Syphon and its application
A syphon is a long bent pipe which is used to carry water from a reservoir at a higher elevation to another reservoir at a lower elevation when the two reservoirs are separated by a hill or higher level ground in between as shown in Figure below
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Fig: Two Reservoirs are Connecting by Siphon |
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As the highest point of the siphon above the I-IGL is the
Summit (S), the water pressure at this point is the least. Further as the
vertical distance between the summit of the siphon and the I-IGL increases, the
water pressure at this point reduces. Theoretically this pressure may be
reduced to -10.3 m of water (if the atmospheric pressure is 10.3 m of water) or
absolute vacuum, because this limit would correspond to a perfect vacuum and
the flow would stop. However, in practice if the pressure is reducing to about
2.5 m of water absolute or 7.8 m of water vacuum, the dissolved air or other gases
would come out of the solution and collect at the summit of the siphon in
sufficient quantity to form an air - lock, which will obstruct the continuity
of the flow, (or the flow will completely stop). A similar trouble may also be
caused by the formation of the water vapor in the region of low pressure.
- For the continuous supply of water through siphon, following
condition should be met:
- Starting of Siphon:
A syphon can be put in action either by exhausting air thus
creating vacuum in it or by filling it with water. The air can be exhausted by
a vacuum pump. The water in the siphon can be poured through an opening made at
the summit which is only possible by closing he outlets at two ends.
While in operation, the air separates itself form the
flowing water and has the tendency to be collected at the bend. An air vessel
can be provided to get rid of this difficulty, otherwise there will be an
interruption in the flow.
Atmospheric, Absolute, Gauge and Vacuum pressures
Fluid pressure may be measured with respect to any arbitrary
datum. The most common datums are Absolute zero pressure and Local atmospheric
pressure. When pressure is measured above absolute zero (or complete vacuum),
it is called an 'Absolute pressure'. When it is measured either above or below
atmospheric pressures as a datum, it is called 'Gauge pressure'. This is
because practically all pressure gauges read zero when open to atmosphere and
read only the difference between the pressure of the fluid to which they are
connected and the atmospheric pressure.
All values of absolute pressure are positive, since in the
case of fluids the lowest absolute pressure which can possibly exist
corresponds to absolute zero or complete vacuum. However, Gage pressures are
positive if they are above that of the atmosphere and negative if they are
vacuum pressures. Figure illustrates the relation between atmospheric,
absolute, gauge and vacuum pressures.
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Fig: Relationship Between Atmospheric, Absolute, Gauge and Vacuum Pressures |
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