| 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. |