Since rainfall in Ladakh is so low (less than 10cms a year), cultivation can only take place in areas where rivers or streams can provide water for irrigation. Villages are therefore located either along valley floors or in the alluvial fans of met-water streams. Water is brought to the fields by a complex series of canals, or 'yuras', sometimes many miles long, which rely entirely on the force of gravity. Areas of land which otherwise might be cultivated remain dry if they are above the level of the available water.
As a means of providing water to such land, and alternatively to provide water in the house for domestic use, we have introduced the hydraulic ram pump. These pumps use the force of a relatively large supply of falling water to drive a relatively small quantity to a higher level. Water is drawn from a channel and flows down a drive pipe to the pump. The flow of water causes oscillation of an impulse valve, which forces water through a second, non-return valve and up the delivery pipe to a storage tank. Waste water is returned to the stream.
Commercial ram pumps have been available for many years, and are both effective and long lasting. However, they are also quite expensive. Our efforts have been directed towards producing a relatively low-cost pump which can be made from standard plumbing parts. The mode we have developed can be put together by local craftsmen with only the most basic workshop facilities. Machine tools are not required.
Ramp pumps operate over a relatively wide range of supply heads some as low as one metre and with flows as small as 5 litres per second. However, performance depends upon correct tuning and adjustment. We have found that the pumps work best at about 70 to 90 cycles per minute.
The body of the hydraulic ram pump is constructed of standard pipe fitting readily available throughout India. Two sizes of pump bodies have been constructed, but the relative proportions of the components do not vary.
We have specifically designed the impulse valve for its robustness and reliability. Other valve units were tested, but most could not tolerate wear, and required regular maintenance. The vale plate is made of mild steel, and is attached to a 10mm brass shaft. This is supported by a replaceable bronze bush set in a mild steel housing. The shaft is threaded on one end to adjust the stroke. Weights can also be added to adjust the rate of oscillation.
The drive pipe is one of the most important elements of any ram pump installation. The pipe contains the pressure surge and must be of sufficient strength to resist damage. Energy is lost due to the expansion of the materials, and to minimise this loss all materials should be as inelastic as possible. Drive pipes in our installation are of good quality G.I. Stock.
The diameter of the drive pipe should be large enough to minimize frictional losses caused during the rapid velocity changes of the water column in the pipe. However, diameter is often determined by cost and availability, and within broad limits performance varies little. The length of the pipe should be calculated to ensure that the compression wave cause by the water hammer reaches the open end of the pipe before pressure can be dissipated and the impulse valve allowed to open.
The ratio of diameter to the length of the drive pipe (L/D) is important. This ratio determines the characteristics of the water hammer within the drive pipe and the ability of the column of water to accelerate after it has stopped. Experiments have shown the ratio should be with the range:150-1000. For practical purposes, the drive pipe should be set at a gradient of one in four (25%).
The delivery pipe, unlike the drive pipe. Needs only to be sufficiently strong to support the static head of the column of water it contains. Plastic or rubber hose is adequate, providing that the diameter is sufficient to avoid major reductions in efficiency due to friction within the pipe. We have used 15mm galvanised steel pipes with rubber hose connections at bends.
The air chamber contains the compressed air which serves to cushion the effect of the water hammer and dampens the pressure surge in the delivery pipe. This provides a steady flow, minimising the frictional losses. In addition, the cushioning effect of the air prevents 'pounding' of the ram pump body caused by the pressure changes in the system. Air has to be replenished through a vent hole to ensure that the dampening effect of the hydraulic spring is not lost.
Our pumps have proved to operate very satisfactorily over a wide range of flows and heads, and are thus adaptable to meet particular demands. They are also almost maintenance-free. We have had pumps in operation for more than four years, and none of the impulse valves has yet required replacement. One pump we installed? at Matho monastery? raises water more than 45 metres from a supply head of only four metres, (Since it was only replacing a large number of labourers who were taking water up to the top of the monastery for construction purposes, it paid for itself in less than one day!) With careful location and tuning, efficiencies of 60% are easily reached The principal expenses of any ram pump insulation are the pipe connections from the supply tank and to the storage tank. Drive pipes should be of good quality G. I. Stock, while rubber hose can be used for the delivery pipe. Although frictional losses may result, using smaller diameter pipes may reduce the cost, and this should be considered when determining the cost/ benefit. A pump can be constructed in one day and thus additional labour costs are minimal.
Hydraulic Ram Pump Design
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