inherently safe design for vertical cylinder

unsaint33

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I have a two way valve (with two solenoids) and a two way pneumatic cylinder that moves up and down.

Is there a way to make a inherently safe system that stops the piston, not moving either up or down when light curtain is broken? Obviously, if electricity is lost, the cylinder piston will come down.
 
That Nexengroup thing look interesting I wish I could have a real look at one
As for stopping or holding position on power failure. That is actually doable with the right hardware
And provided the air line remain intact.
I think it would be an interesting project to work on.
Some years ago is did a similar, in that case we had to lift a set of pinch roles on an e-stop or power failure.
 
+1 on using rod locks. We have used them on a few vertical applications. Two things to consider and specify:
1) must release with air pressure and clamp down on loss of air pressure. This will make it fail-safe so if air pressure is low or there is a loss of power, then the cylinder does not drift over time.
2) based on your application and the risk assessment, you may want to spec the lock to be dynamic, meaning it will hold the cylinder still even if the cylinder has full pressure applied to either port. Don't forget to consider the effect of the load on the cylinder when choosing a lock. Not all rod locks are dynamic, but instead are just designed to hold the cylinder in place when no pressure is applied.
 
Piloted non-return valve mounted directly on one or both piston ports.

This closes the ports if pressure drops or a flexible pipe breaks

Only one if the risk only exists in one direction, for example if the piston lifts a load
 
Originally posted by lfe:

Piloted non-return valve mounted directly on one or both piston ports.
Click to expand...

They will actually let you use those as a component in the SRP/CS? I have a very similar application and everyone I talk to in the US says that is not allowable in my case based on requirements from 13849. There is no good way to monitor that the PO checks are really doing what they are supposed to. so we can easily make things redundant but we can't monitor them. In my case my risk assessment ended up indicating a Category 3 PLd design was necessary. If you can get down to a single channel non-monitored category the PO checks might be OK.

I am in the process of also looking at the Nexen NexSafe stuff, both free-standing rod locks and profiled rail brakes. I have also looked into the Sitema Safety Catcher and Safety Brake products, which are also free-standing unidirectional rod locks. They are pricey but they look pretty cool.

From what I can tell, to do this "right" you may need to crack out the checkbook and be prepared to add a bunch of zeros. Knowing what I know now I would have definitely steered clear of pneumatics.

Keith
 
kamenges said:
They will actually let you use those as a component in the SRP/CS? I have a very similar application and everyone I talk to in the US says that is not allowable in my case based on requirements from 13849. There is no good way to monitor that the PO checks are really doing what they are supposed to. so we can easily make things redundant but we can't monitor them. In my case my risk assessment ended up indicating a Category 3 PLd design was necessary. If you can get down to a single channel non-monitored category the PO checks might be OK.

I am in the process of also looking at the Nexen NexSafe stuff, both free-standing rod locks and profiled rail brakes. I have also looked into the Sitema Safety Catcher and Safety Brake products, which are also free-standing unidirectional rod locks. They are pricey but they look pretty cool.

From what I can tell, to do this "right" you may need to crack out the checkbook and be prepared to add a bunch of zeros. Knowing what I know now I would have definitely steered clear of pneumatics.

Keith
Click to expand...

Don't know if it will get you there but maybe see Ross SV27 series dual pilot operated check sensing valves.
 
Thanks, bill4807. That just MIGHT get me there. It depends on who I talk to. Some tell me that having stored potential pneumatic energy in the safe stopped state is not allowed. Other say it is OK. The Ross product gives me the monitoring and the data I need but still leaves me with the stored energy issue. I will need to dig into this further. But this is a good thing to know about.

Keith
 
kamenges said:
Thanks, bill4807. That just MIGHT get me there. It depends on who I talk to. Some tell me that having stored potential pneumatic energy in the safe stopped state is not allowed. Other say it is OK. The Ross product gives me the monitoring and the data I need but still leaves me with the stored energy issue. I will need to dig into this further. But this is a good thing to know about.

Keith
Click to expand...

Hi keith,

No problem. So i take it you are not using an open center/exhaust center valve then if you are storing energy?
Exhaust center would exhaust from valve to PO check, but if they are concerned with energy from cylinder to opposite PO check then a manual bleeder/override valve could be inserted. For instance festo 184586.
Then maintenance as a procedure could relieve pressure before working on it.
Hope it helps.
 
I never heard mentioned what happens when they push an estop? I know light curtain is considered estop like you stated. But does the pneumatic have an estop on the dump valve? what happens on power loss?
 
Jim3846 said:
I never heard mentioned what happens when they push an estop? I know light curtain is considered estop like you stated. But does the pneumatic have an estop on the dump valve? what happens on power loss?
Click to expand...


IMHO Still not a safety rated system! What happens if the pneumatic lines to the cylinder leaks/breaks??


Safety rated spring applied/air released rod locks are still my preferred choice.


My 2 cents.
 

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