The problem: when the tank runs dry you'd like to use the town water.
Known existing solutions:
- Put a ball valve in the bottom of the tank.
- Use a float switch to turn on a solenoid to stop the tank running dry.
- Refill the tank with a hose.
- Have a stop-cock to connect the mains into the high pressure side
- Use a float switch to turn on a solenoid to connect the mains to the high pressure side.
The solutions are all commonly used, and I know an instance of each. They are all wrong for one reason or other:
- The pump still has to run even though town water is already available at a high pressure.
- Some kind of manual operation needs to happen to switch over or to top up. People forget and tanks over fill or valves get left on, wasting town water when pump water is available.
- Power has to be available for the system to work.
I have implemented a cheap and robust alternative as proposed in ATA's Renew (forgot which one). The idea is to use a device called a 'pressure reducing valve' to provide water at a pressure just lower than the pump switch on pressure, so that if the pump is inactive the town water is available. The renew design called for a variable pressure reducing valve, at a cost of $300 wholesale. And they don't make them go low enough for my little rivaflow irrigation pump. This design uses a $6 plastic version with a fixed rating of 100kPa.
Thus, the pump can simply be switched off when the tank runs dry. We can do this using a float switch and a relay (the pressure switch itself may have a relay you can subvert).
After ringing a number of plumbing supplies and being told that my idea wouldn't work (when it is plainly clear that it must) and anyway, you can't get pressure valves like that, I found a suitable pressure reducing valve at the local big box hardware store. The device is actually designed for very low pressure irrigation systems, but it is well made with a thick HDPE case, solid looking white nylon valve assembly and a heavy gauge membrane. The high side is rated to 3MPa.
(insert photo here)
The final layout of my rainwater irrigation system is:
A nice additional feature is that if your water demand exceeds the pump capacity the mains kicks in seamlessly (within the inertia of the pressure reducing valve and water in the pipe etc). It is good to have the valve as close as possible to the manifold as a result.
1 comment:
Wow - great tip, thanks - I've been looking for something like that to recommend to others! Can you post (or email me) the maker/model of the Valve?
In the heavy rain season I hope to divert rainwater to my washing machine, and may try to reduce potable water used in downstairs flushing, using gravity.
Upstairs, where I have a big clawfoot tub, I allow grey-water first to hydrate and clean the air overnight to reduce allergies and sore throats, and aid sleep. One can easily see how the ocean absorbs carbon this way - if you leave the water for more than a day you'll see it get dirtier, & silt gathers on the bottom. I re-use bathwater for flushing, basin refill, and plants already. But I do it manually using Lemonade pitchers. Some greywater also goes to the garden with me in 5 gallon buckets. Makes for a great, light workout that fits easily into a Home-Office routine. Since housemates and guests aren't into it, I'd love to have a diverter valve flow the grey-water directly to irrigation in dry months, before others arrive at my house.
During Coffee-breaks I deadhead for more flowers, harvest veggies for the kitchen, and hand-water plants using greywater. Self-employment perks keep on coming.
I am now looking for cheap, bulk-purchase or recycled materials for Rain-barrel and Stormwater tanks, and irrigation fitting supplies for a beighborhood project - in which we'd like to assist more than a hundred homes and businesses reduce expenses, be greener, and qualify for sewer bill discounts. If anyone reading this can help - you'd receive our heartfelt thanks - and maybe a modest profit!
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