Pneumatic logic circuit

[ewelly]

Hi, I have a pneumatic logic question. I have an application where I need to have valve X pass air unless one of two limit valves is made. My issue is whatever I come up with dumps line pressure thru the exhaust of 1 limit when the other is made. Thought about a shuttle valve but this will lock up because it can't exhaust.

The application is a stroker with a cutting head. Want the head to turn on when it comes off the LS and stay on until it reaches the LS at the other end then turn off again.

Any suggestions appreciated, air logic isn't something I use very often.

 

[budt]

Not enough info to make anything but a guess.

What I think you are asking for is a common circuit for a Cylinder and could be used for a Motor.

What is necessary is a description of the cycle progression you want in a manner anyone can follow.

I have heard, in my younger days, of stroker engines but I'm pretty sure that is not what you are looking for.

What causes the "head," whatever that is, to "turn on when it comes off the limit switch?" What input causes it to "Come off the Limit switch?" Is the motion continuous? If so what auses it to stop?

The more specifics you provide the better the chance of getting workable feedback. A sketch would help also.



Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[ewelly]

Let me try again. The stroker is a linear slide driven by an air motor. The cutting head attached to the trolley on the slide will move off of the LS when an operator moves a hand valve to drive the stroker air motor. When it reaches the end of travel it stops by a hard stop and stalls the air motor until the operator reverses the hand valve. The valve controlling the cutting head will be on unless one of the end switches is made.
This is a manual operation that is only used at a production start-up, so fairly infrequent use.

 

[budt]

I must have a mental block today. I get from your writeup that the Operator shifts the Manually Operated Air Valve to make the Air Motor Rotate and Drive the Trolley Forward. When the Trolley reaches the end of its Forward travel the Operator Reverses the Manually Operated Air Valve to Return the Trolley to its Home Position.

To my way of thinking that is a complete operation and the Limit Switches serve no purpose except the one at Home Position could assure rhe Cutting Head is not in the way of the next part of the machines operation.

"The valve controlling the cutting head will be on unless one of the end switches is made."

Your writeup indicates Valve Controlling the Cutting Head is Maually Operated and does not need any electrics.

As you have probably guessed by now I'm totally confused and have no idea how your circuit functions/opearates and how it might be controlled.

This circuit sounds like one from a teacher in a Pneumatics class who wants you to ask questions like you will be required to do when dealing with most of the people you will be working with/for after you complete your Pneumatics course.

A Pneumatic Logic Circut would have no Limit Switches since they would be repalced by Limit Valves that would give Pilot Pressure to Air Pilot Operated Valves to shift them to do the function called out.

You can see some Air Logic circuits and Air Logic components in a training book I wrote here:

http://www.hydraulicspneumatics.com/200/eBooks/

Look in the Basic Book at Chapter 19 to see Air Logic Control components and some circuit examples of them. Also the Circuits book as several Air Logic Circuits in the "Air Logic" section.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[MechEng2005]

Could you just have two normally-closed limit switches wired in series to signal the valve to open? If it isn't on the limit switch, the valve gets a signal and opens, allowing the air to your system. If either of the limit switches is tripped, no signal to the valve and it goes to exhaust...

-- MechEng2005

 

[ewelly]

Thanks, I will looke thru the book.

The limit valves at each end are to turn off air to the valve operating the cutter. Basically if it is not parked at either end I need the cutter to be on.

I need to have all pneumatic, no electrical switches etc.

 

[ewelly]

Have attached a sketch of the main parts, obviously still need something to make it work.

 

[hydtools]

Why won't a shuttle valve work? When both limit valves are open the shuttle valve and the pilot lines will be vented. When one limit valve is actuated the shuttle will direct that signal to the cutter valve to turn it off while blocking flow to the open limit valve.

Ted

 

[budt]

I'm getting more confused after receiving yor drawing.

There is no "Cutter"

There si a RAISE/LOWER which you've never mentioned before.

TRAVERSE appears to be a Rodless Cylinder that reciprocates and has Limit Valves at both ends to shut off the WATER JET VALVE.

There is a now an Air Motor marked RAISE/LOWER as another operation.

Can you write a Sequence of Events such as:

Start Signal

Air Motor On, Raise

Traverse Move Left

Traverse Move Right

Air Motor On Lower

Air Motor Off

If the Traverse continuously reciprocates indicate it does that until a Stop Signal.

The more information supplied the greater the possibility of a logical answer.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[hydtools]

Run air line from one limit valve to the next then to the head. When either limit valve is actuated it will vent the head and block the air supply.
Limit valves in series. Both must be in normally open position to supply air to the head. When either one is acutated it dumps the air from the head and blocks the input air.

Ted

 

[HEC]

What you need is an "AND" valve where the supply from the two end limits is bought together. Both limits must not be made to allow flow to the Waterjet valve, when one is closed the flow to the Waterjet valve stops, the "AND" valve prevents flow from the limit not made exhausting from the limit switch made.

Mark Hutton

 

[ewelly]

Thanks all for helping the novice, I appreciate all suggestions. Hydtools, it looks like running in series will work great, I was making it way more complex than needed when such a simple fix is right there.

Thanks again.