Pump Question...

[CHOMPERS]

i think its more efficient to choke the output.....??
does anyone known different ???

Yes, I do. "Choking" as you call it is the wrong way of going about it. You should add a tee and then a ball valve to shunt extra water back to the sump. Simply adding a ball valve to restrict the water will increase the load on the pump. This will increase the power drawn and also heat the water. In using excessively large pumps such as these, shunting water back to the sump is not enough to avoid heat build up in the water. The act of pumping causes the temperature of the water to rise. In small volumes and small pumps this is not apparent because of the heat loss in the tank. When the pump is sufficiently large in comparison to the ability of the tank to shed the heat, the temp can rise to well over boiling.

 

[johnptc]

Yes, I do. "Choking" as you call it is the wrong way of going about it. You should add a tee and then a ball valve to shunt extra water back to the sump. Simply adding a ball valve to restrict the water will increase the load on the pump. This will increase the power drawn and also heat the water. In using excessively large pumps such as these, shunting water back to the sump is not enough to avoid heat build up in the water. The act of pumping causes the temperature of the water to rise. In small volumes and small pumps this is not apparent because of the heat loss in the tank. When the pump is sufficiently large in comparison to the ability of the tank to shed the heat, the temp can rise to well over boiling.

well..................in friendly disagreement:

the pump works the hardest when run wide open.highest current draw.....most water pumped

as you choke the output the current drawn by the motor will go down and so does the mechanical work done by the pump. less water is being moved...some heat generated by viscosity....

this is only true with centrifugal pumps....

see for instance www.marchpumps.com
documentation
installation manual under discharge.

the heating effect of pumping water is quite correct and can be a problem in a fish tank....

disscussion most welcome !!!

from a pumps site :
2. Are centrifugal pumps variable speed?
Most centrifugal pumps do not have variable speed motors. However, you can control flow rate on the discharge using a valve.

 

[johnptc]

Bypassing Flow.... not real efficient

The discharge capacity can be regulated by leading a part of the discharge flow back to the suction side of the pump. Bypassing the flow is energy inefficient since the energy to the pump is not reduced... from the web

throttling a little better..........on energy use

variable frequncency drive ( 3 phase) is excellent ....also triming the impeller diameter is used....

 

[Epic Fabrications]

Chompers, are those prices for used motors?


I am a little confused on what I should do now?

Will this set up work? what is a tee?

 

[johnptc]

Chompers, are those prices for used motors?


I am a little confused on what I should do now?

Will this set up work? what is a tee?

a tee fitting looks like the letter T

what type of filter will you be using ??

 

[CHOMPERS]

Hi John,
I couldn't get anything on the marchpumps site other than pop ups. I agree with trimming impellers, but you can't undo it if you trim too much. I found out the hard way. Anyway, if you think about the impeller and how it works it may make better sense in how the efficiency works. The impeller spins the water and the pumping action is created by using the weight of the water to sling it outward. If the water is moving or if the water is not moving, the weight of the water is still inside the impeller. If the water is not moving outward, than it is pushing against the impeller. This force is what causes the extra load on the motor and inturn causes a higher current draw. The work done by the pump is not measured by the output. There is also the issue of static work measured in pressure inside the plumbing prior to valving it. Now think of an air tank: as the tank is pumped up, the air inside heats up due to the compression. This is a measure of the work done on the air. Though there is no flow going out of the tank, the energy required to continue pumping increases exponentially as the pressure goes up. The same is happening inside the plumbing of the water system only that the water does not compress in measureable terms.

 

[CHOMPERS]

Chompers, are those prices for used motors?


I am a little confused on what I should do now?

Will this set up work? what is a tee?

Those are ball park prices for used spa pumps with the motors. Your diagram looks ok, where are you having the confusion?

 

[johnptc]

Hi John,
I couldn't get anything on the marchpumps site other than pop ups. I agree with trimming impellers, but you can't undo it if you trim too much. I found out the hard way. Anyway, if you think about the impeller and how it works it may make better sense in how the efficiency works. The impeller spins the water and the pumping action is created by using the weight of the water to sling it outward. If the water is moving or if the water is not moving, the weight of the water is still inside the impeller. If the water is not moving outward, than it is pushing against the impeller. This force is what causes the extra load on the motor and inturn causes a higher current draw. The work done by the pump is not measured by the output. There is also the issue of static work measured in pressure inside the plumbing prior to valving it. Now think of an air tank: as the tank is pumped up, the air inside heats up due to the compression. This is a measure of the work done on the air. Though there is no flow going out of the tank, the energy required to continue pumping increases exponentially as the pressure goes up. The same is happening inside the plumbing of the water system only that the water does not compress in measureable terms.

ok .... but water doesnt compress... the only other work that can be done is generating heat ....

so the output of a water pump:
output = water pumped + heating from friction

i will try to find other references to output throttling.....

to be continued !!

 

[Epic Fabrications]

I planned on using a Tee, but wasnt aware of its name.. I just call PVC parts "the thing that looks like this" and make a finger position, or just look for myself...

My filtration will be a network of filter cartridges to pass through, followed by river rocks, sponges, and maybe a few recommended after thoughts. Haven't gone into that stage of design yet.

 

[Epic Fabrications]

I greatly appreciate all of your help. Thank you very much.