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NFT Pump Size

Posted by ethnobotany (My Page) on
Mon, Oct 8, 12 at 0:36

Hello all! I have started putting together plans for making my first NFT system and am of course going to need to purchase a pump. The gullies for the system are going to be 4'' x 4'' vinyl fence posts. There are 4 total posts and each are 3 feet in length. The height from where the pump will be situated to the top of the gullies is going to be about 2'.

Excuse me for being a bit of a noob when it comes to pumps. I really have no idea how to calculate the size pump I will need to power this system and need advice on how to figure out the pump I need.


Follow-Up Postings:

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RE: NFT Pump Size

When you say "NFT," do you mean like the lettuce growing machines that only dribble a little bit of water in one end of a precisely angled channel? If that's what you're making, a very small pump will work. That design does not require much water movement. You just need a thin sheet of flowing water on the bottom of the channel. That's your "nutrient film" of the NFT acronym.

Or are you building a machine like GH's aeroflow? That design is often called NFT, even though it is more of a hybrid design. The spray line has holes throughout the length of the channel, and the water level within the tube is adjustable. If that is your plan, then you want a bigger pump. A 350gph mag drive would work well. You want as much pump as you can get - up until the point that it starts to heat up your reservoir water. With a bigger reservoir to displace the heat, you can handle a bigger pump.


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RE: NFT Pump Size

Thanks for responding Cole.

I am doing the original NFT system and will need a water flow of 1-3mm in height, no 360 spray nozzles or anything like that for now. The reservoir will be about 28 gallons (overkill, I know) but it sounds like not only will a large reservoir be more pH stable, but it will also be more heat stable too as you have pointed out.

My only concern about a larger pump size is that the pump is only supposed to put out 1L/min at minimum and 2L/min at maximum according to a couple sources. Some of the pumps have knobs to adjust the flow though so I suspect that will give me the ability to adjust the rate to just what I need.

Do you think I could even get away with this 320 gph pond pump? (linked at bottom)

That one is only $22.99 shipped which is phenomenal given that the local Lowes or Home Depot sells them for more like double to triple the cost.

Here is a link that might be useful: 320 gph eBay pond pump


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RE: NFT Pump Size

I really like this,(QP12),pump. while is says its submersible only, I've used it externally without any problems (though not full time)
also, I really like these cheapies too.
remember, flow really isn't so much a concern, at least not too much flow, as long as the system is recirculating.
the trickiest part honestly is getting them to all flow at the same rate. you'll need a ball valve at each in line to adjust them plus a ball valve at a "T" before them to adjust the overall flow.
Of course if equal flow isn't a major concern, let me know and I'll post pics of how I divide my pump source between two troughs. (pretty equally)


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RE: NFT Pump Size

I agree with Griz that too much flowing water is not a concern. Roots will love it.


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RE: NFT Pump Size

Thank you guys for the help. Grizz, the QP pumps look like a bargain and of better quality than the eBay pumps. Will be looking into purchasing the smaller model. Anyways, I will post a new thread with the system once it is all up and running.

As for now, I will be spending my time figuring out how to make temporary waterproof seals with the caps for the vinyl fencing to make this unit easily cleanable.


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RE: NFT Pump Size

Just use silicon to seal it.
Also, make sure where your input line enters the channel, the flow is directed down the trough (in the direction of the slope) as opposed to just entering vertically and hitting the opposite face of the channel. this will greatly reduce how much liquid actually hits the end of the channel.
At the other end (outflow end), do you need a cap or will the nutrient simply flow out the end?


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RE: NFT Pump Size

fwiw, I like JB-Weld to seal the ends. Rough up the plastic with a wire brush first. Be aware that you're never getting it unglued, though.


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RE: NFT Pump Size

Grizz, I plan to have the system closed at the ends. Reason being this will be inside in the winters and my cat for some reason is highly attracted to moving water (he loves to watch and play with my drip system).

I really want to try to make the system easy to open up and clean because I plan to use it for at least 2 years. At least. So even if that means siliconing the caps and then ripping apart and re-sealing after every crop I am willing to do it.


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RE: NFT Pump Size

You should do some reading about fluid mechanics or your next posts will be about pressure. Learn to read pump curves before buy a pump/build a system.

Pump curves plot flow vs pressure

Photobucket


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RE: NFT Pump Size

Nice picture willard, although it has me confused.

So I plan to use 1/4'' irrigation tubing for the inlets, and the maximum distance the water will travel from pump to the gully will be 2.5'

Do you know of any good resources that I can read to help me understand more about pressure/tubing/matching a pump?


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RE: NFT Pump Size

For what you're doing, that is more info than you need. You need to know what the flow (gph) is at the height above the water where it will discharge (head).
the flow given on a pump is at a head of 0feet. at the max head, the flow is zero.
As soon as your water leaves the pipe it has no pressure, but does have velocity (as dictated by the head it discharges at).
There is actually an equation that will allow you to know the flow at any height between 0 head and max head. I'm not at work right now, but will try to post it monday. (or search the forums as I know I've discussed it before)
you can probably do a google search for quiet pumps and get a chart similar to the one above for the specific pump you're interested in.
All that being said, if you get into a larger scale hydro system, what willard posted becomes much more important.


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RE: NFT Pump Size

Alright, so erm.... I jumped the gun I think.

Was searching eBay/Amazon for pumps and came across one that
cost $60.00 on eBay, yet the markdown was to $19.99 shipped
through Amazon. It is 291 gph and its max head is 6'. Thought,
what the heck that is too good of a deal to pass up! Purchased, received today, hooked everything up with 1/2''
main tube then into splitters connecting to 1/4'' irrigation line that fed into each channel.

I have found that at 1' head with the 1/4'' tubing I get a
combined flow from all 4 channels of 1L/min, and of course
that needs to be more like 4L/min or at least 1L/min per channel.

The thing is, if I use 1/2'' tubing at 1' head then the pump
puts out 10L/min.... What gives? I know there is more resistance... but seriously?!


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RE: NFT Pump Size

Mag-drive pumps only transfer water. They don't really make pressure, so it's extra easy to block the flow.


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RE: NFT Pump Size

That's interesting. I guess this means I should probably
just use 1/2'' tubing for my channels' nutrient intake then?


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RE: NFT Pump Size

yes. you're constricting your flow by stepping down the diameter of the pipes. also, each hard bend you put in your lines reduces the flow also. well there's friction along the pipe too, but for really short distances (<15') it doesn't affect things much.


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RE: NFT Pump Size

You will also have to calculate the pressure drop of the tubing/fittings plus the static head to size a pump.


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RE: NFT Pump Size

Plainly, your piping pressure drop exceeds the pump capacity.

What is causing the pressure drop?


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RE: NFT Pump Size

Thanks for the responses willard. The pump I have is what
robbie calls a magdrive pump. What I envision it doing is
simply moving the water by means of a turbine or propeller
type setup. This moves the water but doesn't create pressure.

That is why, I think, when I add 1/4'' tubing the water flow is severely hindered.

To be honest, I even considered possibly going with an aero
setup instead so I went out and bought some 180degree sprayheads.
What I found was that even when installed in 1/2'' tubing,
directly near the pump outlet where pressure/flow would be
highest, there was insufficient pressure to even spray out
of the sprayhead!

Lesson learned. Whenever this gizmo dies, I will be buying
a different type of pump. BUT, what type of pump that is
called or how to identify the right type of pump, I am not
so sure.

-Mike


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RE: NFT Pump Size

I posted a link to a good web site for your pump window-shopping. (I am not affiliated in any way and have never even ordered from them. They just have a nice site.)

Here is a link that might be useful: Pump Agents


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RE: NFT Pump Size

Ethno, buy a mag pump that delivers about 600-900 gph and it will do what you're wanting. It should run in the range of $30-$40. You mag pump just doesn't have adequate volumetric flow.(though I am surprised it wouldn't run spinners at a 6" head?!?)


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RE: NFT Pump Size

"though I am surprised it wouldn't run spinners at a 6" head?!"

IKR? They're not the spinners though, just static, plastic 180degree sprayheads.

It is 290 gph, and I get 2L/min flow in each of the gullies
at 1.5' head. Amazing that it can move that much water but
it cannot provide ample pressure for a spray head.

I will look into a more powerful mag drive pump then. The
reason I considered switching to the aeroponics type setup
was so that I could place seedlings in rockwool into the system
without having to hand water them until the roots grow down
into the nutrient film. But anyways, I will look into those
pumps from the website Robbie suggested, and also the one
you posted awhile back Grizz.

It wouldn't be as much fun if all this was easy, right? :)


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RE: NFT Pump Size

** meant 2' head


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RE: NFT Pump Size

2L/min is only 31gph, so you can see how much it drops off. BTW, the flow given on the box cover is always at 0' head.
Also, at max head, the flow is zero and the pressure is 0 (well technically, it's atmosperic, but relatively its zero)
You can actually calculate the various flow rates and pressures at different heights. I'll try to find the equation.
When I used to grow plants in systems where the pot wouldn't touch the bottom of the net, I always started them in flat trays (actually, an old plate or two)and bottom watered them until the roots started to grow out the bottom. set up a self watering system and you don't have to pay them much mind until you're ready to transplant.


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RE: NFT Pump Size

"2L/min is only 31gph, so you can see how much it drops off"

Yeah but there are 4 gullies flowing @ 2L/min,meaning total flow is 31 gph * 4 = 124 gph. That is still less than 50% of
max flow found @ 0' head though.

"You can actually calculate the various flow rates and pressures at different heights. I'll try to find the equation. "

I will be very interested to hear this equation! Is it related
to the Bernoulli's equation? I remember that vaguely from
taking the MCAT earlier this year but it was kindof
complicated


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RE: NFT Pump Size

I say again, learn to read pump curves and learn something about fluid mechanics.

You've already tried to bootstrap this and failed.....spend some time learning.


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RE: NFT Pump Size

Ethno;
here is the equation I was speaking about:



It came out of "Fundamentals of Engineering (FE) Discipline Specific Reference Handbook" produced by the National Council of Examiners for Engineering and Surveying.
I think it runs about $50, but it's chalk full of useful equations if you're into math and/or able to comprehend it.
If you have any questions about the equation, feel free to ask.


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RE: NFT Pump Size

WEll, I know

g ~ 9.8 m/s^2
gamma for water ~ 1.0 g/mL

Now, the hard part here would be I need to know the velocity
of water at both initial (0' head) and final (2' head), but
also, I would need to know the pressure at 0' head (initial).

So... how do I figure out the initial pressure, and initial
+ final velocities? Could I assume that final velocity is
that exiting each gully, since gravity pulling water through
the very small gradient would add minimally to its velocity?

ALSO, how much pressure is needed for the sprayhead?

*GAH*


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RE: NFT Pump Size

well to figure the velocity at 0' head, you divide the rated gph (volumetric flow) by the area of the pipe.
Also, the pressure where ever the water leaves the pipe is always zero. (i.e it is no longer constrained and "spreads out"(so to speak) as needed). At that point it's plug and chug to figure out velocity where it comes out of the pipe.


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RE: NFT Pump Size

OK, so, I have decided to upgrade the system to a true
aeroponics system with high pressure. To do this I plan on
trying out a 70 psi, 4L/min, diaphragm pump. Link at the
bottom of the page.

What do you guys think of that pump? I know some people run
high pressure aeroponics on 100+ psi, but the pump I have my
eyes set on is only $35 shipped compared to 3X that for the
100psi pumps.

I will say I learned from the last time that saving money by
buying a cheap pump may actually end up being more expensive
if you get the wrong one *DOH*

SOOO let me know what you guys think about that one. Advice
much appreciated.

Also, I am looking into good spray heads for high-pressure
systems. Anyone know of quality brands that will create a
very fine mist?

Here is a link that might be useful: 70 psi Diaphragm Pump (eBay)


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RE: NFT Pump Size

You saw that it's 12-volt, right? Does it produce pressure immediately, or does it charge a tank? The smaller, cheaper pumps tend to charge tanks, which is fine, you just have to buy a tank. It takes a bigger pump, like a well pump, to make pressure immediately.

The point of high-pressure aero is to atomize the mist. The high pressure shoots it against the flat top of the mister head and creates a very fine mist. This happens at about 32-35 psi. I think any higher pressure is overkill, although it won't hurt at all.

A shallow well pump from a place like Home Depot is about $150 and it will do the job. You'll need a cycle timer that costs about $100. Buy a spare and save your receipts, because they like to break. Well pumps also use a lot of power for the brief time when they're running and require at least a 15 amp circuit.

At the moment, I'm most interested in the tiny pumps that charge tanks, and then the roots are misted with the pressure from the tank. I posted a link to one below.

Here is a link that might be useful: a tiny, tank-charging aero pump


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RE: NFT Pump Size

Thats an interesting concept. So you would need some type
of external tank that could withstand and hold pressure, right?

Crap, I didn't take into consideration the 12 volts. How much
do transformers cost? That is what I would need to be able
to connect the 12V to my wall outlet right?

I know some of the aeroponic commercial brand pumps like the
ones MistKing sells are 24V diaphragm pumps, so they must
be useable.

Another aeroponic company called multiponics uses a
pressure boost pump by aquatec. Looking into that currently.


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RE: NFT Pump Size

you need a tank to hold the pressurized water because those expensive pumps are not made to cycle on and off 2 or 3 times a minute and will be very short lived. you use the pump to pressurize a tank then you use a simple cycle timer to trip a solenoid to allow water from the tank to the sprayer heads.
they make a sprayer head that will hold some pressure in the line to keep them from dripping. also, the sprayer heads are rated for a certain pressure.
Search this forum for Hex and aeroponics to find a plethora of relevant information on setting it up.


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RE: NFT Pump Size

Thanks grizz. Also looking into this combo package that contains a booster pump, solenoid, pressure gauge, transformer, and a pressure switch.

http://www.ebay.com:80/soc/itm/350566278635

Apparently this other pump, which is a bit pricier than the one above, is a "bypass" pump that can run the rapid cycles needed for aero without harming the pump

http://www.steam-brite.com/store/shurflo-100psi-viton-pump-bypass-p-4663.html


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RE: NFT Pump Size

Make sure that your pipes, valves and accessories can run at the pressure you will use. Most hydro stuff fails at high pressures.

Schedule 40 steel pipe is rated at 125 psig, por ejemplo.

This post was edited by willard3 on Fri, Nov 30, 12 at 10:39


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