How Does A Reciprocating Pump Work?

A pump is a device that uses to transfer different fluids from one location to another. Pumps have multiple types according to different applications. A reciprocating pump is a favourite type of pump from the category of positive displacement pumps. In this article, we will deeply discuss various aspects of the reciprocating pump.

What is a Reciprocating Pump?

A reciprocating pump is a mechanical device that changes the mechanical energy of the fluid into hydraulic energy (pressure energy). It uses a piston or plunger for pumping the fluid from one location to another. Because a reciprocating pump uses a piston or plunger for pumping purposes, therefore, it is also known as a piston pump.

In this pump, the piston reciprocates in an upward and downward position inside the pump cylinder. As the piston moves toward BDC, it sucks fluid while it pressurizes the fluid when it moves toward TDC.

The reciprocating pump works according to the motion of the piston downward and upward movement. In contrast, dynamic pumps use an impeller and diffuser to pump the fluid from low head areas to high head areas. In 200 BC, the reciprocating pump was invented by the Greek discoverer Ctesibius.

The working of these compressors is totally dependent on their piston. If the piston damages then reciprocating pumps cant transfer fluids. Therefore, proper working of the piston is very important in these pumps. During the working of the reciprocating pump, the piston converts the kinetic energy of the fluid and converts it into pressure energy. 

reciprocating pump

The reciprocating pump uses when a relatively small quantity of the fluid is transported under high pressure. This type of pump is more appropriate for small flow rates at high pressure as compared to centrifugal pumps.

A certain amount of liquid (mainly sump) must be applied and transported from the lowest to the highest area when using a plunger or piston pump. For example, if you go to the bike water servicing, you can check that the water used for servicing is gathered from the sump and sprayed onto the bike by providing pressure through the nozzle.

Reciprocating Pump Working Principle

The reciprocating pump works on the principle of positive displacement. A reciprocating piston pump consists of a piston that moves back and forth in a cylinder. The piston is connected with a crankshaft with the help of a connecting rod. This piston moves as the connecting rod move due to the motion of the crankshaft. The crankshaft connects with a motor that rotates it.

The pump cylinder is connected to a suction pipe and a discharge pipe with a suction valve and a delivery valve. The inlet and outlet valves act as check valves that allow the fluid flow to flow in one direction. The fluid sucks into the cylinder through the inlet valve. The fluid exits the cylinder of the pump through the outlet valve.

A reciprocating pump works in the following way:

reciprocating pump working
Reciprocating Pump Working

As you can see in the above diagram, when the crankshaft is at A position, the piston has a far-left position inside the cylinder. As the crankshaft rotates from A to C (θ = 0 ° to 180 °), the piston in the cylinder moves to the extreme right side.

During the right-side movement of the piston, a partial vacuum is created inside the cylinder. However, the atmospheric pressure acts on the surface of the fluid in the sump, and this pressure is higher than the pressure in the cylinder.

Due to the cylinder inner and sump pressure difference, the pump sucks fluid from the sump into the suction pipe.

The fluid opens the inlet valve of the pump and starts entering into the cylinder. As the suction process completes, the crankshaft rotates from C to A (θ = 180° to θ = 360°), and the piston also moves from the right position of the cylinder to the left position.

When the piston inside the cylinder moves to the left, it reduces the cylinder volume. Due to this reason, the cylinder’s internal fluid pressure becomes higher than the atmospheric pressure.

As the piston pressurizes fluid and cylinder inner pressure becomes higher than the atmospheric pressure, the inlet valve closes, and the discharge valve opens, and fluid delivers into the delivery pipe and delivers to the desired location.

Parts of the Piston Pump

The major components of the reciprocating or piston pump are given below in detail.

  1. Section Valve
  2. Delivery Valve
  3. Suction Pipe
  4. Delivery Pipe
  5. Cylinder
  6. Connecting rod
  7. Crank
  8. Piston and piston rod
  9. Air Vessel
  10. Strainer

reciprocating pump components

1) Suction Valve

It includes in the most significant components of the reciprocating pump. The suction or inlet valve is a one-way valve. In other words, this type of valve allows flow only in one direction. The suction valve inserts between the cylinder and the suction pipe. As the liquid discharges, this valve opens, while during suction, it closes.

Read also: How does a Centrifugal Pump Work?

2) Suction Pipe

The suction pipe uses to draw water from the storage tank into the pump cylinder. This part of the reciprocating pump connects the inlet valve with the reservoir. It connects the pump inlet to the water tank.

3) Pressure Valve

The discharge valve includes in the essential parts of the reciprocating pump. It is also a one-way valve. This valve makes a connection between the delivery pipe and the cylinder.

During the suction process, this valve closes while it opens during the delivery process of the fluid.

4) Delivery Pipe

Delivery pipe uses to deliver fluids from the pump cylinder to the desired height or position. It directly connects with the delivery valve of the cylinder of the piston pump.

5) Cylinder

cast-iron or Alloy steel uses for the manufacturing of the pump cylinder. The piston rod and piston arrange in the pump cylinder. The fluid from the suction valve sucks inside the cylinder.

The piston moves forward ad backward inside the cylinder for increasing its pressure. The cylinder connects with a discharge valve from where fluid discharges into a discharge pipe.

6) Piston and Piston Rod

Piston and piston rod include in the most significant parts of the reciprocating pump. A piston is a solid metal part. It moves back and forth inside the cylinder for suction and exits the fluid. When it moves backward, it sucks air inside the cylinder, and when it moves forward, it delivers the fluid. Piston moves due to the movement of the crankshaft. The piston rod supports the piston in linear movement.

7) Crank

The crankshaft is an essential component of the positive displacement pump. It is a solid disc that connects with the piston through the connecting rod. The crank is directly connected to the electrical motor. It rotates when the electrical motor provides power to it.

8) Connecting Rod

Pressure Valve makes a link between the piston and crankshaft. This part of the pump connects the piston with the crankshaft. When the crankshaft rotates, then the connecting rod also rotates. It transforms the linear crankshaft rotation to the piston linear motion.

9) Strainer

There is a filter at the suction pipe end that stops the entry of the solid particles from the water source inside the cylinder. Otherwise, solid particles will block the delivery.

10) Air Vessel

This reciprocating component is connected to the discharge and the suction pipes. It eliminates the need for friction heads. Also, it provides a uniform discharge rate.

Read also: Centrifugal Pump Working

Reciprocating Pump Types

The reciprocating pump has the following major types.

1) Single-Stage Pump

In this type of reciprocating pump, only one cylinder uses for pressurizing the water. These pumps have less efficiency than two-stage pumps. But these have low prices and require less maintenance than two-stage pumps.

2) Two-Stage Pump

As the name of this pump represents that it uses two cylinders for pressurizing the water. First of all, it sucks water or other fluid in the 1st cylinder where the piston increases its pressure after that it sents into the 2nd cylinder. In the 2nd cylinder, another piston increases the pressure of the fluid. After this, the fluid pumps to the desired area.

3) Single Acting Reciprocating Pump

In the single acting reciprocating pump, only one side of the piston works while the other side is fixed. Only one side of the piston uses for suction and delivery purpose. In simple words, the first stroke of the piston sucks the water inside the cylinder while the second stroke converts the kinetic energy of the water into pressure energy and increases its pressure. 

single acting pumps

4) Double Acting Reciprocating Pump

In the double-acting reciprocating pumps, both sides of the piston work. In simple words, when the piston moves backward, it sucks the liquid while it moves forwards, then it reduces the volume of the fluid and pressurizes it.

Double Acting Reciprocating pump

5) Reciprocating Pump with Air Vessel

A reciprocating pump with an air vessel pump has a closed chamber that contains fluid in the bottom section and air in the top section of the chamber. This chamber has an opening on the bottom from where the fluid can move in or out from the vessel. In addition, this vessel has an inlet and outlet valve from where the air enters and discharges from the vessel.

air vessel pump

6) Reciprocating Piston Pump

It is a most famous and common type of reciprocating pump. This pump uses a piston to pump fluid instead of a plunger. In this pump, the piston moves forward and backward. This is used to pump the fluid at high head areas.

7) Diaphragm Pump

A diaphragm pump is a positive displacement pump that utilizes a Teflon, thermoplastic, or rubber diaphragm or membrane. A diaphragm is surrounded by valves. This pump is also known as a membrane pump. It works by temporarily generating a vacuum.

Diaphragm pump

8) Plunger Pump

These reciprocating pumps use a plunger instead of a piston. In these pumps, the movement of the piston is the same as the piston. A plunger pump is best for applications to pump chemicals, saltwater, and oil.

These pumps have low weight, low density, needs low maintenance, and high durability. Plunger pumps use in the beverage, food, petrochemical, gas, oil, nuclear, mining, and medical industries. These have high resistance to impact, thermal shock, vibration, and abrasion. The plunger pump has a compact design and it has easy maintenance. 

Piston Pumps

How to calculate the efficiency of the Reciprocating Pump?

The efficiency of a pump is a ratio between the outpower and input power. The following formula can calculate the reciprocating pump efficiency:

             Efficiency = output power / input power

In the above-given equation, the output power can be calculated by multiplying the fluid flow with the rise of pressure. While the input power can be calculated by multiplying the torque with speed. Use the below-given formulas for calculating the input power and output power:

            Out Power = Pressure Rise * Flow

 Input Power = Torque * Speed

The volumetric efficiency and mechanical efficiency are also a kind of pump efficiency. 

The mechanical efficiency is related to pressure and torque. The mechanical efficiency of your pump tells that how much a pump converts input torque into output pressure.

The volumetric efficiency is related to speed and flow rate. A volumetric efficiency tells that how well a pump converts inlet velocity to outlet flow.

Therefore, the overall efficiency of a reciprocating pump is equal to the product of the volumetric efficiency and the mechanical efficiency.

By using the below-given equations, you can easily calculate flow (Q), Torque (T), Shaft Power and Hydraulic Power of your pump:

reciprocating pump efficiency formulas
Reciprocating Pump efficiency formulas

In the above equations, the shaft power represents input power while the hydraulic power represents output power.

Advantages and Disadvantages of Reciprocating Pump

The reciprocating pump has the following advantages and disadvnatges:

Advantages of Reciprocating Pumps

  1. It uses for providing a high suction head.
  2. These positive displacement pumps don’t need a priming process like a Pressure Valve.
  3. It works due to the movement of the piston, while dynamic pumps work on the impeller rotatory velocity.
  4. It shows a continuous delivery rate.
  5. It doesnt has priming issues.
  6. These pumps dont have cavitation issues.

Disadvantages of Reciprocating Pumps

  1. These pumps require high maintenance.
  2. Most of its parts have high wear and tears.
  3. It has a low flow rate.
  4. It has a high cost.
  5. These pumps aren’t best for viscous liquids.
  6. The piston pump has bulky and heavy in size.
  7. It doesn’t provide uniform torque
  8. It requires high maintenance cost

Applications of Reciprocating Pump

  1. Uses for oil drilling purposes.
  2. It uses for light oil pumping.
  3. The reciprocating pump uses in a pneumatic system.
  4. Supply of small boilers with condensate.
  5. For inflating bicycle tires.
  6. Uses in the industry of natural gas.
  7. Uses in the Petrochemical industry
  8. Piston pump uses in oil refineries.
  9. Uses in the servicing water center for vehicles etc.

FAQ Section

Who Invented Reciprocating Pump?

Greek discoverer Ctesibius invented the reciprocating pump in 200 BC

See More:

  1. What are the different types of Pumps?
  2. What are the different types of Positive displacement Pumps?
  3. How does a Centrifugal Pump Work?

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