Étape 2 - Evaluate a site and size the ram pump
First of all, it is necessary to find surface water that continuously flows on a sufficiently steep slope (about 10% minimum). If it's a dam or lake, make sure that there are positions below.
To evaluate a site, 4 parameters have to be estimated (as shown on the scheme) :
- q water flow
- H lift height
- L driving line lenght
- h fall height
Concerning the water flow, it it not necessary to be really precise, an average value would be enough to size the system. Several techniques are available, depending on your material and time : see Water flow estimation"
The water flow can vary a lot depending on the seasons, so it could be relevant to establish a maximal and minimum flow throughout the year.
The lift height corresponds to the height difference between the pump height and the water reservoir. Concretely you should decide where you want the water to arrive, and measure the height difference between this point and the water source (in average). This measure will be precised later in the process. Slope measuring can be done with this website https://www.geoportail.gouv.fr/carte :
Place GPS coordinates on the map, and use the function "asymetric profile". This correspond to a curve showing the elevation depending on the distance (in m).
The driving line lenght and the fall height are directly related to the river or lake slope. In this case as well, it would be interesting to establish an asymetric profile in order to take distances and elevation gradients into account.
Once the parameters of the site are identified, we will size the pump in order to retrieve the needed flow and a minimal installation coast (the smaller the pump is, the cheaper it will be).
Determine L, H and h:
General Formula: q=((h*Q)/(h + H))0.70
Where 0.70 is the pump efficiency and Q the arrival flow.
Concretely, you will need:
You can also use a fall diagram as shown on the picture to determine H and h.
Sizing of the pump:
To size the pump itself, you have to chose the needed arrival flow. One of the easiest ways to do that is to use the provided table, that gives the final pipe size according to the source flow, the elevation ratio h/H and the final flow.
Using the table, you can proceed as follows:
-choisir le débit de sorti voulu correspondant aux besoins en eau
-trouver la case correspondante en fonction des rapports d'élévations possibles avec votre terrain
-ne pas hésiter à surdimensionner en cas de doute
-vérifier que le débit de votre cours d'eau est bien supérieur à celui indiqué dans la ligne choisie
-lire sur la même ligne les dimensions du bélier pertinente avec votre configuration
On obtient donc le diamètre D du tuyau de batterie (ou conduite motrice) qui est le même pour tous les composants de la pompe.
ex: 26x34 correspond à un diamètre intérieur de 26mm et un diamètre extérieur de 34mm
Attention les dimensions sont donnés en mm mais peuvent être exprimés en pouces sur le marché.
| Millimètres (mm)
| Pouces ou inch
|
| 15x21
| 1/2
|
| 20x27
| 3/4
|
| 26x34
| 1
|
| 33x42
| 1 1/4
|
| 40x49
| 1 1/2
|
| 50x60
| 2
|
L’ensemble de la pompe est donc de même dimension sauf le tuyau de sortie (ou conduite de refoulement) qui est de telle sorte que son diamètre D’ soit égal à la moitié du diamètre du tuyau de batterie : D’=D/2
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