Irrigation solenoid valve restricting flow

OttoGardenerMarch 28, 2014


I have a Danner Model 18 magnetic drive pump:

It sucks water out of the bottom of a 55 gallon drum and pushes it up about 5' through 3/4" PVC to a 1" Rain Bird CPF-100 in-line solenoid valve. I'm getting about 160 gallons/hr. This isn't nearly enough for my system.

So I removed the Rain Bird CPF-100 and it increased to around 720 gallons/hr, which would be plenty.

The Rain Bird valve is obviously designed for a city water supply usually ranging from 50-70psi. I assume this pump isn't producing that kind of pressure.

Do I need to look for a new solenoid valve that doesn't restrict flow so badly? Rain Bird makes something for low flow drip irrigation:

Or is there something else that I can do to make more water get through the valve I have? I noticed that in the pump's instruction sheet it says 1 1/2" Inside Diameter is the minimum hose size that should be used for maximum flow:

If I were to change the pump outlet pipe from 3/4" to 1 1/2" (or 2" since I already have it) on the outlet of the pump, would that improve my situation at all? Thanks.

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Looks like it needs a minimum of 15psi so likely designed for use with the mains water supply. Your pump will do 7.5psi at zero flow according to the spec, so increasing the pipe size wont be much help.

    Bookmark   March 28, 2014 at 1:37PM
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PupillaCharites(FL 9a)

If you just want to know about some manufacturer's part, call their expert gals and guys in tech service and ask them what the best part for your job, if they have another, is at (800) 435-5624.

Pics of your design that requires the pump to always be on would be a nice contribution to the forum :-).

This post was edited by PupillaCharites on Fri, Mar 28, 14 at 16:22

    Bookmark   March 28, 2014 at 4:19PM
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Thanks for the quick responses guys. I actually did phone Rain Bird and I explained my situation. They could only suggest getting a 2" valve instead.

One of these:

I took one of my 1" valves apart and couldn't see why there would be a flow reduction. The openings were at least as large as the 3/4" pipe I'm using.

I understand that these valves will not open until the solenoid is energized and a certain pressure is applied on the inlet. This must be the 15 psi pointed out by hex2006. I decided to call Rain Bird back and ask about it. They confirmed that the valve will not open until 15 psi is reached.

So, either my valve is opening with less than 15 psi or my pump is creating more than that. Rain Bird said all their valves have a minimum of 15 psi. I guess I will need to find something else. I think an automated ball valve would be the best, but those are $200+.

PupillCharites, I am planning a [fake] aeroponic system where the roots are suspended in PVC chambers and sprayed with nutrient solution. From what I have researched, constant power cycling is bad for pump longevity. Because of this, I had planned for the pump to run continuously, with the flow being controlled by solenoid valves.

I have two "zones". One recirculating loop going from the reservoir, through a Venturi aerator and back into itself. The second is to feed the plants. The plants will get sprayed every few minutes, with the recirculation running whenever the plants are not being fed.

Maybe there is a better way to do this?

    Bookmark   March 28, 2014 at 6:49PM
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PupillaCharites(FL 9a)

That's a hard one depending on your daily 'misting' cycle frequency. Hard because frequent intermitent use surely will lead to less of a lifetime, if we just log hours, but these mag drive pumps (no way you get more than 5 psi anywhere with it) are pretty resilient, so if you are *using* it more to avoid turning it off, that's a different question.

So the venturi feedback is also on another actuated valve, like a DPDT toggle scheme, or how do you prevent loss when it's needed to the chamber?

I don't think the venturi is the most efficient way to use your pump's energy by if you have energy to dissipate sure.

Check out the manual online to the Aero-Flo2, not saying it is better, just that I think it is the superior design. Don't get me wrong, you're venturi-ing into exciting territory for sure. I just prefer the security of some liquid flowing since my own hairbrained ideas and abilities have taught me extra complexity = more failures, and short failures is something in this system the plant might not tolerate. Really awesome work to be doing btw!

    Bookmark   March 28, 2014 at 7:18PM
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The planned misting cycle is something like.. mist 1 minute, recirculate and aerate 4 minutes. They always take turns, never running simultaneously.

Recirculating Loop:
Reservoir -> Pump -> Solenoid Valve #1 -> Venturi aerator -> Reservoir

Feed Loop:
Reservoir -> Pump -> Solenoid Valve #2 -> Plants -> Drain to Reservoir

Valve #1: open, Valve #2: closed

Valve #1: closed, Valve #2: open

"Hard because frequent intermitent use surely will lead to less of a lifetime, if we just log hours, but these mag drive pumps (no way you get more than 5 psi anywhere with it) are pretty resilient, so if you are *using* it more to avoid turning it off, that's a different question."

Could you explain this in more detail? What is a different question? From what I have read, these pumps are designed for continuous operation. Power cycling wears them out.

Everything I read seems to stress the importance of ample dissolved oxygen. I considered things like air pumps or powerheads, but after learning about Venturis and seeing demonstrations, it seemed to do a good enough, or even better job, and I don't need another electrical device to worry about. I figured if I'm doing the recirculating anyways, I may as well aerate at the same time. I actually thought it was less complex than the alternatives.

I actually picked up an Aero Flo 20 second-hand. I've incorporated the two grow chambers into my system. Which part of the design do you feel is superior? As far as I can tell, it's essentially an NFT system that sprays a stream out of the inner pipe instead of coming from just one end of the chamber.

    Bookmark   March 28, 2014 at 8:50PM
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PupillaCharites(FL 9a)

Two mechanical solenoid switches and their valves, a better timer/controller and having to dump unused energy (with a cool venturi) instead of a single timer and airstone if you wanted? I could see it in a big fishtank needing currents, with fish *depleting the DO* but not in a little reservoir with a waterfall. Don't mind naysayers and keep at it Definitely! It could be a better mousetrap that will leave us all eating crow, far reaching in hydroponics as this innocuous thing that so changed the world!

I don't think either of us has enough performance specifications on both system configurations to them justice. There are way too many assumptions in play here that have not been tested head-to-head. Let me randomly list some of them.

The electromechanical lifetimes of both actuators under continuous operation.

The possibility a solenoid will stick, or that the valve it controls get clogged, etc.

The electromechanical lifetime of a magnetically driven pump where power is cut and connected at high daily frequencies.

The electromechanical lifetime of a magnetically driven pump where load is switched, depending on mechanical switching speed and pressure differential stress through each switch of load.

Will the return waterfall + the Aeroflo type delivery will get you the same DO for the dripping roots with a simple return waterfall from a DWC spray system like AeroFlo2 as your dripping roots will get, or do better?

Your pump is warming the reservoir more until you get the sizing very fine tuned. All that extra runtime you are dissipating by not turning the pump off is warming the reservoir and lowering the ability correspondingly due to the inverse relationship of DO(T).

I didn't realize you had already studied the Aeroflo, but it makes a lot of sense that having one got you thinking along the lines of your design. I personally would spend all the power I had at my disposition in getting a finer mist. The finer the mist, the cooler the water and when it goes splat on the roots, the greater the DO as well as absorption, *I believe*.

Experimenting would be fun though and you will probably gain a lot of experience by the time you go through it all.

In the ignorance of both of us, we need the spec and ageing tests of the candidate pumps. An electrocardiogram of the power amplitude during switching vs. what happens with the surge from off. I wouldn't be surprised if both type of operation caused a similar integration of the power pulses (power 'jerks').

I'm sure I'm off on some of my assumptions but there are many. For that reason I appreciate the AeroFlo as a very dependable system, with the caveat that I've never owned one and just am impressed by their keep-it-simple design.

You sound like you have some engineering talents, so I hope you know I’m just being your sounding board and am impressed you are tackling something as cool as this for which I have plenty of theoretical hurdles. Best of luck, and think ‘patent’ while you’re at it, I would!

    Bookmark   March 28, 2014 at 11:55PM
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One method for running the pump constantly is to fit a tee, atach a "normally open" solenoid that leads directly to the res and put a low pressure check valve in the line leading to the nozzles During the OFF period the pump aerates the res. During the ON period the solenoid closes sending the flow to the nozzles.
I run a large outdoor high pressure (80psi) aero setup in the summer using a manual pump and a large accumulator. 12v dc cycle timer and solenoids run on a 7 A/h SLA battery charged by a 20w solar panel.

    Bookmark   March 29, 2014 at 3:19AM
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Ask for a pump curve and learnj to read it before you buy another pump. Any pump mfg. has a pump curve

    Bookmark   March 29, 2014 at 9:30AM
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The pump is ok, its the rainbird solenoid that isnt compatable with the application. Buying the right pump for the job is always a good plan, a1000gph pond pump isnt the most energy efficient method of running a handful of nozzles at a few psi.

    Bookmark   March 29, 2014 at 12:04PM
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PupillaCharites(FL 9a)

LOL, what, a cheap pump and two expensive solenoid valves...or maybe an expensive pump and two cheapo solenoid valves, or perhaps the improvement of a tee and one valve. The solenoid valves are fine when used with the appropriate pumps and flowrates. I think the OP will benefit by studying the behavior of pumps as exampled in the graphs posted by willard above.

It is not clear what his expectation is for the 'misting' quality and that's where it's all at. He needs to start upstream and work backwards. What is the pressure he needs in the mist sprayers. He should first experiment with them once he has them in hand to see the misting that is acceptable, if any, instead. Only then can he know his best case scenario if it's a direct shot up from pump to manifold. Then properly size the pump. If he wants solenoid control then he should look for something that matches. But then he will see that if you can't plug the flow with your thumb easily, the solenoid will likely be relatively expensive.

If someone can help him by posting an economical solenoid valve option that will work with this pump it would be helpful. The OP does not understand how pricey a quality example solenoid needed for this application is. I didn't even hear enough about the design to know the diameter of the pipe being used, so this is just all over the place. Studying the pump performance curves to see the power requirement. For use with the posted pump sample head vs flowrate for various powers, use: 75 Watts = 0.10 HP

This post was edited by PupillaCharites on Sat, Mar 29, 14 at 18:00

    Bookmark   March 29, 2014 at 5:57PM
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Thanks for your input, everyone. I ended up getting some reasonably priced stainless steel 24VAC actuated ball valves from

I put a normally open valve on the recirculation line, and a normally closed valve on the feed line. With these, I am able to do exactly what I had planned with my low pressure pump running 24/7.

This post was edited by OttoGardener on Wed, Apr 23, 14 at 11:28

    Bookmark   April 23, 2014 at 11:23AM
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Good to hear you got it sorted, solenoids will handle the 2000+ operations per week better than any pump. Some of mine do 1500 a day ;)
Look forward to seeing the results.

This post was edited by hex2006 on Wed, Apr 23, 14 at 13:13

    Bookmark   April 23, 2014 at 1:11PM
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