# Best way to throttle back pump?



## playthecello (May 14, 2009)

Hello fellow DIY-ers,

After reading and being totally inspired by xmuller's pvc pipe canister filter, I grabbed some paper and started sketching up copy-cat plans for my next summer project. I'm thinking about "borrowing" his basic canister (and genius media basket) design, but instead of mounting the pump inside the canister lid, I want to use an in-line pump. Then while I'm at it, I figure it can not only power the filter, but also a heater module, my Gamma uv sterilizer and (if I have enough space) a co2 reactor. (Ambitious, yes, but I'm going to have a lot of free time this summer that I need to fill.)

I'm assuming that having all these in-line stages will create a fair bit of head pressure on the pump (probably a Quiet One, of TBD size), but my tank is only 29 gallons, and getting a bigger pump to compensate for the head will probably end up turning the water in my tank over a few thousand times per hour (I exaggerate slightly.)

My plan is to get a "big" pump along with a flow meter, and dial it back to the 150-200 gph range, thus leaving the possibility of getting a bigger tank without having to re-build everything. How have people done this? A ball valve seems like the obvious answer, but doesn't a ball valve reduce flow by increasing the head resistance? That seems like a waste of energy to me. What about wiring it into a rheostat/dimmer switch? If one of them can dim the 500 watts of floodlights in you kitchen, it should work to slow down a 50 watt pump, right?

Thanks!

PS - Would you recommend putting the pump before all the stuff, after the stuff, or does it not make a difference?


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## redman88 (Jan 6, 2009)

i have of recirculating the water through the filter, by diverting after the pump have a ball valve on the dirverson


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## nokturnalkid (Feb 27, 2007)

I don't think that reducing the power going into the pump is a good thing, might do more harm than good. Even if you had a 1000gph pump, all that in-line stuff will help diffuse all that extra power$ in the end, you might end up with only 400 gph which is prettty good flow. I have nearly 800gph in my 30g. Also, to further help flow, I would put returns on both ends of the tank. Definately though, put the pump before anything. You don't want to starve your pump of water when you filter starts clogging up. Hth....


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## TAB (Feb 7, 2009)

putting a valve on the out put of the pump is the best method. in some cases it will actually result in less power used.


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## intothenew (Aug 1, 2008)

A by-pass circuit would be my recommendation. 


We have all at some time clogged the inlet on a vacuum cleaner. What happens? There is a noticeable change in the speed of the "pump", albeit air pump. This same phenomenon happens when you restrict the outlet. This can be explained by understanding mass flow. No air is entering or existing the system, therefore the "pump" is simply idling, and only moving the small amount of air trapped in the "pump" housing. Power consumption is reduced, you might think this to be a good thing. This can only be applied to non positive displacement pumps.


The trouble with that scenario is the lack of mass flow. These units have been designed such that mass flow cools the "pump", and in most cases the "motor" also.

You can have your cake and eat it too if you design in a by-pass circuit. The "pump" will receive the correct amount of mass flow, and you can tune the throughput by how much you divert to by-pass.


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## playthecello (May 14, 2009)

Thanks for your input. I hadn't thought of a by-pass. I'll definitely keep that in mind when I actually get to constructing. I had been assuming that it would even be necessary in the first place, but now I'm not as sure. 

One more thought - would using two smaller (but equal) pumps on either side of the filter (and everything else) be more effective than having one large pump? One to push through, and another to push back up into the tank, instead of making one do everything?


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## JERP (Feb 4, 2003)

just use a larger outlet. A larger outlet will dilute the "thrust" of the water output.

A larger inlet can be used as well to reduce suction.


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## intothenew (Aug 1, 2008)

Here is a pdf for you to download. It makes for great bed time reading. Don't get hung up on the Church that this is from, the hymns ring true for us also.

One properly sized pump is the most efficient and cost effective way to go.


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## Diana K (Dec 20, 2007)

I have ball valves downstream from the pumps in the sumps of several tanks. 
The pumps are sized to be just a little bit too much, not way too much. 
The pumps are in the sump, after the filter media, but there is generous bypass if the filter media is ever plugged, so the pump will never starve for this reason. 
The sumps are supplied by self-restarting PVC siphons that simply refuse to work any faster, so the water return is slowed just a bit with the ball valve. 
I would recommend some mechanical filtering before the pump. It does not have to be very fine (fine media plugs up pretty fast). Things like Java moss, though, can wind around the pump parts and stop the pump. 
Outlets from these pumps are spread out so there is not a strong blast from a point source. I made spray bars. 

A more complex way to plumb this, but gives you more control is with a manifold after the pump. Each device you want to run has its own ball valve, so it can be on all the way open, or off, or anywhere in between. 
I am especially in favor of some sort of control over the UV sterilizer. These devices have certain optimum flow rates depending on what you are killing. To simply race the water through, full blast is to not allow the proper contact time so the organisms are not killed by the UV. A ball valve on each part of the manifold will allow you to direct the proper amount of water through the UV. 

After each device the water can be reunited or returned to the tank separately, allowing for gentler return flow, and more than one location for the return flow. 

Also, a manifold allows the pump to work more efficiently because it is not actually slowed down (possibly leading to over heating). If the flow is still too much then certainly one of the Tees can lead to a bypass or return loop.


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## playthecello (May 14, 2009)

Thanks and more thanks, everyone.

intothenew: Thanks for the link. I read (most of) the primer, and you're right, there's a lot of really useful stuff in there. 

Diana K: I really like the idea of having a manifold. I hadn't thought of needing different flow rates for different things. My UV is a 15 watt Gamma (a craigslist gem), which according to the chart is good for up to 700 gph for parasite control. I'm hoping to not have more than 250-ish total, so that shouldn't be a problem, but putting the co2 reactor on its own line might give me a little more control over how much ends up going into the tank. Soda bottle co2 + smaller tank = mind of its own, so any little bit would help.


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## macclellan (Feb 28, 2007)

You can dial in flow better with gate valves than ball valves.

Meh, I'm lazy. If I had a 30g tank, I'd just buy a used Rena XP1 for $50 and call it a day. Oh wait, that's what I did for my 30g. lol


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