We will learn pump basics in this article. So, what is a pump? Let us try to understand. When we are required to lift fluid from a lower elevation to a higher elevation, external equipment is required. This equipment is the pump.
Around 20% of the world’s electrical power is consumed by pumps in many ways.
What is Pump & Basics?
Pump Basics
Let’s concentrate on the basics of the pump. Pumps are used in almost all kinds of industries, as follows, to lift or transfer fluids from one place to another:
Pump Definition
The pump has a driving component that is a motor (sometimes maybe an engine), and a power source is connected to the motor.
Once the pump is switched ON, electricity is supplied to the motor, and the pump does a mechanical action and changed the electrical energy into hydraulic energy, and lifts or transfers fluids from a lower elevation region to a higher elevation region.
Hence, A pump is defined as the mechanical equipment which lifts or transfers fluids from a lower elevation region to a higher elevation region. by converting electrical energy into hydraulic energy.
Function of Pump
The main function of pumps are as follows,
- Pump lifts liquids from lower elevation to higher elevation.
- It helps to circulation liquids from one point to another point.
- It increases the pressure or the head of pump to meet the required discharge pressure requirements.
- If a system loss the pressure, pumps are used to increase the pressure of the system to make it stable.
- Pumps are used to transfer required liquid flow rate.
Pump Basics Terms
To understand the pump or it’s working principle, there are few pump basics terms are required to know. These are.
# Volumetric flow rate - Volume flow rate means the capacity of the liquid per unit time which is transfer through the pumps.
- It is the rate of water flow.
- Pump capacity is expressed in volumetric flow rate and head.
- It is measure in m3/s or ft3/s.
- The volume of flow, ‘V’ and time is ‘t’, then the volume flow rate,
q = V/t
If the mass flow rate is ‘m’, and density is ‘ρ’, and the volume flow rate,
Then, we can write,
m = ρ x q,
or, q = m/ρ
Hence, it can be defined as the ratio of mass flow rate to density.
In S.I. units, the volumetric flow rate is measured in m/s, and F.P.S unit, it is measured in
ft/min.
# Shut-off head - The shut-off head is one of the most important parameters in the pump. It is defined as the head with respect to zero volumetric flow rate.
# Static Head - Static head means the height difference between the elevation of the source of liquid and the elevation of the discharge liquid.
- Suction static head is totally depending on the elevation.
- It doesn’t depend on the flow rate.
- It depends on the specific gravity of the liquid, at a given pressure.
# Static suction head (hs) - The static suction head is a part of the static head.
- It is used when liquid source is above the pump center line.
- It describes the height from the liquid source to the pump center.
- Normally it is denoted by ‘hs’.
- This value is considered as +ve.
- Doesn’t depend on the liquid flow rate.
- Depends on the specific gravity, at a given pressure.
# Suction lift - This term is used when pump is placed above the liquid surface, elevation wise.
- This is the vertical distance between the liquid surface and the pump center line, when pump is placed above.
- This height is limited to 10m, due to the limitation of atmosphere.
- This value is considered as, -ve, as it is always opposite direction to static suction head.
# Static discharge head (hd) - The static discharge head is also a part of the static head.
- It is used to specify the distance between the elevation of the liquid in the destination and - the pump center line.
- Normally it is denoted by ‘hd’.
- Doesn’t depend on the liquid flow rate.
- Depends on the specific gravity, at a given pressure.
# Friction head - The pump has a piping system and all pipes will have many fittings, bends, straight lengths based on the system design. Hence, these all provide the resistanceto the flow which is required to overcome so flow will be continuous in the system.
- This head is known as friction head & it is the loss that needs to be overcome.
- The friction head depends on the following,
* Size of the pipe
* Pipe condition
* Age of pipe
* Type of pipe
* Nos of fitting
* Nos. of bends
* Pipe length
* Total system configuration
* Liquid flow rate
* Type of liquid
# Total Head - The total head in a system is defined as the total pressure difference between the inlet and outlet of the pump.
- In case of source is above the pump, difference between the discharge head and the suction head plus the friction head.
- In case of source is below, it is the sum of discharge head, suction lift, and friction loss.
TDH = Static Height + Static Lift + Friction Loss
# Vapor pressure - at a given temperature, vapor pressure is the pressure that is exerted by the gas in equilibrium with either a solid or liquid in a closed container.
- It is the pressure, in which molecules enter the vapor state at a specified temperature. If you boil a liquid, you can observe it.
- It is simply an indication of the evaporation rate of the liquid.
- If the temperature increases, vapor pressure will also increase.
Various units are used for vapor pressure:
Pascals (Pa),
bar (bar),
tor (mm Hg),
atmospheres (atm),
# Net Positive Suction Head - The Net Positive Suction Head – NPSH – is defined as the difference between the Suction Head, and the Liquids Vapor Head and can be expressed as
NPSH = hs – hv,
Where,
Hs – Suction head
Hv – Liquid vapor head
There are two terms which are very important,
a] NPSHr
b] NPSHa
NPSHr
NPSHr means NPSH required for the pump selection. It is one of the main functions of the selection of pumps so that the pump will not have any cavitationproblems during operation.
- It is the lowest value of NPSH in which pump will run without any cavitation.
- It is normally provided by manufacturer.
Best wat way to determine it by actual testing.
NPSH-R is the value at which the discharge pressure is reduced by 3% because of the onset of cavitation.
NPSHa
NPSHa means NPSH available. It is calculated from the suction side of the pump.
- It is basically a function of the system based on which a pump operates.
There are two options.
Option-1
: NPSHa when the pump is below the source,
NPSHa = Pa + hs – pv – pf
Where,
Pa – Absolute pressure head on the liquid surface
Hs – static head above pumps center line
pv – absolute liquid vapor pressure head at pumping temperature
pf – the suction friction head losses.
Option-2
: NPSHa when the pump is above the source,
NPSHa = Pa – hs – pv- pf
NPSH-A is always more than NPSH-R for any operating conditions to avoid cavitation of pumps.
# Specific speed - Specific speed or pump specific speed is defined as the parameter to specify the size or shape of the pump impeller. It is a dimensionless parameter.
Specific speed means, the following,
- It helps to select appropriate impeller size.
- It depends on shaft speed.
- It also depends on the flow rate and differential head at BEP.
- It is essential when comparison between two pumps are required.
- It doesn’t depend on pump size.
The friction head depends on the following,
* Shaft speed
* Flow rate
* Differential head etc.
# Theoritical pumping power - Theoretical Pump power calculation, P
Here, P = ρ x g x q x h,
Where,
P = Power, in Watt
ρ = Density of fluid, kg/m
g = Gravitational acceleration, m/s
q = Flow rate, m/s
h = Head, m
# Actual pumping power - Actual Pump power calculation, P’
Here, P’ = Theoretical pumping power / pump efficiency
P’ = ρ x g x q x h / η
[Where, η = efficiency of pump]
After pump basics, let get into the types of pumps.
What are the Different Types of Pumps Used in Industries?
Centrifugal pump -
A centrifugal pump is a pump that uses an impeller (=a rotating part) to move a liquid around in a circular movement.
Screw pump -
a pump in which the working pressure is created by means of screw-shaped impellers in the vertical water column.
Gear Pump -
It moves a fluid by repeatedly enclosing a fixed volume using interlocking cogs or gears, transferring it mechanically using a cyclic pumping action. It delivers a smooth pulse-free flow proportional to the rotational speed of its gears.
Mono pump -
This pump consists essentially of a rubber stator in the form of a double internal helix and a single helical rotor which rolls in the stator with a slightly eccentric motion.
Piston Pump -
The piston pump can be defined as it is a positive displacement pump. These pumps use a piston, diaphragm, otherwise plunger for moving liquids. These pumps use check valves as the input and output valves.
Diaphragm Pump -
A diaphragm pump is a hydraulically or mechanically actuated positive displacement pump that uses a combination of reciprocating action and either a flapper valve or a ball valve to transfer liquids.
Metering Pump -
A metering pump moves a precise amount of liquid during a specified time period yielding an accurate volumetric flow. Metering pumps are used to pump chemicals, solutions, etc…
How Does a Pump Work?
There are so many types of pumps and the working principle of each pump is different. However, the basic principle is the same and here, we are going toexplain how does a pump work in general.
Let’s get in the step-by-step explanation!
Step #1 Start of Driver
The pump is connected to a motor or engine or any other driver and the driver is required to start to operate.
Step #2 Intake of Fluid
We have already learned that pumps transfer fluid from one place to another. Hence, it is necessary to get the fluid into the pump. In case of reciprocating pumps , a negative pressure is created in the cylinder due to the movement of the piston.
However,
pump priming is required for the centrifugal pump, as the impeller cannot create much pressure difference in the pump.
Step #3 Limitation of Negative Pressure
Pressure should not be below the vapor pressure, else, bubbles will be formed and cavitation can occur which will damage the pump.
Step #4 Increase in Pressure Energy
In a centrifugal pump, volute and diffuser help to increase the pressure of the fluid. Centrifugal force is created due to the rotation of the impeller and thisforce is acted on the fluid too.
Water is transferred through the volute (gradually increased cross-section) and velocity is reduced which is further converted into pressure.
In case of a reciprocating pump, the piston is connected to the crank through the connecting rod, and the crank is connected to a driver. After sucking the fluid,the piston moves opposite, and pressure is generated on the fluid.
Hence, we have got the basics of the pump working philosophy.
Troubleshooting for Pump & Pumping System
What are the reasons for Low Discharge Pressure?
There may be a wide reason for low discharge pressure, although the pump is designed for high pressure. Let’s see what are the main reasons for lowdischarge pressure.
Condition of Suction System
The pump takes the liquid through a suction strainer. The suction strainer filtrates the liquid so that unwanted particles are not able to pass through the pump.If the suction strainer is not clean properly, the flow rate will be reduced which contributes to a reduction of discharge pressure.
Suction valve
Check if the suction valve is slightly closed during start-up. It should be fully open.
Size of the orifice or nozzle
Check if the orifice size or nozzle size is matching with designed size. A change in nozzle size will result in a change in discharge pressure. If nozzle size, is highwith respect to the design size, then the flow rate may increase but there will be a reduction of pressure.
Pump speed
Pump impeller speed shall be in line with the designed speed. The reduction in pump speed may result in a reduction in pump discharge pressure. The pumpimpeller, as well as the pump shaft, is coupled with the motor shaft.
Coupling should be checked and also motor wiring, winding, bearing, etc. shall be checked properly. Also, check the belt condition, tightening of belts, etc.
Pump priming
The pump should have proper priming in case of centrifugal pump or non-self-priming pumps. If priming is not done completely, its efficiency, as well asdischarge pressure, will be reduced.
Materials of pump
Pump material shall be properly selected based on the applications. The same needs to be checked if all are as per the design and conditions of each part. Anywrong material selection or any problem in any parts shall be taken into considerations.
Advantages of Pumps
These are many advantages of Pump, as follows:
- Pumps are very useful equipment to transfer fluids.
- It is available from a very small capacity to a very large capacity.
- It is widely used as circulating equipment in many systems like chilled water circuits, cooling tower circuits, and many more.
- Noise is less comparative with other rotating devices.
- Pumps can be used (reciprocating pump) for gaseous applications as well.
- No leakage, fewer losses.
- A wide range of constructions, a wide variety of materials is used for pumps.
Disadvantages of Pump
These may be some disadvantages as well of Pump:
- Operation of pumps is smooth, however, it may be encountered cavitation. It hurts the pump.
- The pump can have corrosion problems.
- Many times, handling fluids may have problems. For example, reciprocating pumps are not suitable for viscous fluids.
- Centrifugal pumps cannot work without priming.
- There is a limitation of piston or impeller speed.
Applications of Pump
The application of pump is wide, a few of them are listed below:
- Water storage & transfer.
- Domestic application.
- Sewage & slurries application.
- Fire fighting & protection system
- Manufacturing, chemical, oil & gas, pharmaceutical, food, aviation, HVAC, etc. industries.
- Aquarium, water fountain, and pond filtering, etc.
- Even in the automobile sector, pumps are used.
- In thermal power plants, or nuclear power plants , or hydroelectric power plants, pumps are one of the vital equipment.
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