Module 4: pumps Flashcards
What are the three phases in the operation of the reciprocating positive displacement pump
Suction phase
Discharge phase
Cycle Repeat
How does a reciprocating positive displacement pump operate?
A reciprocating positive displacement pump operates by repeatedly drawing in and displacing a specific volume of liquid through a system of valves and a reciprocating mechanism that varies the size of the internal cavity.
What happens in the suction phase of the reciprocating positive displacement pump.
Mechanism: A piston, plunger, or diaphragm moves in one direction (usually backward) within a cylinder or chamber.
Action: This motion increases the volume of the chamber, creating a vacuum or low-pressure area.
Result: Liquid is drawn into the chamber from the inlet due to atmospheric pressure or the system’s pressure differential, opening the suction valve.
What happens in the discharge phase of the reciprocating positive displacement pump.
Mechanism: The piston, plunger, or diaphragm reverses its motion (usually forward), decreasing the volume of the chamber.
Action: The increased pressure inside the chamber forces the liquid out through the discharge valve.
Result: The suction valve closes to prevent backflow, ensuring the liquid exits through the discharge outlet.
What happens in the cycle repeat phase of the reciprocating positive displacement pump.
The reciprocating motion repeats continuously, enabling a steady flow of liquid with each cycle.
What are the two (2) characteristics of a positive displacement pump?
Constant flow rate
Pressure build up
What are the key components of an external gear positive displacement pump?
Drive Gear: Connected to a motor and drives the motion.
Idle Gear: Rotates in sync with the drive gear due to their meshing teeth.
Pump Housing: Encases the gears and provides sealing for fluid transfer.
Inlet and Outlet Ports: Allow fluid entry and exit.
What are the three phases in the operation of the external gear positive displacement pump?
Suction
Transfer
Discharge
What happens during the suction phase of the external gear positive displacement pump?
As the gears rotate, the teeth disengage at the inlet side, increasing the volume between the gear teeth and the housing.
This expansion creates a vacuum, drawing fluid into the pump from the inlet port.
What happens during the transfer phase of the external gear positive displacement pump?
The fluid is trapped between the gear teeth and the pump housing as the gears continue to rotate.
The trapped fluid is carried around the outer circumference of the gears (not through the meshing teeth) to the discharge side.
The design prevents fluid leakage back to the inlet.
What happens during the discharge phase of the external gear positive displacement pump?
As the gears continue to rotate, the teeth re-engage on the discharge side, reducing the volume and forcing the fluid out through the outlet port.
This positive displacement action ensures consistent and accurate fluid delivery.
What are the key features of the external gear positive displacement pump?
Positive Displacement
Non-Pulsating Flow
Sealing Effect
Advantages of the external gear positive displacement pump?
Suitable for handling viscous fluids like oils and syrups.
Compact and reliable design with high efficiency.
Can operate at high pressures.
Low maintenance due to fewer moving parts.
Limitations of the external gear positive displacement pump?
Not ideal for handling abrasive fluids (can wear down gears).
Limited ability to handle fluids with solid particles.
Requires good alignment to prevent wear and noise.
Applications of the external gear positive displacement pump?
Lubrication systems.
Fuel transfer in engines.
Chemical and polymer processing.
Hydraulic power systems.
Give examples of where a gear pump may be used:
Lubrication Systems
Fuel Transfer
Hydraulic Systems
Cooling Systems
Give examples of where a vane pump may be used:
Fuel Polishing Systems
Bilge Water Removal
Refrigeration and Air Conditioning
Deck Operations
Give examples of where a Progressive Cavity Pump may be used:
Sludge and Wastewater Handling
Chemical Dosing
Cargo Transfer
Ballast Water Management
What precautions must be taken when running a rotary vane pump with a rubber impeller?
Avoid Running Dry
Monitor for Overheating
Check Compatibility with Fluid
Avoid Excessive Back Pressure
Regular Inspection and Maintenance
Proper Alignment and Installation
Prevent Cavitation
Flush After Use (if Applicable)
Operate Within Speed Limits
Avoid Pumping Solids or Abrasives
Describe how an axial piston pump may be modified for variable flow
An axial piston pump can be modified to provide variable flow by altering the mechanism that controls the angle of the swashplate or the cylinder block inclination. This adjustment changes the stroke length of the pistons, thereby varying the volume of fluid displaced per revolution
Describe the principle of operation of a centrifugal pump.
The principle of operation of a centrifugal pump is based on the conversion of mechanical energy into hydraulic energy (pressure and kinetic energy) using centrifugal force. It operates by imparting velocity to the fluid through the rotation of an impeller and then converting this velocity into pressure.
What key elements should be included in a simple sketch of a centrifugal pump:
Impeller
Eye
Vane
Volute casing
Discharge
What are the four phases in the operation of a centrifugal pump:
Suction phase
Acceleration of fluid
Conversion to pressure
Discharge phase
What are the advantages of a centrifugal pump?
Simple and robust design with fewer moving parts.
Handles large volumes of fluid efficiently.
Suitable for low-viscosity fluids.
Cost-effective and requires minimal maintenance.
What are the limitations of a centrifugal pump?
Cannot handle high-viscosity fluids effectively.
Requires priming to avoid air binding (unless self-priming).
Flow rate and pressure are sensitive to system conditions.
Explain in detail why centrifugal pumps must be primed.
Centrifugal pumps must be primed to ensure proper operation because they rely on the continuous movement of liquid to create flow and pressure. Unlike positive displacement pumps, centrifugal pumps cannot displace air effectively. If air is present in the pump casing or suction line, the pump will lose its ability to generate suction and fail to move liquid. This phenomenon is known as air binding.
Explain the impact of air in the pump casing for a centrifugal pump:
Disrupted Flow
No Suction
Cavitation Risk
Advantages of an axial flow pump:
High Flow Rates
Efficiency for Low Head
Compact Design
Self-Priming Capability
Low NPSH Requirement
Reversibility
Disadvantages of an axial flow pump:
Limited Pressure Capability
Risk of Cavitation
High Initial Cost
Requires Large Diameter Discharge
Limited Range of Applications:
Where are axial flow pumps used?
Marine ballast systems, irrigation, cooling water systems, and flood control.
What is the advantage of a water ejector?
No moving parts
Ability to handle solids and viscous fluids
Simplicity in design and operation.
Low power requirements and suitability for remote, hazardous, or electrically constrained environments.
Define a suction head
Suction head refers to the vertical distance or pressure difference between the liquid source and the pump’s suction inlet.
Define a discharge head
Discharge head refers to the vertical distance between the pump’s discharge outlet and the surface of the liquid or the level to which the fluid is being pumped.
Define a Net Positive Suction Head (NPSH)
NPSH can be defined as the difference between the pressure at the suction side and the vapor pressure of the liquid being pumped, adjusted for atmospheric pressure.
Define Total Head
Total head is the sum of the energy in the fluid at the pump’s suction and discharge sides. It is the total height to which the pump can raise the fluid, accounting for both the static lift and the pressure head
