydraulic circuit schematics pretty easily, maybe on the tony's uk lathe site.

(The other two dials below the trip lever adjust the table speed, so that's readily available also. They are flow control so not too pressure-dependent).

btw, the lever on the right beings the wheelhead in to a solid stop, accurate within tenths (honest, real tenths) so if that's what you need, it's also achievable. But that's what you already have, right ? Good repeatability but done with a mechanical stop and you want to get away from that ? I can verify that the table controls are reliable within less than a grind relief but haven't ever tried running right up to a shoulder. I'd think you'd want ten thou to feel comfy doing that.
I could probably duplicate that with a regular spool valve, if a poppet ends up not being right

I mostly want to get away form hitting maximum tonnage every stroke, and also avoid adding shims or large screw jacks (I'm using plastic dies most of the time, and they don't take kindly to death hugs). I could use big screws that can handle 40 tons, but one of these presses has four synchronized cylinders and I'd need a beefy mechanism to bottom them uniformly with easy adjustment.
 
I could probably duplicate that with a regular spool valve, if a poppet ends up not being right
I'm sure a lot of ways to do it, just thinking the whole thing is all set up in one unit this way, easy to mount, not a bunch of pieces to bolt together.

With your description, seems like these (I think they are spool valves) could be one pretty simple way to go. But I'm not a hydraulics engineer, most likely there's a bunch of other ways too. Probably some better ones :)
 
Only way I have seen accurate hydraulics is proportional valves with encoder feed back. They wouldn’t limit pressure- being as long as piston is moving max pressure will never happen.
Extremely accurate once tuned. Also pricey.
I have been playing with helm steering pump attached to a stepper. If you can pre-load you cylinder with fair resitance the repeatability is good. These have cogging movement, repeatability has to fall within the cog.
Cheap and no other valves, just the pump.
 
Only way I have seen accurate hydraulics is proportional valves with encoder feed back. They wouldn’t limit pressure- being as long as piston is moving max pressure will never happen.
Extremely accurate once tuned. Also pricey.
I have been playing with helm steering pump attached to a stepper. If you can pre-load you cylinder with fair resitance the repeatability is good. These have cogging movement, repeatability has to fall within the cog.
Cheap and no other valves, just the pump.
That's funny, one of the presses I am working on (frame is waiting for powder coat) uses a hydraulic steering valve for control
 
I'm having a hard time figuring what you are trying to do. You say over squeezing? Once the squeezing starts unless it is some kind of deep draw mechanisim there is very little to no stroke change. In that case you would use a dump valve to relieve the over pressure. That is very easy with an adjustable relief valve. No need to worry about stopping the stroke. Stroke control is usually for positioning which you still would have to stop or dump the pressure at the position You could put a NO valve in the return line at the other end of the cylinder to stop the piston by closing the valve which you could operate with a manual PB valve to supply pilot pressure.You would need some thing to control the shock, a relief valve or an accumulator on incomming line depends on the pressures involved. Air cyls use a magnetic piston and an external sensor that you can move along the cyl to control the stroke.
There are all kinds of literature available.Parker would be a good source. Time to crack the books.
 
I'm having a hard time figuring what you are trying to do. You say over squeezing? Once the squeezing starts unless it is some kind of deep draw mechanisim there is very little to no stroke change. In that case you would use a dump valve to relieve the over pressure. That is very easy with an adjustable relief valve. No need to worry about stopping the stroke. Stroke control is usually for positioning which you still would have to stop or dump the pressure at the position You could put a NO valve in the return line at the other end of the cylinder to stop the piston by closing the valve which you could operate with a manual PB valve to supply pilot pressure.You would need some thing to control the shock, a relief valve or an accumulator on incomming line depends on the pressures involved. Air cyls use a magnetic piston and an external sensor that you can move along the cyl to control the stroke.
There are all kinds of literature available.Parker would be a good source. Time to crack the books.
The tooling cannot survive the full tonnage available, so I use shims and blocks. But I'd rather just turn a crank to a number.
 
Seems like you just need an adjustable pressure relief valve.Easy and adjustable for different jobs. You should have a relief valve for max safe pressure anyway. Forget about shims and stroke for control.Nothing simpler than a knob and gauge.
 








 
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