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.

 Table 1.  Ram Performance Data for a Supply of 1liter/minute 
Liters Delivered over 24 Hours
Working Fall (m)Lift - Vertical Height to which Wateris Raised Above the Ram (m)
1.5 13596.57054361915    
2.0 2201561057953332519.512.5  
2.5 2802001251006640.532.52415.512 
3.0  260180130876551402717.512
3.5   215150100 75604631.52014
4.0   255173115866953362316
5.0   3102361551189471.5503623
6.0    28218514011293.564.547.534.5
7.0     216163130109826048
8.0      187149125946955
9.0      2121681401058462
10.0      2451871561179369
12.0      29522518714011383
14.0       26521816713297
16.0        250187150110
18.0        280210169124
20.0         237188140
Components of Hydraulic Ram

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.

Table 2.  Range of Drive Pipe Lengths  
for Various Pipe Diameters 
Drive Pipe Size (mm)Length (meters)
The drive pipe diameter is usually chosen based on the size of theram and the manufacturer's recommendations as shown in Table 3.  Thelength is four to six times the vertical fall.
Table 3.  Drive Pipe Diameters by 
Hydram Manufacturer's Size Number
Hydram Size1233.5456
Pipe Size (mm)32385163.576101127
Ram. Rams can be constructed using commercially available check valves orby fabricating check valves.  They are also available as manufacturedunits in various sizes and pumping capacities.  Rams can be used intandem to pump water if one ram is not large enough to supply the need. Each ram must have its own drive pipe, but all can pump through a commondelivery pipe as shown in Figure 3.

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.

Table 4.  Hydram Capacity by Manufacturer's SizeNumber
 Size of Hydram
Volume of Drive Water Needed (liters/min)7-1612-2527-5545-9668-137136-270180-410136-270180-410
Maximum Lift (m)150150120120120105105105 
Delivery Pipe.  The delivery pipe can be of any material thatcan withstand the water pressure.  The size of the line can be estimatedusing Table 5.
Table 5.  Sizing the Delivery Pipe
Delivery Pipe Size (mm)Flow (liters/min)
Storage Tank.  This is located at a level to provide waterto the point of use.  The size is based on the maximum demand perday.

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.