(Last update : September 2009)
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MIETBP is a French acronym (Micro Irrigation Evolutive Très Basse Pression) meaning “Evolvable Very Low Pressure Micro Irrigation”
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André Sautou
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I have developed in my (kitchen and flower) garden a drip irrigation system deliberately designed so as to be simple, rational, cheap, durable, within reach of any do-it-yourself-oriented gardener and that many others would probably adopt if they could find on the market the appropriate drip emitters (requirements precised in chapter V, last paragraphs preceding the photos).
Many visitors suggested I should make this system known on the Internet. I have complied to that suggestion in 2008 and decided to describe it on the present website, in French, in English and in Spanish.
Precisions : The MIETBP system belongs to the public domain. No patent is attached to its working principle and will never be. It just takes advantage from basic laws and obvious facts of physics that anybody can recognize by him(her)self. My only intention is to share the knowledge many years of experimentation have allowed me to gather.
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To my readers, from a teacher : Playing with three verbs.
“What you can, you do ; what you can’t, you teach”, says an English proverb, not very nice for teachers.
Well, I prefer to say “What I can, I do and teach”.
And I teach this lesson : “Yes, you can ; then, why not try and do it yourself ?”.
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Summary :
I / Initial specifications
II/ Solution adopted so as to fulfil the wanted specifications
III/ Realisation
IV/ Annotated descriptive diagrams
V/ Complementary explanations and photos
VI/ Evaluations of pressure losses
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I / Initial specifications :
I conceived this system between 1990 and 1992 with the aim to reach the following objectives :
1°/ The system must permit a permanent evolvability (additions and suppressions) depending on crops coming to an end whilst others are just being undertaken.
2°/ It must be composed of simple elements, stored in proper order in the tool shed (ready to be used when required) and able to be easily assembled (allowing branching at any point of the network) as well as easily dismounted (so as to be replaced in the stock when no longer needed). Stored elements ranging according to a common-ratio-2-geometric progression will allow to compose any wanted length.
3°/ The system must have the capability to irrigate a maximum length of about 350 m, from the only source available in my garden : the city water distribution network, from which I get water under a 6-bar pressure through a garden-meter (therefore exonerated from sewage-water-evacuation taxes, the price being then reduced by around 60% when compared to the cost of the same water delivered through the house-meter).
4°/ The pressure must be easily measured, controlled, limited, equalised and well balanced all over the irrigation network.
II/ Solution adopted so as to fulfil the wanted specifications :
One solution appeared to me quite obvious : the irrigation network must operate on very low pressure (less then 0,25 bar), this pressure being then easily measured by means of a transparent vertical hose (or at least a vertical hose fitted with a transparent 1-m-long superior part) acting as a manometer, the maximum height reasonably conceivable ranging around 2.5 m (8 ft). The junctions connecting the assembled elements will be watertight if the exterior diameter of each male connecting part (rigid or semi-rigid) slightly exceeds the interior diameter of the corresponding female part (flexible and slightly elastic). No clamps will be needed, as the pressure will always be kept very low, being limited under the effect of overflow shedding at the top of the vertical hose.
III/ Realisation :
After a few experiments (during the summer 1990), it appeared to me
1°/ that the system described below (Chapters IV ans V) would comply to the specifications listed above and be operational under a 0.2-bar pressure (2 m {6.7 ft} of water column ) controlled by means of a 2.35-m-{7.8-ft}-high vertical hose fixed on a prop.
2°/ that the global network should be hierarchised and structured into several sectors ;
3°/ that each sector should
-> be horizontal (knowing that a 20-cm {8 inch}drop entails a 10% pressure variation) ;
-> begin with a flow-and-pressure-adjustment tap (The flow and the pressure are simultaneously adjusted. My measures had shown that the average irrigation flow per unit of length was approximately proportional to the pressure within the 0.13-to-0.23-bar domain {4.3 to 7.7 ft of water column}).
-> include within one of its forks (generally close to the starting point and clearly visible from the adjustment tap) the transparent vertical hose used as a manometer and pressure limiter ;
4°/ that the intermediate pressure (measured in metres of water column) on the general-distribution network (between the source and the beginning of each sector) should be well above the maximum drop separating the upper and lower sectors (around 1.5 m in my garden), for instance around 10 m {33 feet} of water column (= 1 bar = around 15 psi).
During the summer 1991 I developed a global watering length of 80 m structured into 2 sectors. The validity of the system relatively to the wanted specifications was confirmed. I achieved the installation the next year (summer 1992), with a 350-m watering capability, the global network being structured into 6 sectors.
IV/ Annotated descriptive diagrams : (Click on the diagrams to enlarge)
Notice : The transparent vertical hose may be placed anywhere on the sector, on condition that the water level be clearly visible from the adjustment tap. However it is better to place it at the beginning of one of the forks when the total irrigation length on the sector may get over 50 m {around 170 ft }. More explanations are given in chapter VI, with evaluations of pressure losses.
V/ Complementary explanations and photos :
Le kitchen garden (western side of the house) is divided into three terraces, each of them constituting an 18-m-{60-ft}-long 4.6-m-{15-ft} wide sector (including a 0.5-m {1.7 ft} wide servicing walk). The tilling is generally done along the width direction, so that each row of crop measures 4 m {around 13 ft} and therefore most often needs two 2-m (8-soaking-ring) watering elements. Up to six rows (24 m, 96 drippers) may be irrigated from every connecting tee, without exeeding 70 m (280 drippers) on the whole sector. The pressure difference between the beginning of the sector and the end of each branching remains then below 20%.
{The next update will include evaluations of head losses calculated by using the Extended Bernoulli equation and the formula of Lechapt and Calmon.}
The flexible female connections joining the watering elements are portions of standard 15-mm-interior-diameter hose of quantified length (8 to 12 cm, 20 cm, 30 cm, 50 cm, 1 m, 2 m, 4 m and 8 m) used complementarily with 8-to-12-cm-long 16-mm-exterior-diameter rigid male connections.
The four holes bringing water under each oozing ring were bored by means of a drill equipped with a 2-mm-diameter bit. I built a device allowing to fix a 2-m-long portion of hose, position and bore the 8 first couples of diametrically opposed holes, operate a 90° rotation and bore the 8 complementary couples of diametrically opposed holes.
The oozing rings were cut out of 15-mm-interior-diameter porous hose, using a sharp cutter and a mitre box (fitted with a piece of wood allowing to systematically cut 22-mm long rings). The watering element can easily be slipped into a ring (so as to put this one into its proper location), using a special blocking device, after having previously immersed the rings into concentrated soapy water.
Two complementary kinds of connecting tees are used : female tees (flexible 15-mm-interior-diameter hose on the input and the two outputs) and male tees (semi-rigid 16-mm-exterior-diameter hose on the input and the two outputs). Both are made by water-tightly assembling standard commercial tees of suited diameter with short portions of the desired kind of hose. The interior diameter of the standard tee must be equal or as close as possible to 13 mm so as to limit singular pressure losses.
Every fork (branching) of a sector ends with a stopper. Stoppers are made with a 8-to-12-cm-long portion of flexible 15-mm-interior-diameter hose open on one side and shut on the other side with a sparkling-wine plastics cork.
Every connection between a male part (Øexterior = 16 mm) and a female part (Øinterior = 15 mm) can be easily done or undone, is sufficiently water-tight and withstand without any clamp the 0.2-bar pressure (2 m of water column). The system is therefore very simple and evolvable, as one can easily add or suppress elements depending on the evolution of the crops. Every significant modification of length must be followed by a new adjustment of the flow so as to recover the wanted 2-m level on the transparent vertical hose. Any modification on one sector does not change significantly the flow and pressure on the other sectors when the intermediate pressure (on the general distribution network) is adjusted around 1 bar.
After every use, the watering elements are systematically washed with a fountain, then immersed for at least 24 hours in a 2-m high PVC-column containing 50 L of diluted hydrochloric acid (so as to eliminate calcareous deposits ; the solution contains 3 L of commercial concentrated hydrochloric acid added with water).
After 13 years, as the oozing rings had become slightly overstretched, I decided to replace them all during the winter 2005.
I also had to change the electro-valve in 2008.
The system could be simplified by replacing the electro-valve (programmed by a standard on-off-voltage timer) by a plain manually-operated tap. You open it when you want to begin your watering … but you must not forget to close it three quarters of hour later !
Apart from these two renovations, the set of initial elements still works satisfactorily in spite of the facts that many flexible connections have become more or less rigidified under the effect of aging.
The oozing rings used as drip emitters in my experimentation of the MITBP system were cut out of a kit of Lifecell micro-porous hose, commercialised in France by IIS France. The oozing flow each emitter delivers results essentially from a lateral diffusion from the 4 central holes (towards each of the two circular ends) along the cylindrical surface separating the ring and the overlapped pipe, the water finally dripping through each of the two circumferences delimitating the interface (A slight diffusion through the wall of the ring also occurs, but its contribution to the flow is quite negligible at very low pressure). At a 2-m-of-water-column pressure (0.2 bar) the flow they deliver during the first four or five years of use ranges somewhere between 1 and 2 L/hour/dripper {around 0.25 and 0.50 US gallon/hour/dripper}, keeping stable all over a summer season. But it increases with aging, as the rings become ever more loose, as also increases the variability from one emitter to another. This defect (the main inconvenient observed on the MIETBP prototype I have developed) may be corrected by clasping each ring inside a rigid sheath tightly enclosing it in such a manner that its overstretching is compensated. My next season of experimentation will be devoted to such correction.
[The normal utilisation of porous pipes (the one they have been designed for) takes advantage from the process of diffusion through the wall of the pipe, needing then a pressure ranging at some point between 0.3 and 1.5 bar (3 and 15 m of water column). This mode of utilisation is therefore inappropriate to the MIETBP system. But everything gets different when one uses rings (cut out of the same material) encircling holes bored in a pipe. In this configuration, the lateral diffusion through the interface becomes the preponderant mode of diffusion, starting with a much lower pressure, delivering a flow approximately proportional to the pressure and of convenient intensity (for drip irrigation purposes) in the range extending from 1.3 to 2.3 m of water column, hence being quite applicable to the production of drip emitters satisfying the MIETBP system’s requirements.]
More generally, the MIETBP system can be developed with any kind of drip emitters able to deliver a flow proportional to the pressure within the 1.3-to-2.3-m-of-water-column range, with a value ranging between 1 and 2 L/hour/emitter {around 0.25 and 0.50 US gallon/hour/emitter} at a 2-m-of-water-column pressure. Let us precise, though, that the drippers are best suited to most uses when they can be slightly buried (which is the case with porous rings). Any source able to deliver filtered water under a stabilised pressure adjustable between 0.5 and 1.5 bar (5 and 15 m of water column) is convenient for feeding a MIETBP network similar to the one I have developed in my garden, implying several terraced sectors. But a plain tap (faucet) able to deliver an adjustable flow may as well be used for irrigating a watering length able to evolve between 10 and 70 m, on a small horizontal surface which constitutes in this case the only sector. One can also feed this only sector with water stored inside a heightened tank, on condition to filter that water.
It appears clearly, now, that the criteria of choice of drip emitters adapted to the MIETBP system radically differ from the ones applying to all other present-day-existing micro-irrigation systems. Usually operating between 2 and 10 m of water column (low pressure) and submitted to important variations, those other emitters have generally been designed so as to deliver a flow depending as little as possible upon the pressure. But such property is of course irrelevant when the pressure is easily controlled, mastered, stabilised and adjusted very close to a well defined value all over the irrigation network, which is one of the main specificities of the MIETBP system. It is necessary, on the contrary, in order to make the adjustment, that the flow be dependant upon the pressure. And proportionality is the ideal relationship relatively to that necessity.
VI/ Evaluations of pressure losses :
(Will be published soon)
