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Continuous Pump vs Timed Pump
http://byap.backyardmagazines.com/forum/viewtopic.php?f=1&t=2505		 Page 1 of 3
Author:  gemmell [ Dec 6th, '07, 13:19 ]
Post subject:  Continuous Pump vs Timed Pump
I did a quick search of the forums and whilst there is a fair bit of stuff scattered through the forums, I didn't see something addressing this directly.



I'm designing my second system, and I was going to base it on the CHIFT PIST system. Basically I was going to have a continously on pump in the sump, pumping into the main tank. The main tank would then overflow into the growbeds.

However, after some recent discussions, some people have said that having a big pump on a timer is better. Really, for my purposes they would have exactly the same effect - a big pump could just turn on for 3 minutes and then the beds could fill slowly from the overflow.

Gah, a picture, a picture!

Attachments:
File comment: For a Continuous Flow, I have a smaller pump in the sump, and whatever it pumps up ends up overflowing out in to the beds. Because it's continuous, there is no level change in the main tank.
ContFlow.jpg
ContFlow.jpg [ 20.14 KiB | Viewed 5995 times ]
File comment: For a timed flow, I have a big pump in the sump, which pumps for a couple of minutes then turns off. The tank then overflows until the water level drops below the outlet.
TimedFlow.jpg
TimedFlow.jpg [ 19 KiB | Viewed 5999 times ]
Author:  gemmell [ Dec 6th, '07, 13:29 ]
Post subject:  Re: Continuous Pump vs Timed Pump
Seems to be a fair bit of support for the big pumps. But I'd lose my "CHIFT" (Constant Height In Fish Tank) if I used this method. However some people are reporting that small pumps can get air locks etc and become unstable. My real question is who has used small, continuously on pumps to good effect in their system, and who has done one and then decided to replace it with a big pump, and why?

Here are some immediate pro's and con's:
If I used a small pump:
Pros
* I'd have a CHIFT (though I'm not quite sure why I like this - maybe I just like saying it :lol: ).
* No possibility that I could overflow the main tank / run sump dry
* Pretty good on a power out - so long as the sump is big enough, wouldn't lose any water.
* Good reliability
Cons
* Possibility of getting an airlock in the pump line and losing some flow - EDIT: Apparently this isn't a reality for a continuous flow pump.

If I used a large pump:
Pros
* Power of the big pump would flush the pipes of crap and air each time it turned on
* Also pretty good on a power out - so long as the sump is big enough, wouldn't lose any water.
* Good reliability (based on this thread)
Cons
* If my timer didn't kick in I may overflow the sump, if it didn't turn off I could run the sump dry or overflow the fish tank.
* Wouldn't have CHIFT (maybe fish like CHIFT?)
* MAY need a large spike of current when it kicks in, thus requiring more robust electrical gear
Author:  veggie boy [ Dec 6th, '07, 14:32 ]
Post subject: 
Gemmell - my system is as you describe. If you look at Ausyponics thread a few pages back I listed my advantages for using this type of system and autosiphons. I am happy with this system. The redundancy able to be easilly built in is a major pro in my view.
Author:  Sleepe [ Dec 6th, '07, 15:46 ]
Post subject: 
Gemmell

While you may have thought I had support for large pumps, because of the discussion on Kuda's system, it was only because of the way he had it set up. He is running header tanks and having to lift a lot of water a fair hight.

I have been running a smallish pump 24/7 on my pond, which has a waterfall and upper pond and stream for 15years. Only has to lift just over a metre so sensible for the system and only pulls 120watts, I have never had an airlock because it is a submersible and is just pushing (not pulling) water.

Even some of the smaller sump pumps now have vortex impellers and can handle small solids.

I do not like timers (sorry everyone) and would go with a float switch even on a continuous runner in a sump (just in case). You could pump dry on a continuous as well as a timed if there is a stuff up. Don't bother on the pond as the water has nowhere else to go but back down to the pond.
Author:  earthbound [ Dec 6th, '07, 15:56 ]
Post subject: 
I don't think that the CHIFT PIST design is much good for a large pump really, but I guess this would depend on the size of the system, and the size of the "large" pump.. This is based on my small system that used this style where I only had a small pump 1000L/h.

I guess there would be some many determining factors and one of the main ones would be how quickly you can get the water out of the fish tank and into the beds..
Author:  DownRiverDan [ Dec 6th, '07, 17:08 ]
Post subject: 
you could still have a CHIFT PIST and have header tanks like in Kudapacats system. then you could pump a very large amount of water very quickly into header then slowly drain into fish tank then to growbeds w/autosiphons then back to sump.

much simpler to forgo the expense and unknown reliability of timer and the more powerful pump and just use a pump thats slightly oversize than you need running continous IMHO

I have not experienced any airlocks at all in my system just a water lock due to stuck comet in the fish tank venturii
Author:  veggie boy [ Dec 6th, '07, 18:15 ]
Post subject: 
The best thing about a continuous CHIFT PIST system is that ability to use very cheap but reliable pond pumps. A large system can be run with just a couple of $35 pumps, with redundancy built in, in that if 1 pump fails the other will keep it running albeit at a longer cycling rate.
Author:  veggie boy [ Dec 6th, '07, 18:16 ]
Post subject: 
What I am saying is that I would not use a big pump for a CHIFT PIST system - I agree with Joel.
Author:  earthbound [ Dec 6th, '07, 18:37 ]
Post subject: 
Yeah, but you lose oxygenation and solids removal... Well, perhaps not as much with the CHIFT PIST style... But with the systems I'm doing at the moment there's something to be said for the drain tank and the second pump pumping back into the fish tank. With a venturi on the return line, and an elbow on the end of the return pipe you get great oxygenation and water movement...

But then my little system on the back verandah with a 4-5000L tank and tiny growbed on continuous flow, there's only a 60 watt pond pump and probably 15-20 kgs of silver perch in there... :?

Sooo many variables...
Author:  KudaPucat [ Dec 6th, '07, 19:32 ]
Post subject: 
My system is a hybrid.
It is a CHIFT PIST with a cyclical pump.
This is only so I can expand/downsize as necessary without replacing or altering the pump.
I hate timers. Time is unrelated to reality. If you get a blockage in my system, and use a timer, you will possible pump 1000L onto the ground!!!!!!!!
Sump floats are the way to go.

Regatrding float switches. I was talking to ss recently, and he said to me if you wanted to use two floats for a large hysteresis you'd need a micro. Which for some reason I accepted.

But after some thought it can be achieved with two float switches and a relay. I haven't drawn the simple circuit, but if anybody's interested I'll go to the effort ;-)
Author:  earthbound [ Dec 6th, '07, 19:38 ]
Post subject: 
Beware though, float switches can be very dependent on water volume in a system... This is the main issue I have with my first big system, if theres not enough water in the system, then the level doesn;t rise enough to turn the pump on..
Author:  KudaPucat [ Dec 6th, '07, 19:54 ]
Post subject: 
earthbound wrote:
Beware though, float switches can be very dependent on water volume in a system... This is the main issue I have with my first big system, if theres not enough water in the system, then the level doesn;t rise enough to turn the pump on..


I have tested mine extensively, and know it will work... under most conditions... startup conditions exist... not sure how to deal with them yet.
Author:  EllKayBee [ Dec 6th, '07, 19:54 ]
Post subject: 
Quote:
However some people are reporting that small pumps can get air locks etc and become unstable.


Gemmell, think you got it wrong here, the discussion on air locks was in reference to using a siphon to keep 2(or more) tanks at an equal height...I can't recall any other discussion on air locks being a problem with small pumps.....now I'll go back and read the posts following the above quote and prolly make a big **** of myself :oops:
Author:  KudaPucat [ Dec 6th, '07, 20:05 ]
Post subject: 
EllKayBee wrote:
Quote:
However some people are reporting that small pumps can get air locks etc and become unstable.


Gemmell, think you got it wrong here, the discussion on air locks was in reference to using a siphon to keep 2(or more) tanks at an equal height...I can't recall any other discussion on air locks being a problem with small pumps.....now I'll go back and read the posts following the above quote and prolly make a big **** of myself :oops:


Les he's referring to my system I think, the small pump wasn't enough to clear the airlocks caused in subsequent tank siphons.

A continuous pump wont allow airlocks anywhere. Whether it's big or small (unless it's turned off) but that's a startup condition.,.. if you need to bleed a line to start a pump only the first time, it doesn't matter too much.

My system and the discussion of airlocks, was to prime, or auto bleed my siphons using the pressure from the big pump... A smaller pump would suit my system better (as many have suggested) excepting for the fact that i plan to expand gradually (as the hip pocket allows)

Enough about me.

IMHO if you plan to expand, use a cyclical pump.
If you build a turnkey system that will be as it is forever:
use a continuous - or close to continuous pump
use float switches to cater for unforeseen problems.

That is my rule. (because I always think big, I will always use cyclical - I am inspecting my roof to see if I can put grow beds up there ;-) well I did consider it.)
Author:  EllKayBee [ Dec 6th, '07, 20:16 ]
Post subject: 
Gemmell - i use a small pump and have found them pretty reliable also

Hah!...see, told ya I would make a **** of myself....haven't read your thread fully KP
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