a question regarding pumps i couldn't answer

[mitten]

And add to this mix the fact that Tsurumi's US distributorship is now Aquascape only.

Steve Bekkins, I figure you know this. Tsurumi's POMU2 does about 47 GPM at 5 feet drawing 352 watts, but retails at only $212.00. Asking for 33% more flow using 33% less amperage, even when paying twice as much may be unavailable and has been unavailable in the places I'm able to look.

I believe this is an illustration of what you meant by less efficient, as long as there is a centrifigal able to checkmark these three boxes. Not hard. W. Lim's Wave 1 with 1/8 HP pumps 60 GPM at 8 FT (better), uses only 132 watts (better) and costs just over $400, 409 at AES. First pump I checked, so there must be more.

So, buck for buck, centrifigal pumps are more efficient at moving water by using electricity.

Wouldn't it be nice to have an 1/8 HP and 1/4 HP propeller pump available also though? 80 GPM at 6 FT using 132 watts for $400? I'll buy it.

Mickey the windowman

[frankchong]

Any one pump whether submersible or centrifugal has a very narrow range to operate at maximum efficiency. For example Lowara stainless steel centrifugal pump, you can have one delivering 20 cubic meter per hour at 3 meter head requires only 1/2 horse power. You can also have another pump in the same family doing the same job but require 3/4 hp.

Major pump manufacturers made their pump in accordance to EN 733 or DIN 24255 standard. Each family of pumps are made in a series of frame sizes to cater to full range of hydraulic head H and flowrate Q. However if you study the hydraulic performance curve of the pump. You would realise that for one particular frame size there is only one particular H and Q where the pump would operate at an optimum efficiency typically 64%. If your requirement for H and Q matches the optimum efficiency you solve half the problem. Next, from the hydraulic curve you can derive the power required for the pump. If the curve indicates 0.55 hp is required. You have another problem. Motor also manufactured in standard frame sizes from 1/8, 1/4, 1/2, 3/4, and so forth. In this case you have to use a 3/4 hp motor to drive 0.55 hp pump. It is like running a 6 cylincer engine where a 4 cylinder can do the job, more power consumption. Study the Baldor motor catalogue one can see the no load amperes required to run a 1/2 hp and 3/4 hp motor, you would know what i meant.

If you choose to buy off the self centrifugal pump. Typically the label will tell you it could operate at a range of Q at a range of H. What happens here is they would install an oversize motor to cover the maxim Q recommended to prevent motor overheating. Please bear in mind, out of these range of Q and H claimed. There is only one particular Q and one particular H where your pump is operating at optimum efficiency. It if hits your Q and H you are lucky, otherwise you would just be burning dollars.

It is the same scenerio in submersible pump. However in this case where cooling of motor is not a problem. The manufacturer would match the motor size more closely to the pump requirement rather than putting in standard frame size motor. ( This was what i meant by taylor made. Sorry for the confusion )

More consideration. If your centrifugal pump is installed at the last chamber after all the filtration. You can select a maximum efficient closed stainless steel impeller. Otherwise you need a less efficient open impeller in order to allow solids to pass through.( Limited particulate size though.)

Self priming swing pool type pump is the least efficient of all. The manufacturer will not even publish the hydraulic curve, because it would be counter productive to do so.

Not all submersible pumps are created equal. Some are sump pumps only good for intermittent operation to drain storm water. You must be looking at using sewage pumps where it is designed to handle agressive low ph water and sludge. The pump impellers are designed to allow solids up to 30 mm to pass through. If it is constructed in cast iron, it would be very heavy and robust to allow for progressive corrossion before failure. The best material would be corrosion free, a combination of stainless steel and high impact plastic.

Do not belief what the label tells you. The wattage indicated on the submersible pump label tells you the power input requirement for the pump. It gives you some idea of its pumping capacity. It does not tell you the actual amperes the motor will draw or its efficiency. For example I run a 150 watt Tsurumi PU series pump. I installed an am meter on this circuit and it measure exactly 1 amp.
My voltage is 240 volts. It actually draws POWER = Voltage X Ampere X Power Factor( typicaly 0.85). Power = 240x1x0.85=204 watts.

There are some pumps labeled at 150 watts but could draw current as high as 2 amperes. Try installing a permanent am meter in the power circuit you would be surprised. With the ammeter, I no longer need to feel whether the pump is working. I know exactly how hard my pump is working or near failure.

Compare the power concumption of self priming centrifugal and good sewage submersible pump with equal flow rate by using ammeter. You may have a different perspective to green the earth.

[bekko]

Thank you frankchong. I will reserve my opinion about the efficiency of submersible pumps until I have real data.

In most catalogs and brochures for fractional horsepower pumps they provide a curve with Q plotted against H. They could easily plot amps on a third axis within the same graph, but they do not. The only time you also get the power consumption curve is when shopping for large capacity pumps of many horsepower.

Intuition would lead a person to believe that the "sweet spot" (maximum efficiency) is neither at the point of maximum H where Q approaches zero nor the point of maximum Q where H approaches zero, but somewhere in between. However, buying and installing several different pumps only to check the amp draw and select the most efficient one is not an option for most of us. In the absence of real data, are there any general guidelines for making an educated guess about the point of maximum efficiency? Is it likely to be near the center of the Q/H curve?

Also, the plot of amp draw superimposed on a Q/H graph would make a fairly normal inverted bell curve. Correct? There must be practical design limits to the range of the amp draw curve. For example, if the point of maximum efficiency is 1 amp, the maximum possible amp draw will not be 10 amps but something much less. The smaller the range, the broader will be the bottom of that inverted bell curve (area of lowest amp draw). Thus, the amp draw will initially increase very gradually as you move away from the sweet spot. The net effect should be that the annual electrical cost does not change much as long as you are in the vaciity of that sweet spot. Does that make sense.... and is it correct?

-steve hop

[frankchong]

As a user of pump myself I can understand the difficulties in choosing a pump that meets all our requirement and you bet I have tried many. That it must be efficient, draws minimum current, high flow rate, low noise, reliable. From catalogues alone one can never be sure, because a lot of data is purposely left out. Only a flow meter and ammeter could tell the performance of a pump. Adding to this confusion.

The name tag on the submersible indicates the power output of the motor which is same as the power input to the pump. No one can be sure of its power consumption, because the manufacturer would not tell you the motor efficiency in its catalog. You can take 10 different makes of submersible pump rated at 150 watt. The power consumption to each pump would be different so is the flowrate at the same H. We can only tell the power consumption by measuring the current drawn by each pump.

For a swimming pool type pump coupled to standard frame size motor. The name plate indicates the output power of the motor. The current rating of the motor always indicate no load current. If the name plate says power = 1/2 hp. Current 3 amperes. It means this motor is capable of delivering 1/2 hp to the pump. It draws a current of 3 amp when running free without any load. One can never tell how many amps it would draw when it is in operation. Only by measurement you can tell the power consumption. Therefore by comparing the name tag of submersible pump and standard frame size centrifugal pump one cannot tell which is more efficient until you measure its power consumption and flowrate at a fix hydraulic head.

If you have to guess the sweet spot of the pump, my opinion would be to target the operating hydraulic head to be at 1/3 away from the lowest recommended head. Let's say if the hydraulic head of system is 2 meters. Try to choose a pump that have a recommended range of 0.5 meter to 6 meter.

If we plot a power consumption graph with Y axis as Q (flowrate) and X axis as H (hydraulic head). The power consumption will increase quite linear at low Q and low H. Then the curve will incease exponentially upwards at a higher H.
This concept is not difficult to comprehend. If we have to deliver the same Q at a higher H. The pump will have less hydraulic efficiencies due to more eddies and frictional losses within the pump housing. Therefore requiring more power to deliver. For that reason always try to oversize the pipe, there would be more savings in the long run.

One can short cut the learning experience by measuring current consumption, hydraulic head and flowrate of friends pump. By comparing different makes a better picture will develop.

There is no fix and fast rule to say sub pump is more efficient than centrifugal
or vice versa. It depends whether the pump you selected operates at its optimum efficiency, which is only at one particular Q and H.

For centrifugal pump one can say with certainty, a closed impeller pump would be more efficient than a pump with semi open or open impeller and self priming type with open impeller would be the worst.

[bekko]

Thank you again frankchong. I do not know where I got the idea that the power consumption would make a bell curve. I must have been thinking about the plot of efficiency against flow.

Many manufacturers do not provide a recommended head and only give a plot of Q/H from the point where Q=0 to the point where the curve breaks near H=0. The flow is often x axis and head is y axis. Like this...
http://www.aquaticeco.com/index.cfm/...mages/iid/7692
This graph is for Wave pumps from the Aquatic Ecosystems catalog. With no other information available, you would anticipate that the sweet spot will be about one-third up the curve from the bottom - about 125 gpm and 18 feet for the HSW1. Is this correct? That is a very useful rule-of-thumb.

-steveh op