Reciprocating Pump: Basic, Working Principle, Parts & Type

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Reciprocating Pump: Basic, Working Principle, Parts & Type

The Reciprocating pump is a widely used positive displacement pump in many industries where large delivery pressure is required. In this kind of pump, the piston moves forward & backward and mechanical energy is converted into hydraulic energy.

These pumps are the best choice among all other kinds of pumps.

In this session, we will learn all details about this Pump.

Let’s explore!

Reciprocating Pump – Introduction

Do you want to learn all about the Reciprocating pump? We have already got the basic idea about the positive displacement pump. Reciprocating Pumps are one kind of Positive Displacement type pump. It works based on the movement of the piston in,

  • forward direction and
  • backward direction and increase the pressure of the liquid.
reciprocating pumps
Reciprocating pumps

We will discuss the basics of reciprocating pumps with a lot of examples & diagrams. A single-acting reciprocating pump is the simplest reciprocating pump. Here, we will consider the same for an easy explanation as well as understanding.

Single-acting means only a single side of the piston is acting.

  • One number (1) piston
  • One number (1) suction pipe
  • One number (1) suction valve
  • One number (1) delivery pipe
  • One number (1) suction valve

What is Reciprocating Pump?

Reciprocating Pump Definition

The reciprocating pump means a machine or especially hydraulic machine which converts mechanical energy into hydraulic energy.

So, what is these energies?

  • Mechanical energy means the energy which is created by the motion of mechanical device or position of the device.
  • Hydraulic energy means the energy which is created by the water.

Reciprocating pumps are used when a certain quantity of liquid needs to be transported from the lower level to a higher level. Higher level means pressure should be high enough.

In this case, a certain volume of liquid is collected within the pump enclosed area and increased the pressure in line with requirements. There are so many places, where high-pressure with low volume pumps are required. So, what to do?

It’s simple! Select Reciprocating pumps!

Reciprocating Pump Explanation

If you observe when filling oil in the car, you will see that there are some big tanks in the underground. This big tank is filled with oil. But when we go to fill our car tank, that time we see fuel is coming from the nozzle.

Here, fuel is coming from the underground tank to the nozzle.

In-tank, the pressure of fuel is very less but when it is injected into the car, the pressure is very high This is due to reciprocating pumps that are installed between.

History of Reciprocating Pump

It was long ago; Egyptians have invented the shadoof in 2000 BC. Later, a Greek inventor as well as mathematician, Ctesibius invented a basic pump. It consists of one water source, an air pump, valves, a tank, and a row of pipes.

Main Components of Reciprocating Pump and Functions:

Reciprocating pumps are used in many industries as well as our few home applications too. Now, whatever the application, a reciprocating pump consists of several parts.

The various important parts of Reciprocating Pump are as follows.

  • A sump of liquid, or water sump or water reservoir
  • Strainer
  • Suction Pipe
  • Suction Valve (non-return valve)
  • Cylinder or liquid cylinder
  • Piston or plunger and Piston rod
  • Piston rings
  • Packing
  • Crank and Connecting rod
  • Delivery valve (non-return valve)
  • Delivery pipe
  • Air Vessel

The explanation for the parts of Reciprocating Pump are as follows:

Water Sump

Sump means a reservoir or a simple language, a source of water. Water is sucked by the pumps from the sump. Later on, water is undergoing a process by the piston within the pump cylinder. Finally, it is transported to the delivery pipes and ready for application.

Important: No water sump means no water; hence, the pump will not be in action.

Strainer

We all know that if the water is having dirt or dust particles or solid particles, or other pollutants, the same will be entered within the pump cylinder. These unwanted foreign particles can jam the cylinder, reduce efficiency. In short, this problem will affect the working principle of reciprocating pumps. It can clog the suction pipe as well as choked the delivery.

To avert this problem, a wire mesh is provided at the end of the suction pipe to prevent the entrance of these foreign particles from the sump to the cylinder.

reciprocating pump suction strainer
Reciprocating pump suction strainer

Important: Without a strainer, dirt will come into the system, and impact on the workability of pumps.

Suction Pipe

We got a water sump, now this sump needs to be connected to the pump basically the cylinder of the pump.

There is a pipe that is connected and helps to suck the liquid from the sump to the pump. This pipe is known as a suction pipe.

Since it is on the suction side of the pump & helps to suck, this pipe is known as the suction pipe. There is a valve in the suction pipe.

Important: Without a suction pipe, the pump will not be connected with the reservoir, hence, the pump will not work.

Suction Valve

The suction valve is fitted in the suction pipe. Why is the suction valve important? What will be the problem if there is no suction valve? Let me explain, the purpose of this valve.

This valve allows liquid from the water sump to pump only not the reverse flow to the reservoir. Hence, no return will be encountered in the reservoir. Due to this no return philosophy, it is called a non-return valve.

So, the flow will be always in one direction.

If there is suction, then only this valve will be opened.

This valve will be closed during the discharge of liquid to the outside.

Important: If this valve is not provided, during the discharge there will be backflow of liquid to the sump which is not acceptable.

Cylinder

This is a hollow tube-shaped cylinder known as the body or the casing of pumps. This is commonly fitted with a metallic lining referred to as a ‘cylinder liner‘. The liner helps for the smooth operation and is replaceable when it becomes worn and inefficient.

This cylinder is consisting of piston and piston arrangements and it is the main portion where water is undergoing a change of pressure. This cylinder may be made of cast iron, or steel, or any other suitable material based on the applications.

Piston and Piston rod

Piston and piston rod arrangement is the main workforce in the cylinder. A piston is a solid type cylindrical part and moves forward and background inside the cylinder, to perform suction and delivery of liquid.

In the case of the suction:

  • the piston moves back inside the cylinder
  • the piston moves in the forward direction for discharging liquid

Now, to move backward and forward of the piston, there is a rod that helps the piston to have continuous linear motion.

Important: If the piston is not there, the pressure of the liquid will not change and if the piston rod is not there. The piston cannot move or acts.

reciprocating pump piston piston rod
Reciprocating pump piston piston rod

Piston Rings

The piston head is fitted with the piston rings for sealing. It helps to seal against the cylinder lining and minimize internal leakage.

It is mandatory for the smooth operation of reciprocating pumps.

Packing

The piston is moving backward and forward continuously in the cylinder. Hence, a packing is required to seal the joint between the piston and the cylinder tightly to prevent leakage of liquid from the cylinder.

Improper packing may create many problems in reciprocating pumps:

  • Problem in lubrication
  • Excessive friction.
  • Misalignment of piston or piston rod
  • May cause wear
  • Reduce the efficiency of the pump etc.

Crank and Connecting Rod

The crank is the metallic part of the pump.  It looks like a solid circular disc and it is connected to the power source.  The power source can be the engine or the motor, etc. The name connecting rod simplifies that it is connecting something. Here, it is connecting crank and piston. When the engine or motor rotates, the crank also rotates. Due to this rotation, the connecting rod converts this rotary motion into linear motion into the piston.

crank connecting rod
Crank connecting rod

Important: Connecting rod makes the connection between Crank and piston. It changes the crank rotational motion into the linear motion of the piston.

Delivery Pipe

When the liquid comes out from the pump the delivery pipe comes into the picture. The delivery of water from the outlet of the pump to the desired place in the main purpose of the delivery pipe.

Important: If the delivery pipe is not there, the pump cannot deliver the required liquid at the desired locations.

Delivery valve

The delivery valve, like the suction valve, acts as a non-return valve and it is placed in the delivery of pumps. Like the suction valve, a delivery valve is also a Non-return valve.

  • During the suction of the pump, the delivery valve is closed and
  • During Discharge, there will be a pressure of a liquid and the suction valve is closed
  • In the same way, due to pressure, the delivery valve is opened to transfer the liquid.

Important: The delivery valve is essential. If it is not there, the pump will not work properly & in case of a pump stop, backflow will happen which is very dangerous for pump health.

Air Vessel

There are frictional heads in both suction and discharge pipes, and these all need to be removed from the system to have a uniform discharge rate by reducing the acceleration head.

Air vessels are related to each suction and discharge pipe and offer a uniform discharge rate.

Hence, we have got an idea about the basic components of a reciprocating pump. Let’s try to understand the working philosophy of the reciprocating pump!

reciprocating pump air vessels pump
Reciprocating pump air vessels pump

Working Principle of a Reciprocating Pump with Diagram

The reciprocating pump consists of a piston in an enclosed cylinder, crank, piston, connecting rod.

Connection details:

  • The connecting rod is one of the main parts of the pump and it connects the crank and the piston.
  • Crank connects the driving motor or the driving machine and connecting rod.

Due to the rotation of the crank, the piston also moves forward and backward inside the cylinder by means of a connecting rod.

Pumps or the cylinder are connected to the suction pipe with a non-return suction valve and discharge pipe with a non-return discharge valve. Non-return valve means it will not allow the liquid to flow in the opposite direction.

The suction valve allows liquid from the suction pipe to the cylinder only. In the same way, the delivery valve allows liquid from the cylinder to the delivery pipe.

When the crank starts its rotation, the piston will start moving in the cylinder.

A nice animated video made by ‘Learn & Grow’ may be helpful for this article.

Let’s analyze, working principle of the reciprocating pump in a few steps:

Step #1

The crank is at point A; it will make an angle θ=0º with respect to the horizontal line. Look at the image, the piston is at point P, extreme left side, inside the cylinder.

reciprocating pump working principle step 1
Reciprocating pump working principle step 1

Step #2

When power will be supplied to the reciprocating pump, the crank will start to rotate by the electric motor.

When A moves towards point C, the angle increases, and the piston will move towards the right in the cylinder. When A reaches at point C, the angle becomes angle θ=180º and the piston reaches to point Q.

reciprocating pump working rule step 2
Reciprocating pump working rule step 2

When the piston moves towards the right side, a partial vacuum will be created left side of the cylinder. Vacuum means the pressure, which is less than the atmospheric pressure.

reciprocating pump working suction-mech
Reciprocating pump working suction-mech

Now, on the suction side of the pump, the surface of the water is having normal atmospheric pressure. Since the cylinder creates a vacuum or less pressure than the atmospheric pressure, the liquid will be forced into the suction pipe of the pump. This liquid then opens the suction valve and enters the cylinder.

Step #3

When the crank rotates from C (θ=180º) to A (θ=360º), then the piston will move from the extreme right position towards the left side in the cylinder.

When the piston starts to move the left side, it will increase the pressure of the liquid inside that region and that will be more than atmospheric pressure.

reciprocating pump working step 3
Reciprocating pump working step 3

Due to that pressure, it reaches to the delivery pipe via a delivery valve. Now, since the valve is a non-return type, water will not be back.

Hence, the crank changes its rotational motion into linear motion and makes the movement of the piston inside the cylinder.

Step #4

Due to this higher pressure, the Suction valve will be closed, and the delivery valve will be opened. Hence, the liquid is forced into the delivery pipe through the pump outlet and raised the required height.

Reciprocating Pump – Expression & Explanations

Work Done

reciprocating pump working diagram
Reciprocating pump working diagram

If, A   = cross-section area of the cylinder

L       = Stroke length, that means travel of piston in each forward or backward stroke

V       = volume of discharge in one revolution = area x length = A x L, m3

N       = RPM, that means rotation per minute or

N/60 = rotation per second

Qh     = work done per second, m3/s

Qh     = discharge in single revolution x nos. of revolution per second

          = V x N/60

          = A x L x N/60

          = ALN/60

Qh = ALN / 60

This is for single-acting reciprocating pumps, if we derive the equation for double-acting reciprocating pumps, it will be simply double that means

Qh    = 2 ALN/60

Qh = 2ALN / 60

Power Requirement

We can derive, the power requirements for reciprocating pumps as well,

If, hs = suction head, m

hd     = discharge head, m

ρ        = density of liquid, kg/m3

g       = acceleration of gravity, N-m/s2

Q       = discharge of liquid, m3/s

Then, the power requirement will be,

P       = Power Requirement, watt

          = ρgQh

          = ρgQ (hs+hd)

P = ρgQ (hs+hd)

Slip of reciprocating Pump

Slip means the loss of capacity due to friction, it can be calculated as

Slip                       = Theoretical discharge – Actual discharge

% of slip    = (Qth – Qact)/Qth x 100%

% of slip= (Qth – Qact)/Qth x 100%

Let us try to see one example, for calculating pump work done, power requirement & slip percentage.

Let’s take,

A single-acting reciprocating pump with 200mm piston diameter, stroke length 400mm, rotational speed 60RPM. Now, the water to be pumped at 20m height. Find out, theoretical discharge. If the actual discharge is 20.2litre/sec, then what will be volumetric efficiency, slip & power requirement. Mechanical efficiency 80%.

Answer with explanation:

Theoretical Discharge

If, d   = piston diameter = 200mm = 0.2m

A       = cross sectional area = 3.14 x d2/4 = 3.14 x 0.2 x 0.2 / 4 = 0.0314m2

N       = rotational speed = 60

L       = Stroke length = 400mm = 0.4m

Qth   = discharge of liquid

          = ALN/60

          = 0.0314 x 0.4 x 60/60 m3/s

          = 0.013 m3/s

          = 13 litre/s

Hence, theoretical discharge is 13lit/s

Volumetric efficiency

N       = volumetric efficiency

Qact = 11.96 litre/sec

Here,

N       = actual discharge / theoretical discharge

          = 11.96 / 13 x 100%

          = 92%

Hence, volumetric efficiency is 92%

Slip

Slip   = (Qth – Qact)/Qth x 100%

          = (13 – 11.96) / 13 x 100%

          = 80%

Power Input

We know,

ρ        = density of water =1000kg/m3

g       = gravitational acceleration = 9.81 N-s/m2

Q       = 0.013 m3/sec

H       = total head = 20m

Power required   = ρgQ (hs+hd)

                              = ρqQH

                             = 1000 x 9.81 x 0.013 x 20

                              = 2550.6 watt

                              = 2.55 kW

Mechanical efficiency   = 80%

Power input required    = Power required / efficiency

                                      = 2.55/0.8

                                      = 3.19kW

Therefore, in this way, the water is sucked and discharged from the sump to the desired location and we can calculate discharge, slip, power inputs, etc. This is simple calculation to understand the subject matter, without reciprocating pump detail calculation.

Reciprocating Pump Types

Reciprocating pumps are classified in few categories, based on mechanism, air vessel, or numbers of cylinders.

Based on Mechanism:

Single-Acting Reciprocating Pump

  • ‘Single’ implies one delivery pipe, delivery valve along with one suction pipe, suction valve.
  • Only one side of the piston acts on the liquid.
  • The liquid is sucked in one direction that is suction stroke and it delivers that is called deliver stroke.
single acting reciprocating pump
Single acting reciprocating pump

Double Acting Reciprocating Pump

In each double acting reciprocating pump, there will be two suctions pipes, two suction valves, two delivery pipes and two delivers valves.

  • When the piston is in between the cylinder, one side will have one suction and one delivery pipe
  • Another side also will have the same things.
  • It means both sides of the piston works on the liquid.
double acting reciprocating pump
Double acting reciprocating pump

Based on Air Vessel:

Pump with Air Vessel

  • In this case, the continuous flow of water at a uniform rate.
  • It reduces the acceleration head.
  • This pump accumulates water in the vessel by compressing air.
reciprocating pump vessel
Reciprocating pump vessel

Pump without air vessel

  • When the In this case, some amount of air present in the water.
  • In domestic applications, these types of pumps used.

Based on Number of Cylinders

Single cylinder

Here, a single-cylinder or one cylinder is connected to a shaft.

Double cylinder:

In this pump, double cylinders or two cylinders are attached to a single shaft. Here, each cylinder is having separate suction and delivery system.

Triple cylinder:

In this pump, three-cylinders are connected.

Apart from all the above, reciprocating pump, there are three different pumps are widely used:

  • Piston pump
  • Plunger pump
  • Diaphragm pump

Piston Pump

The piston pump is a single or double-acting pump. In a single-acting piston pump, pump sucked liquid in suction stroke and the pump delivers liquid in discharge.

For example:

  • Well-pumps,
  • Football pumps
  • Cycle pumps,

In double-acting piston pumps, both sides of the piston compress the liquid. Fluid comes in contact with both sides of the piston. These pumps can be:

  • Simplex (one cylinder),
  • Duplex (two cylinders),
  • Triplex (three cylinders) and so on.

Plunger Pump:

The plunger pump is a single-acting pump. These pumps are able to build very high pressure.

  • These pumps can be vertical or, horizontal
  • These pumps can be simplex or multiplex.
  • These pumps are widely used for building up the highest pressure in many industries.
plunger pump
Plunger pump

Diaphragm Pump

Diaphragm pumps are widely used in chemical injections and other industries.

  • The operation is possible both hydraulically or mechanically.
  • These can be simplex or multiplex design
  • It can have variable stroke arrangements.

Diaphragm pumps are the best suitable pump when the system required zero leakage.

diaphragm pump
Diaphragm-pump

Reciprocating Pump Application

The main application of the Reciprocating pump is discussed here.

Reciprocating pumps are widely used for a long and in various industries. Proper selection in the proper industry is a vital role, improper selection results in repeatable works. The following industries are widely used reciprocating pumps:

  • Oil drilling operations.
  • Oil production, oil disposal, oil injections.
  • Offshore oil applications.
  • Light oil pumping.
  • Gas industries
  • Petrochemical industries
  • Pneumatic pressure applications.
  • Oil refineries
  • Feeding Boiler/condensate returns/heat exchanger/evaporator tube cleaning/pipe cleaning
  • Vehicle cleaning workshops.
  • Tank cleaning/vessel cleaning
  • Wet sandblasting
  • Hydro testing of tanks, vessels, pipes, valves & fittings, hoses & systems
  • Boiler feeding
  • High-pressure pumps for the RO system (Reverse osmosis)
  • Cleaning services, like vehicle cleaning or glass cleaning, etc.
  • Firefighting system this kind of pumps are used
  • Sewer cleaning
  • Wastewater treatment process
  • Paper manufacturing, pulp manufacturing industries
  • Mining industries
  • HVAC system
  • Refrigeration industries
  • Chemical processing, food processing, etc.,

Reciprocating Pump Advantages

There are few major advantages of the Reciprocating Pump and the same is explained:

  • High pressure can be obtained at the outlet of the pump.
  • The high-pressure liquid can be supplied to the desired height.
  • No priming process is required in this pump except few conditions and this a one of the main advantages over centrifugal pumps.
  • Reciprocating Pump provides a high suction lift since it can create high negative pressure in the cylinder.
  • Air can be used as the working fluid in reciprocating pump.
  • The liquid flow rate of a centrifugal pump may fluctuate but the reciprocating pump provides a steady flow rate.

These pumps operate at very higher efficiencies than other pumps, generally reaching levels of 90% or more efficiency.

Reciprocating Pump Disadvantages

The major disadvantages of Reciprocating Pumps are:

  • Maintenance is very high due to the wear and tear of the components.
  • The flow rate is low means discharge is limited.
  • The initial cost is very high.
  • These are bulky and heavy.
  • It is very difficult to handle viscous liquids.
  • There may be a problem in the alignment of the piston or piston rod.

Reciprocating Pumps Package

In addition, when we talk about a reciprocating pump package, many components are associated with it, these are, as follows:

  • Reciprocating pump that means casing, piston, bearing housing or bracket, etc.,
  • Base frame,
  • Driver, it may be a motor or diesel engine or turbine-driven or gas engine driven,
  • All valves, suction & delivery pipes
  • Strainers
  • Pressure gauges or pressure transmitter to measure the pressure in suction and discharge side
  • Shut off valves
  • Safety valves
  • Auxiliaries like sealing system, cooling system, etc.,

Note on Advantage & Disadvantage

Based on the above discussion on the advantage and disadvantages of reciprocating pumps, sometimes it is very difficult to select the pumps. There are some pros and cons for both the pumps and the following points needs to be considered:

  • Location of the pump to be installed.
  • Which kind of fluids to be handled.
  • Type of Operation requirements

Type of maintenance requirements and facilities.

Reciprocating Pumps Additional Note

  • In reciprocating pumps, a piston can create very high pressure and it should not be operated in a closed discharge system. A safety relief system is mandatory to prevent damage to the pump or driver against high pressure.
  • The flow in the reciprocating pump is always uneven or pulsating. This can be smoothed out by using few tools like dampeners or stabilizers at the inlet and outlet piping which also protects the entire pumping mechanism.

Manufacturers of Reciprocating Pump

There are a lof or manufacturers available, few of them are listed,

  • Milton Roy
  • Liwa
  • Flowserve
  • DMW
  • RUHRPUMPEN GMBH etc.

Conclusion

So, we have learned the basics of Reciprocating Pump! Any doubt, please don’t hesitate to write to us! Remember, Centrifugal pumps are different in terms of construction, working principles, and application.

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