by shock it is essential to keep air in the air vessel. As air tends to be carried away in the delivery stroke, a “‘snifting valve” should be fitted in the ram below valve V, to admit a small quantity of air when the rebound of the water causes pressure to fall below atmospheric. The Double-acting Ram. A diagrammatic section of a ram on the double-acting principle is shown in Fig. 214. It is really a combination of a ram and a pump. The pure water enters the pure water supply pipe, P.W.S., and passes through a valve into the space above the upper piston, U.P. The impure water enters the lower part of the apparatus, through the pipe marked I.W.I. and passes on to the dash valve, D.V., working this part on just the same principle as with the single-acting ram, except that when the dash valve closes, the impure water does not rise higher into the: apparatus, but merely exerts its force on the underside of the lower piston, forcing it up and so displacing the pure water into the pure water delivery pipe. The upper and lower pistons are con- nected by means of a rigid rod, through which a weighted lever passes at L, to facilitate the downward movement after the pure water has been displaced. In this case, also, the cycle of events continues so long as the supplies are kept up. The pistons must of course be tightly fitting to prevent the passage of impure water. Fig. 215 gives an enlarged and more detailed section of the lower part of the apparatus, showing by a thick line the cup leather put to the pistons to ensure this result.<Callout type="important" title="Tight Fitting Pistons">The tight fitting of the pistons is crucial to prevent impure water from contaminating the pure supply.</Callout> The Hydrostat Ram. An improvement on the hydraulic ram is the hydrostat, manufactured by Hydrautomat Ltd. In this there are two cylinders of widely different diameters, one vertically over the other, their pistons being on one common vertical piston-rod, so that movement of the one entails similar movement of the other. In the large cylinder, water, which will be referred to as the driv- ing water, is admitted alternately above and below the piston and is exhausted from the other end to waste, or to some house or district situated at a lower level. THE BUILDING—ITS WATER SUPPLY 241 In the smaller cylinder, water, which we shall refer to as the driven water, is admitted, either from the same source or from another source of purer quality, and is forced to the high level at which the supply is needed, either to a reservoir or direct to the consumers. The entrance of the driving water to each end of the large cylinder, and its exhaust from the other end, are automatically controlled by an ingenious moving valve appliance. The entrance and exhaust of the driven water to and from the smaller cylinder are controlled by ordinary lift valves.<Callout type="tip" title="Automatic Control">The automatic control mechanisms in hydrostats reduce the need for manual intervention.</Callout> The superiority of the hydrostat over the hydraulic ram lies in the fact that it is noiseless in action, less liable to wear and tear, and more efficient. Not only is it useful for lifting water from a stream for the supply of an isolated dwelling at a high level, but it is also much utilised for “boosting” up pressure in certain mains of public water supplies. The driving water in such a case is the water which is supplied to some low-lying district and is not run to waste, whilst the driven water is that which is needed for the supply of some district which is abnormally high in level.<Callout type="risk" title="Waste Water Management">Improper management of driving water can lead to wastage or contamination.</Callout> The appliance is quite automatic in action, and will adjust its rate of working to the amount of driving water available and to the amount of driven water being consumed. It is unnecessary to provide a reservoir at the high level to receive the driven supply, unless the maximum rate of consumption at the high level exceeds the maximum rate at which the hydrostat will work, which of course depends upon the amount of driving water available.<Callout type="gear" title="Hydraulic Ram and Hydrostat Equipment">Specific equipment like hydraulic rams and hydrostats are essential for efficient water supply systems.</Callout> Power Required for Pumps. Before concluding this chapter it would not be out of place to explain how the power required to pump water can be calculated, for which purpose a numerical example will be worked. It will be supposed that it is required, during the hours at which the pumps are to be worked, to raise 1500 gallons per hour through a height of 160 feet. One gallon of water weighs 10 lb., so that the weight lifted per 2 i ; . 15,000 hour is 15,000 lb., and the weight lifted per minute is 7a 250 lb. Wh eee Horsepower output of pump = 33909) where W = weight in lb. lifted per minute and h = lift in feet; so that in the present instance the horsepower output of pump 242 THE BUILDING—ITS WATER SUPPLY _ 250 x 160 88,000 40 =5 -11- The engine required to drive the pump must have more power than this, since the efficiency of small pumping plants seldom exceeds 60 per cent. Taking the efficiency in the present case as 40 per cent., 40 : Power output of pump = 700 * horsepower of engine. : 100 .. Horsepower of engine = “qo * power output of pump. 10 oe a eo In the above example it has been supposed that the delivery pipe is of ample diameter, so that the frictional resistance therein does not appreciably increase the head against which the pump has to work.
Key Takeaways
- Double-acting rams and hydrostats are essential for efficient water supply systems.
- Tight fitting pistons prevent contamination in double-acting rams.
- Hydrostats offer automatic control, reducing manual intervention.
- Proper management of driving water is crucial to avoid wastage or contamination.
Practical Tips
- Ensure that the pistons are tightly fitted to prevent impure water from contaminating the pure supply.
- Utilize hydrostats for their noiseless and efficient operation in public water supplies.
- Calculate the power required for pumps accurately using the provided formula.
Warnings & Risks
- Improper management of driving water can lead to wastage or contamination, which could compromise the purity of the water supply.
- Manual intervention is still necessary despite the automatic control mechanisms in hydrostats.
- The efficiency of small pumping plants rarely exceeds 60%, so ensure that your engine has sufficient power.
Modern Application
While historical techniques like hydraulic rams and hydrostats have been improved upon with modern technology, understanding these principles remains crucial for survival preparedness. Modern systems often incorporate similar automatic controls and efficient water lifting mechanisms to ensure a reliable supply in isolated or emergency situations.
Frequently Asked Questions
Q: What is the importance of tight fitting pistons in double-acting rams?
Tight fitting pistons are crucial to prevent impure water from contaminating the pure supply, ensuring that only clean water reaches consumers.
Q: How does a hydrostat differ from a hydraulic ram?
A hydrostat is an improvement over the hydraulic ram as it is noiseless in action, less liable to wear and tear, and more efficient. It uses two cylinders of different diameters with automatic control mechanisms for driving and driven water.
Q: What factors should be considered when calculating the power required for pumps?
When calculating the power required for pumps, consider the weight lifted per minute, the lift in feet, and the efficiency of small pumping plants. The example provided uses a formula to determine the horsepower output based on these factors.