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.
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,
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.
The reciprocating pump means a machine or especially hydraulic machine which converts mechanical energy into hydraulic energy.
So, what is these energies?
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!
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.
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.
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.
The explanation for the parts of Reciprocating Pump are as follows:
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.
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.
Important: Without a strainer, dirt will come into the system, and impact on the workability of pumps.
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.
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.
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 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:
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.
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.
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:
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.
Important: Connecting rod makes the connection between Crank and piston. It changes the crank rotational motion into the linear motion of the piston.
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.
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.
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.
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!
The reciprocating pump consists of a piston in an enclosed cylinder, crank, piston, 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:
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.
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.
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.
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.
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.
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.
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.
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
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
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
= 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.
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:
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
= 0.0314 x 0.4 x 60/60 m3/s
= 0.013 m3/s
= 13 litre/s
Hence, theoretical discharge is 13lit/s
N = volumetric efficiency
Qact = 11.96 litre/sec
N = actual discharge / theoretical discharge
= 11.96 / 13 x 100%
Hence, volumetric efficiency is 92%
Slip = (Qth – Qact)/Qth x 100%
= (13 – 11.96) / 13 x 100%
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)
= 1000 x 9.81 x 0.013 x 20
= 2550.6 watt
= 2.55 kW
Mechanical efficiency = 80%
Power input required = Power required / efficiency
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 pumps are classified in few categories, based on mechanism, air vessel, or numbers of cylinders.
In each double acting reciprocating pump, there will be two suctions pipes, two suction valves, two delivery pipes and two delivers valves.
Here, a single-cylinder or one cylinder is connected to a shaft.
In this pump, double cylinders or two cylinders are attached to a single shaft. Here, each cylinder is having separate suction and delivery system.
In this pump, three-cylinders are connected.
Apart from all the above, reciprocating pump, there are three different pumps are widely used:
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.
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:
The plunger pump is a single-acting pump. These pumps are able to build very high pressure.
Diaphragm pumps are widely used in chemical injections and other industries.
Diaphragm pumps are the best suitable pump when the system required zero leakage.
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:
There are few major advantages of the Reciprocating Pump and the same is explained:
These pumps operate at very higher efficiencies than other pumps, generally reaching levels of 90% or more efficiency.
The major disadvantages of Reciprocating Pumps are:
In addition, when we talk about a reciprocating pump package, many components are associated with it, these are, as follows:
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:
Type of maintenance requirements and facilities.
There are a lof or manufacturers available, few of them are listed,
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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