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Sunday, 15 September 2019

September 15, 2019

WORKING PRINCIPLE OF RECIPROCATING PUMP

We were discussing a new topic i.e. reciprocating pump in our recent post and we have seen there the basics of a pump and main components of a reciprocating pump.  

Today we will start here with the working principle of reciprocating pump and we will also find out here the discharge through a reciprocating pump and work done by reciprocating pump with the help of this post. 

Working principle of reciprocating pump 

If the mechanical energy is converted in to stored mechanical energy or pressure energy by sucking the liquid in to a cylinder in which a piston is reciprocating backward and forward, which exerts the thrust on the liquid and increases its hydraulic energy or pressure energy, the hydraulic machine will be termed as reciprocating pump. 

There are following main components of a reciprocating pump mentioned here. Following figure displayed here indicates the reciprocating pump. 
  1. A cylinder with a piston, piston rod, connecting rod, crank and crank shaft 
  2. Suction pipe 
  3. Delivery pipe 
  4. Suction valve 
  5. Delivery Valve 

Above figure indicates the single acting reciprocating pump. Piston will move within a cylinder in forward and backward direction towards inner dead center and outer dead center i.e. piston will execute the reciprocating motion within the tight fit cylinder. 

Reciprocating movement of piston within tight fit cylinder will be executed by connecting the piston with crank with the help of connecting rod as displayed in figure. Crank will be fixed with crank shaft which will be rotated by an electric motor. 

Suction pipe and delivery pipe will be fixed with the cylinder by means of suction valve and delivery valve respectively as displayed in above figure. 

Suction valve and delivery valve will be check valve i.e. non return valve and hence water may flow in one direction only through these valves. 

Let us see how a reciprocating pump works 

When piston will move towards right i.e. towards outer dead center, there will be fall in pressure of liquid and hence due to reduction in pressure suction valve will be opened and liquid will enter in to the cylinder. This movement of piston inside the cylinder will be termed as suction stroke. 

When piston will move towards left i.e. towards inner dead center, there will be increase in pressure of liquid and hence due to increase in pressure of liquid suction valve will be closed and delivery valve will be opened and liquid under high pressure will flow through the delivery valve to delivery pipe of reciprocating pump. 

Discharge through a reciprocating pump 

Let us consider the following terms as mentioned here for a reciprocating pump displayed above in figure. 

D = Diameter of the cylinder 
A = Cross sectional area of the piston or cylinder 
r = Radius of crank 
N = R.P.M of crank 
L = Length of the stroke = 2 x r 
hs = Suction head or Height of the cylinder axis from the water surface in the sump 
hd = Discharge head or height of delivery point from the cylinder axis 

Volume of water delivered in one revolution = Area x Length of stroke 
Volume of water delivered in one revolution = A x L 
Number of revolution per second = N/60 
Volume of water delivered per second = Volume of water delivered in one revolution x Number of revolution per second 
Volume of water delivered per second = A x L x N/60 
Volume of water delivered per second = A L N/60 

Discharge of the pump per second = A L N/60 


Work done by reciprocating pump

Work done by reciprocating pump will be given by following equation as mentioned here

Work done by reciprocating pump = Weight of water lifted per second x Total water through which water is lifted 

Work done by reciprocating pump = ρ x g x Discharge of the pump per second x Total water through which water is lifted 

Work done by reciprocating pump = ρ g A L N x (hs + hd) / 60 


So, we have seen here the working principle of reciprocating pump. We have also secured here the expressions for discharge through a reciprocating pump and work done by reciprocating pump with the help of this post.  

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

Further we will find out, in our next post, working principle of reciprocating pump.  

Reference: 

Fluid mechanics, By R. K. Bansal 

Image courtesy: Google  

Also read 

September 15, 2019

MAIN COMPONENTS OF A RECIPROCATING PUMP

In our last sessions, we were discussing the various important topics based on the centrifugal pumps and those topics could be accessed by finding the post centrifugal pump working principle

Today we will start here a new topic i.e. reciprocating pump. We will first find out here the basics of a pump, then we will introduce reciprocating pump and further we will see here main components of a reciprocating pump with the help of this post. We will also see the working principle of a reciprocating pump, but that will be discussed in our next post. 

So let us start here with the basics of a pump and introduction to reciprocating pump 

Hydraulic machines which convert the mechanical energy in to stored energy of fluid will be termed as pumps. Compressors, fans and blowers are also come under this category of hydraulic machines as they also convert mechanical energy in to stored energy of fluid. 

But, we will be interested here only about the pumps. So we will not discuss here about the compressors, fans and blowers. These types of hydraulic machines will be discussed further in our next posts. 

Stored energy of fluid is also termed as hydraulic energy and hence pumps are basically defined as the hydraulic machines which convert the mechanical energy in to hydraulic energy. 

We can also say that output of pumps will be in the form of stored mechanical energy. In case of pumps, stored mechanical energy comes in the form of static pressure or static head. 

If the mechanical energy is converted in to stored mechanical energy or pressure energy by means of centrifugal force acting on the fluid, the hydraulic machine will be termed as centrifugal pump. 

If the mechanical energy is converted in to stored mechanical energy or pressure energy by sucking the liquid in to a cylinder in which a piston is reciprocating backward and forward, which exerts the thrust on the liquid and increases its hydraulic energy or pressure energy, the hydraulic machine will be termed as reciprocating pump. 

Main components of a reciprocating pump 

There are following main components of a reciprocating pump mentioned here. Following figure displayed here indicates the reciprocating pump. 



  1. A cylinder with a piston, piston rod, connecting rod, crank and crank shaft 
  2. Suction pipe 
  3. Delivery pipe 
  4. Suction valve 
  5. Delivery Valve 

Above figure indicates the single acting reciprocating pump. Piston will move within a cylinder in forward and backward direction towards inner dead center and outer dead center i.e. piston will execute the reciprocating motion within the tight fit cylinder. 

Reciprocating movement of piston within tight fit cylinder will be executed by connecting the piston with crank with the help of connecting rod as displayed in figure. Crank will be fixed with crank shaft which will be rotated by an electric motor. 

Suction pipe and delivery pipe will be fixed with the cylinder by means of suction valve and delivery valve respectively as displayed in above figure. 

Suction valve and delivery valve will be check valve i.e. non return valve and hence water may flow in one direction only through these valves. 

When piston will move towards right i.e. towards outer dead center, there will be fall in pressure of liquid and hence due to reduction in pressure suction valve will be opened and liquid will enter in to the cylinder. 

When piston will move towards left i.e. towards inner dead center, there will be increase in pressure of liquid and hence due to increase in pressure of liquid suction valve will be closed and delivery valve will be opened and liquid under high pressure will flow through the delivery valve to delivery pipe of reciprocating pump. 

So, we have seen here the basic of a pump and we have also find out the meaning of a reciprocating pump. Before completing this post, we have also seen the main components of a reciprocating pump and their function too in a reciprocating pump operation. 

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.  

Further we will find out, in our next post, working principle of reciprocating pump. 

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google  

Also read 

September 15, 2019

CENTRIFUGAL PUMP WORKING PRINCIPLE

In our recent posts, we were focused on centrifugal pump working principle. We have seen various posts based on the centrifugal pump working principle and these posts are as mentioned below.

Here we have written each post based on centrifugal pump working principle for easy access and to secure complete information about the centrifugal pump working principle.

Posts based on centrifugal pump working principle
  1. Pumps and basic pumping system 
  2. Total head developed by the centrifugal pump 
  3. Parts of centrifugal pump and their function 
  4. Heads and efficiencies of a centrifugal pump
  5. Work done by the centrifugal pump on water 
  6. Expression for minimum starting speed of a centrifugal pump
  7. Multistage centrifugal pumpscavitation in hydraulic machine 
  8. Specific speed of a centrifugal pumpcavitation in hydraulic turbines
  9. Cavitation in centrifugal pumps 
  10. Maximum suction lift of centrifugal pump
  11. Net positive suction head of centrifugal pump
  12. Axial flow pump working principle


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

Further we will find out, in our next post, main components of reciprocating pump. 

Reference: 

Fluid mechanics, By R. K. Bansal 

Fluid Machines, By Prof. S. K. Som
Image courtesy: Google 

Also read 

Saturday, 14 September 2019

September 14, 2019

AXIAL FLOW PUMP WORKING PRINCIPLE

We were discussing the pumps and basic pumping systemtotal head developed by the centrifugal pumpparts of centrifugal pump and their functionheads and efficiencies of a centrifugal pumpwork done by the centrifugal pump on waterexpression for minimum starting speed of a centrifugal pumpmultistage centrifugal pumpscavitation in hydraulic machinespecific speed of a centrifugal pumpcavitation in hydraulic turbinescavitation in centrifugal pumps, maximum suction lift of centrifugal pump and net positive suction head of centrifugal pump  in our previous post.

Today, we will find out here a new topic i.e. axial flow pump working principle with the help of this post. We will find out here the basics behind the axial flow pump, components of axial flow pump and further we will see the working principle of axial flow pump. 

Axial flow pump working principle 

Axial flow pump could be defined as a pump where liquid i.e. water will flow in axial direction. Here we have used one term i.e. axial direction. Axial direction means liquid will flow in the direction of axis of rotation. 

In case of axial flow pump, inlet and outlet of fluid will not vary in radial location from its axis of rotation. 

Axial flow pump could be considered as the converse of an axial flow reaction turbine.
Axial flow pumps will be used when we need to deliver the higher flow rate and relatively lower head. 

Axial flow pump: Components and their function 

Following figure shows here the basic schematic view of an axial flow pump. 


There will be a central hub in an axial flow pump as shown in figure and a number of vanes or blades will be mounted over this central hub of axial flow pump. Therefore, the central hub with a number of vanes or blades will be called as the rotor or impeller of the axial flow pump. 

Impeller blades will be mounted over the central hub of axial flow pump in such a way that liquid i.e. water may flow axially through these impeller blades. 

Impeller will be rotated within a cylindrical housing as displayed in above figure. There will be a clearance between impeller and cylindrical housing and this clearance should be as less as possible in order to avoid the leakage. 

Now we will see here the stationary inlet guide vanes of an axial flow pump as shown in above figure. These stationary guide vanes are provided at inlet of an axial flow pump in order to direct the liquid i.e. water in correct way to the impeller blades without any shock. 

There will also be some stationary outlet guide vanes at the outlet of an axial flow pump as shown in above figure. Stationary outlet guide vanes are basically provided at the outlet of an axial flow pump in order to change the direction of motion of liquid coming from the outlet of impeller. 

When liquid will come from the impeller outlet, it will have whirling component of velocity along with the axial component of velocity. Stationary outlet guide vanes will reduce this whirling component of velocity. After passing through the stationary outlet guide vanes, liquid will flow almost in axial direction i.e. in a direction parallel to the axis of rotation. 

We must note it here that the number of impeller blades will vary from 2 to 8 in an axial flow pump.
Ratio of hub diameter to the rotor diameter for an axial flow pump will be in the range of 0.3 to 0.6. 

Therefore, we have seen here the basics of axial flow pump. We have also discussed here the various important components of axial flow pump and their function too with the help of this post. 

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

Further we will find out, in our next post. 

Reference: 

Fluid mechanics, By R. K. Bansal 
Fluid Machines, By Prof. S. K. Som

Image courtesy: Google 

Also read 

Wednesday, 11 September 2019

September 11, 2019

NET POSITIVE SUCTION HEAD OF CENTRIFUGAL PUMP

We were discussing the pumps and basic pumping systemtotal head developed by the centrifugal pumpparts of centrifugal pump and their functionheads and efficiencies of a centrifugal pumpwork done by the centrifugal pump on waterexpression for minimum starting speed of a centrifugal pumpmultistage centrifugal pumpscavitation in hydraulic machine, specific speed of a centrifugal pump, cavitation in hydraulic turbines, cavitation in centrifugal pumps and maximum suction lift of centrifugal pump in our previous post. 

Now we will find out here the net positive suction head of centrifugal pump with the help of this post. After reading this post, we will be able to understand the meaning and importance of net positive suction head in installation of a centrifugal pump for transporting the liquid up to a desired height from a given sump. 

Net positive suction head of centrifugal pump 

Net positive suction head i.e. NPSH is a very important term which is used in pump industries. Net positive suction head of centrifugal pump will be of two types. One is net positive suction head required and another is net positive suction head available. 

Net positive suction head required is basically provided by manufacturer of pump. Pump manufacturer will provide the minimum suction condition of a pump in terms of net positive suction head or NPSH. Net positive suction head required will be dependent over the design of pump, speed of the pump and capacity of the pump. 

Net positive suction head available will be determined during pump installation. We must note it here that in order to avoid the problem of cavitation, net positive suction head available should not be less than the net positive suction head required. 

Net positive suction head available should always be greater than or equal to the net positive suction head required for smooth operation of a centrifugal pump. Otherwise there will be problem of cavitation and metallic surface of pump will be eroded. 

Net positive suction head (NPSH): Definition 

Net positive suction head is basically defined as the total head required to make the liquid flow through the suction pipe to the pump impeller. 

Net positive suction head could be determined as the absolute pressure head at the inlet of the pump minus vapour pressure head of liquid plus the velocity head. Vapour pressure head of liquid will be used in absolute unit. 

Net positive suction head = Absolute pressure head - vapour pressure head + velocity head 

Determination of net positive suction head

Let us consider a centrifugal pump as displayed here in following figure. Centrifugal pump will lift the water from a reservoir i.e. sump. 

There will be one centrifugal pump, as displayed in figure, which will lift the liquid (say water for example) from sump and will deliver it to the higher reservoir.  

There will be one inlet pipe and one outlet pipe. Inlet pipe will connect the sump with the inlet of the centrifugal pump and outlet pipe or discharge pipe will connect the discharge or outlet of centrifugal pump with the higher reservoir. 

Liquid or water will enter in to the inlet pipe and will go to the centrifugal pump. Centrifugal pump will provide the energy to the liquid. At the outlet of the pump, liquid will be discharged with a high pressure head and therefore liquid could be lifted up to high level and will be discharged to higher reservoir. 

Net positive suction head = Absolute pressure head - vapour pressure head + velocity head

Net positive suction head = P1 /ρg - PV /ρg + V2S/2g

Now we will find out the value of term P1 /ρg i.e. Absolute pressure head and it could be determined as followed. 

Let us consider the following terms from above figure 

hS = Suction lift of suction height i.e. the vertical height or depth between free surface of liquid and center of centrifugal pump impeller eye 

VS = Velocity of liquid flowing to centrifugal pump through inlet or suction pipe of centrifugal pump 

Now we will apply the Bernoulli’s equation at the free surface of liquid in the sump and section 1 in the suction pipe just at the inlet of the pump. We have also considered the free surface of liquid as datum line.
 
Where, 

Pa = Atmospheric pressure on the free surface of liquid 
Va= Velocity of liquid at the free surface of liquid 
Za = Height of free surface from datum line 
P1 = Absolute pressure at the inlet of pump  
V1= Velocity of liquid through suction pipe = V
Z1 = Height of inlet of pump from datum line = hS
Pa /ρg = P1 /ρg + V2S/2g + hS + hfs

P1 /ρg = Pa /ρg – [V2S/2g + hS + hfs ]
Because, 

Za = Height of free surface from datum line = 0 
Va= Velocity of liquid at the free surface of liquid = 0
V1= Velocity of liquid through suction pipe = V

Now we will use the value of P1 /ρg i.e. Absolute pressure head in NPSH equation and we will have following equation for net positive suction head as mentioned here. 

Net positive suction head = Pa /ρg – [V2s/2g + hs + hfs ] - Pv /ρg + V2s/2g 

NPSH = Pa /ρg - hs - hfs - Pv /ρg 

NPSH = Ha - hs - hfs Hv 

NPSH = Ha - hs - hfs Hv


Where, 

Ha = Atmospheric pressure head 
HV = Vapour pressure head 
hS = Suction lift of suction height i.e. the vertical height or depth between free surface of liquid and center of centrifugal pump impeller eye 
hfs = Loss of head due to friction 

Above equation will provide the net positive suction head available for a given centrifugal pump. 

Therefore, we have seen here the definition, importance and calculation of net positive suction head of centrifugal pump. We have also discussed above that in order to secure the cavitation free operation of centrifugal pump, net positive suction head available must be larger than the net positive suction head required.  

Do you have any suggestions? Please write in comment box.  

Further we will find out, in our next post, axial flow pump working principle

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google 

Also read 

September 11, 2019

MAXIMUM SUCTION LIFT OF CENTRIFUGAL PUMP

We were discussing the pumps and basic pumping systemtotal head developed by the centrifugal pumpparts of centrifugal pump and their functionheads and efficiencies of a centrifugal pumpwork done by the centrifugal pump on waterexpression for minimum starting speed of a centrifugal pumpmultistage centrifugal pumpscavitation in hydraulic machine, specific speed of a centrifugal pump, cavitation in hydraulic turbines and cavitation in centrifugal pumps in our previous post. 

Now we will find out here the maximum suction lift of centrifugal pump with the help of this post.  

Maximum suction lift of  centrifugal pump 

Let us consider a centrifugal pump as displayed here in following figure. Centrifugal pump will lift the water from a reservoir i.e. sump. 

There will be one centrifugal pump, as displayed in figure, which will lift the liquid (say water for example) from sump and will deliver it to the higher reservoir. 

There will be one inlet pipe and one outlet pipe. Inlet pipe will connect the sump with the inlet of the centrifugal pump and outlet pipe or discharge pipe will connect the discharge or outlet of centrifugal pump with the higher reservoir. 

Liquid or water will enter in to the inlet pipe and will go to the centrifugal pump. Centrifugal pump will provide the energy to the liquid. At the outlet of the pump, liquid will be discharged with a high pressure head and therefore liquid could be lifted up to high level and will be discharged to higher reservoir. 

Let us consider the following terms from above figure 

hS = Suction lift of suction height i.e. the vertical height or depth between free surface of liquid and center of centrifugal pump impeller eye 

VS = Velocity of liquid flowing to centrifugal pump through inlet or suction pipe of centrifugal pump 

Now we will apply the Bernoulli’s equation at the free surface of liquid in the sump and section 1 in the suction pipe just at the inlet of the pump. We have also considered the free surface of liquid as datum line.

Where, 
Pa = Atmospheric pressure on the free surface of liquid 
Va= Velocity of liquid at the free surface of liquid 
Za = Height of free surface from datum line 
P1 = Absolute pressure at the inlet of pump  
V1= Velocity of liquid through suction pipe = V
Z1 = Height of inlet of pump from datum line = hS

Pa /ρg = P1 /ρg + V2S/2g + hS + hfs

P1 /ρg = Pa /ρg – [V2S/2g + hS + hfs ]
Because, 

P1 = Absolute pressure at the inlet of pump = 0 
V1= Velocity of liquid through suction pipe = V

Now we must note it here that in order to secure the maximum suction lift, pressure at the inlet of the pump must not be less than the vapour pressure of liquid otherwise there will be problem of cavitation. Therefore, for limiting case, we will consider pressure at the inlet of the pump equal to the vapour pressure of liquid. 

i.e. P1= PV = Vapour pressure of the liquid in absolute units 

PV /ρg = Pa /ρg – [V2S/2g + hS + hfs

Pa /ρg = PV /ρg + [V2S/2g + hS + hfs

Where, 
Pa /ρg = Atmospheric pressure head = Ha 
PV /ρg = Vapour pressure head = H
Ha = HV + V2S/2g + hS + hfs
hS = Ha - HV - V2S/2g - hfs 


Above equation will provide the maximum suction lift or maximum suction height for a given centrifugal pump. 

Therefore we must note it here that suction lift for any centrifugal pump should not be more than the value of suction lift secured from above derived equation. 

If the suction lift of centrifugal pump will be more than the value of suction lift secured from above derived equation, vapourisation of liquid flowing through pump will take place at inlet of the centrifugal pump. Hence, there will be a great probability of cavitation. 

Therefore in order to avoid the problem of cavitation, suction lift for any centrifugal pump should not be more than the value of suction lift secured from above derived equation. 

Do  you have any suggestions? Please write in comment box. 

Further we will find out, in our next post, net positive suction head of pump

Reference: 

Fluid mechanics, By R. K. Bansal 
Image courtesy: Google  

Also read