Losses in Hydraulic Machines

1. Introduction

Hydraulic machines (such as turbines and pumps) convert energy between fluid and mechanical forms. During this process, some energy is always lost due to various factors, reducing overall efficiency.

These losses are broadly classified into:

• Hydraulic losses
• Mechanical losses
• Volumetric losses

2. Hydraulic Losses

These losses occur due to the flow of fluid inside the machine.

(a) Friction Loss

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• Caused by friction between fluid and surfaces (pipes, blades, casing)
• Depends on:
  • Surface roughness
  • Flow velocity
  • Fluid viscosity

(b) Shock or Impact Loss

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• Occurs when fluid enters or leaves blades at incorrect angle
• Causes turbulence and energy loss
• Reduced by proper blade design

(c) Eddy or Turbulence Loss

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• Due to formation of vortices (eddies)
• Occurs at sudden changes in direction or area
• More in turbulent flow

(d) Leakage Loss (Hydraulic Part)

• Fluid leaks through clearances between moving parts
• Reduces useful flow

3. Mechanical Losses

These losses are due to mechanical friction in moving parts.

(a) Bearing Friction Loss

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• Occurs in bearings supporting the shaft
• Depends on lubrication and load

(b) Disc Friction Loss

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• Caused by rotation of impeller in fluid
• Fluid resists motion of rotating parts

(c) Stuffing Box and Seal Friction

• Friction between shaft and sealing elements
• Prevents leakage but causes power loss

4. Volumetric Losses

These losses reduce the actual discharge.

(a) Leakage through Clearances

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• Occurs between:
  • Impeller and casing
  • Piston and cylinder (in pumps)

(b) Recirculation Loss

• Fluid flows backward due to pressure difference
• Occurs at off-design conditions

5. Other Losses

(a) Cavitation Loss

• Formation and collapse of vapor bubbles
• Causes:
  • Noise
  • Vibration
  • Surface damage

(b) Exit Loss

• Kinetic energy lost when fluid leaves machine
• Not fully converted into useful work

6. Summary of Losses

Type of Loss	Cause	Effect
Hydraulic Loss	Friction, turbulence	Reduces fluid energy
Mechanical Loss	Bearing, seal friction	Reduces shaft power
Volumetric Loss	Leakage	Reduces discharge
Cavitation Loss	Vapor bubble collapse	Damage and efficiency loss

7. Methods to Reduce Losses

• Smooth surface finish
• Proper blade design
• Efficient lubrication
• Maintain correct clearances
• Operate at design conditions
• Avoid cavitation (proper pressure conditions)

8. Effect on Efficiency

Losses reduce:

• Hydraulic efficiency
• Mechanical efficiency
• Overall efficiency

$$\eta_{overall} = \eta_h \times \eta_m \times \eta_v$$

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