Short Answer:

Hydraulic machines are devices that use fluid power to perform mechanical work. They are classified mainly based on the direction of energy conversion. The two major types are hydraulic turbines, which convert fluid energy into mechanical energy, and hydraulic pumps, which convert mechanical energy into fluid energy. These machines are widely used in industries, power plants, and various hydraulic systems.

The classification also depends on the working principle, such as reaction or impulse type, and on flow direction, like axial flow or radial flow machines. Each type has its own design, application, and energy conversion process.

Detailed Explanation:

Classification of Hydraulic Machines

Hydraulic machines are mechanical devices that utilize the energy of fluids (liquids) to perform work. The working principle of these machines is based on the transfer of energy between a moving fluid and a mechanical element. Depending on whether energy is given to or taken from the fluid, hydraulic machines can be broadly classified into two main categories — hydraulic turbines and hydraulic pumps.

1. Based on Energy Conversion

The most common and fundamental classification is according to the direction of energy conversion:

• Hydraulic Turbines:
  These machines convert hydraulic (fluid) energy into mechanical energy. In turbines, water or another liquid flows through the blades, causing them to rotate. The mechanical energy obtained is often used to drive an electric generator.
  Example: Pelton wheel, Francis turbine, Kaplan turbine.
• Hydraulic Pumps:
  These machines do the opposite — they convert mechanical energy (from a motor or engine) into hydraulic energy. The fluid is pressurized and made to flow through a system to perform tasks like lifting, pressing, or moving mechanical parts.
  Example: Centrifugal pump, reciprocating pump, gear pump, and vane pump.

2. Based on Type of Fluid Flow

Hydraulic machines can also be classified depending on how the fluid flows through the runner or impeller:

• Axial Flow Machines:
  The fluid flows parallel to the axis of rotation. Examples include Kaplan turbines and propeller pumps. These are suitable for low head and high discharge conditions.
• Radial Flow Machines:
  The fluid flows perpendicular to the axis of rotation, either from the center outward or inward. Examples include Francis turbines and centrifugal pumps.
• Mixed Flow Machines:
  The flow is partly radial and partly axial, as seen in mixed-flow turbines and pumps. This design offers a balance between discharge and head.

3. Based on the Operating Principle

Hydraulic turbines and pumps are further classified by their operating principles:

• Impulse Machines:
  In these machines, the fluid’s pressure remains constant, and only its velocity changes as it strikes the blades. The entire energy conversion happens due to the kinetic energy of the jet.
  Example: Pelton wheel turbine.
• Reaction Machines:
  In these machines, both the pressure and velocity of the fluid change while passing through the runner or impeller. The blades are designed to create a pressure difference that produces torque and rotation.
  Example: Francis turbine, Kaplan turbine.

4. Based on Head and Discharge

Hydraulic turbines and pumps can also be grouped according to the head (height of water column) and discharge (flow rate):

• High Head Machines: Operate with high water heads, such as Pelton turbines.
• Medium Head Machines: Operate with medium heads and discharges, like Francis turbines.
• Low Head Machines: Operate with low heads and high discharge, like Kaplan turbines and propeller pumps.

This classification helps in selecting the right machine for specific hydraulic conditions.

5. Based on Specific Speed

Specific speed is a dimensionless parameter that helps identify the type of machine based on its speed, flow, and head.

• Low Specific Speed: Impulse machines (Pelton wheel).
• Medium Specific Speed: Mixed flow machines (Francis turbine).
• High Specific Speed: Axial flow machines (Kaplan turbine).

6. Based on Direction of Energy Transfer

• Turbines (Energy Receiver): Fluid gives energy to the rotor.
• Pumps (Energy Giver): Rotor gives energy to the fluid.

This simple classification shows the dual nature of hydraulic machines — either extracting energy from or supplying energy to fluids.

Conclusion

Hydraulic machines are essential components in power generation, water supply, and industrial systems. They are mainly classified as hydraulic turbines and hydraulic pumps based on the direction of energy conversion. Further classifications are based on flow direction, operation principle, and head-discharge characteristics. Understanding these classifications helps in selecting suitable machines for different engineering applications and ensures efficient fluid energy utilization.