In this essay we will discuss about the valves and fittings used in water works and pipes.
Essay # 1. Sluice-Valves:
These are also known as gate-valves and are most commonly used in water works practice. These valves are cheaper, offer less resistance to the flow of water than offer valves, used for the same purpose.
Gate-valves control the flow of water through pipes, and are fixed in main lines bringing water from the source to a town, at 3 to 5 kilometres intervals, thus dividing the pipe line into different sections. During repairs only one section can be cut off by closing the sluice valves at both ends.
This valve is made of cast iron with brass, bronze or stainless steel mountings and its ends are screwed flanged or spigot and socketed on the pipe. It mainly consists of a wedge-shaped circular disc fitted closely in a recess against the opening in the valve. This is connected to a nut or wheel above by means of a thread spindle passing through a gland and suffixing box arrangement.
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When the wheel is rotated the spindle rises up, raising the disc along with it. The opening in the valve thus gets uncovered and the water from one section of the pipe line passes into another. The valve can be closed by rotating the spindle in another direction.
Figure 19.1 shows the sectional view of a gate valve. Small-sized gate valves are burled underground, and can be operated from the surface through a stop box. Larger valves are operated in under-ground chambers and are opened or closed through gearing.
Essay # 2. Pressure Relief Valves:
These valves relieve high pressure in pipe lines. Figure 19.2 illustrates such type of valve, which is intended to release excessive pressure that may build up in a closed pipe. It essentially consists of a disc controlled by a spring which can be adjusted for any pressure. When the pressure in the pipe line exceeds the desired pressure, the disc is forced off form its seat and excessive pressure is relieved through cross-pipe, after this the disc comes down automatically due to force of spring.
Essay # 3. Check-Valves:
These are also called reflux valves or non-return and are automatic devices which allow water to flow only in one direction and prevent it from flowing in reverse direction. One such type of valve consists of a metallic disc hinged from the crown which fits tightly against the annular valve seat.
The arrow indicates the direction of flow of water. When water flows, the disc rotates round the hinge and the remains in a horizontal plane. The water therefore passes off without any obstruction. Now if the flow reverses, the disc automatically falls down by rotating round the hinge and remains tightly pressed against the valve seat by the pressure of water itself, in this way it does not allow the water to How in reverse direction check valve.
Essay # 4. Air-Relief Valves:
When water enters in pipe lines, it also carries some air with it which tends to accumulate at high points of the pipe. When the quantity of air increases, it cause serious blockage to the flow of water. Therefore it is most essential to remove the accumulated air from the pipe line. Air-relief valves are used for this purpose.
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These valves consist of a cast iron chamber bolted on the pipe over the opening in the crown. A weighted float and a lever in it are so adjusted that when the chamber is filled with water under pressure from the pipe line below, the float and the lever remains released up preventing the flow of water through the valve.
But when air goes on accumulating at the top and builds up some pressure the water level gets depressed and the float sinks down with the lever and opens the valve. The accumulated air escapes out through the opening. The water level in the chamber again rises, raising the float with it and the valve gets closed. Thus these valves are automatic in action. Figure 19.4 shows two types of air-relief valves.
Essay # 5. Drain-Valves:
In the summits of mains, it is possible that some suspended impurities may settle down and cause obstruction to the flow of water. In the distribution system at dead ends, if water is not taken out it will stagnate and bacteria will be born in it. To avoid the above difficulties drain-valves are provided at all such points.
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These are also called scour-valves or blow-off valves. At the summit of main pipe, a branch is taken off from the lowest point, in which drain-valve is fixed. When drain-valve is opened the water rushes out thus removing all the silt, clay etc. from the main line.
Essay # 6. Hydrants:
These devices are used for tapping water from mains for lire extinguishing, street, washing, watering gardens, flushing sewer lines and for so many other purposes. These are generally provided at all junctions of roads and at 100-130 metres apart along the roads.
They are also sometimes used for filling the municipal water carts, to the water requirement during construction of roads, washing of roads, drains, sewers, sprinkling of public lawns etc.
In the case of fire break-out in a locality, the fire-fighting squad connect their hose with the fire hydrant and do the extinguishing of the fire by sprinkling water over it. For engine, which develops the required pressure in the fire hose.
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Usually the pressure neat in the nozzle of the fire hose is kept about 35 m. The diameter to the lire hose nozzle is about 28 mm. In case of big cities water pressure up to 100 m may be required; therefore engines, fire hose, nozzles etc. must be designed to bear this pressure.
Generally the following pressure is maintained in the pipe lines at fire hydrant position:
(a) 7-14m head of water if pumped through motor.
(b) 35-50 m head of water, if no pumps are used and water directly flows through the hydrants to fire.
In case of serious fire the water is drawn from served fire hydrants from the locality.
Following are the requirements of a good hydrant:
1. It should be easily connectable to the hose pipe.
2. It should be cheap in cost as well as maintenance.
3. It should be easily detachable during the panicky atmosphere of fire in the locality.
4. It should be reliable and should not go out of order during fire and operation,
5. It should allow to draw sufficient quantity of water.
Hydrants are of two types:
(a) Flush hydrant, and
(b) Post hydrant.
(a) Flush Hydrant:
Fig. 19.5 illustrates this type of hydrant. It is installed in an underground brick chamber flush with the foot path. It is covered from the top by a C.I. cover. To locate the position of this hydrant even in darkness, some distinct sign is provided near it at the side of road with letters ‘F.H.’ written on it.
(b) Post Hydrant:
Fig. 19.6 illustrates this type of hydrant. The barrel of the hydrant remains projected about 60-90 cm above the ground surface. These hydrants have a long stem with screw and nut at the top to regulate the flow of water. The post hydrant is connected to the main pipe, through a branch pipe and it can be operated by means of a gate valve. The diameter of the hose is usually 63 mm and the best position of this hydrant is in the back of kerb line.
Essay # 7. Meters:
To determine the quantity of water flowing through pipes some devices are required which are called meters. These are required to measure the quantities of water supplied to private houses, industries, public building etc.
Meters can be classified as follows:
(a) The positive displacement type.
(b) The velocity of inferential type.
(a) Displacement type:
These are used for measuring small flows of water. These are designed on displacement principle and record the number of times a vessel of known volume is fitted and emptied. From this the rate of flow is calculated automatically. These types of meters include rotary, reciprocating, oscillating and Nutating disc meters. Fig. 19.7 shows nutating disc meter and rotary water meter.
I.S. 779-1968 lays down the specification for the domestic water meters and I.S. 2373-1973 specify the specifications for bulk or large quantity measuring water meters. Good quality domestic water meters are available in the market. The installation and maintenance of domestic water meters is governed by I.S. 2041 -1963. The testing of the water meters is done as per I.S. 6784- 1973.
(b) Velocity or Inferential type:
These are generally venturi or turbine. They consist of a device by which a vane or propeller turns in direct ratio to the rate of flow of water around the propeller. The venturi type meters consist of two tapering cast iron conical pipes, one long and other short joined together at their small ends.
Two vertical piezometer tubes are two vertical piezometer tubes are provided one at the big end of short reducer and second at the junction of the small end. These piezometer tubes are connected to an apparatus, which measures the difference of water level between them. By means of an automatic device a graph is recorded of the discharge through the venturi tube. Such meters are usually provided at the head of main supply pipe.
Following are the advantages and disadvantages of venturi or inferential meters:
(i) They are cheap in initial cost.
(ii) Loss of water head in them is very low as compared with other meters.
(iii) They do not give very accurate results.
(iv) They can be installed on true horizontal pipes.
Requirements of Good Meter:
The good meter should have the following characteristics:
(i) It should not offer any resistance to the flow of water.
(ii) It should record even a leak of 10 litres/hour.
(iii) It should measure the discharge up to 2% accuracy.
(iv) All its parts should be of non-corrosive alloy.
(v) It can be easily maintained and repaired.
(vi) It should have screen on its inlet side, to exclude the clay, silt, grit etc.
(vii) It should be economical.
Advantages and Disadvantages of Metering:
Following are the advantages of metering in the town or cities:
(i) The wastage of water is reduced, giving financial saving to all.
(ii) The consumers have to pay only for the quantity of water they use actually.
(iii) When metering is not done, the consumers have to pay on flat rate charges, due to which the poor have to pay more than the quantity of water actually used by them. Therefore in metering none pay more or less, which is great advantage of it.
(iv) The waste water survey can be done easily.
(v) The careless consumers are penalized and the careful one gets benefit.
(vi) The loads on treatment plants are reduced.
Following are the disadvantages of meters is costly:
(i) The installation and maintenance of meters is costly.
(ii) Meters cause loss of head, thus decrease the available head and increase the cost of pumping.
(iii) Consumers use less quantity of water, which causes insanitary conditions.
(iv) If meters become defective, the consumers or corporation may be in loss for the time, the defects are not removed.
(v) When the meter does not show any consumption, the stand-by charges will be somewhat unjust.
(vi) It is much economical to do waste survey by inspection than by water meters.
(vii) Consumers stop gardening, which affects economy and appearance of the community.
Essay # 8. Stop-Cock and Water-Tap:
These are generally provided inside the building and in streets for taking water. Large number of firms manufactures varieties of stop-cocks and water-taps. The most common types of stop-cocks and water-taps are shown in Fig. 19.9.
Street stand posts should be provided in the pipe-lines after some intervals. In the buildings these are provided just inside or outside to stop the supply of water, whenever required during repairs or beak-age in plumbing fittings. All the taps and stop cocks should be tested before use. They should be made of rust-proof metal alloys.
Essay # 9. Pipe Fittings:
In addition to the pipes, valves, taps, various types of pipe fittings such as unions, caps, plugs, flanges, nipples, crosses, tees, elbows, bends etc. are used during laying of distribution pipes.
Common pipe fittings are shown in Fig. 19.10.
