We were discussing the basics of reciprocating
pump, main
components of a reciprocating pump, working
principle of reciprocating pump, ideal
indicator diagram of reciprocating pump, effect
of acceleration and friction on indicator diagram of reciprocating pump, expression
for acceleration head in the suction pipe of a reciprocating pump, double
acting reciprocating pump: working principle, discharge, work done and power
required, slip
and negative slip in reciprocating pump and maximum speed of a reciprocating pump in our recent posts.
Today we will see here air vessel in reciprocating
pump with the help of this post. We will first understand here the concept of an
air vessel and further we will see here the functions and importance of air
vessel in the operation of reciprocating pump and it could be easily understood
by reading this post i.e. air vessel in reciprocating pump.
Air vessel in reciprocating pump
An air vessel is basically a closed chamber from its
one side which will have compressed air in the top and water or liquid at the
bottom of the chamber. At the base of the chamber, there will be an opening
through which liquid may flow in to the air vessel or out from the air vessel.
Air vessels will be installed at suction side and
delivery side of the reciprocating pump as displayed here in following figure.
These air vessels will be installed as close as
possible with the cylinder of the reciprocating pump.
Air vessel is installed with reciprocating pump in
order to secure the following task.
- To secure the continuous flow of liquid with uniform rate of flow
- To save the suction and discharge pipe
- To save the considerable amount of work in overcoming the frictional resistance in the suction and delivery pipes
- To run the reciprocating pump at a high speed without separation
Air vessel acts on the same principle on the basis
of which hydraulic accumulator and flywheel work. It stores energy when there
will be availability of additional energy and it releases the energy when it is
required.
Air vessel stores and releases additional energy
with the help of compressed air contained in the top of the chamber of air
vessel.
When liquid will flow in to the vessel, air
containing at the top of the chamber of air vessel will be compressed and when
liquid will flow out from the vessel, air containing at the top of the chamber
of air vessel will be expanded.
During suction stroke
Let us consider the air vessel installed at the
suction side of reciprocating pump. At start of suction stroke of reciprocating
pump or during first half of suction stroke, acceleration head will be maximum
and hence more water will be required through suction pipe during starting of
suction stroke. In that case, air vessel will provide the additional water to
the reciprocating pump.
As air vessel will be installed very close with the
cylinder of reciprocating pump, therefore water will flow with approximate same
flow rate through the rest part of the suction pipe. Hence, there will not be
any problem of cavitation in rest part of suction pipe. Rest part of suction
pipe means the portion of suction pipe below the air vessel and it will be the
larger portion of suction pipe.
At the end of suction stroke, there will be
retardation and hence less water will be required through the suction pipe and
hence additional water will flow to the air vessel and air vessel will store
the energy in terms of water by compressing the air contained in the top of the
chamber. This stored energy of air vessel will be utilized during the start of
next suction stroke.
During delivery stroke
Let us consider the air vessel installed at the delivery
side of reciprocating pump. At start of delivery stroke of reciprocating pump
or during first half of delivery stroke, acceleration head will be maximum and
hence more water will be discharged to delivery pipe of reciprocating pump during
starting of delivery stroke.
In that case, additional water will flow to the air
vessel and air contained above the water in the top of chamber will be
compressed or we can say that energy will be stored in the air vessel. This
stored energy of air vessel will be utilized during the second part of delivery
stroke.
As air vessel will be installed very close with the
cylinder of reciprocating pump, therefore water will flow with approximate same
flow rate through the rest part of the delivery pipe. Hence, there will not be
any problem of cavitation in rest part of delivery pipe. Rest part of delivery
pipe means the portion of delivery pipe above the air vessel and it will be the
larger portion of delivery pipe.
At the end of delivery stroke, there will be
retardation and hence less water will be discharged through the delivery pipe
and hence additional water will be given by the air vessel and air vessel will
release the energy in terms of water by expanding the air contained in the top
of the chamber.
Therefore, we have seen here the basic principle of
air vessel in reciprocating pump and we have also seen here that how air vessel
helps to maintain the uniform discharge in the operation of reciprocating pump.
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Reference:
Fluid mechanics, By R. K. Bansal
Image courtesy: Google
Also read
Fundamentals of thermal engineering
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