Requirements -- Dropping Air in machine

Timeismoney08

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Join Date
Jul 2012
Location
United States
Posts
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Good Morning,

So as I understand, all control power needs to be dropped, along with the Air and hydraulics inside a machine when someone enters it. Maybe someone can enlighten me on where this standard exists..

Pneumatically:
What do you do if the cylinders can't drop air without adversely affecting the machine? I imagine you need spring return cylinders, but what if it needs to hold two different positions?

Electrically:
What if I had an area where the operator could load at a given moment, but when something else, like a robot, enters another area and we need to drop control power?


If you have any diagrams of how it is done electrically or pneumatically, it would really be appreciated! I'm just trying to get a better understanding on how to do these things. Also, if you have any part numbers or examples for air dump valves, I would love to see.



Thank you in advance!
 
First you need to do a risk assessment to determine what level of protection is needed.
OSHA does not require you to crash your machine on an emergency stop so you need to determine how to remove potential energy safely. On the other hand they don't require a ZES (zero energy state) when you are in machine, instead they require you to determine
What safety precautions are needed IES (intermediate energy state) while in the machine.
Documentation and training are key parts. Have a procedure in place and at machine center JSA (job safety analysis)
We utilize ZES when performing maintenance and Guards are being removed, and IES
When setting up machine or inspection.
Consult your Safety Manager on all your written Documentation and Training, The bigger the paper trail the better.
 
First you need to do a risk assessment to determine what level of protection is needed.
OSHA does not require you to crash your machine on an emergency stop so you need to determine how to remove potential energy safely. On the other hand they don't require a ZES (zero energy state) when you are in machine, instead they require you to determine
What safety precautions are needed IES (intermediate energy state) while in the machine.
Documentation and training are key parts. Have a procedure in place and at machine center JSA (job safety analysis)
We utilize ZES when performing maintenance and Guards are being removed, and IES
When setting up machine or inspection.
Consult your Safety Manager on all your written Documentation and Training, The bigger the paper trail the better.


Thank you so much for this information.

I've looked over some risk assessments, but never done one to be honest. Is there a document to follow on how to do this? and do most companies make their own or do they follow a standard risk assessment?

What is ZES and IES?


Thank you
 
Also, I thought you always had to dump the air. Is there a certain amount of force an object has to produce to make it unsafe for human interaction? Do you know the value or where to find it?

We have an application where people think it is unsafe, but the air cylinder is so small, it shouldn't harm anyone if it came down on them.


Thank you!!!
 
You don't have to "dump air" on a non ZES lock out. I have print machines that open up to change print plates, make adjustments and so on. I need to keep ink rolls turning and ink pumping. also they need power to turn print roll to mount die, Our IES procedure is to remove a key switch labeled IES, the key can only be removed in the safe position, this prevents the machine from running, prevents the machine from open or close and other functions that we have assessed that we need disabled while a person is in machine.
If you are concerned about a particular item associated with your machine you can assess how to address such as inserting pins to prevent from dropping. have the pins actuate a switch interlocked to machine so they cant be left in on a start up.
There are several documents related to creating a Job Safety Analysis, but get your operators and maintenance involve since they are the ones using it, consult the OEM
on their recommendations and upgrades. Chances are if it is an older piece of equipment there probably have been safety upgrades, and if there has been a recordable accident on one of their pieces of equipment they will know
Liability wise don't bypass or modify an OEM safety device, You can add more
 
This is quite an informative read:

https://machinerysafety101.com/2009...ing_wp_cron=1534088721.0668070316314697265625

It's written specifically for EU and Canada, for some reason, so not everything will apply for the US, but the though process is the same, but basically echos what is said above, it all starts with a risk assessment.

There is no legal requirement, but in the UK, Pilz actually run a week long course as a starter into machine safety.

It's really not the thing to read a website and go about re-designing your factory.
 
I agree with janner_10 A lot of prep work and consultation should be applied before any safety changes are made to a machine. I always leave it to Management to do the paperwork (we have onsite Safety Manager who consults Contacted Safety Company)
Make sure you have Proper Documentation relieving you of the Liability for implementing Their Change.
 
+++1 on the risk assement.
You should be using 3 position valves, center position blocked
or floating depending on assement.
Most, if not all material handling robots have a latching clamp that will
hold it’s position when air is dropped, if the clamped position is not achieved, then dumping
air would cause a serious problem.
 
There are also pneumatic cylinders with "rod lock" brakes that engage when air is removed. Sizing them properly is critical, but they can hold at any position.
 
There are also pneumatic cylinders with "rod lock" brakes that engage when air is removed. Sizing them properly is critical, but they can hold at any position.

I've heard of these, but only on larger cylinders. I wonder if they make them for smaller cylinders. I imagine it costs more than blocking off both air ports to make the cylinder hold in position, but you lose the worry of what happens when the air line blows off or is taken off.


Thanks for all the great suggestions!
 
I've heard of these, but only on larger cylinders. I wonder if they make them for smaller cylinders. I imagine it costs more than blocking off both air ports to make the cylinder hold in position, but you lose the worry of what happens when the air line blows off or is taken off.


Thanks for all the great suggestions!

Blocking off both ports to make a cylinder hold in position doesn't even really work on paper. It might work in the extended position, but there is always leakage and you don't want to rely on a block center valve if you can avoid it.

I think the smallest diameter cylinder I have used with a brake was around 3" diameter, but the length of the cylinder is always longer than the same stroke without a brake, so if it isn't designed into the machine, it can be hard or impossible to retrofit. Some cases there is not that much work to modify it. It also requires another air circuit to release the brake.
 
Blocking off both ports to make a cylinder hold in position doesn't even really work on paper. It might work in the extended position, but there is always leakage and you don't want to rely on a block center valve if you can avoid it.

I think the smallest diameter cylinder I have used with a brake was around 3" diameter, but the length of the cylinder is always longer than the same stroke without a brake, so if it isn't designed into the machine, it can be hard or impossible to retrofit. Some cases there is not that much work to modify it. It also requires another air circuit to release the brake.

So correct me if I'm wrong, but isn't that how the 3 position valves work?

Thanks!
 
You definitly need a risk assessment.
But For these reasons we use open center valves, Rod locks for anything over a certain weight, and check valves/manual overrides for lightly loaded vertical application. That can be manually released for maintenance when they need too. Also at the main air in supply a ross or festo manual or solenoid operated soft start. Almost every movement has at least a meter-in flow control above 40 mm stroke.
Be aware if you try to use the solenoid operated lockout ithe pilot will not shift if you are filling a holding tank. It needs a little back pressure. So it takes to long to shift when you really want it to.
 
So correct me if I'm wrong, but isn't that how the 3 position valves work?

Thanks!

It depends on what is in the center envelope of the valve. With hydraulics, a block center valve can work reasonably well due to the incompressibility of the fluid and the better sealing it allows.

With pneumatics, a block center position will usually allow the cylinder to drift toward the rod end since the gas can pass across the piston seal and even past the valve ports. If the valve is to be fully extended, you are better off leaving powered in that position with a two position double solenoid valve.

With pneumatics when I need a cylinder to "float" (be movable by the operator) or hold a position, I typically use 3 position open center valves. When I need it to hold still for an undetermined period of time, I trust a rod lock brake or locking pin more than a particular valve arrangement.

By open center, I mean both cylinder ports open to exhaust and the supply port blocked. I've seen it called open center, exhaust center, and dump center.
 
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