Recent Updates

Monday, 26 August 2019

PUMPS AND PUMPING SYSTEM

Today we will start here the basics of pumping system and net head developed by the centrifugal pump with the help of this post. First we will see here the basics of pumping system and after that we will find out the net head developed by the centrifugal pump. 

We have used here terms i.e. centrifugal pump and pumping system. Centrifugal pump will be a very important component in a pumping system where centrifugal pump is being used to lift the fluid mostly water. 

Therefore, we must have brief information here about the centrifugal pump. 

Centrifugal 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. 

Centrifugal pumps are radial flow pumps. The flow in the centrifugal pumps will be in the radial outward directions and therefore a centrifugal pump act as a reverse of an inward radial flow reaction turbine

The centrifugal pump works on the principle of forced vortex flow which means that when a certain mass of liquid will be rotated by an external torque, the rise in pressure head of the rotating liquid will take place. 

The rise in pressure head at any point of the rotating liquid will be proportional to the square of tangential velocity of the liquid at that point.

Rise in pressure head at any point of the rotating liquid V2

Where, V is the tangential velocity of the liquid at that point. 

Therefore, the rise in pressure head at the outlet of impeller will be more as radius will be more at the outlet of impeller. Hence, liquid will be discharged at the outlet with a high pressure head and therefore liquid could be lifted up to high level. 

General pumping system 

Following figure displayed here indicates the general pumping system. 

As we can see here, there are two reservoirs. The first one is lower reservoir or sump and the second one is higher reservoir. 

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. 

There will be two pressure gauges, one pressure gauge will be fixed at the inlet of centrifugal pump and will be termed as inlet pressure gauge which will indicate the pressure of liquid at the inlet of centrifugal pump. Other pressure gauge will be fixed at the outlet of centrifugal pump and will be termed as outlet pressure gauge which will indicate the pressure of liquid at the outlet or discharge of centrifugal pump. 

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 see here the important designated nomenclatures as displayed in above figure. 

The free surface of liquid in the lower reservoir will be at height HA and the difference between the free surface of liquid in higher reservoir and lower reservoir is HS

Vertical distance of discharge plane of centrifugal pump from datum line is Z2 and vertical distance of suction or inlet plane of centrifugal pump from datum line is Z1

So, we have seen here the basic pumping system with its various important nomenclatures and also we have seen the basic role of a centrifugal pump in a pumping system. 

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

Further we will find out, in our next post, the net or total head developed by the centrifugal pump

Reference: 

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

Also read 

No comments:

Post a Comment