Hydraulic proportional valve force control

Plc_User

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Join Date
Dec 2005
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Belgium
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In the attached picture, you can see a hydraulic schematic of our installation with a proportional valve (Atos) with integrated force control (pressure transmitters from up- and downside of the cilinders are connected to the valve electronics.
My question is, will the proportional valve be able to fully control force on the cilinder, considering the check valve (nr12 ont the drawing)in the hydraulic line to the cilinder.
Someone told me the valve will never be able to reduce the pressure on the bottomside of the cilinder.
But won't there be pressure on the other side of the cilinder at that moment to open the check valve?
Please share me your hydraulic experience?

proportional valve.jpg
 
Is there away to take into account the different areas on each side of the piston. You can't do this with knowing pressures alone.

It looks like there is a pilot operated check valve that is piloted of the oil pressure on the rod side. If the rod side pressure isn't high enough the check valve will not open. This doesn't make sense to me.

It also looks like there is a counter balance valve #36. Yuk.

I would have used a normal Atos valve with a 0 overlap spool and one of our controllers. I would not use the pilot operated check valve (POCV) or the counter balance valve (CBV).

Someone told me the valve will never be able to reduce the pressure on the bottomside of the cylinder.
Yes, because of the CBV, but the valve is sensing pressure at the valve. Is there a way to tell the valve the there is a CBV in the circuit? I don't see how the Atos valve can control force not knowing the areas of the piston and that there is a CBV in the circuit.

Who ever is designing this doesn't have any experience at designing for force control.

Gook Luck, you will need it.
 
I think I have your answer.
Say for instance you supply 100psi to the rod ends of the cylinder and say the cylinder is 2 inch bore with 1 inch rod. This becomes 235.619 pounds of force at the piston.

Due to the difference of area because of the rod the 235.619 is dispersed across the whole two inches and becomes 75 pounds of force which would appear at the check valve thereby always imparting a 25 psi pressure drop across the pilot allowing it to open.
 
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Is there away to take into account the different areas on each side of the piston. You can't do this with knowing pressures alone.

It looks like there is a pilot operated check valve that is piloted of the oil pressure on the rod side. If the rod side pressure isn't high enough the check valve will not open. This doesn't make sense to me.

It also looks like there is a counter balance valve #36. Yuk.

I would have used a normal Atos valve with a 0 overlap spool and one of our controllers. I would not use the pilot operated check valve (POCV) or the counter balance valve (CBV).


Yes, because of the CBV, but the valve is sensing pressure at the valve. Is there a way to tell the valve the there is a CBV in the circuit? I don't see how the Atos valve can control force not knowing the areas of the piston and that there is a CBV in the circuit.

Who ever is designing this doesn't have any experience at designing for force control.

Gook Luck, you will need it.

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.
I thought the pilot valve was there not to lose oil to the tank if the hydraulic is not active?
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
 
The drawing is very fuzzy my end, but, the piloted check valve, is IMHO in the wrong place, it should be as close to the cylinders as posible.
This, plus is appears in the down leg of the cylinders?
Whilst this would be conventional if the cylinders were powered to lower, if this is the way you describe it, then the cylinders are vertical, with a load below, thus IMHO the check valve shoud trap the fluid in the cylinders in the event of system failure, therefore be in the lines on the annular side of the cylinder, not the full bore side.
Also in the event of a catastrophic line failure on the annular side of the cylinders, there appears to be nothing to prevent the load from falling?
The internal porting on the piloted check valve will prevent the pilot fluid having any realistic influence on the flow of fluid from the load cylinder.

Is this a new machine?
Is it already working?
 
The drawing is very fuzzy my end, but, the piloted check valve, is IMHO in the wrong place, it should be as close to the cylinders as posible.
This, plus is appears in the down leg of the cylinders?
Whilst this would be conventional if the cylinders were powered to lower, if this is the way you describe it, then the cylinders are vertical, with a load below, thus IMHO the check valve shoud trap the fluid in the cylinders in the event of system failure, therefore be in the lines on the annular side of the cylinder, not the full bore side.
Also in the event of a catastrophic line failure on the annular side of the cylinders, there appears to be nothing to prevent the load from falling?
The internal porting on the piloted check valve will prevent the pilot fluid having any realistic influence on the flow of fluid from the load cylinder.

Is this a new machine?
Is it already working?

The machine is new and we have problems regulating the exact demanded force.
 
Is there a conventional pressure reducing valve between your proportional DCV & the cylinder?
I can't make out the exact symbol as it is, as I say fuzzy my end.
 
OK, if that is a counterbalance check valve, then it's in the right place, in the circuit, but I'm not sure if it is physically in the right place.

Have the cylinders been bled correctly curing commissioning?

Again the internal porting should negate the affect of the pilot pressure and should have little affect on the main flow.
 
Are you the end user, i.e. customer, or the machine builder?
Was the system designed to be force control by the OEM?
Is the CBC valve working correctly?
I can't see from the symbol, and IIRC it should not be, but, is there variability on the spring of the CBC valve indicated on the drawing?
If you are load holding then you may have to have the CBC valve to make the thing safe.

Are you load holding, or is this a kind of press?
 
I am mahcine builder, we hired in a company for the hydraulic part.
The aim was to be able to regulate the downforce of the press continuously with the proportional valve. We give a flow and a force setpoint to the valve. But now they say when the measured force (in our plc we also read in the pressure and do calculation of the force, just for indication, for now we do not regulate in the plc, we only give a force setpoint) is above setpoint, the plc should release pressure, so the proportional valve only seems to work up to the setpoint, once above, we have to release pressure ourselves (because of the checkvalve they say).
The CBC is indeed for safety of the press.
 
OK now I am beginning to understand your predicament.

Let me have a think for a few hours, as I'm also programming an Omron PLC for the first time!

I'll come back to you later for good or bad I hope, but, others may come in with something first.
 

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