Pump input sizing

[scottward]

Hi Guys,

I've been reading some very useful threads on here about selecting the size of input/output plumbing for pumps.

I have a couple of questions though:

1. When using an external pump, to drive water through, for example, an AM1000, I understand that it's better to upsize the plumbing on the intake side of the pump, as this improves the efficiency of the pump. An obvious question here - why did the manufacturers not upsize the intake of the pump if it works better with a larger pipe coming into it?

2. I have an Eheim 2217 and it came with all the hoses required. The intake hose for this Eheim is the exact size that fits the intake of the pump, it is not doubled (i.e. upsized). Does this mean that the Eheim 2217 (and others in the series) would also perform better with a larger diameter hoses on the intake side?

Scott.

 

[hani]

Am not sure i understand the question,but the intake on the 2217 is larger than the output.

 

[shoggoth43]

Usually the inlet size is "upsized" just for turbulence issues within the inlet pipes. There's no reason to upsize much, if any, beyond the provided sizes unless you're after every last shred of possible performance. Think of it like a car, there's no reason to modify your car for performance unless you feel you have to. It should otherwise work just fine as rated with the provided sizes.

-
S

 

[scottward]

Hi guys,

Thanks for the replies.

The input on my external water pump is 3/4", so I just bought some hose that fits this perfectly. From reading other threads, it's sounds like I should really be using at least 1" hose? Is that correct? If so, my original question still stands as to why the manufacturer wouldn't just make the input of the pump 1" anyway.

I suppose with the Eheim there is something 'different' about it making upsizing (i.e. larger than manufacturer supplied) of the input hose pointless?

Scott.

 

[shoggoth43]

I usually only see upsizing once you start hitting 1000+ GPH. Below that the only reason for upsizing I could see would be to reduce the effect of a kink in a hose or if you have several 90 degree fittings or something like that on your input. If it's just a straight Eheim cannister with the usual inlet/spraybar combo I wouldn't even worry about it unless you have some tight bends in the tubing. Also, be aware that some of the larger tubing sizes are actually easier to kink compared with the smaller ones. The 1" size you can get reinforced but it's something like 2$ a foot, so it's not cheap.

-
S

 

[scottward]

Ok, fair enough with the Eheim.

Regarding external water pumps in general, that are connected inline, so my original question 1 - the pump I have has an inlet to which I can fit 3/4" tubing. From what I've been reading, it sounds like I would be better fitting at least a 1" line to the inlet of this pump (only going to 3/4" right where the connection take place).

Is this correct regarding upsizing the inlet plumbing or am I just confussed? ;-)

Scott.

 

[jonny_ftm]

Outlet in Eheim pumps is smaller than inlet. Of course, tubing is same id, but the outlet is much more restricted on its end than inlet, which gives the needed difference. Above a certain level, the pump won't give you more flow despite all the increase in inlet size. I doubt modifying inlet size tubing ID will have any impact unless, like shoggoth43 said, there are many resistances on the inlet path (90° elbows, long tubing, many Y...). The already open end of inlet is giving all the needed flow.

Also, if you put a foam on inlet to avoid shrimplets and small fish being sucked, an increase in inlet tube ID could be of some help

 

[shoggoth43]

Correct regarding upsizing. Again, IF you feel the need to do so. If you have a 3/4" inlet and you run a short straight pipe/tube right to it, then you likely won't see much of an improvement. If your inlet has some gyrations and a 90 degree bend or two before the pump inlet, then upsizing is probably not a bad idea although you still may not see much in the way of improvement.

-
S

 

[jeremy v]

Scott,

I think your eheim 2217 should be fine the way it is. There are several things to think about when sizing a pump intake line. The first is making sure that the water in the intake is not going so fast as to cause a lot of resistance on the pump from the friction of the pipe itself. That is usually prevented by making the intake one size larger than the output, whch yours is. Intake friction causes the pump to have to spend a portion of its energy pulling water into itself in addition to pumping out water instead of only pumping out water. This extra energy needed to pull water into the input reduces efficiency and overall flow rates. The second thing to think about is aesthetics. People like to have the intake lines in their tanks as small as possible to minimize in-tank clutter and visual distractions. The third important factor is that it is good to have an intake line that isn't too large when the water going through it hasn't been filtered first. The water needs to be fast enough to prevent any air bubbles or debris that may enter the intake line from settling out or staying in the intake line and blocking flow. If the flow is not fast enough a leaf or air bubble that gets in there may just sit in the intake because the water velocity isn't fast enough to suck it through the intake and into the filter media. The fourth important aspect comes in to play if you ever turn your eheim off and drain your tank for a water change etc. and the water level goes down low enough to cause the siphon to be lost on the intake line. If your intake line is too large in diameter the eheim might not be strong enough to automatically recreate the siphon when the pump is turned back on after refilling your tank, or more likely it might not be strong enough to pull that last bubble of air out of the hose at the high point where the intake line goes over the back of the tank. If that bubble isn't pulled out it then becomes a restriction to flow and you are right back where you started.

Your situation with an eheim 2217 is also different from many of the other applications where intake upsizing has been discussed and recommended. You have a canister setup which means a closed system, unlike something like a sump. You have the benefit of having the entire difference in height of the water column from the water level in the tank down to the top of the canister filter (most likely 3-4 feet) helping (since there is a vacuum on the intake line) to push water into the canister filter for you via gravity. That is a significant factor and it is what allows you to get by with a smaller intake pipe than you would need with the same pump on say a sump filter where there is only a foot or so of water pressure pushing the water into the intake. The greater the difference in height between the top of the tank and the top of the canister filter the smaller the intake line diameter can be and still be very efficient.

I would leave it alone. The stock setup is not the ideal in every way, but it is a well balanced compromise between all the factors that are important to most. Your losses are minimal anyways.

Have a good one, Jeremy

 

[scottward]

Hi Jeremy, thanks for the info about the Eheim.

Regarding external pumps, used 'in-line', what is the general consesus regarding input sizing on those?

Scott.

 

[shoggoth43]

For closed loop systems, there's not much difference than with the Eheim. For the open systems like a sump, pretty much what's been said. If you really want to minimize the issue, get a submersible pump and toss it in the sump and you'll have as much water flow to it as you can get as long as you don't suck air into it by letting the water level get too low. If the price difference is minimal to feed the pump, consider the upsize for a future upgrade path to a larger unit.

Minimize any major bends or kinks in your plumbing. If you can avoid flush 90 degree fittings do so. Two 45 degree fittings will generally come close to a 90 degree fitting in friction losses depending on diameter and you end up with more fittings to potentially leak. Better yet are the larger radius turn fittings if you can find them, or spaflex or other tubing for sweeping turns. Avoid T fittings if at all possible. Y or cone splitters are better if you need to break off for additional branches.

If you find you need to reduce water speed but do so without restriction, a 90 degree, or pair, is a good option.

-
S

Hi Jeremy, thanks for the info about the Eheim.

Regarding external pumps, used 'in-line', what is the general consesus regarding input sizing on those?

Scott.

 

[scottward]

Thanks guys, some good info there for me.

Scott.

 

[Left C]

Another thing to consider when thinking of different diameter (or radius) pipes is that the difference in area changes by the square of the radius. So a small increase or decrease can make a big difference in flow.

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