Throttled Pump Power Use
- Thread starter JVJordan
- Start date
AZDesertRat
In Memoriam
That is correct.
Here is an example using a Eheim 1260 that I tested awhile back.
I used a 10 psi pressure gauge, ball valve and 1" residential water meter on the discharge side of the pump and a Kill A Watt meter to monitor power.
Open discharge = 63 watts @782 GPH
1 psi (2.31 feet of head)= 60 watts @ 499 GPH
2 psi (4.6 feet of head) = 54 watts @ 433 GPH
3 psi (7 feet of head) = 50 watts @ 356 GPH
3.5 psi (8 feet of head) = 46 watts @ 300 GPH
4 psi (9.5 feet of head) = 43 watts @ 253 GPH
As you increase the head or discharge pressure you reduce the flow which reduces the amount of work being required of the pump. This is true of all centrifugal pumps but not positive displacement pumps which are not too common in our hobby anyway.
Here is an example using a Eheim 1260 that I tested awhile back.
I used a 10 psi pressure gauge, ball valve and 1" residential water meter on the discharge side of the pump and a Kill A Watt meter to monitor power.
Open discharge = 63 watts @782 GPH
1 psi (2.31 feet of head)= 60 watts @ 499 GPH
2 psi (4.6 feet of head) = 54 watts @ 433 GPH
3 psi (7 feet of head) = 50 watts @ 356 GPH
3.5 psi (8 feet of head) = 46 watts @ 300 GPH
4 psi (9.5 feet of head) = 43 watts @ 253 GPH
As you increase the head or discharge pressure you reduce the flow which reduces the amount of work being required of the pump. This is true of all centrifugal pumps but not positive displacement pumps which are not too common in our hobby anyway.
AZDesertRat
In Memoriam
So far I have only been able to test pumps I have on hand or those friends loaned me. I will have to see if I can find locals with pressure rated pumps to test. Its going to be pretty much the same though but with higher wattages throughout the curve due to the nature of high head pumps.
I'm not sure why the total input power to the pump would decrease but according to the numbers it still takes more watts per gallon per hour to move the water when the ball valve is closed more and more.
W gph W per gph
63 782 0.08056266
60 499 0.120240481
54 433 0.124711316
50 356 0.140449438
46 300 0.153333333
43 253 0.169960474
W gph W per gph
63 782 0.08056266
60 499 0.120240481
54 433 0.124711316
50 356 0.140449438
46 300 0.153333333
43 253 0.169960474
BeanAnimal
Premium Member
ikatobiko, it depends on the motor/impeller combination. Each pump will have a point called BEP (Best Operating Point). At head pressures above and below that point the pump will lose efficiency.
dots
Premium Member
http://www.pumped101.com/
http://www.pumped101.com/efficiency.pdf
http://www.motorsanddrives.com/cowern/motorterms8.html
http://www.driedger.ca/ce1_cp/CE1_CP.html
The key to pump selection is finding a pump that operates at it peak effeciency based on your system conditions. If not, the pump will not preform at its peak flow, pressure, which may vibrate or cavitate. The relations between these characteristics in pump applications such as ours are governed by the Affinity Laws as seen in one of the links. There is such a law that relates power used as discussed here, but there is nothing for free and the efficiencies and pump performance is changed.
It is true, throttling the suction does decrease the amperage draw, but this also shifts the duty point of the pump, creating a less efficient pump, which in turn can lessen flow or TDH. The main concern with suction throttling is it effect the Net Positive Suction Head and the increase possibility of cavitation by moving the duty point to the far left of the curve, (another misdiagnosed reefer problem that is usually air entrainment instead), if the pump was already poorly matched with the system, this can only compound the system.
http://www.pumped101.com/efficiency.pdf
http://www.motorsanddrives.com/cowern/motorterms8.html
http://www.driedger.ca/ce1_cp/CE1_CP.html
The key to pump selection is finding a pump that operates at it peak effeciency based on your system conditions. If not, the pump will not preform at its peak flow, pressure, which may vibrate or cavitate. The relations between these characteristics in pump applications such as ours are governed by the Affinity Laws as seen in one of the links. There is such a law that relates power used as discussed here, but there is nothing for free and the efficiencies and pump performance is changed.
It is true, throttling the suction does decrease the amperage draw, but this also shifts the duty point of the pump, creating a less efficient pump, which in turn can lessen flow or TDH. The main concern with suction throttling is it effect the Net Positive Suction Head and the increase possibility of cavitation by moving the duty point to the far left of the curve, (another misdiagnosed reefer problem that is usually air entrainment instead), if the pump was already poorly matched with the system, this can only compound the system.
BeanAnimal
Premium Member
Dots,
We are not talking about "suction throttling". We are talking about throttling a pump by increasing the static head, in this case with a ball valve on the pressure side of the pump. Using your terminology, this would be "pressure throttling". This is perfectly acceptable and not harmful to the pump, nor does it increase the chances of cavitation. Actually, the contrary is true! If a pump is cavitating due to a restrictive suction side, the output can be throttled to prevent the cavitation.
As I indicated above, each combination of impeller, volute and motor will have a different efficiency curve. Someplace on that curve is the BEP for the given combination and pump RPM (BPM will change with RPM). Since most of us DO NOT employ the use of a VFD, we can pretty much ignore Affinity laws and BEP. All one needs to do is look at a simple pump curve to size the pump.
We are not talking about "suction throttling". We are talking about throttling a pump by increasing the static head, in this case with a ball valve on the pressure side of the pump. Using your terminology, this would be "pressure throttling". This is perfectly acceptable and not harmful to the pump, nor does it increase the chances of cavitation. Actually, the contrary is true! If a pump is cavitating due to a restrictive suction side, the output can be throttled to prevent the cavitation.
As I indicated above, each combination of impeller, volute and motor will have a different efficiency curve. Someplace on that curve is the BEP for the given combination and pump RPM (BPM will change with RPM). Since most of us DO NOT employ the use of a VFD, we can pretty much ignore Affinity laws and BEP. All one needs to do is look at a simple pump curve to size the pump.
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dots
Premium Member
I will give you the fact that I skipped over the side you were discussing, however, you can't "ignore" the affinity laws as they are the relationships that create the pump curve.
My second error was copying an old post as I see it could confuse,the main reason I did was I thought it had the Affinity laws in the links. So here it is, if you follow the math, combined with the law of Conservation of Energy is the source of this counter intuitive result of amperage drop.
http://www.engineeringtoolbox.com/affinity-laws-d_408.html
My main point in responding to these questions is "that there is never anything for free", and don't want people to make it more difficult than it already is for themselves chasing thier tails buying big mismatched overpriced pumps that don't perform for thier monies worth.
Ignoring "BEP" is like ignoring the fact you could get 50 miles per gallon, as opposed to the 30 you currently are. But thats fine, as most of these "fish tank" pump manufacturers rarely put BEP on thier curves.
This leads into another problem, so say we ignore BEP and we are on the ragged edge on the left side of the curve, you just compounded the selection error by shifting the duty point even more, further decreasing pump effeciency.
You are correct, each impeller trim, power supplied, motor effeciency, RPM, volute, Hp, and discharge diameter combined with the required conditions are all the are the metrics that are imputed into each specific curve. However, to make that leap of faith, they need to be inputed into those governing princibles of centrifugal pumps.
Because we are dealing with such small numbers, it doesn't matter.....but when people get into their 3rd or 4th tank and it is on the 300gal side, they wonder why they can't pump water up from the basement sump, and just have a glorified heater. And why did this happen, they never learned how to select a pump in the first place.
Now it seems I was mistaken by not reading which side, but here is what I am saying.......whch is the big picture in all of this.
Most people have pumps hitting duty points that are probably nowhere near the curve and are mismatched for thier needs, and most likely bought it because some joker said it was a "good" pump. Yes, you are correct throttling does work but is a tuning device for specific applications, (process pressure control or flow control, neither of which we are concerned with and even fewer of which understand), and throttling of either side can only compound mismatched pump performance issues where most of the time one doesn't even know where they are on the curve to begin with, or act as a band-aid fix. I like simple too.
There is a graph in here that shows the effeciency benefits of different methods of pump control......again which I say we have no reason for to begin with, in the first place. One of these links I believed stated that discharge throttling was like driving with one foot on the brake and the other on the gas at the same time. Other than my grandmother, I don't know who thinks thats a better way to drive.
http://www.engineeringtoolbox.com/pumps-discharge-regulation-d_310.html
Thank you for pointing out that I had that first post backwards, the last thing I want to is make it even more confusing.
I thought this was a good article on where cavitation comes from
http://www.engineeringtoolbox.com/npsh-net-positive-suction-head-d_634.html
My second error was copying an old post as I see it could confuse,the main reason I did was I thought it had the Affinity laws in the links. So here it is, if you follow the math, combined with the law of Conservation of Energy is the source of this counter intuitive result of amperage drop.
http://www.engineeringtoolbox.com/affinity-laws-d_408.html
My main point in responding to these questions is "that there is never anything for free", and don't want people to make it more difficult than it already is for themselves chasing thier tails buying big mismatched overpriced pumps that don't perform for thier monies worth.
Ignoring "BEP" is like ignoring the fact you could get 50 miles per gallon, as opposed to the 30 you currently are. But thats fine, as most of these "fish tank" pump manufacturers rarely put BEP on thier curves.
This leads into another problem, so say we ignore BEP and we are on the ragged edge on the left side of the curve, you just compounded the selection error by shifting the duty point even more, further decreasing pump effeciency.
You are correct, each impeller trim, power supplied, motor effeciency, RPM, volute, Hp, and discharge diameter combined with the required conditions are all the are the metrics that are imputed into each specific curve. However, to make that leap of faith, they need to be inputed into those governing princibles of centrifugal pumps.
Because we are dealing with such small numbers, it doesn't matter.....but when people get into their 3rd or 4th tank and it is on the 300gal side, they wonder why they can't pump water up from the basement sump, and just have a glorified heater. And why did this happen, they never learned how to select a pump in the first place.
Now it seems I was mistaken by not reading which side, but here is what I am saying.......whch is the big picture in all of this.
Most people have pumps hitting duty points that are probably nowhere near the curve and are mismatched for thier needs, and most likely bought it because some joker said it was a "good" pump. Yes, you are correct throttling does work but is a tuning device for specific applications, (process pressure control or flow control, neither of which we are concerned with and even fewer of which understand), and throttling of either side can only compound mismatched pump performance issues where most of the time one doesn't even know where they are on the curve to begin with, or act as a band-aid fix. I like simple too.
There is a graph in here that shows the effeciency benefits of different methods of pump control......again which I say we have no reason for to begin with, in the first place. One of these links I believed stated that discharge throttling was like driving with one foot on the brake and the other on the gas at the same time. Other than my grandmother, I don't know who thinks thats a better way to drive.
http://www.engineeringtoolbox.com/pumps-discharge-regulation-d_310.html
Thank you for pointing out that I had that first post backwards, the last thing I want to is make it even more confusing.
I thought this was a good article on where cavitation comes from
http://www.engineeringtoolbox.com/npsh-net-positive-suction-head-d_634.html
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BeanAnimal
Premium Member
Dots,
With all due respect, I did not read any of the links you posted. I have a firm grasp of how pump curves are derived and the variables that influence the values that form the curve.
While I agree that properly sizing a pump to an application can save money, the reality is that we are not building or specifying pumps or their motors. We have a very small selection of pumps in the hobby.
Most of us choose a pump based on many factors other than the ideal power consumption for the given head. In addition most people defer upsizing their plumbing by 1 or 2 sizes, which in many cases would greatly increase the efficiency of their chosen pump.
You are correct, most people do not know where their setup falls on the pump curve. Actualy most folks have never looked at a pump curve
People choose pumps based on many criteria. Those criteria tend limit the choices when it comes to matching a pump to the system for best efficiency. For example, take the Velocity T4. It is not all that efficient and it contributes most of its heat to the water. However, it is DEAD silent. Take the Reeflo Dart as another example. It is somewhat quiet because it is low RPM. Due to the large diameter impeller and volute design it requires a HUGE suction intake to prevent cavitation that would otherwise form at the edge of the impeller. The comparable IWAKI is louder due to a smaller high speed impeller and volute. It can be supplied with an intake that is MUCH smaller while still not causing cavitation. Both pumps are fairly efficient but have two vasty different operating environments.
With all due respect, I did not read any of the links you posted. I have a firm grasp of how pump curves are derived and the variables that influence the values that form the curve.
While I agree that properly sizing a pump to an application can save money, the reality is that we are not building or specifying pumps or their motors. We have a very small selection of pumps in the hobby.
Most of us choose a pump based on many factors other than the ideal power consumption for the given head. In addition most people defer upsizing their plumbing by 1 or 2 sizes, which in many cases would greatly increase the efficiency of their chosen pump.
You are correct, most people do not know where their setup falls on the pump curve. Actualy most folks have never looked at a pump curve
People choose pumps based on many criteria. Those criteria tend limit the choices when it comes to matching a pump to the system for best efficiency. For example, take the Velocity T4. It is not all that efficient and it contributes most of its heat to the water. However, it is DEAD silent. Take the Reeflo Dart as another example. It is somewhat quiet because it is low RPM. Due to the large diameter impeller and volute design it requires a HUGE suction intake to prevent cavitation that would otherwise form at the edge of the impeller. The comparable IWAKI is louder due to a smaller high speed impeller and volute. It can be supplied with an intake that is MUCH smaller while still not causing cavitation. Both pumps are fairly efficient but have two vasty different operating environments.
dots
Premium Member
Too bad.....
Its all good, I realize you do have a knowledge of the subject, and it seems we are "preaching to the choir" here and have probably scared off JVJordan. You are correct, the BEP is not the end all give all and other design considerations need to be taken into account, but its a starting point and where one would want to be in the best case scenario.
I do hope the big picture I was thinking wasn't lost in all this, in getting it right the first time makes it easier in the long run, which would start by people looking for those curves AFTER they design thier plumbing. Which is funny, being these pumps can literaly be called the "heart" of your system, very little is spoke on how to select a pump step by step, as compared to lighting.
If you get a chance, check those sites out....but like I said, it was to show what was going on with the amps when throttled, the application used for and what it does to the duty point as there is a lot going on.
Its all good, I realize you do have a knowledge of the subject, and it seems we are "preaching to the choir" here and have probably scared off JVJordan. You are correct, the BEP is not the end all give all and other design considerations need to be taken into account, but its a starting point and where one would want to be in the best case scenario.
I do hope the big picture I was thinking wasn't lost in all this, in getting it right the first time makes it easier in the long run, which would start by people looking for those curves AFTER they design thier plumbing. Which is funny, being these pumps can literaly be called the "heart" of your system, very little is spoke on how to select a pump step by step, as compared to lighting.
If you get a chance, check those sites out....but like I said, it was to show what was going on with the amps when throttled, the application used for and what it does to the duty point as there is a lot going on.
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JMaxwell
Most Interesting
How about an opinion on this? I could use the help.
http://www.reefcentral.com/forums/showthread.php?s=&threadid=1370165
- JSM
http://www.reefcentral.com/forums/showthread.php?s=&threadid=1370165
- JSM
ReefEnabler
Premium Member
Heres a good question related to efficiency
I know that the Darts and Snappers etc have a 2" threaded intake.
how important is it for the bulkhead to be 2"? Or would a 1.5" bulkhead work if the plumbing increases to 2" right after?
I have a snapper for my frag tank and fuge. I currently have planned to use 1" plumbing (already got the ball valves for this). I checked on the RC headloss calc and since I'm pushing water up 6.5 feet, increasing to 1.5" plumbing would dramatically increase flow rates.
Would increasing the plumbing to 1.5" for most of the vertical run still have positive effects, even if the valves near the end are still 1"???
Thanks for and tips!
ryan
I know that the Darts and Snappers etc have a 2" threaded intake.
how important is it for the bulkhead to be 2"? Or would a 1.5" bulkhead work if the plumbing increases to 2" right after?
I have a snapper for my frag tank and fuge. I currently have planned to use 1" plumbing (already got the ball valves for this). I checked on the RC headloss calc and since I'm pushing water up 6.5 feet, increasing to 1.5" plumbing would dramatically increase flow rates.
Would increasing the plumbing to 1.5" for most of the vertical run still have positive effects, even if the valves near the end are still 1"???
Thanks for and tips!
ryan
