What is a water pump?

A water pump is a mechanical device for moving and transferring all kinds of liquids that, by increasing the pressure, causes the liquids to move to a higher height (with increasing head) or even lower (pond or tank). Pumps have many different applications in different industries. Pumps use a variety of energy sources, including manual, electric, internal combustion, and wind-powered pumps. Pumps come in a variety of sizes, from microscopic sizes for medical work to large industrial pumps. .

In other words, the pump takes mechanical energy from an external source, such as an engine, and transfers it to the fluid that is passing through it. As a result, the fluid energy increases after leaving the pump. Pumps are used to transfer or move fluid from one point to another in a piping or hydraulic system. Pumps have different types, each with a specific application.

Units of measurement in the pump

In the following, we will examine a series of technical and key words that have basic uses in the pump manufacturing industry, along with their meanings. All sizes and units of measurement are technically expressed.


The rate at which a fluid passes through a section per unit time is a definition of flow and is usually denoted by Q. Flow measurement is done in bulk and based on two categories of units of measurement:

Mass units: The rate at which a mass of fluid passes through a certain fraction of time is calculated, such as Kg / h
Volumetric units: The rate at which a volumetric mass passes through a fluid per unit time is calculated, such as lit / min (liters per minute) and m3 / s (cubic meters per second).
In other words, the amount of fluid or liquid that passes and exits at a certain unit of time through a specific point such as the pump outlet or pipe cross section, is called flow, which can be in liters per minute, liters per second and Or cubic meters per hour. It should be noted that there is a similar relationship between the amount of fluid passing through the pipe and the amount of electricity passing through a wire, so that the amount of hydraulic head is equal to the amount of voltage and electrical potential energy and the amount of hydraulic current is equal to the amount of ampere and electric current. . As the thinner the conduction wire, the lower the current through the wire, the lower the diameter and cross section of the water pipe. Just as we need a voltage difference to transmit electricity to a power cable through a wire, a special head must be defined to transfer fluid through a pipe. Determining the same amount of head on both sides of a horizontal pipe causes the fluid inside the pipe to have no current because, as the power cable resists the passage of electricity.

Head (height) or pump pressure

That is, to what height (under standard conditions) can a pump raise the fluid under pressure? For centrifugal water pumps, the head or water pressure is expressed in meters (m) or feet (ft), and for rotary and positive displacement pumps, the pump pressure is expressed in bar, PSI and kPa (kpa). . In other words, Head means height and refers to the difference in level. For example, a pump with a flow rate equal to Q per second and a height of 30 meters is able to pump a quantity of Q liters of fluid per second to a height of 30 meters. The amount of pumping height of each pump is calculated based on the impeller diameter and the rotation speed of the pump motor, and the type of fluid being pumped is not important. In other words, in the above example, the pump is able to pump a quantity of Q liters of pumped fluid, including pure water, oil or mercury, etc. to a height of 30 liters per second, and the difference is only in the amount of pump power consumed to pump fluids. Be.


The amount of pressure is the amount of pressure applied to each unit of the ground (for example, Kg / cm2) and care must be taken not to confuse it with the amount of height. In the case of pumping liquids, the amount of pressure that the liquid exerts on the ground surface is equal to the product of the pumping height multiplied by the specific weight of the pumped liquid. Therefore, the volume of several kilometers of air on the surface of the earth, on the surface of the sea produces only a pressure equal to one Kg / cm2, ie a pressure close to about one atmosphere. But it produces the same amount of compressive fluid equal to 700 to 800 times the air pressure. Because the specific gravity of the liquid is 700 to 800 times greater than the weight of the air. Keep in mind that the amount of water pressure at a height of 10 meters is something close to one Kg / cm2. By installing a manometer in the pump outlet, the following pressures can be measured.

Oil – specific gravity 2.1 Kg / cm2 = 00.7 * 0.001 * 30 * 100 = 0.7 Kg / cm3
Water – specific gravity 0.3 Kg / cm2 = 00.1 * 0.001 * 30 * 100 = 1.0 Kg / cm3
Mercury – specific gravity 40.8 Kg / cm2 = 13.6 * 0.001 * 30 * 100 = 13.6 Kg / cm3

Pump height drop

As the fluid passes through the pipes, filters or valves and due to friction with their inner wall, the amount of fluid flow and consequently the pumping height is reduced to a certain extent, which is called height drop. Like electricity current, which increases with decreasing current (amps) in the cable. As the fluid flow rate increases, the flow rate decreases and therefore the pumping height decreases. Therefore, with the passage of fluid through more pipes, filters and valves, the drop in height increases accordingly.

Fluid mass

The specific gravity of a fluid or liquid is its weight / fluid in a particular unit of measurement, usually measured in units of Kg / dm3 or Kg / l. It should be noted that each 1dm3 is equal to 1 liter.

Note: Now considering the relationship between the amount of flow and the amount


Output power

The amount of power (energy) applied to the fluid by the pump is called the output power of the pump, which depends on the three factors of flow, height and weight of the fluid.

For example, the output power of the pump used to pump gasoline is much lower than the output power of the pump used to pump sulfuric acid because the weights of the two fluids are different. All pumps are able to pump fluids with the help of electric motors or motors that are installed inside the device. The power required by the pump to operate and pump fluids is called power consumption.


The power input to the pump by the motor and its transfer to the fluid is called the power consumption of the pump. Due to factors such as fluid friction with pipes or natural hydraulic drops in the device, the output power of the pump is always less than its consumption power, which is usually less than one and is calculated as a percentage, which is called the efficiency of the pump. .


By dividing the output power of the pump by the power consumption, the efficiency of the pump is obtained. For example, a pump that has a efficiency of 75%, ie only the pump returns a percentage of power consumption and 25% of it is wasted due to fluid friction with pipes and other devices or heat inside the pipe and device. As a result, the higher the efficiency of the pump, the lower the power dissipation percentage. Therefore, its energy consumption is lower.

If the output power of the two pumps is equal to 1 HP while the efficiency of the first pump is 50 and the other is 60%, we conclude that the amount of power required to provide the output power of 1 HP for the first pump is 2 HP and for the second pump is only 1.67 HP is.

Therefore, the most important parameter to determine the quality of the device and the amount of energy savings is the efficiency parameter.

Classification of pumps based on function

There are different categories of pumps according to function, internal structure, fluid transfer method, material, pumping liquid, installation status, etc. One of the common and comprehensive methods for classifying pumps is the method of energy transfer to fluid, which is divided into two methods: dynamic and displacement:

Positive Displacement Pump

Dynamic Pump or Non Positive Displacement Pumps
Positive Displacement Pump
Positive displacement pumps are classified into two types: rotary (reciprocating) and reciprocating (reciprocating):

PumpTypes of rotary pumps

Gear pump
Lob pump
Vane pump
Progressive vacuum pump
Screw pump
Types of reciprocating pumps or Reciprocating

Submersible drainage sump pump
Diaphragm pump


What is a Rotary Pump?

In this type of pump, the displacement is done by rotating the gear, camshaft or blades. As mentioned before, this type of pump has a great variety, which we will describe in the following of each type of this product.

What is a Gear Pump?

One of the most common pumps to increase the hydraulic power of the fluid is the gear pump. Gear pumps use gears to move liquids and are produced in two types of internal and external gears. This type of pump is a type of positive displacement pumps because it moves a certain and constant amount of liquid in each cycle.

What is a Lobe Pump?

Lobe pump or ear pump is used in various industries such as paper making, food, biotechnology, pharmaceutical, chemical. The reason for various applications of lobe pump is high hygienic quality, reliability, corrosion resistant in steam environments.

What is a Vane Pumps?

Wayne pumps or vane pumps are a type of positive displacement pumps and rotary pumps that are very similar to gear pumps in terms of operation. In a vane pump, the fins are mounted on a rotor that is located inside the cavity. In some cases, these vanes have different lengths to maintain the connection of the walls in which the pump rotates. They are commonly used in high pressure hydraulic pumps and power and supercharge systems.

What is a Progressive Cavity Pumps or Mono Pump?

Also known as Mardoni or single-screw pumps, these pumps advance fluid through discrete cavities on a helical rotor. The volumetric flow rate is proportional to the rotational speed of the rotor. Therefore, these pumps are suitable for measuring liquids and pumping viscous fluid.

What is a pre-pump or peripheral pump?

In pre-pumped pumps, the suction chamber is larger than the drain, which reduces the pressure in the suction chamber, making it easier for fluid to enter the pump. But the discharge part is smaller and this factor pushes the fluid more intensely. When the pump is turned on, the pump impeller directs the fluid from the suction port to the outlet.


What is a Screw Pump?

A screw pump is a positive displacement pump. For this reason, with each rotation, a certain volume of fluid is displaced. Therefore, with increasing rotational speed, fluid flow also increases. In all screw pumps, the rotation speed of the pump is determined according to the viscosity of the fluid. If the viscosity increases, a lower speed is selected for rotation.


What is a Reciprocating Pump?

In this type of pumps, energy transfer should be done periodically. The driving force in these pumps is usually an electric motor. In these pumps, the piston moves up and down inside the cylinder. The function of this system is that if the piston moves to one side, a suction is created inside the cylinder and the fluid moves in through the valve. When the piston returns, this sucked fluid is expelled through another valve. These pumps are used in viscous and oily fluids. In the following, we will introduce the types of reciprocating pumps.

What is a Diaphragm Pump?

Diaphragm pump is another type of positive or discontinuous displacement pump. In a diaphragm pump, the current is cut off and connected due to the movement of this diaphragm. Diaphragm pumps are used to move fluids with different viscosities (very concentrated fluids such as honey or resin and liquid glue to very dilute fluids such as water). In these pumps, unlike other pumps, there is no impeller and the action of moving the fluid by a flexible plate, which is usually made of elastometer, is used.

Types of diaphragm pumps

Manual diaphragm pump
Electric diaphragm pump
Pneumatic or pneumatic diaphragm pump
It is more used in the pneumatic system industry due to the lack of need for electricity.

Ability to pump diaphragm

Create proper output pressure up to 1200bar
Ability to work with viscous fluids
Efficiency above 97%
Ability to work with minimal lubrication
Ability to immerse in fluid
Dry operation capability
No mechanical flood
Can be used in flammable or explosive environments
Suction capability of barrels and tanks with various dimensions
The barrel pneumatic diaphragm pump works with compressed air and has a high suction power, and as a result, it is used to pump all kinds of fluids.

What is a floating or planar piston pump?

These types of pumps have a rotating mechanism and are from the group of positive displacement pumps, whose principles of operation in pumping fluid are the same as reciprocating pumps, with the difference that instead of one cylinder and piston, they have a large number of cylinders and pistons. Pumps are used in cases where high outlet pressure (from 100 to 1000) times is required. In these pumps, by rotating the rotary mechanism, the pistons go back and forth inside the cylinder and draw the oil into the cylinder chamber and then pump it into the system. Piston pumps are generally made in two types, stainless steel and bronze.


Types of piston pumps

Carwash pump
Home car wash pump
Industrial car wash pump
Hot and cold water car wash pump
Electric car wash pump, gasoline car wash pump and diesel car wash pump
Fog pump
Sprayer pump
Dynamic Pump or Non Positive Displacement Pumps
In this type of pump, a rotating actuator blade converts kinetic energy into pressure or velocity. In the following, we will introduce the types of this product.

What is a Centrifugal Pumps?

Centrifugal pumps are the most widely used and widely used type of pump in the industry. It accounts for about 75% of pump consumption in the industry. They are considered as ideal pumps because these pumps always provide a certain amount of fluid flow at a constant pressure in any situation. These pumps are based on centrifugal force. The working mechanism in such pumps directs the fluid out of the center when the pump blade rotates inside it, and when the fluid exits the center, the replacement fluid under atmospheric pressure or artificial pressure and higher towards the center. The fluid that comes out is drawn and discharged through the outlet path. This fluid will have a pressure, the amount of which can be calculated by the impeller step and its rotational speed.

What is a Centrifugal Pumps?

The centrifugal pump can be classified according to the type of shell, the type of impeller and how the shaft is located and the number of floors.

In terms of shell

A) Screw pump

In these pumps, the screw or screw housing is designed so that the duct opens in the direction of rotation of the impeller. As a result, as the cross section increases, the dynamic pressure (due to velocity) becomes static pressure.

B) Spray pump (diffuser)

In these pumps, the impeller is surrounded by fixed blades called guide vanes. These blades open apart as they move away from the center, and as the cross-sectional area increases, the speed decreases and the pressure increases.

In terms of shell cutting

A) Integrated shell

The body of single-stage centrifugal pumps is usually disposed of uniformly. The impeller and internal components of the pump are often open on both sides or at least one side of the shell.

B) Multi-piece shell

In this case, the shell can be cut in different directions. If the cutting plate is along the axis, the shell is cut horizontally. If the cutting plate is vertical, the shell is called a vertical cut.

Suction and thrust opening condition

The position of the suction and thrust openings in the pumps is also different and in some it is adjustable. This feature is not available in one-piece pumps. In multi-piece pumps, changing the position of the thrust opening allows the pump to better adapt to its position in the network, which leads to less use of connections and reduced costs.

In terms of butterflies

The impellers are divided according to the mechanical structure, how the liquid enters the impeller and its exit direction.

A) Mechanical building

Depending on the type and viscosity of the transfer fluid, the impeller can be open, semi-open and closed.

Types of centrifugal pumps in terms of impeller type

a) Closed license
b) Semi-open impeller
c) Open license
The open impeller is used as sludge and for dredging. The semi-open impeller is used to transfer viscous fluids such as sewage, pulp, sugar solution, etc. In the closed impeller model, the impeller blades are placed between two wrapping plates, which are used to transfer low viscosity fluids. The closed impeller has a higher efficiency than the other two impellers.

B) Division in terms of liquid entering the pump

Pumps are divided into single suction and double suction models in terms of fluid entering the impeller. A significant problem with single-suction pumps is their axial hydraulic imbalance. By adding a rim to specific parts of the impeller, it is possible to balance the axial forces on it. The balance of dual suction pumps will result in better performance in pumping high capacity water.

C) Classification based on the direction of liquid flow

In terms of liquid flow, impellers are divided into three categories: radial flow impellers, axial flow impellers and mixed flow impellers. Radial flow impeller is used in cases where high head and low flow are required. The axial flow impeller is used for high flow and low head and the mixed flow impeller is used for pressure and medium flow.

Classification of centrifugal pumps in terms of number of floors

Pumps can be single-stage or multi-stage, or in other words, single-stage or multi-stage.

Division based on the direction of the butterfly period

The direction of the butterfly period can be backward and forward.

Advantages of centrifugal pumps

simple design
The price is right
Occupy little space
Variety in the genus of butterflies
Generate uniform pressure
Possibility to change the performance by turning the impeller (Of course, it should be noted that turning changes more than ten percent efficiency and the similarity rules of the pump will no longer apply)
Because they can be used at high speeds, they can be connected directly to the electric motor.
Uniform volumetric flow of fluid
Low running costs compared to other pumps
Disadvantages of centrifugal pumps

Normally does not provide high pressure and flow.
They are very expensive for high pressures (class pumps).
They need to be sealed.
They do not pump highly viscous fluids effectively.

What is an Axial Flow Pump?

These types of pumps are centrifugal type that are used in both linear and ground types according to different capacities. Cast iron body is made of two types of circulating pumps and steel body circulating pumps and are able to pump fluids up to 130 to 100 degrees Celsius. These pumps are often used for water circulation.

What is an Axial Flow Pump?

One of the important points in ground and linear pumps is that linear pumps usually only produce discharge. While ground pumps produce both flow and pressure.

Circulator pump features

They have little functional sound.
These types of pumps are made in two types of single-phase and three-phase and single-cycle, two-cycle, three-cycle and four-cycle.
The motor speed of these pumps is 1500 and 3000.
The body is mostly made of cast iron and steel.
The butterfly is made of cast iron, steel and brass.
These electric pumps are available in two types: intermediate (coupling) and atarum or dry and unmediated motor.
These types of pumps do not have negative suction.

What is the difference between mechanical pumps and positive displacement?
Displacement pumps are used for small amounts of flow at high pressures and for viscous liquids, and dynamic pumps are usually used for medium pressures and high flows.
In displacement pumps, the desired energy is directly converted to pressure, and in mechanical pumps, the added energy is first converted rapidly and then to pressure in a diffuser or diffuser.
In displacement pumps, the maximum pressure is determined according to the system pressure, which means that as long as the pump drive has power, the pump reaches its required level of the system. The maximum energy (pressure or head) in dynamic pumps is limited, which is created by completely closing the outlet valve at zero flow.
In displacement pumps, energy is sent to the fluid at certain periods, and in dynamic pumps, energy is sent continuously to the fluid and fluid.
What is cavitation in a pump?
Cavitation (also known as corrosion, bubbling, cavitation, vacuuming) is a phenomenon in which the reduction of fluid pressure relative to the partial pressure of liquid vapor (p_v) causes evaporation and bubbles to form. These bubbles enter the high pressure area with water from the low pressure area and burst (collapse). In this case, water moves towards it to fill the empty space created by the collapse and microjets are formed at high speed. This phenomenon is seen in centrifugal pumps, ship propellers, torpedoes and dam overflows.

Improper design of the suction pond causes the formation of vortices in the fluid flow pattern and therefore the suction of compressed air bubbles into the pump is often seen, which is one of the major problems in pumps.

The most common of these is pump impeller wear when there is a sudden change in the direction of fluid movement. Cavitation is usually divided into static and transient.

The most important effects of cavitation

Changes in fluid hydrodynamics (reduction of head and flow)
Damage to the boundaries between solid and fluid (impeller corrosion)
Create vibration and vibration
Create imbalance
What is cavitation in a pump?

What is the cavitation force?

When the bubbles enter the high-pressure area from the low-pressure area, they collapse and hit the walls of the pump with the speed of sound, which makes a lot of noise. The speed of sound in water is 4800 feet per second, the force of which is calculated as follows:

Hv = V2 / 2g = (4800FT / sec) 2 ÷ 2 (32.16FT) = 358209FT

Pressure (psi) = (HEAD * Sp.gr) ÷ 2.31 = 358209 ÷ 2.31 = 155069 psi

The calculated number shows that the cavitation phenomenon can destroy the pump in a short time. The following figure shows the pressure gradient when cavitation occurs in a centrifugal pump:

Cavitation in the pump

The fluid enters the pump from point a and at point b the pressure drops to a pressure lower than the vapor pressure and a bubble is formed (due to evaporation) and when the fluid moves towards the outlet pressure zone (d), at point c Condensation occurs and bubbles burst.

Types of cavitation

Evaporative cavitation
Classical cavitation (NPSH failure)
Internal re-circulation cavitation
Air aspiration cavitation
Vane passing syndrome cavitation
Turbulence cavitation

Evaporative cavitation

The above definition of cavitation is called evaporative cavitation, which is the most common type of cavitation and covers 70% of cavities. This phenomenon also occurs when (NPSHA) is less than (NPSHR) is also called NPSH failure. Most damage to the pump impeller occurs in this type of cavitation.

Sometimes the sound of pebbles hitting the impeller inside the pump can be heard. If we close the discharge valve slowly and the sound stops, it indicates cavitation problem.

NPSHR What is the net positive positive height required for suction?

The NPSHR parameter (net positive suction head) plays an important role in selecting pumps that have a high inlet fluid temperature. In fact, a fluid evaporates when its pressure is too low or its temperature is too high, and NPSHR refers to the minimum amount of pressure required to prevent cavitation. In order to prevent cavitation, the system pressure must always be higher than the liquid vapor pressure at operating temperature at all stages of suction, impeller entry and discharge.

The cavitation phenomenon occurs when the available net positive suction height of NPSHA is less than that recommended by the manufacturer. NPSHA depends on various factors such as ambient pressure, physical properties of the liquid, diameter of the suction pipe and so on. This parameter is calculated according to the following formula:

NPSHA = {(P1 + Pb – Pv) / γ} – Z1 – Hr

Z1max = {(P1 + Pb) / γ} – {NPSHR + (Pv / γ) + Hr}

Z1: Level difference between pump shaft and pumped fluid level
p1: The amount of air pressure on the surface of the fluid. In case of suction of fluid from open tank or contact of fluid surface with air, the value of P1 is equal to 0
pb: Atmospheric pressure
pv: The vapor pressure of the fluid being pumped at the source temperature
c: specific gravity of the fluid
Hr: drop of the head in the suction pipe
Most centrifugal pump manufacturers recommend that the NPSHA be at least 0.5 m higher than the NPSHR to prevent cavitation. Some sources suggest that the NPSHA should be approximately 20% higher than the NPSHR. In any case, this difference should not be less than 0.5 meters.

Note: As the pump flow increases, the NPSHR value increases, which is greater in the right range of the best operating point (BEP). That is why it is important to select the pump in the BEP range.

Solutions to prevent injuries due to cavitation performance

Speed ​​reduction that reduces the amount of head caused by the drop.
Increasing the impeller diameter and decreasing the speed (it should be noted that reducing the speed does not prevent the supply of the head).
Using two smaller pumps in parallel will reduce head drop.
Pv reduction (fluid temperature reduction)
Consider the pump suction port larger than the thrust port
Cavitation disposal methods

Increased pressure in the suction of the pump (for example, in boilers due to the high temperature of the fluid to prevent cavitation, a device called a deaerator is used to create artificial pressure before the pump)

Reduce pump flow

Do not use the valve close to the suction of the pump
Correction of piping in pump suction
Washing and descaling in pipes and fittings, especially in pump suction
Use of inductor in pump suction
Use a pump with less NPSHR than NPSHA piping system
Increase NPSHA piping system
The following figure shows an example of installing a centrifugal pump to pump fluid with a flow rate of 235 liters per minute to pump water at four different temperatures.

Now we examine the performance of the pump in 4 different modes. If the NPSH value required to supply the set head is 3.25 m, we can obtain the desired vapor pressure and fluid mass temperature from the relevant tables. Suction head drop is also calculated according to the following formula: