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 and slip and negative slip in reciprocating pump in our recent
posts. Â
Today
we will see here another important topic i.e. maximum speed of a reciprocating
pump with the help of this post.Â
Maximum speed of a reciprocating pumpÂ
Maximum
speed of a reciprocating pump will be determined on the basis of fact that the
pressure in the cylinder during suction and delivery stroke, should not fall
below than the vapour pressure of liquid, flowing through suction and delivery
pipe.Â
If
the pressure in the cylinder will be lower than the vapour pressure of liquid, there
will be problem of cavitation inside the cylinder and also there will not be
continuous flow of liquid or we can say that separation of liquid will take
place.Â
The
pressure at which separation of liquid will take place will be considered as
separation pressure and head corresponding to separation pressure will be
termed as separation pressure head.Â
Now
we will determine here the maximum speed of reciprocating pump during its suction
stroke and delivery stroke.Â
Maximum speed of reciprocating pump during suction stroke
Let
us recall the indicator diagram of reciprocating pump. We can say that the
absolute pressure at the start of suction stroke will be lower and hence
separation of liquid may take place at the start of suction stroke only.Â
In
that case, absolute pressure head in the cylinder at the start of suction
stroke will be equal to the separation pressure head of liquid and we can write
the following equation as mentioned below.Â
Where,Â
hsep
= Separation pressure head
hs
= Suction head Â
Hatm
= Atmospheric pressure head
has
= Acceleration head in suction pipeÂ
Above
equation is the equation for maximum speed of reciprocating pump during suction
stroke without any problem of separation of liquid during suction stroke.Â
Maximum speed of reciprocating pump during delivery strokeÂ
During
delivery stroke, the probability of liquid separation will be only at the end
of delivery stroke. The pressure head in the cylinder at the end of delivery
stroke will be given by following equation as mentioned here.Â
Pressure
head in the cylinder at the end of delivery stroke = (Hatm + hd
- had)Â
In
order to avoid the separation of liquid, above pressure head must be higher
than the separation pressure head i.e. hsep.Â
In
limiting case, we can have the following equation as mentioned below.Â
Where,
has
= Acceleration head in delivery pipeÂ
Expression of acceleration head in suction pipe and delivery pipe could be found here.Â
Above
equation is the equation for maximum speed of reciprocating pump during delivery
stroke without any problem of separation of liquid during delivery stroke.Â
Now
we have seen here the expression for maximum speed of reciprocating pump for two
cases i.e. suction stroke and delivery stroke.Â
We
will find out the minimum value of reciprocating pump speed from above two
cases and that value will be the maximum speed of reciprocating pump without
separation of liquid during suction and delivery strokes.Â
Do
you have any suggestions? Please write in comment box and also drop your email
id in the given mail box which is given at right hand side of page for further
and continuous update from www.hkdivedi.com.
Reference:Â
Fluid
mechanics, By R. K. BansalÂ
Image
courtesy: Google Â
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