Pump Control, how does it work?

[BigMax]

I have previously bench tested and commissioned a particular type of pump control softstarter for use in 'critical' pump starting applications. This particular type of starter is basically of open loop type, ie current is not measured via CTs or similar and an external thermal overload is required for motor protection. During commissioning I witnessed amazing performance, during the critical soft stop phase the softstarter prevented previously experienced severe hammer as the associated non return valve was literally slamming closed (these were BIG pumps, without the softstarter the closing of the non-return valves was like a cannon going off!!). Previous attempts using another softstarter type / brand with supposed pump application ability (not a dedicated pump starter though) was not successful.

 

My observations led me to believe that the dedicated pump control softstarter was somehow able to ‘sense’ motor speed. It didn’t simply progressively reduce motor Voltage during soft stop, allowing the bottom to fall out of the motor torque curve and the pump to stall. It actually seemed to constantly adjust the motor Voltage, providing a very smooth and constant deceleration rate, allowing the afore mentioned non-return valve to close gently.

 

Inspection of the construction of this particular type of softstarter reveals an ‘unspectacular’ design. Basic uP control with the usual mix of power components is all that can be seen.

 

Does anybody have any clues on how such a starter is able to perform in this manner, with no visible means of feedback from the motor? Thanks in advance for any thoughts and suggestions.

 

BigMax:D

[theDOG]

Hi BigMax,

I think I know the make of Soft Starter you are talking about...I have also seen the same results. I have also been very curious about this for some time. Alas, I do not know the answer :-(

I am also curious about "Pump start". A typical closed loop current controlled soft starter will have a sharp torque transition at around 80 - 90% speed, which invariably leads to fluid hammer. How does the "Pump start" control differ?

[BigMax]

Hi Mr The Dog,

 

I believe some softstarters advertised as suitable for pump control basically have 2 stage ramp control in order to 'soften' the torque peak you mention. While this provides a better pump start / stop than a linear Voltage ramp or constant current start soft starter, they fall short of the performance of the starter mentioned in my original post.

 

You mention that you may know of the brand I am describing, are you able to provide any technical explanation for the performance? ;b;

 

Cheers!

 

BigMax

[theDOG]

Hello BigMax;

 

I think that the pump control is one of the unsolved mysteries of the world! Unfortunately, I have no idea on how it is achieved.

I have seen the starter used on pumps where the pump speed is controlled like a VSD!! My guess is that the reason the manufacturer keeps this information as proprietary is because it (seems to) out-perform all other manufacturers...my opinion® only ;-)

[GGOSS]

Hi theDOG,

 

Please note the following comments are NOT directed at you, or in fact any other member of this forum.

 

There is no doubt that some 'pump controllers' work better than others in some situations, but I find it difficult to 'take seriously' any one manufacturer/supplier who says his/her product will outperform ALL others in ALL pumping/hydraulic situations.

 

What are your thoughts?

 

Regards,

GGOSS:mad:

[theDOG]

I agree with your comments....most pumping applications do not require the sophistication offered by the controller mentioned in this topic.

But it is interesting to know that someone else believes (as I do), that this starter is not matched by any other when used in "critical" or difficult pumping applications. Until I see otherwise, my personal opinion will remain.

[GGOSS]

theDOG,

 

I am fully aware of the product to which you refer and have also witnessed the VFD like characteristics that are achievable, particularly when the commissioning engineer knows what he is looking for and is able to 'adjust' the product accordingly. The reason I mention the latter is because more often than not unskilled product users form an opinion about the performance of a product (arising from their inability to set it up correctly) that is in fact very far from correct.

 

I also agree that 'in the main' the developer of the product to which you refer, whether by design or shear fluke, has done an excellent job. And like you, if I came accross a 'diffficult' pumping application and had a choice of soft starter products only, I would most probably choose that very same product.

 

However, the message I was trying to get accross was; please do not be overly confident becuase you will at some stage come accross a pumping application that gives you a lot of grief and you will come unstuck! Under those circumstances you may well find a far less sophisticated product will outperform what is considered the best.

 

I hope I have clarified my position.

 

Regards,

GGOSS

[marke]

Any design is full of compromises. The secret is finding the best fit for the job in hand. Know your applications well, know your products well, understand the motors characteristics and it begins to come clear. There is no one perfect unit. I wish there was, but costs prohibit that approach!

 

Best regards,

[BigMax]

Mr GGOSS,

 

OK, I'll bite.

 

You wrote above;

 

"However, the message I was trying to get accross was; please do not be overly confident becuase you will at some stage come accross a pumping application that gives you a lot of grief and you will come unstuck! Under those circumstances you may well find a far less sophisticated product will outperform what is considered the best."

 

Your statement is all very cryptic and sage like. Please give an example of a pumping application wherein the product mentioned in my original post would not be suitable, thus making us all become 'unstuck'

 

Cheers!

 

BigMax;c;

[GGOSS]

BigMAX,

 

As you are aware, this is a non-commercial forum hence I am unable to mention company names. What I can advise however is that one of the leading pump suppliers in Australia has conducted his own independant studies and found that the product to which you refer did not perform as well as two other products also tested on that very same application. This tests results were made available to a number of people and these were further supported by chart recording of current and pressure.

 

What we don't know for certain is how well versed the commissioning engineer was with each of the products being tested ie whether he was able to configure them to achieve best possible performance?.

 

Putting this said pump controller aside, I have also witnessed on several occasions now simple 2-phase compact starters outpreform other products said to have an advanced level of soft stop or pump control functionality.

 

Having said al this, I must go back to my previous comment and that is if I was faced with a difficult pumping application, the starter you refer to would most certainly be my first choice, but I never make the assumption that this WILL deliver the performance I require.

 

Regards,

GGOSS

[GGOSS]

BigMax & theDOG,

 

Got a spare 3 minutes and 6.4Mb free space on your hard drive?

 

The I would suggest you go to:

 

http://www.benshaw.com/presentations/video...eos/index.shtml

 

and click on 'video 14'.

 

Once you've done that I trust you will come back to me and our fellow forum members and advise if the product dipicted does or does not provide at least equal performance to the one to which you refer.

 

You will note that as this is not a product that I am not involved with, I have absolutely nothing to gain by referring you to this information.

 

However I sincerely hope that you will gain something from it!

 

Regards,

GGOSS:cool:

[theDOG]

Interseting video....

I have a few comments regarding the operation of that particular soft starter application;

1. The pumps are used with full damper control - not a check (non-return) valve as suggested. This is seen during stopping (around the 3 minute mark), the pump stops but the pressure gauge is still reducing (even taking into account the pressure gauge damping). You can also hear the flow of fluid.

2. This is a current limiting soft starter using a current ramp. There is a steep increase in speed at around 85-90% speed - watch the gauge!

 

Conclusion;

Any type of current limiting soft starter will provide a very similar result to what is shown on that video. There is certainly no proof that this soft starter provides linear acceleration and decceleration of the motor/pump connected. With full damper control (not a check valve), there is no requirement for any type of soft stop!

 

Again, my opinion only!

 

Cheers.

[BigMax]

Mr GGOSS,

 

Yep I viewed the vid also (after eventually getting RealPlayer happening) and I don't really think the performance was 'equivalent' to that described in my original post, although the two applications don't seem very similar.

 

The text describes a 1.5Mile pipe to a holding tank, but doesn't mention head or such unfortunately..... I agree with TheDog's comments, you can really see and hear the pump(motor) speed take off once the pull-out torque speed is reached. It doesn't seem that the starter in the vid had any type of speed 'feedback' as the type I mention seems to.....

 

I guess I'm not willing to conceed (yet) that a simple softstarter could work in too many pumping applications, particularly when there is any suggestion of criticality.

 

ANYWAY, I wouldn't want to risk the embarrassment of installing a simple softstarter, only to find it's a dismal failure......

 

BTW, some of the other vids on your referred site are interesting too, thanks for the link info.

 

Cheers!

 

BigMax:D

[theDOG]

BigMax,

 

I hate to be a nit picker but...

 

In your previous post you stated;

"you can really see and hear the pump(motor) speed take off once the pull-out torque speed is reached."

This should read "you can really see and hear the pump(motor) speed take off once the breakdown torque speed is approached."

Pull out torque generally occurs at about 30-40% of synchronous speed, while breakdown torque appears between 70-90% of synchronous speed (dependant on rotor construction and material). The region between pull out torque and breakdown torque is the critical stage in surface mount pumping applications. This is where the motor goes from least torque to maximum torque = maximum acceleration torque = incresed speed = increased flow and pressure = fluid hammer.

 

BTW, I believe that you would probably get better performance out of a fixed voltage soft starter on the application shown in the video....set up correctly of course.

[BigMax]

Mr The Dog,

 

No, I think you are confusing 'Pull Up" with "Pull Out". Since when does Pullout torque occur at 30-40% speed?

 

I think we may have some confusion here with definitions, my "Pullout Torque" is the same as your "Breakdown Torque".

 

Pullout refers to the speed at which the motor reaches maximum torque with maximum rotor impedance. The term "Pullout" is related to the same region of synchronous motor operation, whereby if the load is sufficient the motor is 'pulled out' of synchronous operation and the available torque at lower speeds is minimal.

 

I enjoy a round of nit-picking:P

 

Cheers!

 

BigMax

[theDOG]

Oops....you're right!! I haven't heard of the term "Pull out torque" for a very long time. Sorry for the confusion.

Now, where is that humble pie.....;e;

[GGOSS]

Hi BigMax & theDOG,

 

Please accept my sincere appology for not responding to your posts over the last couple of weeks. The boss (no, not my wife, my real boss) sent me bush to promote a new range of products. Unfortunately there was no internet or email access, just lots of pubs with lots of beer and lots of country folk that can really put the stuff down. And as I was keen not to offend, I did my very best to go one for one with each of them for the full two week block! ;d;

 

To TheDOG, for the benefit of all forum members and visitors I would like you to clarify one point for us please.

 

To date you have referred to the soft starter being discussed as an open loop voltage/current limiting controller in some posts and a device that provides linear starting and stopping of pumps in other posts. Is it one or the other or both? How can linear acceleration of pumps be achieved given the device controls torque not speed?

 

Regards,

GGOSS

[theDOG]

GGOSS;

Glad to see you made it back it one piece!

 

I think you are getting confused with another topic. I have made only one reference to a fixed voltage starter and that was in regard to the operation of the pumps in the video (the link you posted on the 26/9). I stated that I believe a fixed voltage controller would perform better than the unit that was shown in the video. I did not state that the "Pump control" soft starter in discussion in this topic is a fixed voltage controller.

 

On the subject of linear acceleration....you ask "How can linear acceleration of pumps be achieved given the device controls torque not speed?"

That is the question that BigMax raises as the subject of this topic! It seems as if no-one knows, or if someone does know they are not willing to part with that information.

 

BTW, a soft starter doesn't control torque. It controls voltage which influences torque which in turn influences acceleration torque which in turn influences acceleration time etc.