Cannonier10

Pneumatic Air

6 posts in this topic

Short backstory:

We have a machine programmed with AB that has several banks of air solenoids.  This is an older machine so the solenoid banks are of the older variety.  On each bank there is a pressure switch that is outputted into a Allen Bradley 1734 Safety RIO module.  We are adding new modules to this machine after about 10 years and the Mec Eng. chose Festo CPX banks, but they did not put pressure switches on them.

Question:

Is it a requirement (OSHA, OMAC, ISO...etc. any of them really) to have a pressure switch for air module?  Or are they used to just make the machine smarter?  The big concern that I have is that the customer will notice that these new CPX's don't have pressure switches to monitor the status of the air like every other bank on the machine, then questions will be asked...yatta yatta...

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It is not a requirement that I am aware of unless maybe you are in a specialized industry.  What do the pneumatic banks control?  It makes me wonder why the pressure switches are wired into a "1734 Safety RIO module".  What happens when a pressure switch is not made?  Does it cause the safety system to shut down all or part of the machine?  Or possibly lock a gate closed?  If the pneumatic system controls vertical cylinders and air pressure is required to hold the cylinders up, it could cause a safety concern if pressure is lost.  Without more info, I can only guess.  Give us an idea of what the pneumatic banks control and why you think the pressure switches are wired into safety modules.

Aside from all of that, I do like air pressure switches on my machines.  I typically only do it on the main air supply to the machine, though.  I do not put them at every valve bank.

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The banks control a variety of things really...There are usually several solenoid valves on each bank, and those solenoids can control Belt tensioners, raising and lowering of anvils or conveyors, blowoffs...etc.  These individual solenoid outputs are controlled in the normal routines of the controller.  In the safety routine though, if the main bank solenoid output is closed, then we are constantly checking the input to the 1734 Safety RIO which is a pressure switch on the bank.  So if we turn air on to the bank, we are checking to make sure that enough air is present for all the individual solenoids...if not we have a safety fault.  Also, I wasn't guessing...the pressure switches ARE wired into the safety modules...

The problem is that recently we made upgrades to the machine, and the upgrades did not contain a pressure switch...do we need them?

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I know you stated they were wired into the safety modules.  That was not the question.  I was just wondering why you think they are wired into safety modules.  If the air pressure is critical to safety, that is why.  If it is just critical to machine operation, then a normal input module would suffice.  Let's not let that trip us up, though.  I am not aware of any regulation that requires you to have a safety switch on each bank.  I could be wrong, though and if someone know differently, please share because I like to learn.  Only you and the machine designers can determine if anything is needed.  If you want to maintain consistency with the rest of the machine, could you just add pressure switches to the input air lines to the new Festo valve banks?  That would allow you to keep the Festo valve banks and still maintain the same standard that was set on the original part of the machine.  I don't think it is necessary for the switch to be integral to the valve bank.

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I think we can add the switches.  Both options would work because I know that we use digital pressure sensors that are just mounted to a backplate, and Festo makes switches that can be installed onto the bank itself.  I guess I am leaning on trying to convince them that we need them.  Because whether the switch is outputted into Safety or not, as it stands we don't have any pressure feedback on the bank.  Maybe it isn't required for safety...but at least knowing that the bank has pressure should be required...

Edited by Cannonier10
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I'm going to ask some questions you probably can't answer right away, but I think you should give serious consideration to.  

1.  If they exist what do the original machine Functional System Description , Risk Analysis and FMEA say about why pressure switches are wired to safety modules?

2. What do the Updated Functional System Description , Risk Analysis and FMEA say about the need to pressure monitor the air to the new devices you are adding?

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