Restricting pump lowers power consumption?

[Netta Fish]

I have read a couple reviews on pumps and found out that using a ball valve to restrict flow will also lower the power consumption. Does making your pump work harder save electricity? and if so how?

 

[mrvoodoo]

umm - I work HVAC energy field and that strategy does not work on large industrial pumps - no idea why it would on a smaller pump for the aquarium. Like you said, it's working harder. For our industrial pumps you use a differential pressure reading to run a variable drive to slow the pump down which saves energy, if we could save it by valving stuff off - we'd definitely be doing it.

Pump Power Calculator

When you increase the resistance of the fluid leaving the pump, you're basically increasing the head "pressure" - it's like adding another 5-10 feet of pipe height to what you're pumping. If you use that calculator and for ease of use, just change the head figure from 33 to say 66 - which would partially simulate closing a valve down. Watch your power output for both your hydraulic side and your shaft side increase.


Now saying that... it is possible that a larger pump can run more efficiently with a higher head than your smaller pump with a smaller head. So to get your flow where you'd need it, you would have to valve it off a bit and in the grand scheme of things possibly save energy. But a lot of that depends on the pumps themselves at their sizes. I'd personally get a pump that will run your flow at the rate you want it against the head/height of your lines into your tank. That's going to probably be your best energy efficiency.

 

[Netta Fish]

Yes maybe not Industrial pumps but ones in the 1000 gph range for aquariums there may be a difference now I cant get a custom pump to do what I want so I have to compromise. My only question is how this happenes.

This article has pictures to show it
http://www.reefcentral.com/forums/showthread.php?t=1822299

 

[subielover]

It will damage your pump, you can put a valve after the pump to limit the flow and no harm will be done, but by limiting the flow into the pump you will prematurely fry your pump.

 

[gar732]

I think it depends on the pump. Some will burn out if restricted too much. I think centrifugal pumps (or something like that) can be restricted and lower power consumption. This is just what I've read however.

 

[gar732]

+1 restrict on the output side

 

[LegoZ81]

the more restriction (output side) on my Hammerhead gold the lower the flow and power it draws. fully closed output is something like 220w full open is like 280w.
I can pull hard numbers tonight if someone wants....

 

[bct15]

The pump will usae the same amount of power to move less water when throttled down. When you are using a ball valve or any other flow restrictor to reduce flow all you are doing is increasing K, the loss coefficient, (basically increasing the head pressure or the amount of work required for the pump to move a given volume of water). You are not reducing the amount of power being used by the pump, to do that you would need a ball valve on the power cord .

If you were in a way able to somehow reduce the head pressure the pump might use less power to move the given water volume, that is why a larger pump (rated at a higher flow rate at a higher head) might be more efficient than a small pump to move a given water volume. The larger pump may be so much more efficient that it can be throttled back and still more efficient than the small pump...if your pump is highly over rated you might gain a little efficiency by throttling down since you will not lose any performance by throttling it down, but I'm not sure on that.

You should not restrict flow entering a pump, that is risking damage. Pumps often depend on the pressure drop at the inlet to create flow and if that is tampered with you are risking damage. Pumps are designed to operate with an unrestricted inlet.

 

[Troylee]

Couldn't have said it better.... When injecting air into a pump "skimmer pump" it changes everything thou...

The pump will usae the same amount of power to move less water when throttled down. When you are using a ball valve or any other flow restrictor to reduce flow all you are doing is increasing K, the loss coefficient, (basically increasing the head pressure or the amount of work required for the pump to move a given volume of water). You are not reducing the amount of power being used by the pump, to do that you would need a ball valve on the power cord .

If you were in a way able to somehow reduce the head pressure the pump might use less power to move the given water volume, that is why a larger pump (rated at a higher flow rate at a higher head) might be more efficient than a small pump to move a given water volume. The larger pump may be so much more efficient that it can be throttled back and still more efficient than the small pump...if your pump is highly over rated you might gain a little efficiency by throttling down since you will not lose any performance by throttling it down, but I'm not sure on that.

You should not restrict flow entering a pump, that is risking damage. Pumps often depend on the pressure drop at the inlet to create flow and if that is tampered with you are risking damage. Pumps are designed to operate with an unrestricted inlet.

 

[LegoZ81]

I'll take video tonight as proof, but in my experience valving back has reduced wattage draw on my hammerhead gold.
Here is a direct quote from Reeflo on the matter:
"If your pump is producing too much flow, you can reduce the flow by partially closing a
valve on the discharge line. Never restrict the inlet!!! Surprisingly, this will make the motor work
less and use less electricity!! This “valving back” simply causes the pump to operate further back
on its performance curve."

From:
http://www.reeflopumps.com/images/tips.pdf

 

[bct15]

People have a misconception about how ball and gate valves work. They work by restricting flow generally by reducing the area the water can pass through, not by reducing the amount of power to a pump. The increase in resistance to flow results in a lower flow rate at the same power rating. Anybody with an engineering background will know about loss coefficients, every single item in a piping system has one 90 degree elbows, 45 degree elbows, surface roughness within a pipe. Each of re three previous listed items have constant loss coefficients, with the 90 elbow being the highest, followed by the 45 generally speaking. When planning a massive fluid system all fittings must be taken into consideration and pumps must be placed in series, parallel, or placed within the piping system and sized accordingly. A gate or ball valve has a variable loss coefficient that changes as a function of how open or closed the valve is. These valves serve as a means to control flow, and the loss coefficient is very difficult to estimate but there are tables with values for valves at certain positions (open, 25 percent closed, half closed, etc).

With your case, most pumps have a peak efficiency range for a given head pressure. This is not the same as the peak flowrate. With your pump wide open you may be outside if it's peak efficiency range (meaning your pump is over sized for your application). By throttling back and raising the head pressure, you may actually be bringing your pump into it's peak efficiency range (where your pump motor is designed to operate). Which might be why you are seeing a decrease in power consumption, where you are most likely still getting the same amount of flow. This is not always going to be the case for every pump and every situation.

Troylee you are right, when injecting air or any other compressible fluid...standard incompressible fluid dynamics may not always be the governing case.

 

[Netta Fish]

Everyone seems to be missing the point.... Its true on most pumps ... Now what's the reason behind it

 

[mrvoodoo]

With your case, most pumps have a peak efficiency range for a given head pressure. This is not the same as the peak flowrate. With your pump wide open you may be outside if it's peak efficiency range (meaning your pump is over sized for your application). By throttling back and raising the head pressure, you may actually be bringing your pump into it's peak efficiency range (where your pump motor is designed to operate). Which might be why you are seeing a decrease in power consumption, where you are most likely still getting the same amount of flow. This is not always going to be the case for every pump and every situation.

This is most likely the case if you do see any energy reduction by closing off the valve on the discharge side

 

[iani]

It is true with reeflo pumps, I am not sure if it is true with others.

 

[returnofsid]

Some pumps can be restricted, without any harm, AND save power consumption, BUT some cannot. Some pumps, when restricted, will run at a higher temperature, decreasing efficiency.

Ampmasters are one that are able to be restricted, and as restricted, consume less power.

 

[AZDesertRat]

ALL centrifugal pumps can be restricted on the dischare side without harming the pump and it WILL reduce the power consumption. This only applies to centrifugal pumps and most all aquarium water pumps are centrifugal pumps.

Its hard to grasp but read up on Bernoulli's Theory and The Laws of Affinity. Basically what it is is that by restricting the flow you are reducing the amount of work being performed thus reducing the power consumed. It also usually reduces the corresponding heat the pump produces since heat is directly tied to power consumption.

 

[mrvoodoo]

Eh... I got myself confused on this.

The restriction lowers the flow, reducing amps and thus power consumption - but this by no means is increasing the pumps efficiency (which is what I was thinking about). Efficiency is the pump's ability to put out x amount of water with y amount of energy. Creating a restriction in your line will reduce the amount of energy you're using, but doesn't mean the pump is running efficiently (valve it all the way off and you'll still be using power not nearly as much as wide open but you won't be getting any flow)- just means you're running a pump that's too big for what you were needing. It could mean better power bills though.

For us hobbyists I'll give this example:

We want to achieve 500 gallons of flow through our pump so we have a few options. Option 1 buy a pump that produces 500 gph from Dinga Donga incorporated that produces 500 gph at 15w. Option 2 buy a pump that produces 750 gph from WillyWalla Pump company that produces 750 gph at 15w. We can then restrict flow, slowing down the impeller - reducing amps - lowering power consumption, to achieve our 500 gph at say 12w. We've taken a more efficient larger pump and restricted it to the flow we need and got fewer watts than the pump that at its maximum puts out our needed flow.

The absolute best option for us is to find the pump that is most efficient at the flow we desire - not to buy a 500gph pump and sacrifice the flow we need to save a few watts, but to find the right pump. For you it may be finding the 500 gph pump from WillyWalla Pump Company that's running at 12w, or if it's out of stock go with the 750 and reduce it.


--------------------

example regarding efficiency:

PumpX restricted @ 500GPH 12watts (41.67gph per watt)
PumpX restricted @ 550GPH 13watts (42.3gph per watt)
PumpX restricted @ 600GPH 13.5watts (44.4gph per watt)
PumpX wide open @ 700GPH 16 Watts (43.75gph per watt)

You can see by the numbers that 600GPH is the most efficient. A pump's curve chart can help determine where this sweet spot is.

Technical Resource Library from Cole-Parmer
pump curve

Basically, pumps are typically going to be most efficient when there is some restriction because the pumps are designed to push against so much head pressure. Some pumps are going to be efficient with just a few feet of pipe, others need more pipe to hit their sweet spot, or some valve restrictions.

Here's my recommendation, buy a pump that is slightly oversized for 2 reasons:
1. It can run more more efficiently with some added restriction
2. Overtime you'll have some build up or wear and tear, you can then reduce your restriction and match your desired output.

My other recommendation is to buy a pump with low wattage outputs, one designed to be more efficient... personally I'm really liking the reef octopus water blasters. I'll be buying one in the next few weeks. The energy output per gph seems to be much better than what I can find on the other pumps, which in the warranty period should pay for itself in power bills.

 

[Netta Fish]

Eh... I got myself confused on this.

The restriction lowers the flow, reducing amps and thus power consumption - but this by no means is increasing the pumps efficiency (which is what I was thinking about). Efficiency is the pump's ability to put out x amount of water with y amount of energy. Creating a restriction in your line will reduce the amount of energy you're using, but doesn't mean the pump is running efficiently (valve it all the way off and you'll still be using power not nearly as much as wide open but you won't be getting any flow)- just means you're running a pump that's too big for what you were needing. It could mean better power bills though.

For us hobbyists I'll give this example:

We want to achieve 500 gallons of flow through our pump so we have a few options. Option 1 buy a pump that produces 500 gph from Dinga Donga incorporated that produces 500 gph at 15w. Option 2 buy a pump that produces 750 gph from WillyWalla Pump company that produces 750 gph at 15w. We can then restrict flow, slowing down the impeller - reducing amps - lowering power consumption, to achieve our 500 gph at say 12w. We've taken a more efficient larger pump and restricted it to the flow we need and got fewer watts than the pump that at its maximum puts out our needed flow.

The absolute best option for us is to find the pump that is most efficient at the flow we desire - not to buy a 500gph pump and sacrifice the flow we need to save a few watts, but to find the right pump. For you it may be finding the 500 gph pump from WillyWalla Pump Company that's running at 12w, or if it's out of stock go with the 750 and reduce it.


--------------------

example regarding efficiency:

PumpX restricted @ 500GPH 12watts (41.67gph per watt)
PumpX restricted @ 550GPH 13watts (42.3gph per watt)
PumpX restricted @ 600GPH 13.5watts (44.4gph per watt)
PumpX wide open @ 700GPH 16 Watts (43.75gph per watt)

You can see by the numbers that 600GPH is the most efficient. A pump's curve chart can help determine where this sweet spot is.

Technical Resource Library from Cole-Parmer
pump curve

Basically, pumps are typically going to be most efficient when there is some restriction because the pumps are designed to push against so much head pressure. Some pumps are going to be efficient with just a few feet of pipe, others need more pipe to hit their sweet spot, or some valve restrictions.

Here's my recommendation, buy a pump that is slightly oversized for 2 reasons:
1. It can run more more efficiently with some added restriction
2. Overtime you'll have some build up or wear and tear, you can then reduce your restriction and match your desired output.

My other recommendation is to buy a pump with low wattage outputs, one designed to be more efficient... personally I'm really liking the reef octopus water blasters. I'll be buying one in the next few weeks. The energy output per gph seems to be much better than what I can find on the other pumps, which in the warranty period should pay for itself in power bills.

I'm waiting on a water blaster myself that's what's tarted this thread lol

 

[richardb]

if you were to do like i did and now i have no pics to show you what im talking about but you can buy a dimmer switch for lighting from your local home improvement store you can put that inline on the electric cord and you will be able to control your flow and electric consumption but i wouldnt do this if you have never messed with electrical devises before it worked well on my old pond pump it was just to strong for a 55 gallon

 

[Netta Fish]

Not a bad idea. I can do electrical work. but will it damage the pump in the long run?