Need help on unusual garden and orchard irrigation setup

[rustic_philosopher]

Hey all,

I need some advice from wiser folks than me on setting up some irrigation for my garden and orchard. First let me explain the setup I am working with.

• I have a water well as the source of water for the house and ag stuff
• I have a 1000 gallon buried concrete cistern that pull water from the well that is near the garden and orchard area. I have a separate cistern so I can set it up to only pull from the well overnight so both the house and garden dont draw on the well at the same time.
• I have a pressure tank (somewhat small) on the cistern at the moment fed by a submerged pump in the cistern.

Ok, now my rough plan is to bury pex from the cistern pressure tank as main lines between the bed areas and main archard area and then run drip irrigation off that. I have 22 4x12' raised beds, 8 20' rows of grapes and 4 rows of berry bushes I am setting up to be fed by this. I will run in zones to maintain some degree of pressure. I will also put in one or two above ground faucets but I will not be using them at the same time I run the drip irrigation.

The setup will be trunk and branch and while I will try to minimize junctions there will be somewhere between 3-6 junctions (mix of 90 degree, T and X junctions).

The bits I have questions on are around pex size, run length and ideal pressure tank size. The longest run in the setup will likely be close to 300' I think. I have a temporary line I ran to the orchard for feed a temporary hose hookup and I used 3/4" which worked ok.

So....

1. Would it be fine to use 3/4" pex for the main runs and then drop down to 1/2 or 3/8 in the last 10 feet or so to get to the beds (and drip lines) or should I stick with 3/4 throughout.
2. Will 3/4" pex over 300' with a moderate number of junctions paired with a reasonable pressure tank satisfy my described needs?
3. Are there any advantages to dropping down to a smaller pex size for the final 10-15' branches?
4. What size pressure tank should I realistically put in on the cistern since I suspect what I have is too small. I don't know the exact draw down rate since itll be variable with use.
5. To try and reduce pressure loss over the distance, are the low pressure loss pex fittings worthwhile?
6. What am I not considering?

To be clear, I can't exactly estimate the drip irrigation usage in the beds beds because that will depend on how many emitters we install based on what my wife wants to plant.

Before I start on the trenching, etc I wanted to get expert advice from others.

I deeply appreciate your help on this matter.

 

[rustic_philosopher]

Is the right sub forum for this? Surely someone has experience in pressure tanks and irrigation.

 

[wpns]

Why Pex instead of the usual black poly irrigation pipe? Lots of standard pipes, sizes, adapters, valves, etc.

Irrigation systems don't even technically need pressure tanks, they can just use jet pumps, so the pressure is inversely proportional to flow, and the Master Valve output on the controller powers up the pump for the duration of the cycle. You don't want the flow to go to zero for more than a few minutes or the pump head may overheat and melt off any plastic fittings, but that's rare if your system is working properly.

 

[rustic_philosopher]

Not sure what you mean about the pressure tank - I have to have it otherwise I have zero water pressure. I am on a well and the irrigation source is just a concrete cistern as described above so unless you have a pump and pressure tank you don't get water pressure.

In terms of the pex choice, thats mainly just for the long distance runs - once I get to the beds I would switch material but at the longest I will likely have a 300' run from cistern to drip irrigation location.

 

[wpns]

Yes, for a house you need a pressure tank, but for an irrigation system you can get away with _just_ a pump, no pressure tank, no pressure switch, just a centrifugal pump. Turn on the pump and the water flows, and the pressure is inversely proportional to flow, with a maximum of whatever the pump can provide against a closed outlet. The major advantage (besides removing the requirement for all the extra stuff) is that the pump will have one cycle per irrigation run, and the pressure will stay constant for any one zone.

I was going to say that black poly irrigation pipe is a lot less expensive than PEX, but that turns out not to be true, at least for a quick perusal of pricing on Google, so PEX is probably better for long runs.

 

[rustic_philosopher]

I cant speak to all pumps but I am pretty sure my pump is not mean to run for hours at a time. I can recall the well guy talking about the pump burning out if it runs endlessly.

In the case of not having a pressure tank and needing to run 5-6 zones (each being 30-60 minutes) the pump would have to run for basically 6 hours with little to no break.

 

[MicEd69]

I cant speak to all pumps but I am pretty sure my pump is not mean to run for hours at a time. I can recall the well guy talking about the pump burning out if it runs endlessly.

In the case of not having a pressure tank and needing to run 5-6 zones (each being 30-60 minutes) the pump would have to run for basically 6 hours with little to no break.

I would be very leery of any plumber who would say a submersible pump used on a water system for a house or agricultural system would fail if it ran continuously. Pumps fail because they cycle too much, not because they run continuously. As long as there is water flow to avoid overheating, the pump will be happy to run as long as you want it.

 

[wpns]

So what exactly is your pump and how is it connected again?

 

[Valveman]

Sorry I just saw this. As Mic said, pumps are made to run continuously and cycling on and off is what kills them. I have one feeding a stock tank that hasn't shut off since it was installed in 1999. Pumps like to run, cycling on and off destroys them. Drip systems are notorious for cycling pumps to death because drip uses so little GPM. You can run the pump without a pressure tank, as pressure tanks have nothing to do with the pressure and flow which comes from the pump. But as was said, the pressure will be inversely proportional to the flow. Which means small drip zones will see high pressure from the pump.

You can also use a Cycle Stop Valve with or without a pressure tank. Without a pressure tank the CSV acts like a pressure reducing valve and will keep the same pressure on a small zone as on a large zone. With a pressure tank a CSV will still keep constant pressure on any size zone, but the pressure tank/pressure switch will make the pump come on or off automatically by just opening or closing a tap.