INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Jobs

A10VSO Variable displacement pump power control

A10VSO Variable displacement pump power control

(OP)
I am maintaining a hydraulic press which is having a piston of 600 mm. It works up to 280 bars and creates a maximum force of 800 Tons. It is having a Rexroth A10VSO 71 DRS/32 pump which delivers 100 lpm of oil at 1440 rpm. It is coupled with a 35 HP electric motor. Please find attached images of the pump and also the schematic of the hydraulic circuit.

Pump


Pump's name plate


Hydraulic Schematic


Pump's Control Circuit Zoomed


**********************************************************************************
(These are the links to the images in case they don't open up in the post directly)

[img https://drive.google.com/file/d/0B17y4jYQ3IhVN1BxR...]
[img https://drive.google.com/file/d/0B17y4jYQ3IhVQ1Y5d...]
[img https://drive.google.com/file/d/0B17y4jYQ3IhVVzZxO...]
[img https://drive.google.com/file/d/0B17y4jYQ3IhVVkVlN...]
**********************************************************************************

Now my problem:

By looking at the schematic, it suggests the pump to be a power control pump (i.e DFLR in terms of Rexroth’s terminology). But physically (see the image attached) it is NOT a power control pump. Practically, power control is taking place in the circuit - otherwise a pump delivering 100 lpm of oil cannot go up to a pressure of 280 bars with a 35 HP Motor. My question is how power control is taking place in the circuit?

The manufacturer has installed a proportional relief valve (Rexroth DBETE) in the pilot line of the controller. In the machine’s manual it says that by varying the pressure setting of this valve, the flow of the pump can be changed. Again, my question is how is it happening?

As far as I know (and as Rexroth’s product manual says) the flow of A10VSO 71 DRS/32 can be dynamically changed by creating a pressure drop across a variable orifice in the delivery line of the pump. But I don’t see any variable orifice in the circuit. If the flow is dynamically controlled, then power control can be achieved. But, in this circuit, how is flow being dynamically reduced with the rise is pressure so as to achieve power control.

Please help me out. Thank you.

RE: A10VSO Variable displacement pump power control

It's a load sensing pump and it senses the pressure difference across the, what looks to be, the 6.1mm orifice. The one just to the right of the pressure cut off and LS compensators on the drawing.

The proportional pressure relief valve (Item 2) opens at the set pressure. When opening, the flow across the orifice increases, the pressure drop goes up, the LS compensator responds to the difference. At this point, the pump will back off or increase its displacement to maintain the pressure drop over the orifice.

In this respect, the pumps is dynamically controlling flow, against changing pressure, to give constant power control.

Cheers

Adrian

Adrian Wright CEng MIMechE
Engineering Specialist
Hydraulic Systems
Caterpillar (UK) Ltd

RE: A10VSO Variable displacement pump power control

Hello,
You are right, the proportional valve 2 thus limits the maximum pressure force up to 800 tons.

For me two solutions:
a) The name plate does not correspond to the pump scheme. The pressure relief valve designed on the pump rate decrease piston is it not a representation of a power control?
b) There is no integrated power regulation at the pump: It is not uncommon on a press or shears we spend 2 times the rated power of the electric motor for a short time. 100l / min at 280bar this gives 52kW to the shaft of the electric motor.

Greetings

RE: A10VSO Variable displacement pump power control

The pump part number and controller matches what is shown on the drawing. The press manufacturer has simply adapted the control to make it more efficient and to allow a smaller motor.

Is there a problem with the current operation or are you just trying to understand what's happening?

Cheers

Adrian

RE: A10VSO Variable displacement pump power control

(OP)
Thanks for the replies friends. But the concept is still  not clear to me. The pumps name plate says DRS.  That means it is a flow control model with X to T line plugged. Now as Adrian says, the manufacturer has adapted the control to work like a power control. This is what I am not quite clear.

Power will be automatically controlled if we can control the flow dynamically. In a DRS control, the pumps entire flow passes through a variable orifice which creates a pressure drop.  When this happens, the flow controller shifts and gives oil to the back of the yoke piston.  This in turn reduces the flow of the pump . As a result the pressure drop is also reduced. This keeps on happening (the flow gets reduced) until the pressure drop is equal to the spring setting of the DRS control.

The spring of the controller now again tries to increase the flow but the resultant pressure drop again reduces the flow.  The spool modulates to maintain the flow at a required level, say 65 lpm. This is how flow control takes place in a DRS control. Correct me if I am wrong here Adrian.

As  I had stated in my original post that the machine manual says that by varying the pressure setting of the proportional valve (item 2), the flow can be changed.  The actuator will move with different speeds. Now can you explain me (just as I did in the DRS control) how this is happening with a proportional relief valve.  How does the pump maintains is flow level.

I think if we can understand this,  then power control will be automatically understood.

Waiting for your valuable suggestions please.

RE: A10VSO Variable displacement pump power control

Look at the orifice...

You can see that the pump load sense compensator is looking at pressures on either side of the orifice.

When you first start the pump, the pressure at the outlet is what the load sense compensator is set to. The strategy of the pump controller is to always maintain that pressure. It is usually around 1500 - 2000 kPa.

The delta pressure at the compensator will be the same as the pressure drop across the orifice.

By opening the proportional valve, the flow rate at a particular pressure can be set.

Remember that the pump is always trying to maintain the pressure drop across the orifice. In this case, rather than having a variable orifice, the flow is being varied instead. The result is the same, the pressure changes.

So, in order maintain the pressure drop, the pump will increase or decrease the flow rate. This is done by supplying oil to the servo piston. The pump moves the swash plate until it gets the pressure drop it needs.

The name plate on the pump is correct, it's a DRS controller. The only difference is as I say, there is not variable orifice. To change the pressure drop, the proportional valve opens to change flow and pump responds accordingly to maintain flow.

The flow from the pump is directed to the actuators, but the pump control remains independent of the load at the actuators. In this way, you are able to maintain power control independent of load.

It's an elegant solution, it works and the pump name plate is correct. You'll agree once you understand how a load sensing pump works.

Just remember, the control strategy of the pump is to maintain the pressure drop across the orifice. If the proportional valve moves to change the pressure...the pump will change the flow to compensate.

As always, if it's not clear...please don't be afraid to ask.

Cheers

Adrian

RE: A10VSO Variable displacement pump power control

Attention to "HPost": I am like simram1983, I do not understand the explanation. Could you give us the signal values proportional pressure relief valve according to the desired flow rate at the pump?

RE: A10VSO Variable displacement pump power control

I cannot give any values for command signals etc...

I can only explain the principle of operation with information available at this time.

If we can confirm the diameter of the orifice, we can calculate the pressure drop when the pump is at full stroke, then start to look at what flow area would be needed through the proportional valve.

It would also help to know the stand by pressure of the pump

Adrian

RE: A10VSO Variable displacement pump power control

It's a power limiting pump with a load sense compensator. However the LS compensator is only being used to enable the proportional relief valve to adjust the cut-off (maximum) pressure. The 1mm (not 6.1mm) orifice is simply to feed the proportional relief valve.

The power limiting is achieved with the pilot relief valve closest to the pump. As the control piston extends to de-stroke the pump it also increases the pressure setting of this pilot relief (usually a dual spring arrangement to approximate to a hyperbolic constant power curve). So with a reduced flow the pump is allowed to go to a higher pressure thus keeping within the power limit. The initial setting of this pilot relief thus determines the power limit and the setting of the proportional relief sets the normal cut-off pressure.

The ultimate cut-off pressure can still be adjusted manually by means of the pressure limiting compensator spool (the left hand one).

RE: A10VSO Variable displacement pump power control

(OP)
Once again .. Thanks a lot for he replies. Sorry for such a late reply - just joined work again -- was hospitalised..

Well Adrian.. you are correct. I agree with your explanation. You said "It's an elegant solution, it works and the pump name plate is correct. You'll agree once you understand how a load sensing pump works" .. that's correct. I found a document of Parker, explaining the same load sense control in each stage. Am sharing the pdf file here.

http://files.engineering.com/getfile.aspx?folder=2...

https://drive.google.com/file/d/0B17y4jYQ3IhVSlZxN...

Thanks once again for clearing my concepts !!

RE: A10VSO Variable displacement pump power control

Hello...

I am sorry to hear that you have been in hospital, I hope you are better now. Your health is much more important than how this stuff works.

I am glad to help I am glad that the help has been worthwhile.

Good luck!!!

Cheers

Adrian

RE: A10VSO Variable displacement pump power control

Hello Simran and Adrian,

I am in Europe and works on power units with pumps flow rates from 850 to 4680 l/min at 350bar. Obviously the electrical or thermal engines may issue area power. And so I strongly would be interested to understand how you make the other side of the Atlantic Ocean to use pumps without power control. It could be saving a lot to the design.

Simram: you write "In the Machine's manual says it that by varying, the pressure setting of this valve, the flow of the pump can be changed".
Could you give me details on this phenomenon? Do you have a possibility of changing the current to the DBETE? When you change the setting, do not you have a always the same fast speed with no load and a different pressure increase speed? Do you have a closed loop electronic control which measures the intensity of the electric motor or the pressure multiplied by the speed of the cylinder?

RE: A10VSO Variable displacement pump power control

Hello...

Actually, I'm in England.

The relief valve is a proportional valve, so the valve setting is changed by adjusting the current to the coil.

Yes, as the setting is changed, the pump will respond by increasing or decreasing the flow and so the cylinder will speed up or slow down accordingly.

There is usually no need to have a closed loop on applications like this, but it is possible to have pressure or flow feedback or both to give better control or more precise power control.

Cheers

Adrian

RE: A10VSO Variable displacement pump power control

Sorry but I beg to differ.

It's a power limiting control with proportional adjustment of the maximum pressure as per my earlier post.

The pump delivers maximum flow until the pressure increases to a level where the power limit is reached. The pump will then reduce its flow as the pressure increases further to remain approximately within the power limit set. Although it's using a load sense compensator, then is no load sensing taking place.

RE: A10VSO Variable displacement pump power control

Bumblyari is quite correct, it is a subtle adaptation of a load sensing compensator to give power limiting.

Hey ho, at least some people learnt a little about load sensing.

Sorry!!!

Adrian

RE: A10VSO Variable displacement pump power control

I have had a closer look and the following is what "should" be happening. Please note that the original pump with am LAXDS controller shown in the drawing may have been replaced with a similar pump with a DRS controller.

The LAXDS controller has an additional relief that is attached to the pump servo piston to give constant power or constant torque. That controller is not visible on the pictures, which makes me think that the pump may have been swapped.

The principle of the LAXDS controller is to give flow control below the max power/torque curve. This is achieved as described above, by sensing the pressure drop across the 1mm orifice.

The LAXDS and DRS compensators are very similat, both have a margin compensator and a pressure cut off compensator. The margin compensator should be set to 15-20 BAR and when the proportional valve is switched off, there is no pressure on the "x" port and so the pump will sit at the standby pressure.

The cut off compensator will be set to give the maximum pressure. In this case 280 BAR, which happens to be max working pressure of the A10 pumps.

When valve EV3 opens to move the press, the pump outlet pressure would drop and oil would start to flow, but while the delta pressure over the 1mm orifice is higher than the margin compensator setting, the pump flow will remain low. This is where the flow control works. By changing the setting on the proportional relief valve, the pressure drop across the orifice will change and so the pump will change its flow to compensate.

Power and torque are both a function of pressure x flow rate (displacement). The torque limiter works by sensing the servo piston / swash plate to increase the allowable pressure. As the swash plate moves to reduce flow it increases the cracking pressure of the relief valve, so as flow goes down, pressure goes up and vice versa, as flow goes up, the max pressure comes down. Either way, it gives constant power and below that power curve, the flow control is infinitely variable by controlling the current to the proportional valve.

As drawn the system gives Power, Pressure and Flow Control. However, the pictures do not tell the same story.

So whilst I agree that the pump has power control, the flow and pressure control are as described above. It's essentially a load sensing system with a power limiter on top.

It may help to supply some pictures of the other other side of the pump. To see if there is a power limiting valve attached to the servo piston.

Cheers

Adrian

RE: A10VSO Variable displacement pump power control

I agree that the load sense pump in the picture does not appear to be the same as the power limiting one on the circuit.

However the circuit diagram describes a power limiting pump with proportional control of the cut-off pressure ie. no flow control. This is a standard method of achieving remote or proportional pressure limiting when the pump doesn't have a two-stage compensator.

Depending upon what the press is doing depends what type of control is most suited. If it's a gradual squeeze (like a baling press) then the power limit control is useful (to speed up the cycle time). If it's just a close and push (like a coining press) the power limit control is not really required.

It's not necessary to operate EV3 to close the press as it is closed by the two kicker cylinders on either side via EV1. The main press cylinder fills via the prefill valve (sorry can't read its number). Only when the final squeeze is required does EV3 energise which leads me to think that its working stroke is relatively short and so power limiting would not be a big advantage.

RE: A10VSO Variable displacement pump power control

So you are saying that both compensators that are on the drawing and visible in the pictures are actually not working?

Even though the pump supplier's description that matches the schematic diagram, that also describes the operation as being flow and pressure control, with power limiting...that's all wrong too? I can't see that being the case.

It's not worth arguing about, it's educational...

RE: A10VSO Variable displacement pump power control

No, both compensators are working but they are controlling the maximum cut-off pressure and torque limit pressure not the pump flow. The proportional relief valve enables the cut off pressure to be set electronically. The pump flow will of course reduce when the pump power hits the power limit curve but the pump flow is not directly controlled by the proportional relief.

Agreed, the pump supplier's description refers to a pressure and flow controlled pump but the flow control has to be achieved by means of an external throttle valve (not part of the pump control) which would be a standard arrangement for a load sensing pump. However, there is no such flow control in the press circuit but the load sense compensator is being used for the proportional adjustment which as I said is a common arrangement. There is no load sense line coming from the press cylinder and when EV3 is energised there is nothing between the pump and the press cylinder other than a straight-through piece of pipe, so no flow control.

RE: A10VSO Variable displacement pump power control

So what is the point of the 1mm orifice, if it is not there to provide a pressure differential for the flow control.

Yes, it's not a load sensing system as such, but the principle of controlling the flow is to use the proportional valve to change the pressure drop over the orifice.

The power control does what its name suggests.

The margin compensator controls the pump angle to set flow.

The cut off compensator is a spool that sees pump outlet pressure and works against a spring to directly control the servo piston to de-stroke the pump to hold 280 BAR.

I'm done arguing about it, it's pointless. Nothing to be gained...let's move on!

RE: A10VSO Variable displacement pump power control

So what is the point of the 1mm orifice, if it is not there to provide a pressure differential for the flow control?

It can serve two purposes as far as I can see:
- a dampening orifice to calm down the controller
- limiting the flow through the proportional pressure relief valve

RE: A10VSO Variable displacement pump power control

Nope...

The valve will have its own orifice to dampen its action.

Limiting the flow will drive the upstream pressure up and that is pointless.

I wouldn't normally be so insistent, but they way I have explained it really is the way it works.

The orifice is there to provive a pressure differential to control the pump awash plate angle and with it the flow rate.

People come here for advice and if we gave the wrong advice then that would be no good at all.

On the machines I am responsible for, we use the main spool as the variable restriction and we have similar pump that responds to the changing pressure differential. So as the pump speed changes or the spool flow area changes, the pump will respond to hold the flow rate. With this subtle difference as shown above, the speed is fixed and so the flow can be changed by changing the pressure drop across the orifce.

In all honesty, the way pressure and flow control systems work are very similar. It is only the fact that we make so many machines with this sort of control that means I can spot the difference.

It makes no difference to me at all, I just think that it's important to get the facts right.

RE: A10VSO Variable displacement pump power control

Here we go again.

1. Of course the orifice is there to limit the flow as Jacc rightly says. If it wasn’t there you’d be trying to push 100 lpm through a valve rated for probably 5 lpm.

2. The orifice also creates a pressure differential to enable the pump to de-stroke when the pressure differential reaches the setting of the bias spring. However allowing the pump to de-stroke is not the same as controlling the pump flow (try controlling the pump flow with its outlet connected back to tank and see what happens).

3. The proportional relief valve cannot control the pressure drop across the orifice as you say. It can only control the pressure on one side of it. The pressure on the other side will be determined by the load resistance. The point at which the pump flow rate will start to reduce is therefore determined by the setting of the proportional relief valve provided it is set lower than the load pressure. Now, if the magnitude of the load is speed dependent (such as on a fan drive for example) then and only then will controlling the compensator pressure determine the actuator speed.

4. It’s a similar situation to controlling the speed of a cylinder with a simple needle valve. For a given load if you increase the pump relief valve setting upstream of the needle valve the cylinder will move faster but what is the relief valve controlling – flow or pressure ?

5. The way pump pressure and flow control systems work are not similar, they are fundamentally different. To achieve true flow control from the pump alone (ie. not via an external flow control valve) you require a stroke controlled pump with mechanical or electronic feedback from the swashplate angle.

6. So in order to fully explain this circuit we need to know what the press is actually pressing. The proportional relief valve is controlling the pump cut-off pressure so whether that determines the press speed or not depends upon the characteristics of the load. However, in my experience, you are more likely to want to control the pressing force of a press electronically than you are its speed.

RE: A10VSO Variable displacement pump power control

You keep saying that the proportional relief valve is to limit the pressure.

Why have a pressure cut off compensator on the pump and a relief valve on the press as well then?

You will never get full pump flow across the orifice, the delta P over the orifce is sensed by the pump and the pump will back to hold the margin set on the compensator.

Yes, the valve can and does control the flow across the orifice. However, it's all relative to what the press is doing.

Pressure is a direct result of resistance to flow, so the control of pressure and flow is similar, not the same, just similar.

RE: A10VSO Variable displacement pump power control

Sorry Adrian, I agree with 73lafuite and Bumblyari and I don't follow your logic.
An orifice to provide a pressure differential is indeed the core of a Load Sensing principle. However, such an orifice is always in the line of the output flow from the pump. The flow in the orifice on the T'ed of branch to the regulator does not represent the flow from the pump.

As an example, simply connecting the LS port to the P port of an LS pump will force the pump up to maximum flow. Basically it is the same as having an infinitely large orifice in the line of flow, the pump will never be able to deliver enough flow to reach the pressure differential that is set in the pump controller (margin pressure). The pump will swivel to max displacement.
This is how this system is connected as well with the addition of a proportional pressure relief valve on the LS signal line. A similar setup can be seen in the attached pdf, page 25, fourth figure from top. You just have to imagine that the variable orifice in the line of flow is not there (or just fully open all the time).

On mobile machines with LS system the pressure out to cylinder from a certain directional control valve is sometimes limited to a lower setting (on some Caterpillar machines also maybe?). This is achieved by having a small pressure relief valve on the LS signal line on that DCV. The same principle is used on this system, there is a small proportional pressure relief valve on the LS line. This valve limits the maximum pressure of the pump to setting of the prop pressure relief + the margin pressure. Since it is an electrical proportional relief valve the pressure can be controlled at any time.

A small orifice is needed upstreams to limit the flow to the small prop relief valve. Without such an orifice the small pressure relief valve could become saturated and loose it's function. It is common to use a small relief valve in combination with an orifice to pilot control another valve (very common on larger logic element type of valves).

Like you say Adrian, there is most likely an orifice in the regulator itself but for this application it may have been removed. This is also mentioned on page 25 in the pdf.


The application also says a lot about the hydraulic system here. LS systems are indeed brilliant for use in many mobile machine applications where the operator constantly regulates the speed and position of multiple cylinder powered functions. In this case it is a hydraulic press, accurate control of speed and position is not so important, the important thing is to control is pressure. From what I can see on the pictures that prop. relief valve looks like a high end Rexroth unit.

HPost 7 Jan 16 17:06
When valve EV3 opens to move the press, the pump outlet pressure would drop and oil would start to flow, but while the delta pressure over the 1mm orifice is higher than the margin compensator setting, the pump flow will remain low. This is where the flow control works.


Seriously Adrian, when EV3 is closed the pump will be trying to swivel to max as hard as it can. This is not a mobile LS valve, it's not about regulating the flow across that 1mm orifice. On mobile LS valves the LS line is drained to tank when the DCV spool is in neutral position and connected to the load when the DCV opens but that is not the case here.

Yes one could view it as the regulator is trying to keep a constant deltaP across that 1mm orifice (it does for sure) but that view is not helpful in this application (since the orifice sits in a T'ed of branch of the main flow). When the prop press valve is closed the LS port is connected straight to P and will cause the pump to swivel up as much as it can. When the pressure of the prop pressure relief valve is reached, the pressure in on the X port will be limited (thanks to the orifice) and hence the pumps pressure will be limited.
Viewing it like a pressure relief on an LS line makes more sense, the prop. pressure valve controls the pressure of the pump, nothing more, nothing less. You probably know very well how a pressure relief on a LS line work.

RE: A10VSO Variable displacement pump power control

Jacc's got it just about right. Those may be the damping orifices just to the left of the left-hand compensator but the resolution of the diagram isn't really good enough to say.

But in reply to HPost's comments:

The main pressure relief valve is a belt & braces requirement since pump compensator spools are prone to jam and not always in a safe condition.

The manually adjusted cut-off compensator performs a similar back-up function for the proportionally adjusted one (ie. protects against an electrical issue).

The proportional valve allows you to vary the pressing force electronically of course probably via a PLC or other digital controller.

I didn't say the control of flow and pressure are not similar I said that pressure controlled pumps are different to flow controlled pumps.

RE: A10VSO Variable displacement pump power control

HPost
Why have a pressure cut off compensator on the pump and a relief valve on the press as well then?


That is a relevant question. Sure it acts as a backup like Bumblyari says but that may not be the only reason that it is there.
Part of the reason for this long discussion in the first place is that this design is a bit weird, I give you that Adrian. Why is there an LS-spool to start with, why not just a pressure compensator spool?

Looking at the Parker PV pump pdf I posted, page 23, second figure from top, (remote pressure compensator). That pump controller would be perfect for this application and it has one spool less. I can't find a similar option for the A10, the only way using an A10 pumps seems to be this setup with a DRS controller.

It could be also be as simple as Rexroth stocking the A10 with DRS regulator and that there was a long lead time for something more suitable or maybe it was cheaper.

RE: A10VSO Variable displacement pump power control

Back to the original questions:

By looking at the schematic, it suggests the pump to be a power control pump (i.e DFLR in terms of Rexroth’s terminology). But physically (see the image attached) it is NOT a power control pump. Practically, power control is taking place in the circuit - otherwise a pump delivering 100 lpm of oil cannot go up to a pressure of 280 bars with a 35 HP Motor. My question is how power control is taking place in the circuit?

Can you confirm that power control is taking place? You can use a Fluke 434 or similar to measure actual consumed power.
It could like 73lafuite suggested, it is simply running on high power for a short period of time.
My suggestion; I recently saw an old SauerDanfoss amplifier card that had an integrated power controller based on input from the electric motor current measurement. I guess it would be possible to use something similar in the PLC?




The manufacturer has installed a proportional relief valve (Rexroth DBETE) in the pilot line of the controller. In the machine’s manual it says that by varying the pressure setting of this valve, the flow of the pump can be changed. Again, my question is how is it happening?


It is not directly changing the flow, just the pressure. Usually (but not always) an increase in pressure will increase the flow. I think maybe the person who wrote the manual was in a hurry.

RE: A10VSO Variable displacement pump power control

Can OP post some better pictures please. This is an interesting topic that I am struggling to fully understand.

RE: A10VSO Variable displacement pump power control

It could be this way...it could be that way, who knows and more to the point, who is interested enough to argue about the finer points???

Unless we are going to make arrangements to visit the press and instrument it, we will just be making educated guesses at how it actually does function.

I personally have nothing more to add, it looks like it works in a particular way,,,but I have bee doing this long enough to know that I could be completely wrong.

Good luck to you all...

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources


Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close