HYDRAULIC CHAIN SAW

[J_J]

I was looking up data on my hydraulic cd, and they describe a closed center system as one that has a variable displacement pump which will run as needed. It will build up pressure and stop. So when you pull the trigger on that closed center hyd pole pruner, you are now using what's in the line, plus the pump runs to resupply what was used. Now here is the problem as I see it, If you hook up a closed center device to an open center valve system, that fixed displacement pump is running at 100 % and something is going to break or split or explode. What ever is the weakest component in the system.

With the hydraulic chain saw, I might get away with it if I don't exceed the pressure, because the hyd fluid is just turning a motor and returning to tank.

 

[SkogenMe]

I'd be interested to hear how it works....I have been interested in running a pole pruner off my tractor.
Don't know if you have talked to a Stanley rep.
Stanley hydraulics
good luck

 

[Spiffy]

<font color="blue"> a closed center system as one that has a variable displacement pump which will run as needed </font>

That's how I'm seeing it, but if the pruner is different from the chain saw perhaps it's something beyond me.

With any hydraulic motor tool, it should have an inlet and return: the closed center trigger would stop the flow (with the pump maintaining constant pressure and 0 volume), the open center would divert the flow to the return instead of the motor first (with the pump maintaining constant volume and negligable pressure). Wiring it open takes the trigger out of the equation, so your tool now is either open [like a PT] or closed depending on the tractor's valve.

Anyway, barring some other setup, the only concerns I see would be matching the volume (a level of forgivness the closed center pump would allow if the pressures matched, though over-revving would still be possible) and making sure your relief valve setting is in the same ballpark as the tool's max - that should be the "weak" component, a chain binding will max the pressure regardless of system.

 

[J_J]

The pole pruner that I have is a one click action. It works by activating a hyd cylinder to pull a blade, like a pair of shears.

 

[Spiffy]

That makes sense! I have little "weedeater" powered pole pruner so I couldn't get the rotary motor out of my head.

Anway, it looks like no return line? So I'm betting it's esentially a single acting cylinder (pressure close, spring open). "one click" has me a bit confused yet, as I've seen fluid control circuits that do have a built in "timer" or position "sensing", but I don't see any reason for that complexity. <font color="red"> No return? Now I'm getting myself confused, even a single acting needs somewhere to bleed the fluid on return </font>

If it is the single acting cylinder, you would still be alright with the PT's auxillary (if yours is motor spooled: perfect, pressure closed, back to center open), cylinder spooled, I'd run the reverse line back to the tank, so you don't deadhead or have to feather it on reverse. The PTO would be a great setup, but awful quick unless you're just idling.

What does concern me is the max pressure, regardless of an open/closed system: unless, your coordination or timing is perfect, <font color="red">or it does have, position sensing </font>, that thing will deadhead everytime (which, the CCs variable pump would maintain constant pressure, while a OCs relief valve will "chatter" until you release the trigger; obviously the former is nicer here, but either would be harmless or capable of damaging the tool depending upon set pressure).

One last option, if you're planning to use it handheld, instead mounted. You'd need to remove or wire open the trigger, but bolt on the cheapest OC vavle you can find. I suppose the extra weight of the valve and return line might be undesirable though.

Cheap Valve Built in overpressure already set to 2ksi! Double acting though, so "reverse" would be in parrell with the return line.

<font color="red"> edit </font>

 

[Spiffy]

One more really dumb question: If that is the Stanley pruner like in the earlier link, any chance they'd sell you an OC trigger assembly (or tell you if it's just a conversion plug) for a reasonable price?

 

[MossRoad]

That pole pruner is pretty neat. Beats pulling one with a rope. /forums/images/graemlins/laugh.gif

 

[rox]

Did you build that Pole Prunner?
If so does it run jsut on hydrolics?

 

[rox]

Shucks, the stanley website is down, gonna have to check that tomorrow.

 

[J_J]

No, I didn't build this pruner, I bought it as is. I can't find a name on it. It looks like a Stanley. Yes it is hydraulic. closed center, max psi of 2000. It does have the two hose hook up.