Sequential Pneumatic Circuits

[HomerWelsh]

Hi guys,

I would really appreciate some help on this one. I am trying to update a circuit from a cascade design to a one out of n sequential logic design. I have successfully created a 2 out of n but in keeping with the rest of the drill I would like it to be 1 out of n.

I have attached my circuit to show the problem I am having. If anyone has any suggestions they would be greatly appreciated.

Just incase anyone is interested, this is a two stage drill with clamp (3 actuators)with the speed control and logic pneumatically controlled.

Regards

 

[budt]

I am trying to update a circuit from a cascade design to a one out of n sequential logic design.

I have successfully created a 2 out of n but in keeping with the rest of the drill I would like it to be 1 out of n

I am not familiar with "1 or 2 out on n" referece. It may be that those are Electric terms and my understanding of electrical circuits is Slim to None.

I have designed many Air Logic Circuits, even before it was called Air Logic. I have a section in my basic Fluid Power Training book here:

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

that might help. Look at Ch. 19.

In the Advanced book see section 2 on Air Logic circuit designs as well.

Your circuit is drawn using the American National Standards Institue (ANSI) symbols. However, most companies that sell Air Logic Controls use a different set of symbols that look more like the Electrical ones. That is what I've used in my book along with some showing the ABSI Symbol.

The valves operating the cylinders are Double Pilot Operated 5-Way air valves. The Start, EStop and Limit Valves are 3-Way N.C. valves (NC Means No Flow Path in Air and Hydraulic systems) so I always use "Normally Passing r Normally Non-Passing" in any discussion with electric trained persons to eliminate the confusion of reversed terms. So I would call the valves Normally Non-Passing.

The row of 3-Way valves across the middle if the schematic are Double Pilot Operated, Normlly Non-Passing valves used in a similar fasion as Relays in electrical circuits. A Signal to either end moves the Box next to it into position and sets up an Open or Blocked Flow Path. The valve will stay in that position, witout further input, until an opposing signal is applied. Similar to a Snap Action Detented Switch. Nowever, some will shift by themselves when mounted with the shifting element aligned vertically due to nothing like a detent holding them in place. I have also witnessed some being shifted by air exhausting from other valves, especially after some run time that loosens their fit.

The Rectangles with the dumbell in them are ANSI Symbols for what electricicians call "AND" devices. A signal to either end port is blocked from exiting the opposite outlet port or the port on top. However, a Signal to both ports, allows the lowest pressure one to exit the valves top port and supp;y the next valve in line.

This info along with the chapters mentioned above should help you in decipering the circuit, I hope.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[HomerWelsh]

Cheers,

I'll give it a study.

 

[budt]

One other thing about the schematic you have, the symbols are all appear to be drawn right out of the catalog. Some recommend that be done for all schematics, However, for anyone not familiar with the machine it is almost impossible to decipher how the curcuit functions.

I always draw the symbols as they are (will be)located on the machine and show the components in the actuated position when they actually are in that position before the operator hits the start button. I indicate this with the valve Cam Operator in contact with its Cam and draw the flow lines to the valve box that is active at that time. Also the cylinders in their At Rest position since not all cylinders stop in the retracted position. That allows someone not familiar with the operation to diagnose the circuit for function or for trouble shooting.

Since your circuit is not shown this way it is impossible to determine the actual cicruit operation.


That way

Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[hydtools]

Bud, I think you meant 'actual position' and not 'actuated position' in the second paragraph.
Generally, all components are shown in initial or valve neutral/off position.

Ted

 

[budt]

"think you meant 'actual position' and not 'actuated position' in the second paragraph."
Probably would have been more clesr.

"Generally, all components are shown in initial or valve neutral/off position."

I always have a problem with that layout and have had to redraw the schematic showing the actual at rest position to. first understand where the air signals are and are not and then follow what should happen when a start signal is made.

I always make an oversize note that reads, "THIS SCHEMATIC IS SHOWN WITH THE CIRCUIT IN THE "AT REST CONDITION, AIR ON"

I do the same for hydraulic schematics as well.

Most Engineers and Maintenance persons have trouble even reading a Fluid Power schematic much less one that they must figure out what the valve position and condition actually is when the circuit is ready to operate.

Even helped me when I was called to trouble shoot a couple of years down the road and the circuit was long gone from the memory banks that had much more recent schematics floating around.

I try to follow the rules when they work well but have no problem bending them when it clarifies the picture.


Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING

 

[budt]

You can also see how I show schematics for training sessions and at added cost when a customer request' them to make it easier for persons to understand how the circuit works as it progresses through a cycle. The training books also include a section with detailed explanations of the circuit components with cutaway drawings.

if you go to this web page:

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

and open the "Fluid Power Circuits Explained" Ebook you can see how I show shematics for the novice in Fluid Power. The schematic in the Air Logic section on page AL10 with the cycle explanation on AL11 is a simple example of the layout. The first part of that section explains the components with some typical cutaway dawings of components and an explanation of their function. I've used this book as an advanced class for Engineers and Maintenance persons who have completed the basic class and/or have previous knowledge of symbols and the componets the symbol reoresents.

As you know from experience, the lack of Training/Education in all things related to Hydraulics and Pneumatics is less tha satisfactory and downright overlooked in most Engineering programs. That means the end user is on their own when it comes to Fluid Power eqipment and needs all the help they can get.



Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING