Limit stroke of hydraulic cylinder

[bootlegend]

I'm going to show my ignorance here, but suppose I have a hydraulic cylinder that has a total stroke of 100 inches and I only need to use 50 inches. Is there a way to limit the stroke hydraulically? Trying to avoid travel limit switches if possible but I don't want the cylinder to extend past the desired travel.

 

[BrianPetersen]

How "solidly" do you need to stop it at that position ... ? ? ?

If it is to be a physical limit and extending the cylinder beyond the limit results in catastrophe, use a mechanical stop ... or a shorter cylinder. Don't let it happen, even if there is a component failure.

If it would be nice to stop it roughly in this position and it's okay if it drifts beyond that position (overnight, let's say) or it's okay if it goes past that position if there is a problem of some sort, and it's actuated electrically, use a limit switch to cut off the valve solenoid power.

It would be nice if the rest of us, knew what that cylinder was for.

 

[hydtools]

Use a cam operated valve to limit the travel.

Ted

 

[bootlegend]

This cylinder will be used to extend a tube-in-tube support for raising and lowering a conveyor. I don't want the operator to be able to overextend the cylinder past the design position. I can handle some extension past the desired length, but I'd like to limit the ability to extend much further. Otherwise I'll be designing the support for the much extra length. Custom length cylinders have a very long lead time and the limit switches can get dirty in some environments. Are mechanical stops installed inside the cylinder?

I'll talk to the hydraulic supplier about the cam operated valve.

Thanks for the help so far.

 

[LittleInch]

Or meter the amount of fluid going into the arm.

Or have some sort of restriction device or fixed flow pump so you have a constant flowrate and then have a timer which only allows the valve to open for a certain amount of time.

Lots of ways to kill this cat, but you haven't given us much to go on in terms of where the hydraulic supply comes from, what activates the actuator/cylinder ( push button, solenoid valve, valve, nothing?)

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BrianPetersen]

What's the actuation for the valve ... electrical (solenoid-operated directional valve) or mechanical (hand lever)?

Is there any sort of position feedback at all, and if so, what is it?

Mechanical stops can be inside the cylinder or part of the mechanism that the cylinder actuates. It has to withstand full actuation pressure, whatever it is.

Regulating the quantity of fluid to the cylinder without somehow monitoring or travel-limiting the position of the cylinder will be coarse, imprecise, inconsistent.

Position switches don't have to be mechanical limit switches ... it could be a non-contact magnetic or RFID switch. The better ones are used in safety-related applications all the time, and in most applications are considered more reliable and more fault-resistant than mechanical limit switches.

More information = better answers.

 

[LittleInch]

For any solution it is also important to know what the time duration is anticipated for this 50" extension. 1 second, 10 seconds or 100 seconds makes a big difference to which type of control can be used to limit the extension to say 45-55".

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[3DDave]

Cam operated valve is the most direct method. They are typically tougher than electric limit switches.

Example application:

http://www.womackmachine.com/engineering-toolbox/data-sheets/applications-for-cam-actuated-valves/

 

[bootlegend]

I've attached a sketch that should explain what the cylinder will be used for. At this time, a mechanical hand lever for operating the cylinder. The only feedback currently is visually with the inner tube painted red to indicate that the maximum position has been reached. Time duration to extend can be a few minutes. It doesn't have to cycle fast.

After looking a little closer, I think I can accommodate the full cylinder stroke with extra length inner tubes. It isn't preferred and at full extension the conveyor motor may not be strong enough to lift the material or it might even roll backward.

I like the position switches that Brian mentioned. I will suggest those as an alternative to the mechanical switches. At the same time I will inquire about the cam operated valve with they hydraulics supplier.

Thank you all for the responses.

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