|Water For The World |
Designing a Hydraulic Ram Pump
Technical Note No. RWS.4.D.5
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A hydraulic ram or impulse pump is a device which uses the energy of fallingwater to lift a lesser amount of water to a higher elevation than the source.See Figure 1. There are only two moving parts, thus there is littleto wear out. Hydraulic rams are relatively economical to purchaseand install. One can be built with detailed plans and if properlyinstalled, they will give many trouble-free years of service with no pumpingcosts. For these reasons, the hydraulic ram is an attractive solutionwhere a large gravity flow exists. A ram should be considered whenthere is a source that can provide at least seven times more water thanthe ram is to pump and the water is, or can be made, free of trash andsand. There must be a site for the ram at least 0.5m below the watersource and water must be needed at a level higher than the source.
Factors in Design
Before a ram can be selected, several design factors must be known.These are shown in Figure 1 and include:
1. The difference in height between the water source and the pump site(called vertical fall).
2. The difference in height between the pump site and the point ofstorage or use (lift).
3. The quantity (Q) of flow available from the source.
4. The quantity of water required.
5. The length of pipe from the source to the pump site (called thedrive pipe).
6. The length of pipe from the pump to the storage site (called thedelivery pipe).
Once this information has been obtained, a calculation can be made tosee if the amount of water needed can be supplied by a ram. The formulais: D=(S x F x E)/L Where:
D = Amount delivered in liters per 24 hours.
S = Quantity of water supplied in liters per minute.
F = The fall or height of the source above the ram in meters.
E = The efficiency of the ram (for commercial models use 0.66, forhome built use 0.33 unless otherwise indicated).
L = The lift height of the point of use above the ram in meters.
Table 1 solves this formula for rams with efficiencies of 66 percent,a supply of 1 liter per minute, and with the working fall and lift shownin the table. For supplies greater than 1 liter/minute, simply multiplyby the number of liters supplied.
|Working Fall (m)||Lift - Vertical Height to which Wateris Raised Above the Ram (m)|
A hydraulic ram installation consists of a supply, a drive pipe, theram, a supply line and usually a storage tank. These are shown inFigure 1. Each of these component parts is discussed below:
Supply. The intake must be designed to keep trash and sandout of the supply since these can plug up the ram. If the water is notnaturally free of these materials, the intake should be screened or a settlingbasin provided. When the source is remote from the ram site, the supplyline can be designed to conduct the water to a drive pipe as shown in Figure2. The supply line, if needed, should be at least one pipe diameterlarger than the drive pipe.
Drive pipe. The drive pipe must be made of a non-flexiblematerial for maximum efficiency. This is usually galvanized ironpipe, although other materials cased in concrete will work. In order toreduce head loss due to friction, the length of the pipe divided by thediameter of the pipe should be within the range of 150-1,000. Table2 shows the minimum and maximum pipe lengths for various pipe sizes.
|Drive Pipe Size (mm)||Length (meters)|
|Pipe Size (mm)||32||38||51||63.5||76||101||127|
In installing the ram, it is important that it be level, securely attachedto an immovable base, preferably concrete, and that the waste-water bedrained away. The pump can-not operate when submerged. Sincethe ram usually operates on a 24-hour basis the size can be determinedfor delivery over a 24-hour period. Table 4 shows hydraulic ram capacitiesfor one manufacturer's Hydrams.
|Size of Hydram|
|Volume of Drive Water Needed (liters/min)||7-16||12-25||27-55||45-96||68-137||136-270||180-410||136-270||180-410|
|Maximum Lift (m)||150||150||120||120||120||105||105||105|
|Delivery Pipe Size (mm)||Flow (liters/min)|
Sizing a Hydraulic Ram
A small community consists of 10 homes with a total of 60 people. There is a spring l0m lower than the village which drains to a wash whichis 15m below the spring. The spring produces 30,000 liters of waterper day. There is a location for a ram on the bank of the wash. This site is 5m higher than the wash and 35m from the spring. A publicstandpost is planned for the village 200m from the ram site. Thelift required to the top of the storage tank is 23m. The followingare the steps in design.
Identify the necessary design factors:
1. Vertical fall is 10m.
2. Lift is 23m to top of storage tank.
3. Quantity of flow available equals 30,000 liters per day divided by1,440 minutes per day (30,000/1,440) = 20.8 liters per minute.
4. The quantity of water required assuming 40 liters per day per personas maximum use is 60 people x 40 liters per day = 2,400 liters per day.
2,400/1,440 = 1.66 liters per minute (use 2 liters per minute)
5. The length of the drive pipe is 35m.
6. The length of the delivery pipe is 200m.
The above data can be used to size the system. Using Table 1,for a fall of 10m and a lift of 80m, 117 liters can be pumped a day foreach liter per minute supplied. Since 2,400 liters per day is required,the number of liters per minute needed can be found by dividing 2,400 by117:
2,400/117 = 20.5 liters per minute supply required.
From item 3 above, the supply available is 20.8 liters per minute sothe source is sufficient.
Table 3 can now be used to select a ram size. The volume of drivingwater or supply needed is 20.5 liters per minute. From Table 4, aNo. 2 Hydram requires from 12 to 25 liters per minute. A No. 2 Hydram canlift water to a maximum height of 150m according to Table 4. Thiswill be adequate since the lift to the top of the storage tank is 23m. Thus, a No. 2 Hydram would be selected.
Table 3 shows that for a No. 2 Hydram, the minimum drive pipe diameteris 38mm. Table 2 indicates that the minimum and maximum length fora 40mm pipe (the closest size to 38mm) is 6m-40m. Since the spring is 35maway, the length is all right. Table 5 can be used to select a deliverypipe 30mm in diameter which fits the supply needed, 20.5 liters per minute.