Pneumatic Cylinder Extend/Retract Cntrl - Help

Hello All,

I am no expert in valves, Cylinders, or any sort of Pneumatic controls, and in need of some help as to type of control valve that is needed for this application.

Currently, a customer has 6 pneumatic cylinders that are operated manually (Pneumatic Toggle Switches)but wants to Automate the operation.

Each cylinder has to be Manually activated.

1. Up Stroke (Operator turn off the down stroke Toggle Switch and turns on the UP stroke toggle switch.

2. For cylinder down stroke, turns off up stroke and turns on the down stroke switch.

What I want to do is find a control valve that I can accomplish this with 1 PLC Output per/Cylinder instead of using two outputs and two separate solenoid valves for controlling the Extend/retract strokes of the cylinder.

i.e., If I turn on a PLC output on, cylinder Extends.When it is off, it retracts.

So If I was to walk over to SMC Pneumatic, what kind of Solenoid/Manifold do I ask for?

3-Way Valve?

In the interest of safety, I want all cylinders to be at down stroke. I.e. Even if the cylinder is Up, at power off, I need all of them to be at the down position.

Sorry for the trivial question, but I have only worked with pneumatic controls that only required 1 control to turn things on/off as in when PLC out put was on, Device is on and when it is off, the device is off.

In this particular application, To Turn on, device needs an on cmd and to turn off, needs a separate off cmd. (i.e. Device does not go in to off state by simply removing the "ON" cmd"

Thanks for all the help and tips, etc.

Cheers.

If I were you, I would contact a rep for SMC Pneumatic and tell them exactly what you have said here. They are experts on the subject.

skyfox said:

Hello All,

In the interest of safety, I want all cylinders to be at down stroke. I.e. Even if the cylinder is Up, at power off, I need all of them to be at the down position.

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And you need someone with experience with safety in control systems. On the surface, this is a big no-no. E-Stop requires motion to STOP MOVING. Your description indicates you want 2-position spring return valves but if you have vertical motion, this system will not be safe.

If it is safe to let it come down in case of power off, you will need a 5/2 way single solenoid valve, aka spring return valve for each cylinder.

Common types of solenoid valves to control 2 position cylinders are

1. 5/2 way single solenoid valves [while turn on the coil, moves it forward, off retracts it]
2. 5/2 way double solenoid valves [Turn On one of the coil moves it forward, off it, and turn on the other solenoid valves, retract it. In case of power failure/turned off both solenoid coils the axis remain in the last position. Thus it is also known as memory valves]

3. 5/3 way valves - it exist, -but don't want to confuse you on that.

Regards

Also keep in mind that a standard pneumatic valve is not a safety device. You can't guarantee that a valve won't stick in an E-stop situation. I have a feeling there's not much safety on this machine.

You're also remove all sources of power during an E-stop and a standard dump valve cannot guarantee that this will occur. Ross Controls has a bunch of different safety control valves which might help in some of your applications.

jstolaruk said:

And you need someone with experience with safety in control systems. On the surface, this is a big no-no. E-Stop requires motion to STOP MOVING. Your description indicates you want 2-position spring return valves but if you have vertical motion, this system will not be safe.

Click to expand...

I would have to slightly disagree. IMHO E-stop mean to put the machine in a safe stae and 95% of the time that also equal to no motion but there are some cases where things should move to a safe position.

I have worked with several situations where we had to do exactly what the OP is asking.

It all depends on the specific equipment and what your risk assessment calls for.

I think the OP should involve someone more familiar with pneumatic safety in general. We use Ross Valves for all our safety related pneumatics on our 600 tom stamping presses and we are very pleased with their level of support on new projects.

The Plc Kid said:

I would have to slightly disagree. IMHO E-stop mean to put the machine in a safe stae and 95% of the time that also equal to no motion but there are some cases where things should move to a safe position.

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And we'll agree to disagree. 32 years of controls work and I haven't experienced where movement after an e-stop has been acceptable especially on vertical motion. Closest is a category 1 stop on servos.

skyfox,

You really have not given us enough information for us to give you a correct answer. A single solenoid spring return valve will do what you want, but that's just the beginning.

when you power up the system, nothing must move!!
when you hit the e-stop, nothing must move!!
when you loose power, what must NOT move???

you must look at the system as a whole, do a risk assessment, and get safety involved.

when things are clamped in place and operations are being done on parts, you cannot release the part just because you loose power or hit the e-stop.

we typically use double solenoid blocked center valves for these applications.

regards,
james

Thanks everyone for their Input. Appreciate the help.

Everyone raising concerns as to the Safety of this operation (Right Fully So)......I am fully aware of safe operation of control systems. Deal with Chemical systems all the time. In comparison, this is a primitive system and operator has no access to the cylinder area unless Power is turned off and the system is E-Stopped. Access door has a pneumatic lock that only unlocks when system is E-Stopped or powered off. Safe position of the system is all cylinders down.

On Power off - All cylinders Down (Extract Stroke)
Power On - Nothing moves
Estop - All Cylinders down. access door unlocks. E-Stop switches being used have both electrical and Pneumatic connections. When pressed, supplies air to Down (Retract Stroke) of the cylinders. It is plumbed in parallel with the Down Stroke Toggle switches.

chavak,

Thanks for the clarification on the type of valves. Based on your explanation I will be using 5/2 way single solenoid valve.


Thanks everyone for their help and suggestions.

Cheeres.

skyfox said:

I am fully aware of safe operation of control systems. Deal with Chemical systems all the time.

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Oh boy, I've experienced this before. FYI, they're not remotely the same. And the lack of knowledge of pneumatic systems proves that it. Hopefully someone won't get hurt.