What is the simplest way to make a cylinder extend to full stroke, then return by itself all by the push of a button (or lever). Can it be done mechanically or hydraulically, or are electronics going to have to be involved?

Josh Sked:

quote:

Can it be done mechanically or hydraulically,

quote:

What is the simplest way to make a cylinder extend to full stroke, then return by itself all by the push of a button (or lever). Can it be done mechanically or hydraulically,

You can use a Sequence Valve or a Cam Operated 3-Way or 4-Way valve to return a Manually Operated 4-Way that is Pilot Operated Shift to Return to make a hydraulic cylinder automatically cycle from a single Operator Input.

The Cam Operated circuit is positive since the cylinder has to make a physical position before it returns. That means it will not return when some obstacle stops it before completing a stroke.

A Sequence valve will also work as long as you don't care if the cylinder returns prematurely anytime some obstacle causes a pressure buildup before hitting the end of stroke. I've actually used that feature advantageuosly when different sise parts were involved.

You can see Sequence circuits in the Fluid Power Circuits Explained book wnen that section is presented. I also show a Sequence Valve and some circuits in the Basic book in Chapter 14.

Could you run a single acting spool on the valve and throw an accumulator on the other work port of the cylinder?

Yes, However you would have to size the Cylinder And/Or raise working pressure to make up for the RESISTANCE from the BACK PRESSURE in the Accumulator that will increase as the Cylinder advances and pushes more oil into it. The other problem is the expense of the Accumulator and its safety items. A lot more expensive tha a 4-Way valve that would use the available pump flow to return the cylinder.

You could also use a Spring Return Single Acting Cylinder but make sure the Spring is STRONG ENOUGH to return the Cylinder under all possible conditions. You also have to remember the SPRING will reduce the maximum force of the cylinders working stroke.

On Vertical Mount Cylinders you could use the weight to return it with the same resistive force disadvatage.

This message has been edited. Last edited by: Bud T,

The issue with using a single acting setup, is that the spool must still shift to allow fluid to flow back to tank during the retraction stroke.

It looks like we're going to go with a 3 position, 4 way, non-spring to centre DCV pilot operated by two 2 position, 3 way DCV's; one with a push button to start it, one with a cam setup for retraction.

Josh;
You will be able to see how Directional Controls are designated and some of the functions they can perform when Chapter 8 of "Fluid Power Circuits Explained" comes up.

It is the next Chapter to be presentd. at the H&P Magazine site.
http://www.hydraulicspneumatics.com/200/eBooks/

Haha, did I word something wrong there?

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3 position, 4 way, non-spring to centre DCV

I'm wondering what a symbol for that animal would look like.

Ah, good point. There would be no middle position without a spring to centre it.

quote:

Originally posted by Bud T:
Josh Sked:

quote:

Can it be done mechanically or hydraulically,

quote:

What is the simplest way to make a cylinder extend to full stroke, then return by itself all by the push of a button (or lever). Can it be done mechanically or hydraulically,

You can use a Sequence Valve or a Cam Operated 3-Way or 4-Way valve to return a Manually Operated 4-Way that is Pilot Operated Shift to Return to make a hydraulic cylinder automatically cycle from a single Operator Input.

The Cam Operated circuit is positive since the cylinder has to make a physical position before it returns. That means it will not return when some obstacle stops it before completing a stroke.

A Sequence valve will also work as long as you don't care if the cylinder returns prematurely anytime some obstacle causes a pressure buildup before hitting the end of stroke. I've actually used that feature advantageuosly when different sise parts were involved.

You can see Sequence circuits in the Fluid Power Circuits Explained book wnen that section is presented. I also show a Sequence Valve and some circuits in the Basic book in Chapter 14.

Bud, if I were to use a 3 way, 2 position cam operated valve to operate the pilot/manual operated 4-way, 3 position DCV, how do I get the cam operated valve to self reset after the retraction is finished?

quote:

Bud, if I were to use a 3 way, 2 position cam operated valve to operate the pilot/manual operated 4-way, 3 position DCV, how do I get the cam operated valve to self reset after the retraction is finished?

That makes it a little more difficult Josh. My post was for a Double Pilot Operated, 2 Position, Detented valve, All Ports Blocked Center Configuration (Crossover Condition}.
A 3 Position valve that operates the cylinder would need to have the Sequence Valves shift a small 3 or 4-Way Double Piloted valve that would shift the 3 Position Spring Centered valve and hold it shifted until the same Sequence and a small valve would do the same at the opposite end.
The circuit would be started by sending pilot supply from a 2 Position 3-Way to one of the Sequence/Pilot Valve setups. The 2 Position 3-Way would be Spring Return for Single Cycle or Detented for continuous cycle until turning it off.

Here's what I have so far, but how do I prevent the oil from dumping across the relief valve until the button is pushed again after it's done it's cycle?

http://www.toprotege.com/forums/attachment.php?attachmentid=10993&d=1222361052

Josh;
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See if this works. You should be able to click it to enlarge it.

http://memimage.cardomain.com/member_images/4/web/60400..._full.jpg?450311-269

That will work Josh if the DCV has Closed Crossover Condition at least for the "P" Port. Otherwise you lose Pilot Presssure when the valve passes through any condition that lets pump pressure drop.

Like you say though, How do you unload the pump in between cycles to keep the circuit from over heating.

One way is to use a Kick-Down Sequence valve with its Inlet conected to the Retract Line and its Outlet connected to Tank. Set it at a high enough pressure to return the cylinder and when the cylinder fully retracts and builds pressure the Kick-Down Sequence will open and dump the pump to tank until the pressure in that line drops and allows the Kick-Down Sequence to reset.

You can see a Kick-Down Sequence Valve in Chapter 14-3. Several companies make a Kick-Down Sequene valve. One I have used is from Delta Power Hydraulics http://www.delta-power.com/default.aspx


The bad news about a circuit that uses Pressure Control valves to sequence its operation is, when something causes pressure to build the sequence will snd a signal no matter where the cylinder is in its movement path. That is great when you are clamping different thhickness parts and don't want to be continually moving a Limit Switch. But it can cause damage or injury when a short stroke allows a part to be thrown out of a fixture or some other unsafe condition.

Limit Switches or Limit valves are the only fail safe way to assure a cylinder is actually in position before starting the next actuation in a Sequence.

The other bad news about a Sequence circuit is the amount of skill required to adjust the Sequence Valves to operate flawlessly. If it can be done it is very difficult and any change to any other Pressure Control in the circuit can cause the system to do funny things or nothing at all. In the past I've seen them used on complex circuts with 4- separate operations. One UNTRAINED PERSON can mess up the Sequence and a TRAINED person may have to spend half a day to get it back to normal.

Fortuanately the ease of using Solenoid operated valves and Limit Switches to indicate actuator position all fed and controlled by a PLC has almost eliminated the need for Sequence Valves.

This message has been edited. Last edited by: Bud T,