24VAC solenoid watering valves in a gravity fed application?

[tikeda]

I'm trying to get ready for this season's gardening. We had great luck last year with an EarthBox growth system (you can also make these from scratch) but one downside was the need to refill the reservoir at least daily. That's no problem unless you would like to go away for a week or two on vacation.

You can see where this is going...
Others have developed automatic watering systems (an example here) but all seem to hook into their residential water system. I'd like to use a rain barrel as the water source and automatically control a water valve with a Picaxe. 24VAC solenoid valves are often used in lawn watering systems and they are reasonably inexpensive. I noticed that valve manufacturers typically specify a working pressure range of about 15-150 psi (~100-1000 kPa for those living in civilized nations). Does anyone here have working knowledge of those valves? Do they work with low water pressure such as might be found at the bottom of a half-full rain barrel (e.g. <1-2 psi)?

Sure, I could put the barrel on the roof but...

 

[hippy]

I can't comment on solenoid valves but another possibility is windscreen washer pumps. I'm not sure they'd be long lasting as they're designed for intermittent, short use.

 

[KMoffett]

Hippy,

Those windshield washer pumps don't stand up at all. I tried them for an automatic Christmas tree stand watering system. They have nylon bearings that melt after a few minutes of operation.

Ken

 

[martinn]

Generally, typical irrigation type valves require a minimum pressure to move the diaphragm to both open and close the valve. It is usually around 20 psi (138 kPa).

 

[papaof2]

Most of the valves use the solenoid for opening and water pressure for closing. At 0.433 psi per foot of water depth, you need a valve made to work at very low pressure.
I've seen some low pressure valves at DripWorks http://www.dripworksusa.com/store/valves.php#tiptop

However, the lowest listed pressure is 4.3psi, which is still a 10 foot water column - so the barrel on the roof might be a good idea ;-)

There are valves that use either a spring or a solenoid to close the valve, such as an automobile fuel shutoff valve.

Something like this might work:
http://surpluscenter.com/item.asp?UID=2008022419414160&item=20-1306&catname=

I have a couple of valves to test, but my water collection system is curently in transition (55 gallon barrels being replaced by a 250 gallon tank). When the big tank is painted (hopefully Monday, US Eastern time), in position, and filled, I'll be able to do some testing (preliminary testing with the big tank sitting on the driveway indicates that a full tank delivers about 5gpm through a 3/4" hose, albeit at less than 2psi).

I have two devices yet to be interfaced to the rain water collection system. The flowmeter from a Whirlpool Duet clothes washer delivers 815 pulses/gallon and I want to use one of these with a PICAXE to deliver a measured amount of water to the garden. Once the flowmeter interface is functional, I want to use a second flowmeter to monitor the amount of water entering the storage tank.

The Duet washer also has a water level sensor that is operated by the pressure of the "water column" in the washer (there is a limited adjustment range for the 3 set points). I plan to use one of these as a level indicator for the tank (another item the PICAXE will be monitoring). The final design will have an RF link from the solar+NiCd powered PICAXE monitor to a PICAXE-driven display inside the house (maybe by the 12th of Never ;-)

John

 

[tikeda]

Thank you.

Some sort of water pump sounds like a reasonable option, especially because the flow is slightly downhill in this case. Low-volume fountain pumps are just a little more expensive than the solenoid valves and I've just Googled some that operate on 12V (I want to keep the 120VAC 'bits' inside the house).

Hmm... Expanding a water collection system in Georgia. It sounds like that might be necessary this year.

 

[BCJKiwi]

Most solenoid valves use a pilot solenoid valve to turn on water to move the main valve diaphragm, hence the need for pressure. A direct solenoid has to be much bigger. However small valves are often direct acting.

The valve could be pretty small as the flow doesn't need to be fast - it could take all day to refill couldn't it?
So, why not just the float valve out of a toilet cistern.
If you need electric control and the flow is low enough then back to the small direct acting solenoid valve with float switch and a relay should do it for control

ElseIf the barrel could gravity feed then you might investigate some form of motorised valve - could be a ball valve (90deg turn) run off the venerable windscreen wiper motor.
If you want to get really simple (and crude) rig up a motorised clamp on a short length of flexible tubing (think vice or scissors, or even bend the tube in half!) - do I see a peristaltic pump in there somewhere?

If the 'EarthBox' is above the barrel then pump using a centrifugal on the barrel outlet at the bottom of the barrel (so it's always primed).
The problem with pumping downhill is you need to stop the water flowing through the pump when its off due to gravity - back to the valve - or the peristaltic pump, ho hum.

 

[tikeda]

I wondered about downhill pumping. If the pump leaks through when unpowered, I could instead pump up to an 'open' container at the top level of the reservoir which then feeds the water to the box by gravity.

Using a toilet flapper valve is an interesting idea. And I've seen small tubing clamp valves.

I did finally locate solenoid valves with zero psi min. pressure ratings for about $50US (here). I have seen this type used in hot water heating systems. The cost is about twice that of the home watering solenoids and little more that a decent fountain pump.

I'll report back after I've got some parts in hand...

 

[premelec]

The solenoid valve referred above by papaof2 at Surplus Center would appear a straightforward solution - using a diode bridge rectified and capacitor and resistor to prevent buzz changing the 24VAC to DC.

I'd avoid as many pumps and check valves and other complications as possible [and I've maintained a number of rural water systems].

Washing machine solenoid fill valves take more power but are available as scrap - or new - and you can run them on 24 VAC by using a 120 or 220 v to 24v transformer 'backward' to step the voltage up. These open with 0 to 120PSI.
BTW the washing machine tub level switchs are also useful and available as scrap from an appliance repair shop. They operate on small pressure changes - useful for low head gravity systems. .

 

[BCJKiwi]

How about the barrel below the Earthgrow, a small cetrifugal pump running (decorative fountain pump?) continuously with an overflow on the Earthgrow back to the barrel. This way the electrical load is very small, there are no level controls, switches, float valves getting debris in their seats etc etc. If you want to save on power (the pump is bigger than you need to make up for water use), it could be cycled on for an hour, off for an hour etc. Large numbers of starts should be avoided as they draw more power and cause more stress.

 

[Peter M]

Hi Tikeda,
check out this link, looks like they come in several different voltages as well as LOW pressure

http://www.hydralectric.co.uk/detail.asp?ProductRef=2899&Ref=1488&Category=Solenoid+Valves

this site came from mattweth from archive 1

 

[cpedw]

I tackled a similar problem a few years ago but the solution didn't involve a Pacaxe ...
Power is from a 12V solar panel with a 6Ah lead acid battery. The basic watering system is a shallow tank under plantpots, connected by an absorbent cloth to draw water from the tank to the pots. There's a float switch in the tank set to cloes when the level is low. The switch powers a 12V boat's bilge pump similar to this http://www.gaelforcemarine.co.uk/ProductDetailsPage.aspx?product_id=18569 which floats in the large water butt (old film canisters have been attached to the pump to make it float). In addition,the bottom of the water butt has asecond float switch to turn off the power if the butt is empty. Then the plants die.
This arrangement has helped me to grow tomatoes in Edinburgh for several years. It operates for 6 months each year. I can't claim it has never failed but I'm a good bodger, a poor handyman.
Just a thought.
Derek

 

[Summertown]

I live on 6 acres and have a system that sounds simikar to what you have in mind. Our property is on a slope, the valves at the bottom are fine, the valves next the tank are philmac. These are the only valves known in Australia that will work on 0 pressure. If I were you I would install a pump and have it controlled by a flow switch e.g. a Maat. these are inexpensive & reliable. Your concern about leaking fittings is valid, the way I fixed this was to have the pump also fed from via 24V relay that is activated whenever any valve is on. Put another way the pump will only turn on when water is flowing AND a valve is open. This means you use freely available valves.

 

[geoff07]

caravan pumps

I use a Whale caravan water pump (12v, 16 quid) with a built in input filter that connects directly to a 10mm poly pipe and lives in a sock filter in the water butt. This easily gives enough pressure to power a couple of dozen drip nozzles. Don't forget an anti-syphon outlet that lets air leak back in to break the syphon or the entire barrel will empty the first time you prime the pump!

The pumps are available from caravan spares company websites in the UK. I got mine from Camperlands. They are perhaps an inch or so in dia and five inches long.

The system grows some green algae in the summer. I'm told the answer is goldfish in the water butt but have not tried that yet.

I don't use a picaxe for this because I have a small 12v timeswitch also for caravans, and it all runs off an old car battery with a solar panel to recharge.

I do use a picaxe to control the led lighting, though. IKEA have a nice line in low cost 12v led lights. The theory is that you can get photosynthesis even with lowish light levels if the leds are close enough to the plants. It was fun to do, anyway. Next upgrade is to use an old PC fan to suck the hot air at the top of the greenhouse down a piece of tube to warm a stack of bricks as a heat store, thus extending the day. Lots of scope for digital sensors here.

 

[moxhamj]

I'm going to second BCJKiwi's suggestion of using a pond pump with an overflow. If the tank is about a metre or two below the pots then the head works out right. Run the pump for a fixed time and just overflow the water back into the tank. Pond pumps can handle a bit of dirt etc. No solenoids, no level sensors, less things to go wrong.

The other option is geoff07's idea of a caravan pump - the ones I have played with are flexible rubber diaphram pumps with inbuilt valves so they don't suffer from syphon problems. They run up to 40psi or so and then turn off with their own inbuilt pressure sensor. More than enough for running solenoids etc. For algae you can get a bottle of algae killer from a pet shop.