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Sanity Check Please...
Constantin
Member Posts: 3,796
... and the sprinkler contractor comes back from vacation and wonders just how we will incorporate the cistern into our garden watering system. Here is my first stab at how I think it might work and I'd like your collective feedback.
Whether we use a street supply or not, we need a pressure pump to get the pressures to the point where the sprinklers will throw far enough. Thus, the pump is necessary.
In the below sketch, I am assuming a float switch at the bottom of the cistern. When the cistern has water, this switch is closed.
Back at the pump, we have a SPST relay which will be closed as long as the float is floating... thus, the pump will draw its water from the cistern.
Once the float drops (i.e. the cistern is empty), the relay opens and the (normally closed) zone valve is turned on, opens, and allows 30psi house water into the watering system.
The swing-check valve prevents house water from entering the cistern, the backflow preventer is there by code.
Assume that the pipes are 1" dia, 35psi water pressure in the house. The pump is, IIRC, a 1/2hp 50psi pressure pump, though the exact model escapes me at the moment.
My question is: Can it be this simple? Or should I consider a system like "complicated" that uses two zone valves to ensure that the suction from the pump does not try to get more water out of the cistern? (and entrains air instead). Are there perhaps better solutions or solutions that are already pre-made for this kind of problem?
Many thanks for your thoughts!
Whether we use a street supply or not, we need a pressure pump to get the pressures to the point where the sprinklers will throw far enough. Thus, the pump is necessary.
In the below sketch, I am assuming a float switch at the bottom of the cistern. When the cistern has water, this switch is closed.
Back at the pump, we have a SPST relay which will be closed as long as the float is floating... thus, the pump will draw its water from the cistern.
Once the float drops (i.e. the cistern is empty), the relay opens and the (normally closed) zone valve is turned on, opens, and allows 30psi house water into the watering system.
The swing-check valve prevents house water from entering the cistern, the backflow preventer is there by code.
Assume that the pipes are 1" dia, 35psi water pressure in the house. The pump is, IIRC, a 1/2hp 50psi pressure pump, though the exact model escapes me at the moment.
My question is: Can it be this simple? Or should I consider a system like "complicated" that uses two zone valves to ensure that the suction from the pump does not try to get more water out of the cistern? (and entrains air instead). Are there perhaps better solutions or solutions that are already pre-made for this kind of problem?
Many thanks for your thoughts!
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Comments
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Constantin
Assumably the pump you will be using is a jet pump of some sort that will be able to lift the water out of the cistern. If so it will require a foot valve down in the cistern to keep from losing prime. The swing check should be fine to avoid possible backflow into the cistern. I would avoid the zone valve though as it may not be able to handle the rigors of street pressure or potable water. A solenoid valve either fast or slow opening that has a high pressure rating may be a better choice.
Glenn Stanton
Manager of Training
Burnham Hydronics
U.S. Boiler Co., Inc.0 -
Swing check
I would use a spring loaded "line check", instead. You won't need a foot valve, the check does it well. Just like holding your finger over the end of a full straw, it will hold prime. Just don't let it lose prime or you'll be playing with it to bleed the airlock.
I agree with Glenn, use a solenoid valve instead of a zone valve. Much hardier.
Simple is good
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might want to consider some shock arresters for when the solenoids slam shut.0 -
Why not try the simple?
I've tried to think of all kinds of potential problems and they all wind up ridiculous! Only change I can think of is using a DPDT relay to begin with--cost difference is negligible and the extra contacts might come in handy some day...0 -
Pressure
You only have 35psi in the house? Wouldn't your sprinkler pump starve the house when it is running off house pressure.Depending on your cistern size and lawn watering demand, would it not be better to have your house pressure keep the cistern topped up and just have your pump draw independent from your house pressure.
Good Luck
Dobber0 -
Thoughts
The 50 psi pump will more water than your 30 psi supply, so you either need a larger line from the house or you will pull air into through your faucets when the pump is running and cistern goes dry. The size of your cistern will deside how long the 50psi pump can run with city water pushing at the same time. I would be thinking to put in a second switch that shuts off the 50psi pump until the cistern cathes up. Then again if the sprinklers do not total more than 3/4 outlet you might get way with it as it is.
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I agree with Dobber. I've seen similar systems set up to supply house water from a storage tank. The storage tank is supplied from their standard well/pressure tank, and a pump/pressure tank after the storage tank feeds the house. Then all you need is a float type valve or float operated switch to maintain level in the storage tank/cistern. The house water supply could probably be terminated above the cistern like an air gap so you wouldn't have to rely on checks or bfp's.0 -
You are sane
i think the drip system is superior to over watering by way of pumps and sprinklers....might just want to give that a gander ...as a thought.0 -
Wise-Bo
Something to be said for drip systems in many ways; low initial evaporation losses, targeted hydration, low pressure requirements...
Weezbo knows.
Other thoughts/questions semi-related:
Cistern is filled with...harvested rain water? Gray water? Just trying to get you yet another LEED point there, Constantin, on top of the Platinum Plus you probably deserve!0 -
Many thanks....
... as usual, you all are giving me plenty to think about.
As you probably already know, I'm not allowed to install anything "upstream" of the water meters. We have a 1.5" line coming into the house that is split into 2x 1" lines, one for the house, one for the garden. Each use gets its own water meter, as the garden water is not assessed for sewage.
Once the water is through the domestic water meter, it is fed into a Amtrol pressurizer. That raises the pressure from ~37 psi to 65 in-house. Thus, I doubt that we'll be running out of water when the garden pump is running.
For the garden water the idea is to raise the pressure in the system to at least 50 psi to allow it to function well. I would rather not replenish the cistern to any measurable degree with potable water simply because the idea behind the cistern is to collect rain water.
Due to freezing conditions here, the cistern is situated several feet under ground. The garden pump will be mounted with quick connects on a cart, so I can bring it out in the summertime and bring it back in during the winter.
I have taken your collective comments to heart and wonder if the following set up might make more sense... Here, a TACO 1" 3-way valve + motor-driven actuator would switch from the cistern to the city feed and back. This would avoid the ill-effects of solenoid valves slamming shut and seems to afford relative simplicity via the built-in end-switches.
I'd like to think that I would be able to position the float switch in the cistern such that it would not run out of water before the valve switches the water supply to the pump. However, I concur that it's a good idea to be able to maintain prime, so the line valve will likely be near the bottom of the cistern.0 -
Oh it's drip irrigation alright...
... but the sprinkler installer claims he needs the 50 psi to make that system work well in addition to the 2 smallish lawn areas. Methinks that larger pipes = less CV = smaller pump but that may be the wet-head bug in me...
It may amuse you to know that this is allegedly the first cistern registered in the PRC for rainwater harvesting purposes. Seems weird considering how many crunchy granola types live around here, but presumably they didn't pull a permit if they installed one.
The cistern is filled with harvested rain water. Leaf-defier foam keeps it pretty clean of debris. I calculated that if I wanted to have the 4" of optimum "rainfall" per month that the landscapers dream of, I'd need a 6,000 gallon tank farm to fill during the winter and draw down over the summer. That size farm isn't going to happen and so I still need to make some decisions re: what I want and what I do not want watered.
In the end, we may very well only focus on certain areas of the garden for watering and let the rest fend for itself. Given that we get runoff from the top of the hill and adjacent roofs in some parts of the lawn makes me think that wholesale irrigation is not necessary... The plants here looked pretty healthy when we bought the place, so I'm inclined to minimize the irrigation where possible.
Speaking of which, have any of you had any good/bad experiences with the controllers that go on irrigation systems?0 -
Our water temps here are very cold....
water from a cistern is usually warmer and water from roof drain downs into a black barrel in the summer time is usually appreciably higher ....the cold water from the street shocks plants that have their Warm weather feet in the ground:)0 -
You have flowing water up there?
... I thought you had to melt your drinking water year-round, no? :-P0 -
am i missing something?
or is it possible for the cistern water to touch your potable city water..
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Serving Cleveland's eastern suburbs from Cleveland Heights down to Cuyahoga Falls.0 -
*~/:) er...well... O.K. You got me there
buh the -5 this morning doesnt allow for any lengthy chopping of the ice for coffee:) i need to make my dog learn ice carving or something useful:) he is into energy coservation:) His favorite Trick is to unplug the vehicle to save energy:) Basically,i have yet to csee his certificate of fitness card stating that he is allowed to mess with the wiring:)
I just got a great idea !
i could lend you my dog to water the yard:) Hey the Kids a Natural 0 -
Sprinkler
I think your making this alot more complicated than it has to be. How about running the town water to the tank with a high tank ballcock(like inside the toilet)set so it would keep the tank half full at all times. The rain water would be the free bonus on top of that, and the pump could never go dry. Run a second line back to the house to your jet pump that will be in the basement where it could live forever even in winter. Put the pump on top of your pressure tank, and run a third line out of it to your system. EJW0 -
Constantin
Are you using cistern water for domestic purposes such as drinking water?
I like the Backflow preventer but what will protect the source? I would like more protection from back flow from the garden. Why not add a pressure type vacuum breaker before feeding the garden.
Robert O'Connor/NJ0 -
Constantin...I'm familiar with your application.....what I did in my setup is put in three xtrol buffer tanks....50 gallons each....and set them to 30 psi....and put a jet pump set to 50 psi...in my case I'm running water through a 3" pipe to a formal rose garden 1500' away....in your application, especially if you use drip irrigation, I can't imagine you running over 30 psi...in other words you have a flow problem not a pressure problem ...if you are concerned about lack of water(and can't sink a well which is what I did...put in a 300-500 gallon tank underground, or slave the house systenm to replenish...the key in this case would be to set the jet pump only slightly above house pressure...and...check your ph....rain water and house water are neutral.....wells are acidic in the Northeast...John0 -
Yup,
... it can touch, but only after the city water has run through a backflow preventer valve. Plus, the contaminated water will only exit via the irrigation system... no hose bibs and all that.
The plumbing inspector read me the riot act when I suggested using the cistern like that (i.e. just a simple hose connection) to avoid the switcheroo excercise I am going through. After all, a kid might run up to the house, turn on the spigot and get an upset stomach. Cistern water hose bibs would have to have removable keys and a copper plaque "non-potable water".
Don't get me wrong, I understand his point of view, though sometimes the concerns seem a bit overinflated. Then again, I don't work as a plumbing insepector and I'm sure he forgets more in a day than I'll ever know about plumbing systems. Anyway, after all that I decided that the irrigation system is the only place I want to use the cistern water.0 -
I agree with dobber and Al. Be sure you use a solenoid instead of a zone valve. Keeps the water rotated better too, if that matters.0 -
Only the garden drinks from the cistern...
... the requirements to get rainwater certified to be safe for drinking are pretty strict around here.
So if the water going to the garden is only going to get used in the garden and the city water source is protected with a back-flow preventer, then why would an additional breaker be necessary?0 -
Constantin
I must of looked too quick. I thought you were sending cistern water to the house.
My bad?
Robert O'Connor/NJ0 -
No worries...
... you and I would need some impressive roofs and water-use reduction techniques to cover our drinking/washing/etc. needs to any appreciable degree. Even the guys in the Pacific NW (where it practically rains year-round) usually have 5,000 gallon cisterns on hand for the summer months.
Anyway, any thoughts on my latest proposal (i.e. the TACO 3-way valve)?0 -
That's the thing...
... based on the literature I have been reading, 30 psi should be just fine for drip irrigation.... that would make my life a lot easier since I could simply put a 30psi pressure pump + swing check on the cistern and feed the city supply from the other side via the backflow preventer.
However, the professional thinks that we need more pressure to reach the furthest depths of the property. Perhaps this is another instance of where I need to have a heart-to-heart talk about expectations...0 -
Quiet Thursday Afternoon my Butt!
Hey Constantin-
Another thought-provoking thread you have lead!
Stimulating for boys and girls of all ages and areas of expertise.
A modest "thank you" from my modest brain.
Brad0 -
If it were me
I'd use a submersible pump in the tank. Grundfos has a wide range of sizes, including a cute stainless one that fits inside a 2" well for testing.
hot rod
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Must be different forms of drip systems. The ones I have for the vegetable garden, flower beds and hanging plants all use pressure reducers--20 psi comes to mind. Even standard "soaker hose" benefits GREATLY from reduced pressure. The few spray heads I use on the drip system (for lettuce, etc.) atomize the spray if used with high pressure.0 -
why heck
why not use solenoid valve to just refill the cistern directly. If you can employ an air gap you will avoid the use of the Backflow prevention device; and not have the pump suction affecting the house pressure in any way. You guys are lucky it rains in the East; around here it is illegal to collect rainwater, I believe.0 -
My 2-cents!
My two cents worth! In my area, it would be illegal to interconnect a "private source" being the collected rain water, to a public source, water supplied by a public supply, even with the backflow prevention device. ie If there was a well, and a water main was ran through the area, if you wanted to use the well for say hose bibs, you have to run a seperate supply from the well to the hose bibs and the piping has to be clearly identified as being from a now "non-potable" source. If in your area, you are allowed to connect as in your drawing, I am concerned about the dual check backflow preventer. I think that it should be a Reduced Pressure Zone, RPZ, device. Which leads to another issue, the 50psi from the pump could potentially subject the device to back pressure should the zone valve before the device fail. I agree with Plumdog in that you should consider filling the tank with the potable water via an airgap. Perhaps some switching could be devised with floats that the tank would only fill say 1/4 of the way (or whatever amount is needed for a watering cycle) with potable water should the tank run dry of collected water. Then if collected water is available, it can fill the remainder of the tank.0 -
I agree.
I agree that the best method would be to just keep the cistern replenished with a device like a Rockford Tank Valve with float and air gap connection. This could also be set up with provisions for drain down during the winter months for risk of freezing. This would keep it a dedicated irrigation system separated from the potable water supply of Cambridge. Based on what I am seeing every morning when I walk, we may be in serious trouble with available rain water this year. We are having the dryest season in 30 years here in Rhode Island so the odds of the cictern being replenished with rain water seem slim to none.
Glenn Stanton
Manager of Training
Burnham Hydronics
U.S. Boiler Co., Inc.0 -
Very good points...
... the more I think about it, the more it makes sense to simply pull out of the cistern what is needed and replenish the cistern as the need arises. That simplifies the pump system, avoids hemorroids for the plumbing inspector, etc.
The only thing I do not like about filling the cistern (even with an air gap) is the possibility that a valve failure would allow water to run continuously. So, I'd need to aim for a system where the valve will invariably fail shut, not open.0 -
there You Go:) Thats the ticket
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How about......
installing a redundant high water float switch, say 120 volts, down in the cistern that will float on top of the water level. If the water level rises too high mercury contacts in the switch will make and activate a normally open solenoid on the potable makeup water pipe thus closing off any flow and at the same time triggering an alarm or indicator light in the house. These are readily available and are used commonly in sewage ejector systems and sump pumps. They fasten to the pipe that will already be down in the cistern for the pumped water and float up and down on a hinge principle.
Glenn Stanton
Manager of Training
Burnham Hydronics
U.S. Boiler Co., Inc.0 -
My brother from the same mother, another hummer of a plumber...
Just set up a system for that monster Equestrian center that we are working on, and I think it is one that Constantin would LOVE. It has a natural spring with a capcity of like 2 GPM. This is fed by gravity to a catch basin. THe basin holds something like 500 gallons. This pump is protected by a mercury float switch. If the cath basin is low on water, the pump will not fire. If the basin is full, an dthe cistern calls, the submersible turns on and send water to the chlorinator, and down into the 10,000 gallon holding cisterm. Inside the cistern, there is a Grundfos pump (2 actually) that are connected to a Grundfos VFD that operates the pumps based on flow/demand.
Works slick, maintains a real good supply pressure and can respond to changes in demand instantly. I found a foto of the VFD, pressure tanks and chlorinator. Obviously, you wouldn't need teh chlorinators. THis is supplying water to the whole Eq Center including automatic horse waterers. cattle waterers, shop and care takers residence, along with the riding arena restrooms etc.
As long as no one screws up and leaves a hose running someplace, it will work like a champ. It's spring runs 365 days/year and has for the 100 years it has been known about..
Check out Grundfos.
ME0 -
In our area
you'd need an RPZ instead of a DC BFP. Here's a pic from ISH showing the cut-away view of a cistern utilized for flushing WC's, watering the garden and/or doing laundry. Note the pick-up screened pump intake which is suspended below the surface (avoids floating debris) and kept above the bottom (avoids sinkers).
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Many thanks for the suggestions...
... so, how about this for KISS?
The pump is fed via the cistern but stays out of the house because of the Cambridge plumbing inspector. You don't want to bring "contaminated" water into the home... A floating switch keeps the pump energized as long as there is enough water to keep it fed. The pump is shown on the cart but could be a submersible type and kept in the tank year round.
A 1" Solenoid valve opens whenever both other float switches are closed (i.e. hanging down). A vacuum breaker allows the water to empty out of the line running from the cart to the cistern whenever the water is shut off. The backflow preventer will be in the house.
We could even interlock the controller to stop running until the cistern is replenished to the point where there will be enough water in the cistern to do a regular garden dousing.
The more I think about it, the more the submersible Grundfos makes sense... it could eliminate the cart as the vac-breaker + solenoid could be just as well inside as outside the home. OK, so just imagine no cart! Cheers, and thanks!0 -
Cistern
How about another float switch that is set just above the low level float switch ( which I would use to kill power to the pump to prevent dry running of pump) another switch that opens a 24vac irigation valve to fill the cistern with an airgap to prevent backlow and your pump does all the work and cistern only fills with house supply water when needed.
Joe0 -
I'm a bit confused...
... isn't that what I'm proposing in the post right above yours?0
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