Pneumatic safety valve question

[supersonics29]

I am developing a machine which consists of a horizontally mounted cylindrical drum, where the door is front mounted, top opening pneumatically actuated (Picture enclosed).


The door is lifted up by the pneumatic cylinder.



Now there is an obvious possibility of the door crashing down if the air supply to the cylinder is somehow disrupted. I have tried using a 5/3 Direction Control Valve & Pilot operated NRVs on the cylinder, but these do not help.


I want to stop the exhaust of air from the cylinder if, for eg, one of the air pipes from either port on the cylinder, comes off. So the cylinder should stop where it is.


Provision of mechanical stoppers is always a possibility. But I would like to leave it as a last resort.


Any help would be great.

[jboggs]

You want a pilot-operated check valve ("PO check"). Installed directly in the cylinder port, it will prevent flow out of that port unless pressure is also supplied at the other port. It only allows air to flow out of a port if there is a positive pneumatic signal (pressure) supplied to the other port. Any industrial pneumatic distributor can help you with plumbing, etc. You can get them from Clippard, Bimba, Mead, Pneumadyne, Parker, Festo, SMC, and many others. They're available for both pneumatic and hydraulic applications. Make sure you're getting the right type.

[supersonics29]

You want a pilot-operated check valve ("PO check"). Installed directly in the cylinder port, it will prevent flow out of that port unless pressure is also supplied at the other port. It only allows air to flow out of a port if there is a positive pneumatic signal (pressure) supplied to the other port. Any industrial pneumatic distributor can help you with plumbing, etc. You can get them from Clippard, Bimba, Mead, Pneumadyne, Parker, Festo, SMC, and many others. They're available for both pneumatic and hydraulic applications. Make sure you're getting the right type.

Thanks for the response.

I did try using two PO check valves, one at each port. But as soon as I remove the air supply from the pilot valve in the PO check valve mounted on the 'rear' end of the vertically upside down mounted cylinder, the cylinder drops as the air is exhausted from the check valve mounted on the other end.

I am using a 5/3 All Ports Blocked Direction Control Valve. Maybe if I use an All Port Exhaust type of valve, it might help? Also, could you possibly show me how the two PO Check Valves are to be connected in the circuit?

Many thanks in advance.

KV

[jboggs]

What you describe above is exactly how they not supposed to work. You have something wrong, most likely the plumbing. Are you absolutely sure everything is connected to the right port of the check valves? Did those PO checks come with an instruction page?

Back in the day before the internet, engineers relied a great deal on industrial distributors rather than Google and forums. Personal relationships were formed. This is exactly the kind of question your distributor could resolve for you. Who did you buy these valves from? A distributor with application assistants or some on-line warehouse with "order takers" that wouldn't know a PO check from the man in the moon? If the checks are plumbed correctly it shouldn't make any difference what type directional valve you use.

Do you have flow control valves? Are they mounted in the cylinder ports? The most common mistake I have seen over the years, by far, is a misunderstanding of how flow controls work. They are not intended to limit the flow of air INTO a cylinder. They allow free flow in and only restrict the flow OUT of a cylinder. Why am I mentioning this? Because I don't know your level of experience with pneumatics, this is the most common mistake, and if you have made this mistake you could very well also have the PO checks plumbed wrong.

The diagram below is for hydraulics but the concept is the same. The cylinder isn't shown. The flow controls at the top connect directly to the cylinder ports.

[supersonics29]

JBoggs, Sorry for bumping this after such a long time.

It was the Solenoid Valve. A exhaust centre 5/3 valve did the trick!

Thanks.

[jboggs]

That makes sense. Check valves of any type have to have lower pressure on the downstream side to work. If flow in that direction is blocked (or nearly blocked) they won't do much good.