3.5.8 Hydraulic ram pump
Hydraulic ram pump
The principle construction of a hydraulic ram pump is illustrated in figure 3.58a. The supply line must be of a certain length, usually 5-20 meters. The air vessel is located 0,5 to 3 meters below the water surface and pumps water up to a higher level, usually a tank for fresh water supply.
Figure 3.58a Hydraulic ram, diagrammatic sketch.
If the waste valve suddenly closes, the mass of water in the supply pipe is subjected to rapid deceleration which causes a rise in pressure. The delivery valve opens and water is forced up. When the water in the supply line momentarily changes direction, a partial vacuum is created at the waste valve causing it to open, whereupon water begins to flow in the supply line again. The action of water flowing through the waste valve causes it to close again and the cycle is repeated. Together with the liquid-jet pump the hydraulic ram can be regarded as a hydraulic transformer, the hydraulic ram transforms low pressure to high pressure and the jet pump transforms high pressure to low pressure. The following applies for the hydraulic ram:
QP * HP = η * Qd * Hd (Equ 3.58a)
or
Qd = (QP / η) * (HP / Hd) (Equ 3.58b)
where:
Qd = Motive water flow in supply line
QP = Delivered flow in delivery line
Hd = Supply head
HP= Delivery head
η = Efficiency
The efficiency depends upon the quotient z=Hp/Hd according to figure 3.58b. By means of comparison, it may be noted that for large scale water delivery via water turbine, electric grid system and water pump, efficiencies of up to about 50 percent can be obtained, whereas for domestic use via electric grid and water pump the efficiency is usually less than 10 percent.
Figure 3.58b Efficiency for hydraulic ram.
The hydraulic ram has long been used for transporting fresh water for domestic and agricultural purposes. There are installations which have been in use for more than 50 years. Hydraulic rams are sold in many sizes for supply water flows Qd from 60 l/h to 9 m³/h with total delivery heads of up to about 40 m, figure 3.58c.
Figure 3.58c Hydraulic ram pump