Need Help With Pneumatic Circuit

OK, here goes.

1 Air supply to normally closed, spring loaded air valve.

2 From air outlet on valve #1 to inlet of spring loaded double throw valve #2.

3 Outlet A on valve # 2 to spring return air cylinder A.

4 Outlet B on valve #2 to spring return air cylinder B.

When you push on valve #1, air goes to valve #2. At the same time push valve #2 to position A. That will cause cylinder A to extend, and fixture loaded.

Once loading is complete, push valve #2 from position A to position B. That will cause cylinder A to release, and cylinder B to extend, allowing remainder of device assembly to take place. Once completed, release valves A&B. This will allow both cylinders to retract to the original positions.

If the operator takes either hand off the valve, the cylinders will both retract.

If you need, I can find Are Alpha valve numbers for you, tomorrow. If so, you will need to tell me what size air piping you will want to use. Valve sizes will be determined by air piping size. I hope this helps.

Out of the different solutions I've read, yours seems to be simple yet very effective. GA

I lack a lot of skills. I have tried for an hour to paste the drawing I made (with the part #s), and had to give up. I sent the OP a message, and was able to paste it there. If he can get it to attach, perhaps he will send it here. Thanks.

Bit of clarification:

A) Is each of your steps initiated by actuations of the two hand control (THC) - I mean, must the controls be released (stopping further motion) between each step?

B) Have you done any analysis to establish a Safety Integrity Level (SIL), or perhaps Safety Category, for your system?

C) Where are you located? (may have an influence on the safety requirements).

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Contact your local Fluid Power distributor that sells Air equipment and handles Air Logic controls. ARO is good equipment, also Crozuet and Telemechanique have Air Logic.

They should be able to design a circuit to do what you need and usually do it to get a sale. Did it for years as a Salesman, since I retired I design circuits for $75.00/hpur and don't care where you buy the parts.

Along with Festo and SMC

Thanks for all your help with my pneumatics problem. Your answers are appreciated, and have raised some more questions that I need to consider about the fixture and circuit.

The most common way to design this type of circuit is as a mesh of boolean elements with the outputs used as latching elements. Such circuits can be optimally cheap, small (and a lot of fun to design), but they often suffer from being hard to understand and almost impossible to modify.

Another way is to recognise how many discrete states the process goes through, build a (pneumatic) state machine, then use each unique state to perform a defined action. This can be more complicated and expensive for small circuits, but has the advantage of being easy to fault find and (after you understand the basic principle) easy to understand. Festo and others have sequencers that will do this.

But, the best method has all the sensors and solenoids wired back to a small PLC, where the electrical blokes can do the logic for you.

we sell air line and air line systems to auto dealers and service garages we dont make or have any of the "controllers" you would need designed but we have plenty of solenoid valves and gate vales and chek vales fittings and lines in stock we are over stocked on solenoid valves and could sell you a few for cheep most are 1/4" or 1/2" but you can adapt to any size line and they operate at either 12 or 24 volt dc. let me know what the circut desiners recomend and we can help with some of the small parts. we have some 1/4" fr units from graco ill throw one in for free with any other purchase. we also have the Air-compressors and fittings if you need them as well.

http://www.liftandlube.com/Default.asp

Very hard to actuate two separate circuits with hand controls simultanously unless you jury-rig a 3 or 4way valve off the hand controls to do that. My suggestion is to get a cheap PLC unit (try EzPLC.com) and all necessary sensors/switches and run your process thru a PC. Write a PLC program (ladder diagram) for your process. The software for EzPLC can be downloaded for free and they even have a mini-HMI (4" screen - $150US) if you don't want to run your machine off a PC.

Good Luck, let us know what you decide.

UFG

seems like your after a ripple type counter, with the 2HS (2 handed button) as the clock source, and the cylinders activated in this sequance

1-> 00

2-> 10

3-> 01

Then 2HS to cycle back to step 1. Shouldn't be too difficult using pneumatic logic blocks

Check out the Festo "Sub-base" search, you could come up with the logic to do what your asking ;o)

I am still working on this project. What I need to do is slightly different from what I originally posted - the following is what I need to achieve with same two cylinders:

Home Position: 5/16" and 4" cylinders both retracted

Step 1: Actuate THC (Two Hand Control): 5/16" cylinder to extend and hold.

Step 2: Actuate THC:

5/16" cylinder to retract and 4" cylinder to extend under low pressure until a limit switch is tripped, then to high pressure for remainder of rod extension.

Step 2 Notes:

1. The THC must be activated constantly during low-pressure mode until limit switch is tripped. If the THC is released prior to tripping the limit switch, 4" cylinder to retract. When THC is re-actuated, 4" cylinder to repeat low/high pressure step.
2. Releasing THC prior to 4" cylinder tripping limit switch would be deliberate due to incorrectly loaded parts, etc.

Step 3: Actuate THC:

4" Cylinder to retract. Now at Home Position, both cylinders retracted.

Thanks again for your replies, they have been helpful.

I can redraw the diagram for you. I will need to have 2 days because of some time constraints. I hope that will work for you.

The 5/16" and 4' , is that dia, or stroke?

Bob - thanks again for your offer to help, but I believe I will need to combine steps one and two to eliminate a step, so the concept is still subject to change. I may repost later if I still need help.

If you wish to combine steps 1&2, that is easy, just tie the two cylinders to the second valve and add a restrictor in the line to cylinder #2. That will delay it from starting it's movement. The low to high pressure can be done by timing the operation, or inserting a location sensor. These are also available in a pneumatic only design. So far the pneumatic circuit can be done without any electricity.

As your design is still in flux - and sounds as if it will stay that way for a while - I'd go for maximum flexibility. IMHO, you'd get this by using solenoid valves for the cylinders, controlled by a small PLC (as previously suggested by another). There are several devices around, called things like 'programmable relays' - Siemens, Omron & Allen-Bradley make them, among others.

They are simple to program - most if not all have free software you can download to simulate the system before programing it into the device.

With separate valves for the low & high pressure feeds to your 2^nd cylinder, you could then play around with the sequence quickly & easily, with no hardware changes.

Please don't neglect the Safety aspect. Releasing the THC should stop any movement which could cause harm, and this action should be independent of the logic control system.

I agree with you that the solenoid valves are more easily adapted to the changes. The use of the PLC is probably more than I would work with in the designs that have been presented so far. As I sit and read the posts, I am reminded that there is more than one way to skin a cat achieve the results desired. I was half tempted to build the design on my work bench. I could do it with pure air, electric switched air, but I would be need some help with the more complex plc.

I guess it's each to their own - I'm much more familiar with PLC's than pneumatic logic. If anyone needs a leg up with PLC programming I'm happy to help (if I can find the time!).

The Safety aspect is another matter. Having spent hours discussing Safety systems involving pneumatics, the whole area remains grey. So-called Safety dump valves are available (from e.g. Norgren), but when you look at the fine print, they meet very few safety standards. The switch contacts which are supposed to indicate that the valve is in the safe position (dumping the air) are not forced-disconnect safety contacts. I also seems next to impossible to find a safety-rated pressure switch.

All I can think of doing in this case is using the THC to control the air supply directly (which could be a 'genuine' safety function), with signalling via auxiliary switch contacts for feeding the logic.

IF desired, the THC system could rout air to the return portion of the cylinders. This would return both cylinders to retracted position, or the design could cause the cylinders to lock in the position they were at when a hand was removed from THC.