Safety critical valve

[pedrof]

I have a vertical double acting cylinder which is actuated using a 5/3 normally closed valve (festo part number 170248) (full description: 3 position, 5 ported,
4 way, Single Solenoid Air Pilot Actuated,Spring Centered). The user regularly puts their hands underneath this ram.
As I understand it if the power goes off, the valve goes to its closed centre position and everything stays where it is providing there are no leaks down stream. This is viewed as a safety feature.
My question is for safety certification does a failure of the valve itself have to be considered?
I have read that there are ways to mitigate for such a failure but am not sure if we need to worry about this for safety testing.

 

[gerhardl]

Depending in which country and to which safety regualations you are operating.

There is on the market other safety valves that takes (automatically) care of the operational valve failure.

See example.

http://www.herion-systemtechnik.de/uploads/images/pdf/N_en_5_14_100_XSz8_50.pdf

 

[LittleInch]

In my opinion yes. The valve could fail in a number of ways including broken spring(s), stuck solenoid, broken solenoid, loss of air pressure, not just loss of power.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[gerhardl]

Oh yes!

HERION Systemtechnik safety valves for mechanical presses and other safety applications conform to DIN-EN-ISO 13849-1 (performance level e, catagory IV).
BG, OSHA, CSA and other approvals.

Data sheet: N_en_5_14_100_XSz8_50.pdf

Note: several competitors to this make! (google search safety valves for presses EN certified)

 

[pedrof]

OK, just to clarify then can you tell me what would happen to the double acting cylinder in the following scenarios:
1) in a power cut
2) in losing the air supply
3) in a valve malfunction -
I was also looking at the Festo VOFA range, festo number 569819. Would this be suitable?

Thanks for your feedback.