180g Tank Build - 11 mos. and counting.

not sure but i have 2 darts running wide open on my current build so i will be interested to find out. honestly i dont understand the concept that throttling the pump back will make it use less watts. seems like if you throttle it back its putting more resistance on the motor which would increase the amount of current drawn. i mean you use more gas going up a mountain right?
can someone elaborate for me ?

Your analogy is flawed. Pumping water is much better related to hydraulics than gas motors. The impeller does not change speed or slow down to back pressure. By making the aperture (throttle back) smaller but keeping normal pipe size you are lowering the head pressure. That's the best I can describe it since I am not a engineer. We have a few of those mathematicians on here that can prolly get all fancy speak if they see this.

Pete could answer this one, I'd bet. Gotta get him over here on R.A. He just did a really nice plumbing presentation at our meeting last Wednesday. Here's the slides he shared with us: http://www.dfwmas.org/Forums/viewtopic.php?f=1&t=102856

I typed out an appropriate answer to your question, but the site logged me out and I lost most of the reply, so I'll answer much more simply and hopefully not loose a lot more time.

The simple answer is generally speaking (like I said I had a longer reply that explained the theory but I'm not retyping all of it at 12 am) (and some pump guru may tell me why this is an oversimplification but like I said, I'm not retyping the longer answer now) generally speaking a pump that has to be restricted to pump a specific flow at the dynamic head of the system (dynamic head is based on the plumbing parts in the system, total dynamic head is the dynamic head added to the actual head or height from the pump outlet to the highest point in the system) (if the outlet is significantly below the highest point it is possible to create a siphon which complicates the calculations) will have a higher energy usage than a pump that is chosen to specifically pump the desired flow at the system total dynamic head.

This is a generalization and many things come into play, efficiency of the impeller, efficiency of the motor, etc etc, but generally the pump that can produce more flow at the same head will have a larger motor and more electric draw...generally. If you have to restrict it, you will use more energy.

Some pumps can be adjusted electrically to spin slower, but if you spin an impeller that is most efficient when spun fast at a slower speed it won't be as efficient.

If you want specific calculations for your system to see which one is better, I'll need to know all the specifics of your plumbing between the pump outlet and the outfall of the plumbing system including the length and type of all pipe segments and the type and size of all fittings (valves, bends, unions, etc). This is assuming I can find efficiency curves for the snapper/dart combo pump. I'm pretty sure at one point in the past when I was considering that pump I found a pump curve, but I don't know about an efficiency curve.

Blakew

Okay, looked at ReeFlo website and I think you've got things backwards. The dart "wide open" would flow lots more volume than the snapper wide open, so you would want to restrict the snapper. Assuming you meant you wanted to compare the dart if it was restricted to the snapper wide open, then there's no comparison. The snapper uses less energy through out the entire range than the dart.

Only reason I see to put the dart impeller on is if you aren't getting as much flow as you want with the snapper, but then you're going to use more energy.

Blakew

Just reread my first post and it didn't make sense to me so I'll try again.

In the snapper/dart hybrid you have one electric motor that can use two different impellers. With the snapper impeller you can push between 300 and 2600 gph with a total dynamic head (tdh) of between 0 and 11-feet. With the dart impeller you can push between 750 and 4300 gph with a tdh of between 0 and 12-feet. Total dynamic head is the combination of the actual pressure created by the height of the fluid column over the pump and the pressure created by the friction of the fluid moving through the plumbing system between the pump and the outlet.

What this means is that if you plug the pump in with no plumbing attached, the inlet submerged and the outlet exposed to air the pump would push out 2600 gph but the column of water would just barely clear the outlet. If on the other hand you attached a single stick of 6 or 8-inch pvc pipe to the pump (the friction losses would be very small in that size pipe and all you'd be pushing against is the pressure of the column of water in the pipe) the pump would push about 300 gph at 11-foot of height.

Since most systems aren't a straight piece of pipe and have bends, unions etc inline, the maximum amount of fluid (saltwater in this case) the pump can push is limited by the height it's pushing water and the amount of friction losses in the pipe and fittings.

When you add any restriction (bend, wye, union, tee, or valve) you increase the friction in the system (dynamic head) and reduce the flow.

With the dart impeller you definitely would need to install a ball valve and partially close the ball valve, increasing friction (increased dynamic head) and reducing flow to reduce the dart flow to similar flows that the snapper can achieve. With the dart impeller the pump draws more power through out it's operating range than the pump with the snapper impeller, so you'd use more energy to restrict the dart down to snapper type flows.

http://www.reeflopumps.com/images/60...PER-Hybrid.jpg

Blakew

Blakew you are missing what people are referring to, It clearly say that the pumps can be valved back and it will not only reduce flow, but lower watt usage.

No, I don't think I missed something. By partially closing a valve in a system, all that's being accomplished to create more resistance (more friction losses or total dynamic head) in the system. The higher tdh moves the pump to a different point on the pump curve. You aren't changing the characteristics of the pump curve. You'd have to use a different impeller or a different motor (or a variable speed motor) to change the pump curve.

Let's use ReeFlo's pump charts (which are pulled from an actual pump curve by the way and printed in chart form for ease of understanding) to see how ReeFlo's statement and my statement are both true and backed up by their own documentation. If you look at the chart I posted, ReeFlo says at 4-foot of head the pump with the Snapper impeller uses 105 watts. That same configuration uses 100 watts with 7-foot of head. In ReeFlo speak, by valving the pump back, or in engineering speak, by creating more total dynamic head, the pump uses 5 less watts. Note, it does not say valving back the pump will give you a different pump curve.

So even if you increase the head when using the Dart impeller you still stay on the Dart's pump curve and at the Dart's lowest wattage usage you would still be using 137 watts. Much more than the Snapper's 105 max wattage usage.

Blakew

PS After looking at the Snapper/Dart's pump chart, I admit my generalization in my first reply last night was incorrect for the Snapper/Dart hybrid pump. According to ReeFlo's documentation the pump uses less energy at the edges of the pump curve. Must be something in the design of the impellers. Pretty much every pump I spec for sewage systems are more efficient in the center of the curve. ::shrugs::

Blake, this is what I am referring to which does not mention changing head or any other dynamic of your plumbing, it is only changing the aperture of the outlet of the pump.

"All of our pumps can be "valved back" as long as its done on the discharge line. It will not only reduce the flow, it will lower the watt usage and extend the life of the motor and seal!"

So according to this statement the, you can alter the efficiency of the pump "for the good or the bad" by valving it back. Good or bad because there is a point at which the ratio of flow and watt reduction will cause lowered flow without lowering wattage.

I can read that...you're misunderstanding the statement, and you misunderstand how pumps work. As I said "Valved Back" simple adds head to the system. I don't care that it doesn't say that, that is what it does. The chart I posted shows that indeed at a higher head the pump uses less wattage, but it doesn't change the pump curve and somehow get the Dart to use less than 138 watts period. You absolutely are not changing the efficiency of the pump, you absolutely are moving the pump to a different point on the pump curve PERIOD!

You don't understand what you think you understand about how pumps work. "Changing the aperture of the outlet of the pump" will increase head, plain and simple. You can't separate the variables, they are all tied together. Head determines flow and the motor/impeller design determines the wattage used to produce a specific flow against a specific amount of head.


Let's try this a different way.

Let's say there is a system where the total dynamic head of the system is 7-feet. If you use the pump with the Snapper impeller at 7-foot of head the pump would produce 1500 gph flow and use 100 watts of power. If you "Valve back" the pump to say 9-feet of head, the pump would only use 95 watts but you'd only be gettting 900 gph flow. So to save 5% on the electric usage you've reduced the flow by 40%. 40% reducing in flow for 5% savings in electricity is not more efficient.

So using the same pump on the same system but changing the impeller to the Dart impeller, at 7-foot of head the pump would produce approximately 2700 gph using 174 watts. If you "valve back" this pump to say 9-feet of head, the pump would use 168 watts but you'd only be getting 2100 gph. If you "valve back" the Dart version all the way to 1500 gph to match the pump with the Snapper impeller at 7-feet of head, you'd still use 155 +/- watts of energy. 155 watts is using less than 174 watts as per Reeflo's claim, but it is still significantly more than the Snapper's 100 watts to produce the same flow.

Blakew

Maybe what's being misunderstood is what "valved back" means. What they're referring to is closing a valve by a certain amount.

http://www.engineeringtoolbox.com/mi...pes-d_626.html

From the engineering tool box website...the "minor loss coefficients" for a gate valve are as follows: fully open - 0.15, 1/4 closed - 0.26, 1/2 closed - 2.1, 3/4 closed - 17. To determine the head loss (or increase in total dynamic head) by partially closing the valve, you multiply those coefficients by the flow (to use this formula the flow has to be converted from gph to ft/sec). The point is, as these coefficients show, as the valve is closed the friction head loss increases significantly adding to the total dynamic head of the system. This addition of total dynamic head reduces the available flow and in the Snapper/Dart hybrid pump it also reduces the amount of electricity used. However, the reduction in flow is much larger than the reduction in electric usage and is therefore less efficient.

Blakew

Blake, obviously you are passionate about this and you are in fact missing the point. I am not an engineer and neither was that statement from Reeflo intended to be too an engineer. What that statement is meant for is to tell a reefer that by valving back the pump you are not going to increase heat or watts used. Regardless of pumping water to the toilet or the top of the empire state building. The efficiency is not referring to the amount of water moved, it is referring to the amount of electricity being used while the pump is plugged into power. So if you valve back this pump, it is going to use less electricity, end point. The pump people are not saying that the pump will be more efficient in moving water form one place to another, they are saying that valving back the pump uses less electricity.

I hope this is more understandable. I wan't trying to piss you off, I was trying to define the simple statement on the instructions of the pump.

Micheal, what I'm passionate about is being told I'm wrong by someone when all I'm trying to do is share useful knowledge with fellow reefers.

I am an engineer and I am not missing the point. The original poster asked ...

I'm trying to figure out whether to use the snapper changeover on my reeflo pump and throttle it back or use the dart and let it run more wide open...

My reply was that at no point will the Dart ever use less energy than the Snapper. You've tried multiple times to tell me I'm wrong and I've tried multiple times to explain why I'm not wrong.

So if you valve back this pump, it is going to use less electricity, end point. The pump people are not saying that the pump will be more efficient in moving water form one place to another, they are saying that valving back the pump uses less electricity.

I completely agree and even provided an example that show how much less power the pump would use based on a real world example and the data in their published pump table. However, as stated many times in my replies, at no point of valving back the Dart pump will you get less than 138 wattage of electric draw, which is 33 watts more than the highest wattage draw on the Snapper.

I was trying to define the simple statement on the instructions of the pump.

I know you think that's what you're doing, but all you're actually doing is providing misinformation. And as I said before, you don't understand what you think you understand.

In one of your previous post you made the following statement:

does not mention changing head or any other dynamic of your plumbing, it is only changing the aperture of the outlet of the pump.

That is absolutely an incorrect statement. What you don't understand is that changing the aperture of the outlet of the pump ABSOLUTELY DOES CHANGE THE HEAD in the plumbing system. I've tried to explain some of the theory but you're hung up on this idea that head is strictly related to height and it isn't. Head, in pumping terms, is a combination of pressure from the height of the fluid and the friction losses in the plumbing system. By reducing the aperture of the outlet of the pump you are absolutely increasing the friction in the system. Increased friction adds to the "total dynamic head" of the system. When pump manufacturers publish flow values at certain head values (ie 1500 gph at 7-foot of head) they are not talking about the height of water the pump is pushing, they are talking about total dynamic head which includes friction losses in the system.

As I've said multiple times, head, flow and wattage draw are tied together in a pump system. You can't change one without changing the other.

Your statements on efficiency are also wrong but you don't want to learn anything so I won't bother.

Blakew

Here is a quote from Reeflo's website backing up my statements.

4. 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.

There are two elements that cause pressure requirements in your system; vertical lift and “FRICTION LOSS”. Simply stated it is the pressure created by trying to squeeze large flows
through a narrow opening (think bar straw). There are two important aspects 1) It matters the
length of the narrow line (1” bar straw vs. 10” bar straw) and 2) Friction loss increases at an
increasing rate when either flow is increased or pipe is narrowed. The narrower the line the more
the pump has to work (think clogged ateries and your heart).

Here's the link to the Reeflo tips and troubleshooting pdf...http://www.reeflopumps.com/images/tips.pdf

Blakew

Ok, Blennyman, what is your question based on? Blake is correct that you cannot make the Dart version consume less power than the snapper. You can however lower the consumed wattage on the pump, just not to the point where it would be better to throttle back the dart instead of using the snapper. I agree with Blake in his point about the flow vs power consumed.

You can however lower the consumed wattage on the pump, just not to the point where it would be better to throttle back the dart instead of using the snapper.

Now we're on the same page. Absolutely agree with this statement.

More to the possible intent of the original question, based on Reeflo's published data, you can reduce the wattage consumption on the Snapper from a max of 105 watts to a minimum published wattage draw of 70 watts, if you're willing to reduce the flow from 1500 gph to 300 gph.

The only way to know absolutely for sure how much power you're saving is to partially close a valve on the pressure side of your pump and check the wattage draw with a kill-a-watt (you could come real close by doing some calculations). If you're willing to have less flow, you can save some energy. The reduction in flow will be much greater than the reduction in energy costs, but you will save some energy.

Blakew

Not to beat a dead horse, but the title of the blog was "Tuning a Pump for BEP (best efficiency point).

If the goal and intent of the post was to find the point of lowest energy usage then as stated above stick a valve inline and dial back the flow to the minimum flow you're willing to live with.

If the goal and intent of the post was indeed to find the point of best efficiency, that's a horse of a different color.

Pump efficiency in simple terms is how much of the energy put into the pump is converted into useful work. To find the point of best efficiency you'd need an efficiency curve, but we can estimate that point by looking at how much flow the pump is producing.

For the snapper, comparing the first two published data points from the pump curve we get a 14% reduction in flow for a 105% increase in wattage used (not very efficient going from 0-foot of head to 2-foot of head, for the next two data points we get 16% reduction in flow for a 105% increase in wattage used, for the next two data points we get a 20% reduction in flow for a 5% reduction in wattage used (now we're going in the right direction), for the next two data points we get a 40% reduction in flow for a 5% reduction in wattage used (wow fell off the earth on that one), for the next two data points we get a 67% reduction in flow for a 26% reduction in wattage usage.

Based on this information the most efficient operational point is going to be between 1900 gph and 1500 gph. If your current set up is pumping more than 1900 gph and you're willing to live with the reduction in flow, you could dial the gate valve back until the pump was producing somewhere between 1900 gph and 1500 gph and you'd be in the ball park of the most efficient operational point for that pump with your system.

Blakew

See I think that trimming, might be what he was looking for, but, blenny hasn't posted since the first. It seems as though the manufacturer even recommends trimming the output to save seals and energy, like its not meant to be wide open. Kinda like exhaust for a car is supposed to have some resistance.

The statement from the manufacturer is a sales statement. What I mean is they're saying to someone who doesn't need 1500 gph flow through their overflow, "you can still buy this pump and just strict the output so that it's only flowing 1000 gph". In the "real" pump world it's a bad idea. You only get the pump that's big enough to do what you need it to do and no more. What I mean is, if you need 1000 gph at 7-feet of head you don't buy a pump that produces 1500 gph at 7-feet of head and restrict the flow until you get 1000 gph at 8.5 to 9 - feet of head. The pump that produces 1000 gph at 7-feet of head will in almost every case use less energy than the pump that produces 1500 gph at 7-feet of head (even if the second pump is restricted so that it only flows 1000 gph).

As for the car exhaust comparison, you are correct, without some restriction the pump will over rev and you risk cavitation, but just like with a car exhaust if you restrict the exhaust flow too much you loose performance. That's why "johnny go fast types" pull the factory exhaust off of their sports cars and add aftermarket exhaust that are less restrictive. When they do, they get better performance.

Blakew

i curious to find out how it helps save the seal maybe less vibration? anyone know?