Hydraulic proportional valve force control

[shooter]

the check valve 12 should be in supply line not in a cylinder line, rest looks oke however this 36 valve will give problems when controlling force.

 

[Sidewinder]

Shooter,
Possibly not, but your comment has made me look @ the check valve in the full bore side again.
This valve looks like it is configured to only allow fluid out of the cylinder when there is a command on the annular side, I cannot see much point in this, and, this could be also causing issues.

A check valve in this configuration, piloted or not, will never prevent the cylinder from falling under external load, as the cylinder will "suck" fluid past the valve.
My first port of call in re-designing the circuit would be to remove this valve, as I can see no point in it.
I would not relocate it.
This valve only has the function of preventing the cylinders from lifting, as far as I can see, why is this required?
Why stop the cylinders from lifting without pressure, this is physically impossible, so, all this valve does as far as I can see is cause possible issues.

 

[Peter Nachtwey]

The pistons are mounted (upside down) in real the same way as in the drawing, a heavy load is attached to the rod, so I suppose the CBC is for avoid the rod and load to descend when the hydraulic is not active.

Yes, but this is the worst way to do it if using servo control. I repeat, the hydraulic designers do not know how to design for servo control.

I thought the pilot valve was there not to lose oil to the tank if the hydraulic is not active?

I would use energized open blocking valves. POCV are acceptable just not optimal. It also makes a big difference where the POCV is piloted from.

Can the pilot valve be ommited or place somewhere else with the same functionnality?
Max pump pressure is 240 bar.
I know that atos can parametrize the surfaces of the cilinder into the electronic valve

OK, but have you done it and how does the the Atos valve know about the CBV?

 

[Sidewinder]

Peter,
I doubt very, very much that you will legitimately be able to CE mark a press without a CBC valve located where this one is in this press.
The circuit could be improved I don't doubt, but the CBC has to stay put, hopefully it is physically where required.
Valves that require a control input to achieve the same function would not be acceptable for the relevant safety standards.

 

[Peter Nachtwey]

There Can Be Only One!

Peter,
I doubt very, very much that you will legitimately be able to CE mark a press without a CBC valve located where this one is in this press.

Why? A POCV is better in this case and a energized open blocking valve better yet.

The circuit could be improved I don't doubt, but the CBC has to stay put, hopefully it is physically where required.

Hopefully? You don't know?
The CBV is where the valve usually goes in a traditional hydraulic press with bang bang valves

Valves that require a control input to achieve the same function would not be acceptable for the relevant safety standards.

Are you sure?

Do you know what blocking valves do and how they operate?
CBVs and servo control do not mix.
http://hydraulicspneumatics.com/other-technologies/truth-about-problem-valves

 

[Sidewinder]

Peter,
I don't know how to use the forum software to comment on your comments on my post.
However, I will try to explain my comments as best I can below, and if I am lucky these can be related to your comments above.
I don't believe that a valve that requires electrical energising will meet the requirements to CE mark the press as safe, it MUST default to the closed circuit position under the failure of control signals
I have already said that it is in the correct place in the circuit, however, the circuit does not indicate the physical layout of the machine, this valve could be 200m from the cylinder, and have several flexible hoses, welded, compression or threaded joints between it and the cylinders, and unless you have a crystal ball, from the SCHEMATIC diagram, I am at a loss to see how you can say that the valve is in physically the correct location, it may be in the right place in the circuit, but, that is all that can be told from the schematic diagram, that I DO know.
I am sure that a valve that requires a control input to prevent fluid from leaving a cylinder which is required to suspend a load would not be acceptable under the requirements for the safety requirements of a power press under CE marking requirements.
Of that I am ALSO sure.

 

[Plc_User]

I only do the plc-programming. The hydraulic concept is by the other company.
The CBV-valves are attached to the cilinders, which should be ok.
As far as I know they did not include the CBV-valve in the valve software (do you it is possible with some types, brands of proportional force valves?).
I consider the CBV-valves cannot be ommitted for safety reasons.
If the CBV-valve should stay in, is it possible to regulate the force appropriately by the valve? Is ommiting the check valve necessary for that, or should ik be placed in the power line of the valve rather then after the valve?

 

[Peter Nachtwey]

Peter,
I don't believe that a valve that requires electrical energising will meet the requirements to CE mark the press as safe, it MUST default to the closed circuit position under the failure of control signals

Why not? Usually the blocking valve is powered by a series of relays so that if any relay loses power the blocking valve loses power and shuts. This means that you can put the press in a safe condition if any number of things fail. A CBV closes only one the pressure goes away and that wouldn't be as fast as an electrical circuit.

I am sure that a valve that requires a control input to prevent fluid from leaving a cylinder which is required to suspend a load would not be acceptable under the requirements for the safety requirements of a power press under CE marking requirements.
Of that I am ALSO sure.

Even and energized open blocking valve?
I don't see how you guys function over there if what you say is true.
Do you understand why a CBV is bad?

plc_user, I broke my wrist and it hurts typing. Heed my advice or struggle with what you have got. I could have had it tune up and working by now.

 

[Sidewinder]

OK Peter,
Once again I can't comment on your posts in the manner I would like.
It seems you are suggesting a valve that requires power to close the fluid line, this is NOT acceptable.
Any valve that is used in this situation MUST default to closed circuit in the event of a power failure.
That is the requirements.
It also MUST require fluid pressure, thus flow, on the opposing side of the cylinder to open the fluid path, simple electrical control is not acceptable.

I can see why the CBC valve is an issue, but it is not insurmountable I don't think.
This particular design of valve may be unacceptable, but there are others that will function correctly I am sure.

I could have it working by now, but I would not be prepared to personally sign the statute law legal documents that said it was safe to be put onto the market, used, and met the legal requirements for this design of machine that must be done for it to be used anywhere in the EU.

 

[Peter Nachtwey]

OK Peter,
Once again I can't comment on your posts in the manner I would like.
It seems you are suggesting a valve that requires power to close the fluid line, this is NOT acceptable.

Read again, I said energized open. If power is lost they close by springs. The CBVs have springs in them too and close when there isn't enought pressure to keep the valve open.
I don't see the problem with blocking valves.

I can see why the CBC valve is an issue, but it is not insurmountable I don't think.
This particular design of valve may be unacceptable, but there are others that will function correctly I am sure.

The controller doesn't know what the CBV is doing and the CBV interferes with the flow. The CBV will work only if it is piloted by a constant pressure source so it stays open but they the CBV is being used as a POCV. As it is now you can see the CBV is piloted by the pressure on the cap side of the cylinder. What plc-user has now will never work right.

Have you ever controlled a vertical load with servo hydraulics and a CBV before?

 

[Sidewinder]

Peter,
I did not get from your posts that the valve was default closed with no electrical input.
However, I don't care what you say or have done, in the US, nor what I have or have not done.
You must use a hydraulically controlled counter balance valve, of "some" sort, to comply with current CE requirements in the EU as far as I know, having worked for a hydraulics control systems manufacturer, of global standing, this is what our internal specs required, as interpreted by our legal and product specialists to meet the requirements for equipment for use, sale, or being put onto the market in the EU.
I don't believe this has changed since I left them.
Whilst I agree the circuit is not correct, I do not agree that a purely electrically controlled valve in the place of the CBC valve is acceptable.
From where I am, I don't have enough information on the machine, or the system to make concrete recommendations for what is acceptable.
For example, if the press is an Annexe 4 machine under the Machinery Directive, the requirements will be different to those if it is not.
Unless you have information that is not in this thread, or a crystal ball, neither of us can say that at this time.

 

[Peter Nachtwey]

Peter,
I did not get from your posts that the valve was default closed with no electrical input.
However, I don't care what you say or have done, in the US, nor what I have or have not done.
You must use a hydraulically controlled counter balance valve, of "some" sort, to comply with current CE requirements in the EU as far as I know, having worked for a hydraulics control systems manufacturer, of global standing, this is what our internal specs required, as interpreted by our legal and product specialists to meet the requirements for equipment for use, sale, or being put onto the market in the EU.

I can't believe who ever is making the rules over there can be that stupid but maybe they are. Is so bad 4U good 4 us.

I don't believe this has changed since I left them.
Whilst I agree the circuit is not correct, I do not agree that a purely electrically controlled valve in the place of the CBC valve is acceptable.

Why not? Emergency stop and all sort of safety mechanism rely on fail safe electronics. Jets fly by wire?

From where I am, I don't have enough information on the machine, or the system to make concrete recommendations for what is acceptable.

It is clear the CBV is powered by the cap side of the cylinder and this is very bad.

For example, if the press is an Annexe 4 machine under the Machinery Directive, the requirements will be different to those if it is not.
Unless you have information that is not in this thread, or a crystal ball, neither of us can say that at this time.

It is simple. You can't have two devices controlling flow when one works without knowledge of what the other is doing. In plc_user's case it is bad because the Atos valve doesn't know about the CBV so it can't take that into account when computing force. On top of that the CBV better be fast or it too will delay any response.

CBVs were designed for the bang-bang era.