OT: Hydraulics

Can someone help me understand what a regen block / Plate is and what it is used for in a hydraulic system.

This is on a proportional valve for a cylinder.

This is my favorite place when looking for hydraulics info:
http://www.hydraulicspneumatics.com/200/eBooks/Article/True/85297/

The Plc Kid said:

Can someone help me understand what a regen block / Plate is and what it is used for in a hydraulic system.

This is on a proportional valve for a cylinder.

Click to expand...

Regeneration should not be used on high performance servo systems. If the system is moving slowly and the application isn't critical it won't make much difference.

Regeneration systems have a lower natural frequency and can't be accelerated as quickly and still maintain good control.

Take for example a 2" diameter cylinder with a 1" diameter rod. The piston blind side area is 3.14 in² and the rod side area is 2.36 in². So for our example piston the volume ratio of the fluid in the rod side is 3/4 the volume in the blind side.

For a second, pretend there is no load connected to the piston rod. The larger area of the piston blind side will result in a larger force when both sides are at the same pressure. The piston will move in the direction of the larger applied force. The hydraulic fluid from the rod side must flow out, and the regen block redirects that fluid back into the blind side of the cylinder. This means the the pump doesn't have to deliver all of the fluid necessary to move the piston. For every cubic inch of fluid the pump delivers, the cylinder blind side receives 1.75 cubic inches.

OK, now so much for oversimplification, because a piston that doesn't have a load attached isn't much good for anything.

A regenerative circuit does not guarantee that you will be able to move your load, or that you will be able to operate at 1.75x the speed. Force applied is (pressure*blind side area)-(pressure*rod side area). A regenerative circuit operates at a greatly reduced force. Our 2" piston with a 1" rod can deliver no more than 1/4 the force of a non-regenerative circuit (usually slightly less when we account for pressure loss, friction, etc). The reduced force reduces your ability to accelerate the load (accel=Force/mass). If the load is very light (eg, easily accelerated) and the stroke is very long then then a regenerative circuit may pay off. If the load is high and the stroke is short then its doubtful that a regenerative circuit can actually move faster. You'll have to do the math for your particular system to determine if there is a pay off. And unless the payoff is large, eg, a light load with a long stroke and less than precision control is OK, its probably just not worth the hassle on a servo system. Personally, I'm not a fan of regenerative circuits but they do have their place. Last week I was training Bubba on a hydraulic vibratory feeder (very very low force application and not servo/proportional) that used a regenerative circuit to achieve very fast motion with a small pump. I had to explain it several different ways, but I think he finally got it.

Our distinguished colleague Peter has argued till he is blue in the face on other forums trying to get people to understand the relationship between force and actual stroke time. Some people get it. Some don't. Some are hung up on a simplistic approach of using only fluid flow and never will get it. But just take him at his word - he knows it way better than my simplified response above. At any rate, I hope my explanation helped.

Alaric said:

Our distinguished colleague Peter has argued till he is blue in the face on other forums trying to get people to understand that force makes it go.

Click to expand...

You had to say that didn't you ...

I'm hoping The Plc Kid comes back soon because I originally thought he was looking at an existing system trying to figure out what it did. I'm guessing there is more to the circuit than we know about.

Plc_Kid. Please let us know whether this is something new or old. Can you post a schematic and let us know a little more about what you are trying to accomplish?

Norm, While you were posting I edited to "relationship between force and actual stroke time." We don't need to open that can of worms again. We must have cross posted.

After reading your post I re-read the kid's post and you might be right, it does look more like he might be trying to understand an existing system. I expect he'll be back around, the Kid is a regular.

To try to answer the original question in simple terms:
A "regen" block, valve, or plate converts oil directly from the return side of a cylinder to the pressure side directly. Instead of the need for all of the oil to return to the tank then get picked up by the intake of the pump. This works well for very large, slow moving, low pressure systems. It is especially helpful on hydraulic presses and similar devices to get the ram up & down or in & out quickly, before it is pressurized. It will be taken out of the system during pressurization.
HTH

The worms go in, the worms go out

Alaric said:

Norm, While you were posting I edited to "relationship between force and actual stroke time." We don't need to open that can of worms again. We must have cross posted.

Click to expand...

Just to be perfectly correct, in a given hydraulic system you can't talk about flow separately from pressure any more than in a given electrical system you can't talk about voltage separately from current.

In a simple DC electrical system with a constant voltage source the resistance determines how much current flows. In a simple DC electrical system with a constant current source (say a 4-20 mA transmitter) the resistance determines how much voltage is required to drive the current. If there isn't enough voltage available the current won't flow.

You can't fight Ohm's Law.

In a given hydraulic system the load determines how much force is required to move or accelerate a load. The flow rate in a cylinder or motor determines how fast the load moves. You can't fight Newton's Laws or the Law of Conservation of Matter.

Examples:

F=ma force equals mass times acceleration
F=pA force equals pressure times area
V=Q/A velocity equals flow rate divided by area

Hydraulic systems have constant flow sources (like positive displacement gear pumps) and constant pressure sources (like pressure compensated pumps or accumulators). The system analysis must take all factors into consideration and apply the appropriate calculations for all devices.

Flow and force both make it go - how much and how fast can vary with the system.

Tom Jenkins said:

V=Q/A velocity equals flow rate divided by area

Click to expand...

True, that determines max velocity. What trips some people up however is assuming that flow into the cylinder is always the same as max pump output. No mass can be accelerated to full speed instantly, so during the acceleration time to the maximum speed a pump can sustain, the flow into the cylinder must necessarily be less than pump output (+proportional regen flow since we are talking about regenerative circuits). Excess pump output goes over the relief valve if a fixed displacement pump or the pump de-strokes if its a pressure compensated variable displacement pump.

A cylinder already moving at 5 inches per second at max pump flow will cover 5 inches in one second. That part is obvious. A cylinder accelerating under load evenly at 2.5 inches per second squared over the same distance to a final velocity of 5 inches per second will take two seconds to cover the first five inches. A regen cylinder with a 4:1 piston/rod ratio operating an identical load on only 1/4 the same force is going to take 4 seconds to cover the first 5 inches. But at 5 inches its only up to 2/3 the speed the first cylinder was at and only about 40% of its max speed with regeneration. Meanwhile, the cylinder that accelerated at full force to 5ips is now at 15 inches. Once the regen cylinder has accelerated to its max speed of 8.75 inches per second (in 14 seconds), will it catch up with the cylinder moving at 5 inches per second before it reaches the end of its stroke? Only if the stroke is long enough. Like Tom said, you can't fight Newton, you have to factor in your actual load, cylinder size and stroke, pump displacement, etc. to determine if regen will actually buy you anything.

(note, I started with an arbitrary number so it turns out to be a very long cylinder, but I hope it illustrates the concept.)

What an interesting find on a Monday night, I've been absent for a while. Thanks to all that have posted.

Arghh!!! This winds up my integrator into saturation!!!!

Tom and Alaric are both wrong.
An actuator will accelerate until the sum of forces acting on it are 0. At that point there will be no more acceleration and maximum velocity is achieved.
If I add a load the actuator will slow down and the flow will slow to.

A net force causes acceleration
Acceleration is integrated to get velocity.
Flow is caused by a difference in pressure.

The system in question used to have regen blocks and was changed to a system without them. Now we need them back to get some additional speed from this system.

The cylinder is a 4" or 5" bore and has a stroke of 144"

I don't understand the problem

The Plc Kid said:

The system in question used to have regen blocks and was changed to a system without them. Now we need them back to get some additional speed from this system.

The cylinder is a 4" or 5" bore and has a stroke of 144"

Click to expand...

Put back the regen manifold and your system should be like before but I would like to know why it was removed before doing so.

The original system had a custom cut valve block which cracked a couple years after the machine was put into operation and they went back with a stock off the shelf valve block because of the time to get a new custom block.

Has not been a problem for years and now they want to speed this system up and are having a new block cut.

I am working off hearsay as this was all long before my time.

The controls have been modified also. From what i understand the original valves were controlled by a plc 5 QB hydraulic module and the parker valves had onboard electronics.

Now the valves have a seperate electroncs controller in a cabinet about 50 feet away from the valve.

Strange thing is the QB module is providing the input to the parker electronics module which is 0-10 volt input. From my understanding the qb module is a pulse out 0-10 volt module.

IMHO it should not be connected this way but it works. Kinda hard to argue with that.

Just trying to figure this out as now i am stuck with it and no info other than what i have scrapped together and hearsay.