Pump Pressure Types and Variants

Just observe this water droplet. This droplet creates a pressure on the surface it sits. Based on this, please advise how do you define a pressure. 




Good Day Everyone,
This is Karthik and Welcome to the Pump Hydraulics Basics. 


Overview

First Things First
A quick overview of what we are going to discuss in this series. 

Firstly, What is pressure. Then different types/ variants  of pressure. 
Secondly, Bernoulli’s theorem and its significance
Then, the total differential head and how to calculate them. 
More about NPSH and how to calculate them
Then finally about Specific speed and Suction Specific Speed. Some datas and myth busters. 


Pressure 

Pressure is nothing but force per unit area. 
The  person swimming in the pool experiencing the force in his ears and his body is the force acting on his body which is a defined area by itself. 
Hence, when we talk about pressure, we refer to force acting on an unit area. 
The SI unit is N/m2 or Pa. The common metric unit is bar. 




Then what is an absolute pressure ? 
Absolute pressure is the sum of gauge pressure and atmospheric pressure. 

Add caption

Gauge pressure measured by pressure gauges does not consider the atmospheric pressure into consideration. In the pump specification, when the designer mentions the pressure as bar or N/m2 without any reference to gauge or atmospheric, they actually mean gauge pressure



The atmospheric pressure is measured by a barometer.You could find this barometer typically in most of the test bay. The readings are the indication of localised atmospheric pressure values. The values are mostly nearer to 1.013bara





Vacuum Pressure
A quick question . What is Vacuum and how it is measured?
Any pressures < 1.013 bara or the pressures lesser than the local atmospheric pressure are referred to vacuum . 

For eg : 
If the atmospheric pressure = 1 bara
The absolute pressure = 0.9 bara
The % vacuum = 1- (0.9/1) = 10% vacuum
100% vacuum is practically impossible. 

For Vapour Pressure, refer to  Pump Hydraulics_An Introduction 

What is a seal chamber pressure then ?
It is the pressure experienced in the seal chamber or stuffing box as an after effect of pressure generated in the casing. 
For a Centrifugal over hung pump , the seal chamber pressure = Suction Pressure + 25% of Discharge Pressure


For Vertical and PD Pumps, seal chamber pressure = discharge pressure 







If you would like to listen to this segment, the above link is for you to understand the concept a bit better. 

In the next segment, we are going to study about the Bernoulli’s theorem and its significance. Stay Tuned. 

Image Credits:

 1)     All  photos are licensed under CC by NC 2.0


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