Rotary Pumps free study notes

1. Introduction

Rotary pumps are a type of positive displacement pump in which liquid is moved by rotating elements. Unlike centrifugal pumps, they deliver a constant volume of fluid per revolution, regardless of pressure (within limits).

They are widely used for handling:

• Viscous fluids (oil, syrup, chemicals)
• Slurries
• Fuel transfer applications

2. Working Principle

Rotary pumps operate on the principle of trapping a fixed amount of fluid and forcing it from suction to delivery side.

Basic Steps:

1. Fluid enters the pump casing through the suction port
2. Rotating elements (gears, vanes, lobes, screws) trap the fluid
3. Fluid is carried around the casing
4. Fluid is discharged at high pressure

3. Types of Rotary Pumps

(a) Gear Pump

6

• Uses two meshing gears
• Fluid trapped between gear teeth and casing
• Types:
  • External gear pump
  • Internal gear pump

Applications: lubrication systems, fuel oils

(b) Vane Pump

7

• Rotor with sliding vanes
• Vanes move in and out to trap fluid
• Good for medium viscosity fluids

Applications: hydraulic systems, refrigeration

(c) Lobe Pump

8

• Two or more lobes rotate without contact
• Gentle pumping action

Applications: food, pharmaceuticals

(d) Screw Pump

6

• One or more screws rotate
• Fluid moves axially along screw threads

Applications: oil pipelines, marine engines

4. Characteristics of Rotary Pumps

• Deliver constant discharge
• Self-priming
• Suitable for high-viscosity fluids
• Smooth and pulse-free flow (especially screw pumps)
• High efficiency at low speed

5. Performance Parameters

(a) Discharge (Q)

$$Q = V \times N$$

Where:

• V = volume per revolution
• N = speed

(b) Slip

Difference between theoretical and actual discharge:$$\text{Slip} = Q_{theoretical} – Q_{actual}$$

(c) Efficiency

• Volumetric efficiency
• Mechanical efficiency
• Overall efficiency

6. Advantages of Rotary Pumps

• Can handle high-viscosity fluids
• Provide uniform discharge
• High suction lift (self-priming)
• Compact design
• Operate at low speeds

7. Disadvantages

• Not suitable for fluids with solid particles (wear)
• More expensive than centrifugal pumps
• Requires precise manufacturing
• Maintenance needed for seals and clearances

8. Applications

• Oil and petroleum industries
• Chemical processing
• Food and beverage industry
• Hydraulic systems
• Fuel injection systems

9. Comparison with Centrifugal Pumps

Feature	Rotary Pump	Centrifugal Pump
Type	Positive displacement	Dynamic
Discharge	Constant	Varies with head
Fluid type	Viscous fluids	Low-viscosity fluids
Priming	Self-priming	Requires priming
Pressure	High	Moderate

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