Hydraulic Problem

I'm currently working on a machine that will use 2 hydraulic cylinders. The machine has to automatically cycle (out then in) cylinder 1, then cycle
cylinder 2, for as long as hydraulic power is applied.
I have been thinking about how to do this, but the only method I can think off would use 3 individual spool valves, but would require complex mechanisms to operate the spool valves.
I have tried searching the internet for suitable systems but have so far drawn a blank.
Ideally I want a system with a valve for each cylinder direction (ie. 4 valves), and each valve is triggered when the cylinder reaches the end of it's travel, which activates the next valve, for the next cylinder movement, and so on.
Is there a proper name for this kind of hydraulic circuit? I have tried searching for sequential and cascade circuits, but I don't know if these are the correct names.
Any help/suggestions would be gratefully recieved,
Moray
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I think you want to do this with electric solenoid hydraulic control valves. I see McMaster lists a 4 way three position valve for $141.46 each in the 110 catalog, page 875. You have the choice of closed or exhaust center. You'll need one for each cylinder. These valves are used all over on any molding machine, if you're a scrounge they can be had for peanuts.
As to the logic, I'd put limit switches at your end-of-travel which triggers your control valves to change state with relays. If you haven't any experience with electric logic circuits, get some help here. You'll want to put flow restrictors in your hydraulic lines to control the speed of the cylinders.
Karl
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I have looked at doing it using electric valves, but am trying to avoid using electrics. I have seen a similar machine that never used electrics, but I can't figure out how they managed it. Even once I figure it out, I may still use electrics, as it's largely dependant on costs.
Provided I can get the basic circuit, I can then add in flow restrictors/pressure valves as necessary.
It's currently turning into a personal challenge to figure this out.
Thanks moray
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You need some type of switch on the cylinders, be it a hydraulic pilot circuit switch, or electric. You do *NOT* want to use pressure spiking as a method of switching, this is a dangerous thing. You have to have a control circuit, whether it be a hydraulic pilot circuit with piloted valves, or electric with solenoid valves, that is up to you, but I'll about guarantee that an electrical precision limit switch will be much cheaper than a hydraulic one. If precision end position of the cylinders is required (absolute end), you will need a delay from the time the switch makes (either type) until you actually switch the valve. Whichever circuit type you use, when the switch gets made, there is still a little bit of travel left, if you want full extention, the dwell time before switching takes care of that. It would be much easier to do using electrics, as a simple timer fixes you up. Piloting is going to force you into running all kinds of extra piping, and the potential for leaks goes way up.
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On Sun, 26 Sep 2004 14:54:15 +0100, "Moray Cuthill"

You want double-action cylinders vs. spring-return and two cylinders in motion simultaneously? That increases the logic required and doubles the hydraulic flow required. Is this thing portable or fixed? Knowing your application might help us help you.

Logic can be fun. You have default and conditional states for 8 lines, so you'll have to figure out which valves and which controls operate them in which sequence you want.
Default state for the cylinders would be retracted, but do you want full pressure on them after retraction? Different speeds for extension vs. retraction? What about resetting all the cylinders if something happens in the middle of a cycle? Map all the states out on paper and it becomes easier. Write down the position and hydraulic state for each item throughout the machine cycle. Note the overlaps, etc., and go from there.
Using electrical solenoids and electronic logic could be cheaper than mechanicals, too.
Talking with your parts source might be a quicker route. (S)He can tell you what is in stock or what's available.
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calmly ranted:

It's for a self feeding log splitter.
Operation is as follows -
Main cyclinder comes out, then goes back in. The feed cylinder then comes out, and goes back in
There should only ever be 1 cylinder moving at any time. The main cylinder is fixed travel (ie always moves the same stroke) The feed cylinder travel is adjustable.
The machine I looked at, it stopped whenever hydraulic power was removed, and resumed as soon as hydraulic power was reapplied. No electric valves were used. The only supply was from the hydraulic power pack. According to what details I did get about it, it uses 4 identical valves and only operates on 60bar (possible that it might use pressure spiking?). I couldn't really see much of the hydraulics, as most of them were enclosed.
So far I have come up with using 3 spool valves with a complex linkage to work them. I have also managed to design a circuit using pilot operated check valves to control the cylinders, but have not worked out how to get it to switch effectively between cylinders.
Currently I'd just like to know how to get the basic circuit working. Speed control can be added in later on.
Thanks Moray
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On Sun, 26 Sep 2004 18:14:55 +0100, "Moray Cuthill"

I thought you said 4 cylinders which would activate in sequence. ?!?

OK. Are you moving the cylinder attachment point or limiting piston travel?

You'll need an activator on the return stroke of the main cyl to kick in the feed cyl. It's much more easily done using electrically operated sensors. One to watch cut lumber fall, the other to tell the feed cyl to operate. A third to see the feed cyl go out, and a fourth to see it come back, which then resets the hydraulics for the main cyl. These could be 5-12v electronics and solenoids and fed by a car battery on the splitter. Charge it occasionally or feed the battery through the trailer hookup so it charges on the way to the site.
I worked on an Eyetalyun marble polishing machine a few years back which had proximity sensors at all end points for the hydraulics and used a computerized control system. Either proximity sensors or paddle switches could be used.

I've always been interested in hydraulics but haven't yet worked on much. I did a lot of power steering pump work and auto trans work as a mechanic, but no tractor stuff, etc. and only one large hydraulic system. So, I'm no expert, but this is a fun exercise.
I really want to see how you're going to automatically feed this beast, too. That should be the main challenge, wot?
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It has 4 identical valves.

Personally I would limit the piston travel, but see below.

I have been pricing valves, and it is far cheaper to buy 2 CETOP double electrical valves, with flow control slices and a manifold, than what it would cost for the pure hydraulic set-up. So I'll be going the electrical route, however following a conversation with another mechanic today, the penny finally dropped how they managed to do it using pure hydraulics. As the machine only uses 80bar during operation it must use pressure spiking to operate pilot operated spool valves. When the hydraulic cylinder reaches full travel, a relief valve operates allowing hydraulic pressure through to operate the spool valve for the next cylinder. This would explain how the machine starts up from exactly where it was stopped.

I've had experience with quite a few hydraulic systems. Got to repair the lorry hydraulics at work (Telecoms fibre blowing vehicles), which have a screw compressor (110cfm @ 90psi, and air temp must be lees than 20 celsius), 110V alternator and a capstain winch. The only electrics on these are for operating the spool valves to select the circuits. Everything else is controlled hydraulically. Also had plenty experience with tractor hydraulics. And so far, I've managed to solve any problems (although the spool valve that kept blowing the seals out took a while for me to cure - somebody had plumbed it in the wrong way, and the return side was being pressurized)

You line up a load of cut discs (logs) in a feeding chute, and there's a finger feeder moves back + forward to feed them in (distance the finger feeder moves controls the log size). There's still a manual element, but it's greatly reduced.
Thanks for all your help
Moray.
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On Mon, 27 Sep 2004 18:21:02 +0100, "Moray Cuthill"
Mechanically or quantitative hydraulically?

I thought so. Are you going new, used, or new/surplus?

That's about 1,200 psi. What pump will you be using? It sounds as if an automotive steering pump would do, pressurewise.

OK. Does the pilot pressure also reset the main ram prior to sending the feed ram out again? Or are they 4 single-action cylinders working in sequence?

"Fibre blowing vehicles"? Whassat?

That'll do it. I had a tranny which had control problems and found that a student had reversed one of the spools in the control body, too. It shouldn't have FIT backwards but did.

Got it.

Will you be making more than one of these, for sale, etc?

I'm happy to try.
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calmly ranted:

Mechanically.
As I'm in the UK, it'll have to be new. Used /Surplus parts are very hard to find here.

I'll be using a tractor to power the machine, so I'll be able to get a full 160bar of pressure, with a flow rate upto 40litre/min.

Basically, the pilot pressure operates the next ram stroke in sequence, which will either be to retract the current ram, or extend the other ram.
The sequence is - Extend main ram Retract main ram Extend feed ram Retract feed ram
Having just looked into the Direct Sequence valves, I might possibly go for the pure hydraulic route, as these would appear to be quite a simple kind of valve, and shouldn't be too expensive.

What telecoms companies use for blowing the fibre optic cables down cable ducts.

Just the one off, for personal use.

I'm always grateful for any help I get.

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On Tue, 28 Sep 2004 18:15:04 +0100, "Moray Cuthill"

Too much rust from the sea air on your little isle? I haven't looked, but maybe our little surplus store might ship to you.

That's a good rate and pressure. You shouldn't have any trouble getting it to split wood.

Check.
Whatever works, works simply, and is inexpensive should do, eh?

I thought they were pulled through, but what do I know? <g> I've seen electricians (sparkies to you) blow string down to pull a snake which then pulled the wiring, but never the fiber optic cables. The FO cables I've seen here for TV are 2 inches in diameter. It would take a lot of air to blow several kilotons of cable down a run, wot?
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On Tue, 28 Sep 2004 16:01:54 -0700, Larry Jaques

Yeah, they pull in factory made fiber cables - but what they're doing here is blowing the bare fibers (or with a thin cladding) through a roughly 1" innerduct with the air pressure, tying a small piece of foam to the loose end of the fiber to act as a "piston".
Theoretically, they could get several hundred loose fibers into one innerduct like that, rather than the 24 or 48 in a pre-made cable. But if they ever have a case of "backhoe fade" on un-bundled and unmarked fibers like that, they'll pay hell matching every single loose fiber back up to splice them back together.
That, or pull it all out and start over, leaving customers out of service for a week or more as they put it all back together.
(I almost got sent to Fiber School, but they decided based on seniority rather than aptitude. Oh, well...)
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calmly ranted:

They blow the loose fibres up the ducts, using a fibre blowing machine. It's basically a machine with 2 roller tracks that feeds the optics into the duct, and also feeds the compressed air supply down the duct. These machines have only been used for the past couple of years. Prior to that, they used to use a duct motor (air powered ram with what's like 2 balloons on each end) that worked it's way up the duct with a bit rope attached. They would then attach the cable (copper or optic) to the end, and pull the rope back in using the capstan winch. They also used to also use an endless rodding machine, which worked it's way up the duct, with a bit rope tied on.
All the original lorries were sent back to the factory to get upgraded for fibre blowing. This involved fitting a new screw compressor complete with 5 coolers (3 hydraulic + 2 air) oil seperator for the oil that constantly circulates through it, and reworking most of the hydraulic system, and also altering how the engine revved up under load. When we done the course for servicing/repairing these lorries, the main service engineer and the designer took the course. One comment made was 'when we first tried to run the new compressor, it stalled the lorry dead'
In the case of a duct being damaged, there's normally enough surplus capacity in the network to re-route the network. This minimises the impact of a duct being damaged.
Moray
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calmly ranted:

It's probably got more to do with people only buying what they need, and using it until it's beyond use.

Even at that pressure, it can still struggle to split wood, especially if it's a nice knotty bit hardwood

That's the main thing. Have finally worked out a circuit for opertaing the cyclinders in the right sequence.
A basic outline of the circuit operation.
Fluid comes in through a spool valve (single acting 2 position detent - not entirely sure if the detent will be needed???) Fluid goes to feed ram to extend it. Once feed ram strokes out, and the sequence valve pressure reached, main ram extends. Once main ram extends, it operates the spool valve. Fluid now goes to feed ram to retract it. Once feed ram strokes out, another sequence valve pressure is reached, and the main ram retracts. Once main ram retracts, it operates the spool vlave. And the sequence continues.
The reason for the feed ram operating first is it won't need full power, so the sequence valve pressure can be set relativley low, and also allowing full system pressure to be applied to the main ram.
Now I have the this basic circuit, I just need to add the required pilot check valves, to allow the oil to return from the non-powered side of the rams.

These lorries have only been used for the past couple of years. And also the company i work for invented fibre optics, so they tend to use the latest technology.
Thanks moray
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On Wed, 29 Sep 2004 18:23:45 +0100, "Moray Cuthill"

That's what our fathers and forebears did. Kudos.

Have you found valving which will let you obtain that yet?

Sounds good. What about provisions for backing things off if a bypass occurs? (Piece of log jammed behind the ram, etc.?)

It's fun seeing the latest technology in use, isn't it? When my natural gas line was run, instead of trenching, they used an air/hydraulic mole which dug its own tunnel. i hadn't seen one before and it was fun to watch. He didn't quite level it so it came out a couple feet deeper than planned at the street, but he had his backhoe there and found it shortly. (Scoop, metal detect, scoop, metal detect, activate the mole, voila!)
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calmly ranted:

I've found the valves, and had one quote for the direct sequencing valves. And unless I find a much cheaper source, Electrical may still be considered. The quote I had, one sequencing valve was more expensive than a double acting solenoid operated spool valve.

I was looking at the circuit diagram last night, and have decided that a double acting spool would be a better approach, as it simplifies the return lines from the cylinders, and would only require 2 inline check valves to bypass the sequence valves. I'll have to get a good copy of the circuit drawn up and posted on my website. Regarding the rams jamming, the 2 rams never cross paths, which means there shouldn't be any metal to metal contact (unless something breaks). Should the main ram jam, it won't be able to complete it's cycle, so it won't be able to operate the spool valve. This effectively means that maximum pressure will be reached and the machine will stop. Should the feed ram jam, I'll design the feed mechanism so that it has a weak link, to minimize damage. Although the machine will keep cycling with the feed ram jammed, there shouldn't be any major damage. And also, there will always be someone near the machine, either loading in logs, or bagging.

My neighbour seen someone using a mole. They had to lay a pipe up a banking, so they dug a hole at the bottom of the banking, and tried sending the mole uphill. Let's just say, they had to do even more digging to get the mole back
Moray
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On Thu, 30 Sep 2004 20:31:05 +0100, "Moray Cuthill"

Yeah, the valving is the most expensive part of a hydraulic system in smaller situations like this. Longer/larger cylinders can get expensive, too, but the precision valving is where the guys make their bread and butter.

Yes, please.

No, no, I meant pieces of wood. I realized that the rams wouldn't even get close to each other.

Why didn't they use gravity to help speed it downhill? <g> Fools!
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calmly ranted:

Got a quote today, and can get the sequence valves for about 1/2 price of the previous quote, and these ones also come with a check valve built in, so the valve is bypassed for the ram return lines.

I'm working on it. Should get it done tomorrow (saturday).

Just got to keep an eye on the machine. There should always be someone nearby, incase anything goes wrong. Once you get used to the machine, you'll be ables to tell by the sound if anything has went wrong.

You can never make anything idiot proof. There is nobody as ingenious as an idiot
Moray.
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On Fri, 1 Oct 2004 21:14:57 +0100, "Moray Cuthill"

Cool.
Great.
True. IF you pay attention to it. I know a lot of people who don't know how to do either. They don't discern changes in pitch or speed as a problem sound at all. That's always been second nature to me.

I've never figured out how someone so stupid could, at the same time, be so clever as to figure out how to break something which had been tamper/idiot-proofed. C'est la vie.
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http://www.mymodelengines.co.uk/splitter_circuit.gif
Moray
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