Pump Head Increasing

Even if possible, that is not likely to be an efficient choice.

You really should select a larger diameter pump with smaller pipe connections and impeller passages.

Yes it can.

That depends on what a VSD is.....If you mean a VFD, then it should work. but for how long is the question.... 60hz should reach desired rpm....I would check for overheating and be prepared to change out the motor if necessary....

http://ecmweb.com/design/mating-new-variable-frequency-drives-existing-motors

http://ecmweb.com/content/understanding-variable-speed-drives-part-1

A new pump on the existing motor may be a better option.

Maybe, but it depends on the motor design and VSD/VFD design.

I suggest you overlay/compare the pump output curve to VSD/VFD motor speed vs.HP curve and ensure the motor is not going to be overloaded at 1800 RPM with the added 50% increase in pump head mechanical loading.

If still in doubt I would contact the motor manufacturer and discuss the application in detail before proceeding.

I'd contact a pump supplier, with fluid details.

The pump supplier can look at his curves and determine the motor power requirements which we already know.

It's obvious the OP is not qualified to size the pump and is grasping at straws, or VFD's in this case.

I agree that contacting the pump manufacturer would be the easiest solution.

I wonder how old the motor speed control is?

He referred to it as a Variable Speed Drive which I have not heard that terminology in some time.

Did you get you truck AC working right yet?

Speed control is a desperation move.

Bad Schrader valve let Freon leak. That caused the "smoke", but didn't empty the system till I ran it a few days.

Vacuum accumulator was cracked and that made the doors default to defrost.

Valve/Freon no charge. Oil change/new accumulator $120.00. I'm happy.

Great! Should be good for another 100,000 miles!

The viscosity of whatever you are pumping can quickly become a problem, too. If this is a vacuum roughing pump then this should have little effect. Molasses or molten Sodium will be another thing all together. Did I forget to mention cavitation effects.

By pump affinity laws, increasing the rpm by 20% will increase the flow by 20%, the output pressure by 44%, and the power by 72.8%. Throttling the discharge will reduce the power requirement, but will move the pump far to the left of its best efficiency point. Just get the right pump, and don't dick around with expensive VFDs.

The answer is still that "it depends", but what it depends on is much simpler.

It depends on what the kW loading of the motor is right now at the flow and head that you have. Your motor is 7.5kW, that is your finite limit. At 1800RPM, the speed you have ALREADY determined is what it will take to get the desired output, the speed will be 120% if base design speed. So assuming it is a centrifugal pump, the power (kW) REQUIRED by that pump at 120% speed will be 172.3% of what it is now. So IF your motor is loaded to only 4.35 kW right now, increasing the speed to 1800RPM will increase that load requirement to 7.5kW and you are good to go.

That however is highly unlikely. It's more likely that your motor loading is closer to 7kW, in which case when you increase the speed, the PUMP will require 12kW and your motor will be overloaded. This principal is about the fact that the 7.5kW limit is based on the motor design speed being 1500RPM at 400V. When you increase the speed, but not the voltage, your V/Hz ration cannot remain the same and the motor loses torque beyond the base design speed.

So in reality it will come back to what Lyn said, you need a different pump and motor.

Mohamed Alammin,

Just have your client contact CR4 directly.

He very likely will know the fluid details, process parameters, operating conditions and actual requirements for the pump.

You do not appear to be aware of any of this.

Just tell him that you have "retained" an expert international consultation team to advise you.

Another little fib won't matter in the grand scheme of things. He must already think your firm has some knowledgable process/mechanical engineers on staff.

Waiting to hear from your client.

That's all well and good, but it may be difficult for the OP to distinguish valid professional advice from random commentary. He does need a better pump selection.

My hope is that the OP's client is more perceptive than the OP.

But then if that is true, the OP may be looking for another line of work, for which they are more well qualified.

Jeez, my first call would have been to a pump supplier. They would have some incentive to recommend and sell me a pump, at least.

This is interesting, and one of the things I find odd about CR4 postings--the strange aversion to contact with vendors. I'm pretty knowledgeable about pumps, for instance, but even so, people should be asking pump suppliers, rather than me, about their pump needs. (Or maybe they should ask me rather than a pump flak salesperson.)

We're not alone.

I honestly think very few people who come here for pump help realize what it takes to spec one. (Not design it)

Or even the right questions to ask here.

That is really the bothersome thing--the simple not knowing of what sorts of questions to ask, or matters to consider. Some allowance needs to be granted to students, of course, but not to poseurs.

Well it shows that those that know how to ask most likely also are the ones that can find the answer by themselves. So we are left with those that don't even know what the question is or what it takes others to answer the question.

Assuming 43 m3/hr @ 10 met (current duty) is near the pump's BEP, the changed BEP at 1800 RPM will be 51.6 m3/hr @ 14.4 met head

Achieving 15 met head at 1800 RPM is okay. but 15 m3/hr will be nearly minimum continuous safe flow or lower. Thus the efficiency will drop, and may lead to bearing life getting shortened.

Not recommended if the duty is continuous.

Secondly, check the effects of speeding up motor by 20%, whether the motor performance parameters become critical.

Lastly, commercially, the VSD cost may not justify the manoeuvre. It may be better to change the pump.

First you need to check the pump performance curve to see where you are currently operating on the curve. This will tell you everything.

It is conceivable (but very unlikely) that you can do this with a VFD will very little speed change. If you look, for example, at the Goulds 80x50-200 1450rpm curve ( http://www.irrigationtas.com.au/files/products/pumps/ISO.pdf ) you can see that it will do the original duty with a 205mm diameter impeller. If you follow this curve to the left you will see that it produces about 14.5m head at 15 m3/hr, so very little speed change is required, and at about 45% of BEP it is not a bad position on the curve (not too far left).

The problem is that most pump specifiers would not go for this pump size for the original duty because the original duty point is too far to the right of BEP and efficiency is quite low (I would probably have gone for a 100-65-160 or 100-65-200). Any other pump size, as Excel points out above, will almost certainly put the new duty point too far to the left of curve, which is not a good idea. So it would be best to go for a new pump.

(btw. the motor seems rather over-sized, even if there is a high S.G.).

Throw it away and buy the right pump. Simple.

Dear Mr.Mohamad Alammin

I think you know the Centrifugal Pump follows the Affinition Law. which means

The Capacity is Proportional to Speed of the Pump. The Head is Proportional to the SQUARE of the Speed of the Pump. The Power is Proportional to the CUBE of Speed. of the Pump.

You have stated that the Pump speed is to be increased to 1800 RPM from 1500 RPM to get an out put of 15M^3/Hr., at 1800 RPM from 43 M^3/Hr. at 10 M Head.. I think you do not undertake any change in the impeller. If so, asper the affinition law,

The Capacity will increase to 43 x (1800/1500) = 43 x (1.2 ) = 51.6 M^3/Hr.

The Head will increase to 10 x (1800/1500)^2 = 15 x (1.44) = 21.6 Metres

The Power Demand will increase to (7.5) x 1800/1500)^3 = (7.5) x (1.728) = 12.96 KW

While working at 1500 RPM, the Power demand will be 6.32 KW with a over-all efficiency of 68 %.

Hence your proposal to increase speed to 1800 RPM from 1500 RPM for obtaining flow of 15 M^3/Hr. at 15 M Head from 43 M^3/Hr. at 10 M Head is not possible. Even if you start the pump, it will trip.

ALTERNATIVELY,

Study the Pump Performance Character or Family Curve and decide (OR) Consult the Pump Manufacturer, whether a new impeller can be fixed in the same pump shaft and body and if so you can try this. This is mainly for the reason that any standard Pump Manufacturer will design in such a way that for a given Head you can replace the impeller for 2 different DISCHARGE and for a given Discharge you can replace the impeller for 2 different HEADS.

This topic has been discussed in this forum earlier and you search in CR4 and you will get more information.

DHAYANANDHAN.S

Each manufacturer has its own pump curve. Performance and efficiency varies at Head vs. Flow plot. Now, you can not simply determine this by equation. Pump curve is made out of actual tested data of the pump by manufacturer.

Request pump curve from manufacturer if you care on long term basis operation and reliability of your job to clients.

Some might actually push even they see it's less efficient. But you should not, if you are an engineer or not, fulfill your oath, follow the code. Better efficiency of working systems means less stress to environment and better energy saving to client.