Keeping a cylinder from bending

[aczlan]

While researching a hydraulic cylinder application, I came across some information about cylinders designed such that just before they are fully extended, the retract port is exposed so that further extension pressure just bypasses back to the reservoir. Don't know if all cylinders are designed this way but if so, your solution may be nothing more than a clevis adjustment or mounting point adjustment so that your mechanism is in place just as the cylinder bottoms out.

That would only work if you have gravity pushing down on the cylinders. Otherwise, it would be "stuck" in extend position.

Aaron Z

 

[jmc]

That would only work if you have gravity pushing down on the cylinders. Otherwise, it would be "stuck" in extend position.

Aaron Z

Good point. They probably elongated the retract port so that more retraction port is exposed beyond the extended cylinder than below it, yet the limited port exposure still serves as a 'leak' that won't allow full pressure to build. That said, if you need full retraction force after full extension, you're SOL.

 

[dfkrug]

Yes, that's why a I wrote "on or in", since the inside of cylinders vary so much, a spacer would have to be custom machined and the cylinder disassembled to install it. Stopping the retraction is easy with the parts I linked.

The stroke control parts you linked, Kenny, sure look like they are for extension, too. Just put them around
the rod inside the cyl between the piston and the gland. They look like that have springs to grab the rod.
I like that approach best.

A simple work port cross-over relief like this (photo) is the next easiest approach, if the OP does not
want to open the cyl. You can order these pre-set to any pressure and the plumbing is simple, with
no drain ports. This application does not seem to require much pressure.

 

[BHD]

Sounds like you need a pressure relief valve such as those found at: Surplus Center installed on just on that cylinder


Aaron Z

http://www.surpluscenter.com/Hydrau...00-1500-PSI-HYD-CUSHION-VALVE-9-4019-50-L.axd

the HYD CUSHION VALVE will do what you want , it is two relief valves, hooked together and will dump oil from one hose to the other, if over pressured, so even if the vale is in neutral or locked the cylinder is still protected From over load, or if the tractor is has more psi than the cylinder can deal with it will work.

I had a situation where if the load go to great it would bend the cylinder, and the valve solved the problem. and each side can be adjusted independently if needed.

 

[dfkrug]

1/2 NPT 30 GPM 500-1500 PSI HYD CUSHION VALVE

the HYD CUSHION VALVE will do what you want , it is two relief valves, hooked together and will dump oil from one hose to the other, if over pressured, so even if the vale is in neutral or locked the cylinder is still protected From over load, or if the tractor is has more psi than the cylinder can deal with it will work.

That Prince valve is a workport crossover relief valve with dual adjustable RVs. Unless there was a dump
to the tank, it will not protect the cylinder when the control valve is in neutral. If the workport was
connected to a hydraulic rotary motor, then it may work in such a situation since the in and out volumes
would be the same.

 

[J_J]

If the pressure and load is such as to bend the shaft due to the length, then go to a larger diameter shaft, or larger cyl.

Maybe there is a poor relationship between the pivot point and the power point. Incorrect design.

How about some pictures of the cyl mounted?

Redesign to have a better mechanical advantage.

 

[MHarryE]

Cylinders are designed for a specified column strength at a certain pressure. The numbers you provided say your cylinder should be limited to 1200 psi. For safety sake you should get a cylinder that will handle your system pressure.

 

[bdog]

Thanks for all the replies. I had a local hydraulic shop install stops inside of a cylinder. I bought the cylinder from them as my other one was bent and they installed the stops for $45. I measured it where the cylinder stops about 1/2" before the moving piece hits it's stop. Works perfect. I think the pressure relief would have worked also but this was the cheapest and simplest solution.

 

[dfkrug]

I had a local hydraulic shop install stops inside of a cylinder.

That would be my preferred fix, too. I like the simplest, most economical solution, and you got
a fair price for the service.

 

[BHD]

That Prince valve is a workport crossover relief valve with dual adjustable RVs. Unless there was a dump
to the tank, it will not protect the cylinder when the control valve is in neutral. If the workport was
connected to a hydraulic rotary motor, then it may work in such a situation since the in and out volumes
would be the same.

It does not need a return to the tank,

as the cylinder can at a given pressure by pass to the opposite hose, thus if the cylinder is compressed/extended to over design load it moves as the oil is passed from one side to the other via the cushion valve, (just as if one hooked a hose from one end of the cylinder to the other, (but with resistance that is set by the user via the valve),

and if it over pressured by the system, it goes through the cushion valve and back the other line to the tank


All I know is it woks on my two cylinders on my back hoe, as there are situations that if I curl the bucket it can over load the one cylinder and my current design I can not with out rebuilding parts, so I added two of this type of cushion valve and it has worked for a number of years, now and no more bent cylinders, if you do not want to believe my experience then don't.