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Pumps

Pumps. Pump – What is a Pump? A device that moves liquids or gasses by mechanical action How pumps work: Operate by some mechanism (Reciprocating, Rotary) Perform mechanical work – moving the fluid Consume energy to perform the work Types of Pumps: Positive Displacement Velocity Gravity

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Pumps

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  1. Pumps • Pump – What is a Pump? • A device that moves liquids or gasses by mechanical action • How pumps work: • Operate by some mechanism (Reciprocating, Rotary) • Perform mechanical work – moving the fluid • Consume energy to perform the work • Types of Pumps: • Positive Displacement • Velocity • Gravity • Steam

  2. Pumps • Positive Displacement Pumps • How do they work? • They make fluid move by trapping a fixed amount and forcing (displacing) that trapped volume into the discharge pipe. • Theoretically can produce the same flow at a given speed (RPM) no matter what the discharge pressure. • Called “constant flow machines”

  3. Pumps • Must not operate against a closed valve on the discharge side of the pump, it has no shutoff head like centrifugal pumps • When operating against a closed discharge valve it continues to produce flow and the pressure in the discharge line increases until the line bursts, the pump is severely damaged, or both. • A relief valve on the discharge side of the positive displacement pump is therefore necessary

  4. Pumps • Types of Positive Displacement Pumps • Classified according to the mechanism used to move the fluid • Rotary-type: • Internal gear, screw, vane • Reciprocating-type: • Piston or diaphragm pumps • Linear-type positive displacement: • Rope pumps and chain pumps

  5. Pumps • Positive Displacement Rotary Pump • How do they work? • Move fluid using a rotating mechanism that creates a vacuum that captures and draws in the liquid. • Advantages: • Very efficient because they naturally remove air from the lines, eliminating the need to bleed the air from the lines manually. • Disadvantages • Pump has very close clearances between the rotating pump and the outer edge, making it rotate at a slow, steady speed. If operated at high speeds, the fluids cause erosion, which eventually causes enlarged clearances that liquid can pass through, which reduces efficiency.

  6. Pumps • Types of Rotary Positive Displacement Pumps • Gear • A simple type of rotary pump where the liquid is pushed between two gears.

  7. Pumps • Screw Pumps • The shape of the internals is two screws turning against each other pump the liquid. • One or several screws to move fluids or solids along the screw(s) axis • The pumped fluid is moving axially without turbulence. • Eliminates foaming that would otherwise occur in viscous fluids. • Pump fluids of higher viscosity without losing flow rate.

  8. Pumps • Rotary vane • Cylindrical rotor encased in a similarly shaped housing. • As the rotor orbits, the vanes trap fluid between the rotor and the casing, drawing the fluid through the pump.

  9. Pumps • Common Uses of Rotary Vane • High pressure hydraulic pumps and automotive uses including, supercharging, power steering and automatic transmission pumps. • Advantages • Vane extension makes up for wear • Can be used with various materials and viscosities • Can run dry for a little while. • Disadvantages • Very close tolerances are required between the case and the rotating pump. • Cannot operate at too high a speed. Erosion in the pump, causing inefficiency. • Cannot tolerate debris.

  10. Pumps • Reciprocating Positive Displacement Pumps • How do they work? • Move the fluid using one or more oscillating pistons, plungers, or membranes (diaphragms), while valves restrict fluid motion to the desired direction. • Expanding cavity on the suction side and a decreasing cavity on the discharge side. • Liquid flows into the pumps as the cavity on the suction side expands and the liquid flows out of the discharge as the cavity collapses. The volume is constant given each cycle of operation.

  11. Pumps • Types of Reciprocating Positive Displacement Pumps • Plunger - a reciprocating plunger pushes the fluid through one or two open valves, closed by suction on the way back. • Piston - The high-pressure seal reciprocates with the piston. Piston pumps can be used to move liquids or compress gases. Also simple devices for pumping small amounts of liquid or gel manually.

  12. Pumps • When the Piston is actuated up, Liquid and or air is sucked in from the inlet port. • When the Piston is actuated down all the pressure and liquid is released through the outlet port • Diaphragm - the plunger pressurizes hydraulic oil which is used to flex a diaphragm in the pumping cylinder. Diaphragm valves are used to pump hazardous and toxic fluids.

  13. Pumps • Advantages of Positive Displacement Reciprocating Pumps • Long life, reliable service • Low pressure applications • Can be made of multiple materials • Self priming. No need to fill the cylinders

  14. Pumps • Disadvantages of Positive Displacement Reciprocating Pumps • Pulsating flow. • The suction stroke is difficult when pumping thick liquids. • Severe wear when handling fluids with suspended solids. • Low volume rates of compared to other types of pump.

  15. Pumps • Rope Pump • Loose hanging rope is lowered down into a well • Drawn up through a long pipe with the bottom immersed in water. • Round disks or knots matching the diameter of the pipe are attached and pull water to the surface.

  16. Pumps • Velocity Pumps • How do they work? • Kinetic Energy is added to the fluid by increasing the flow velocity. • What is Kinetic Energy? – energy an object possesses due to its motion. • Work needed to accelerate a body of a given mass from rest to its stated velocity. • Having gained this energy during its acceleration, the body maintains this kinetic energy unless its speed changes. The cars of a roller coaster reach their maximum kinetic energy when at the bottom of their path. Other examples, Billiards

  17. Pumps • Most common Velocity Pump to move fluid through piping (water, petroleum, chemicals) • Centrifugal Pump (also called Radial-Flow Pump) • What is radial flow? • Having the working fluid flowing mainly along the radii of rotation

  18. Pumps • Rotating impeller to increase the pressure and flow rate of a fluid • The fluid enters the pump impeller along or near to the rotating axis. • Accelerated by the impeller • Flows radially outward into a diffuser or volute chamber • Exits in the downstream piping system.

  19. Pumps • Potential Issues with Centrifugal Pumps • Not good with solids • Causes impeller wear • Overheating due to low flow • Cavitation due to low suction • Mechanical seal leaks • Lack of prime • Must be filled with water to operate

  20. Pumps • Gravity Pumps • Most Common – Siphon • Steam Pumps • Any type pump driven by steam • Been around long time • Used in remote areas without power source • Railroad Engines

  21. Homework • What are the 4 types of pumps? • Explain how a positive displacement pump works. • What are the types of positive displacement pumps? • Explain how a rotary positive displacement pump works. • What type of Positive displacement pump is good for high viscous fluids? • What are the disadvantages of a Rotary Vane Pump?

  22. Homework • Name the types of Reciprocating Positive Displacement pumps. • Define Kinetic Energy. • Why is a Centrifugal pump alse called a Radial-flow pump? • What is Radial Flow?

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