Exit Festo – your world-wide partner in factory and ... safety Afternoon/2_PM... · F-Be/ [email protected] © Festo Didactic, Training and Consulting 26.10.16 Slide 1 Festo – your

26.10.16 Slide 1© Festo Didactic, Training and ConsultingF-Be/ [email protected]

Festo – your world-wide partner in factory and process automation

• Paul Verbist, 1992->..• 2016-10-20

1

Exit


Facts and figures


Top ten of the bestDo & don’t using pneumatics,

in relation with safety.Paul Verbist



10: Soft start valve

• Target: prevent fast movement, when pressurization.

• Fact: most of the slow start valves on the market switches automatically, when pressure reaches 50% of the nominal pressure

• Means: cylinders must be at least over dimensioned with 70% otherwise they shouldn't move until the valve switches to the maximum flow, generating immediately the maximum pressure, and highest speed!

• Others kind of valves exist also on the market: the PLC decides when to turn on the High flow!


10: Soft start valve



9: Soft start valve.

• Target: prevent fast movement, when pressurization.

• Means: When exhaust, once the pressure falls below 50%, the valve switches back to the low flow, making the exhausting very slow.

• Due to the fact that actuators are over-dimensioned, this creates a dangerous situation, due to the long exhausting time, and residual pressure

• C:\Users\be0vbi\Documents\Snagit\2016-09-06_13-45-14.gif



8: General Exhaust

• Venturi

• Vertical movement

• Inertia: moves will continue

• Valves may not react as expected..(detailledlater)



7: Non return valve

• Non return valves – pilot check valves: danger is still there!

• Monday morning effect: every pneumatic component has leaks!



6: Speed reduction

In normal operation, it’s a good idea,

But:

if something blocks the movement, speed is no more under controle..



5: Work with a lower pressure

• Double working cylinder: force is based on a pressure difference!

• Speed control is not more possible. Speed increases!



4: 2 valves serial mounted = 2 channel to exhaust

• Take care of the “third state”: some valves may stay “closed” between “exhaust” and “open” position:

• In the fact, if the second valve has this problem, nothing should be vented

• This is only a way to prevent “unexcepted start”



3: Cylinder must stop!

• Yes, but..

• The problem is here to put afterward the machine in a running state!• Clamps reacts at a pressure around 2,5 Bars : Slow start valve shouldn’t help• Chambers are exhausted: speed cannot be controlled when restart• Choice the good clamps! Some are intended to stop during movement, some not (parking brake

>< brake pedal).• Check the lifetime! MTTFd is sometime difficult to reach..



2: Wrong choice of the valve

• Poppet or spool valve ?• Norm EN 13849-2 says “use spool valve, because you know where you will have pressure..”• Poppet valve have the advantage that it will always leaks and never allow pressure build-up.

• Pilot air and piloted valves• Be careful with slow start valves and mechanical springs.

• Pneumatic springs:• when exhausting the machine, it can be that this kind of valves shouldn’t return to his rest

position, and stays closed, trapping air in the machine.



1: 5/3 closed in central position

• Goal: stops the cylinder during movement.

• Pseudo: the killer !

• The solution:

• difficult to explain to programmer ;o)

+32 497 585779


Paul Verbist: [email protected] 02 702 32 44

Training and consulting: [email protected]