Meter Out Flow Controller Setup on Vertically Mounted Cylinders

[Finglas]

My hands on knowledge of pneumatics is limited so I would like to validate my understanding of a meter out circuit.

A project I am working on has vertically mounted cylinders which lift product nests upwards. Nests weigh approximately 35kg and 4 cylinders lift the nest upwards. The stroke of the cylinders are 50mm. In the event of an estop, if we use flow controllers on the retract side of the cylinders will this cause them to retract slowly, i.e. a meter out circuit.

 

[BrianPetersen]

That depends on what type of directional valves are controlling the cylinders in question (What spool condition do they go to when de-energised), whether there are pilot-operated check valves in the circuit and how they are connected, and whether there is a safety valve ahead of the non-safety-rated pneumatic part of the circuit and how that's connected.

You can arrange them to stay put, you can arrange them to drop down slowly, or you could end up with random somewhat-unpredictable motion depending on which side of the cylinder happens to have more air in it at the time you have the protective-stop condition, depending on all that ...

The risk of having a suspended load and the risk of having trapped air pressure has to be weighed against the risk of having residual motion subsequent to a protective-stop condition. That's what your risk assessment is for.

 

[Finglas]

It is an 5/3 DCV with exhaust center, SMC SY5300-5U1

When de-energised they exhaust through the centre position.

 

[BrianPetersen]

Which means, a gravity-overhauling load will allow the load to settle down when solenoid power is removed, e.g. under a protective-stop condition. A protective-stop with the cylinder mid-stroke will lead to residual motion while air pressure exhausts (unevenly) from each end of the cylinder. Upon completion of all this, there will not be stored air pressure nor will it be holding the load suspended. Restarting with empty cylinders will be abrupt.

There is no perfect means of motion control with pneumatic cylinders. No matter what spool configuration you choose, there will always be something bad about it. Pick your poison - do the risk assessment.