Plant watering, Drip Line info

[Daniel]

Now this issue is not going to applicable to those that grow acres of tobacco. but for the average back yard grower it might.
In my dessert climate, drip line irrigation is just about the only alternative I have.
This year I am going to try and grow 1651 plants in one lot. this will require 230 feet of 3/4 inch pvc pipe to run from the well to the tobacco patch. luckily it runs slightly down hill which will help preserve line pressure. Branching from that 3/4 inch main line will be as many as 13 1/2 inch drip lines containing 1651 1/2 GPH emitters.

I now have all the components but am very concerned my design will not work.

I have 40 P.S.I. and 27 GPM flow at the well. The system simply calculating at 1/2 GPH per emitter needs 825.5 GPH. In reality tests show that the emitters run closer to .75 GPH

We put 800 emitters into a 50 foot section of 1/2 inch drip line and tested it here at home with 900 GPH of flow and the pressure is unreal at 70 P.S.I. or more. At 800 emitters water nearly stopped flowing out of the end of the drip line when we removed the end cap. that means the system had used all of the water that can physically flow through a 1/2 inch line. Pressure had fallen to 0. The most emitters I can even run here at home in one line is about 750. adding branches will increase how many GPH can even flow through the system.

At the Tobacco patch I have the potential for 1620 GPH at 40 PSI. Can a 3/4 inch PVC line even carry that much water? According to information I have found online it can. But I am not sure that info is reliable. It appears to me they simply may have been crunching numbers rather than actually running water through pipes and testing it.

Also can 1 3/4 inch line supply enough water to 13 1/2 inch branches?

Finally at what point will the entire system not be able to supply enough water to 1651 1/2 GPH emitters?

AS I understand it these emitters require that the pressure remain at least 10PSI to even operate. My tests indicate otherwise. if there is water in the line even at 0 PSI these emitters will on average put out 1/2 GPH. THe emitters at the beginnign of the line actually where a bit over while the last ones where barely flowing. but the emitters in the middle measured at right at 1/2 GPH or a bit more. This tells me that by the time the last emitters where reached. there simply wasn't any water left. taking off the end cap confirmed this. There was barely a trickle of water coming out the end. Keep in mind this was a 900 GPH flow compared to the tobacco patch of 1620 GPH.

I am thinking my main concern is to provide more branches. this gives the water more paths to follow allowing more water per hour to reach emitters. I am just not certain how many branches.

13 sounds like to many, to many by far even. reducing the branches to just 4 is asking each branch to supply water to only 412 to 413 emitters. this is about half of what we tested a 1/2 inch line can supply.

Reducing branches to 2 causes each line to have to supply 825 or 826 emitters and my tests indicate that a 1/2 inch line cannot carry that much water. not even at fairly high pressure.

Anyway I hope to continue to document what I discover and just what answers I do find. In reality I intend to start one branch and run it until it stops flowing. at which time I will estimate where to cut it and then add another branch. So for example I may get 900 or 100 emitters into a single branch and find that I am running out of water. at which point I will evaluate just how short I need to make that branch to insure the second branch will receive enough water. I may be able to operate with as little as two branches.

I also suspect I will find that flow varies to much in longer branches. If this is so I may split into even more branches to even out the flow from every emitter.

I have done just about everything I can think of. otherwise it is now a matter of trial and error. At wost I have to run an extra 135 foot length of PVC and create a second "Zone". Not the end of the world. This causes the person watering the patch to have to go out after 2 hours, shut of one ball valve and open a second and then let that run for 2 hours.

 

[Lakota]

Daniel I think you can figure 1/2' line @ 12 to 14 gpm @ 50 psi, 3/4 18 to24 @ 50 psi. You could build a manifold and few manual timed valves to control your system, how many zones you would need ect. Here is a canadian link to the timer valves.

http://irrigationdirect.ca/cart.php?target=category&category_id=284

 

[Jitterbugdude]

I used drip lines about 10 years ago and thought they sucked. I had a real problem trying to weed my garden with a hoe. Quite a few times I nicked the partially buried line. In addition I couldn't till the garden the following year unless I pulled up all the lines. Talk about a PIA, pulling up about 300 ft of line with all the "t"s and connectors.

Randy B

 

[Jack in NB]

Daniel - Zoning would be the answer. Trial and error!

I use drip tape on mine, laid on the surface of the ground along each row, and cover the double row with black plastic - both to conserve water, and to cut down the weeding problem Randy faced. The drip tape is a lot cheaper, and delivers more water than the emitter system. It drips every foot or so, between plants if they're spaced 3 ft, but as it's under the plastic most of it is available to the plants. Flow rates vary with the type spec'd - with mine, an hour and a half on will deliver an inch of rain equivalent.

It runs on 4 to 8 psi pressure, so I use a gate valve at the feed end to regulate the pressure.

I can run about 100 ft lengths before the tail end runs out of pressure from the flow restriction in the tape itself. If the delivery flow permits, two or more lengths can be hooked in parallel. We've had as many as 8 runs on at once in the nursery, fed from a 1" line.

 

[Chicken]

my experience with drip line,

tells me you'll be o.k. daniel,,,it may take a while for the whole system to fill with water,,, but once the pressure hit's your emitters will start dripping,,

if anyones intrested a good company to order drip line,,and any fittings is,,,, DRIP WORKS . COM,,,,, they also have a free cataloug,,,,which is full of information concerning drip lines,, how they work,,,,e,t,c,

 

[Daniel]

I checked several places for the parts. Irrigation Direct ended up being the lowest price. I will have to wait to report on quality. A big part of why they came out on top price wise was because of the size of the order I placed and my order qualified for free shipping with them. That alone cut over $100 off the order.

In our tests I have noticed a few blown out emitters. not good on the quality standpoint. But even at that it is not to bad. far less than 1%.

It looks like I am going to end up just flying by the seat of my pants on this one. I have done everything reasonable that I can do. I will just build the system turn it on and take some measurements. Adjust as necessary. bottom line I want 1/2 to 3/4 gallon per hour per plant and pressure low enough it does not blow my emitters out.

Randy. Drip irrigation around here solves the weed problem except right at the base of the plant. If you don't put water on it here weeds don't grow. The dry climate can be a blessing if you do things right.

 

[Ishi]

Daniel;
Can you run another line and feed your drip line from each end?

 

[Daniel]

Ishi, I had not really thought of that but I can do it in several ways.
I have 235 feet of 3/4 inch pvc running from the well across the short end of my tobacco field. the field is going to be 95 feet wide. As many as 13 1/2 inch drip lines will then branch off of that pvc. I could branch off of the pvc loop the 1/2 inch line down one row and back up another and connect the other end back to the pvc. I can also make more than one 3/4 inch pvc pipe running to the field as well.

 

[johnlee1933]

Daniel,

I just copied this off the net from a commercial supplier. Note the change in volume vs. diameter. This is for Schedule 40 pipe but for low pressure a lighter weight pipe might work. I am not familiar with PVC pipe costs right now but would guess the incremental cost increase is smaller than the volume increase. Perhaps running a larger line would solve the problem and be cost effective. I don't know about your area but here in CT the water is hard as the devil (Calcium Carbonate). If that is the case in your area you may be pushing the Ph way up.

John

			[SIZE=-1]Assume Gravity to Low Pressure. About 6f/s flow velocity, also suction side of pump[/SIZE]	[SIZE=-1]Assume Average Pressure. (20-100PSI) About 12f/s flow velocity[/SIZE]	[SIZE=-1]Assume "High Pressure" PEAK flow. About 18f/s flow velocity[SUP]*[/SUP][/SIZE]
Sch 40 Pipe Size	ID (range)	OD	GPM[SIZE=-2] (with minimal pressure loss & noise)[/SIZE]	GPH[SIZE=-2] (with minimal pressure loss & noise)[/SIZE]	GPM[SIZE=-2] (with minimal pressure loss & noise)[/SIZE]	GPH[SIZE=-2] (with minimal pressure loss & noise)[/SIZE]	GPM[SIZE=-2] (with significant pressure loss & noise)[/SIZE]	GPH[SIZE=-2] (with significant pressure loss & noise)[/SIZE]
1/2"	.50-.60"	.85"	7 gpm	420 gph	14 gpm	840 gph	21 gpm	1,260 gph
3/4"	.75-.85"	1.06"	11 gpm	660 gph	23 gpm	1,410 gph	36 gpm	2,160 gph
1"	1.00-1.03"	1.33"	16 gpm	960 gph	37 gpm	2,220 gph	58 gpm	3,510 gph
1.25"	1.25-1.36"	1.67"	25 gpm	1,500 gph	62 gpm	3,750 gph	100 gpm	5,940 gph
1.5"	1.50-1.60"	1.90"	35 gpm	2100 gph	81 gpm	4,830 gph	126 gpm	7,560 gph
2"	1.95-2.05"	2.38"	55 gpm	3300 gph	127 gpm	7,650 gph	200 gpm	12,000

 

[Ishi]

Ishi, I had not really thought of that but I can do it in several ways.
I have 235 feet of 3/4 inch pvc running from the well across the short end of my tobacco field. the field is going to be 95 feet wide. As many as 13 1/2 inch drip lines will then branch off of that pvc. I could branch off of the pvc loop the 1/2 inch line down one row and back up another and connect the other end back to the pvc. I can also make more than one 3/4 inch pvc pipe running to the field as well.

I meant run a main line down each end of the field and connect the lines with the emitters to each end of the main lines so that they get water from each end. If this is what you are talking about i misunderstand

 

[Daniel]

Ishi, That might help keep the flow at every emitter more equal. but my description actually has the same effect with 230 feet less pvc pipe.

Johnlee. I have seen that chart before. I hae a suspicion that they jsut crunched numbers to get it. I am not sure they ever went out and actually measured 2160 GPH through a 3/4 inch pipe. There are actually two other charts that work with this one to give the whole picture. IT is a fact that only so much water can fit through a 3/4 inch pipe in a given amount of time.

I do know that I have a flow of 27 gallons per minute through a 3/4 inch pipe at the well. This gives me a potential flow of 1620 gallons per hour. so the amount of water is there no problem. In fact I have about twice the water per hour needed.

 

[Lakota]

Daniel Is there pressure tank at the pump? If there is what is the high kick out and the low kick in? Do you have any fine sand in the well? An inline filter might save you some headaches with the emmiters. I don't know the law where you live but here we have to install a backflow valve to stop any water that could be contaminated ( fertilizer pesticide)from being pulled back into the well. Russ

 

[Jitterbugdude]

Additionally, two things to consider: You can buy cheap flow regulators from the drip supply guys that you install down at your point of use. I'd also check your well cap. Under it should be stamped your flow rate (which you already know) and your recovery rate. You do not want to pump your well dry like my friend did with his 475 foot well.

Randy B

 

[Daniel]

Lakota. Their well is already set up with the back flow and yes it is code here also. I am going to tap in at a manifold that already exists.

Randy, they use this well to fill a duck pond and leave it running all day for their chickens. We have been out there twice and have pretty much gone over what our tobacco woudl require from their weell and they are all good with it. Basically I am thinking it will take 1651 gallons a day in the hottest part of the summer. For them this is very little water. That they have enough water in their well is always a concern. But I am not going to be the heaviest user of water by far. I watch them let as much per day flow out across the ground as I will need. We all looked at that and said put a float valve on the tank watering the chickens and I will just be diverting that lost water to my tobacco. Also keep in mind we traded labor for the use of the land and water. they feel they are getting the better end of the deal. I just hope they come through on their end. I am counting on them to keep the day to day watch on the tobacco.

 

[Chicken]

well, im curious as to how the drip-line worked for you this year???

 

[Daniel]

Chicken, the 3/4 inch line 200 plus feet long was able to supply half a gallon of water to 1651 plants fairly well. But we where right at the edge of over doing it. The emitters we had woudl work as long as there was water in the line.

The flow we had was 27 gallons per minute. So really good flow but low pressure. Pressure did not seem to matter. emitters woudl work right up to 0 pressure.

1 inch pvc and larger drip line (ours was half inch) would have gotten more water per hour to the field.

In all it worked. the plants still died.

 

[Knucklehead]

Daniel- What killed your plants?