Centrifugal pumpsPetroskill course

Hector Nguema Ondo Perez

Introduction to centrifugal pumpsIntroduction to centrifugal pumps

• From Low elevations to high elevations

• From Low pressure to high pressure areas

• To increase the flow rate

Pressure and Head: Head is the height of a liquid

Pressure Gauges

Introduction to centrifugal pumpsSuction lift system

• The higher the vapor pressure, the more readily the liquid vaporizes

• To keep liquid at the pump from vaporizing, the absolute suction pressure must be higher than the liquid's vapor pressure at that temperature

The vapor pressure of a liquid is the equilibrium pressure of a vapor above its liquid (or solid); that is, the pressure of the vapor resulting from evaporation of a liquid (or solid) above a sample of the liquid (or solid) in a closed container

Introduction to centrifugal pumpsCapacity

Pump capacity is the amount of liquid that the pump moves in a given length of time

• Can be changed by increasing pump speed, also speed of the driver, or increasing the impeller size

Horsepower

• Horsepower (HP) is a unit used for measuring rate of work

Pump efficiency =

Pump volumetric efficiency is a measure of its internal leakage

Introduction to centrifugal pumpsNet Positive Suction Head (NPSH)

• Net positive suction head (NPSH) is the absolute suction head minus the vapor pressure head.

• NPSH available is the absolute pressure at the pump suction, converted to head, minus the vapor pressure of the liquid being pumped, converted to head.

• NPSH required is the minimum head needed at the suction to get the liquid into the impeller without vaporizing

NPSH available must be more than NPSH required

• When the absolute suction pressure increases, the NPSH available increases.

• When the vapor pressure increases, the NPSH available decreases.

• When the suction head decreases, the NPSH available decreases

• When the suction head increases, the total head decreases.

• When the discharge head increases, the total head increases

Introduction to centrifugal pumpsPerformance curves

• As the pumping rate increases, NPSH required increases.

• As the flow rate increases, horsepower required increases.

• The efficiency of a pump is relatively low at high and low flow rates

Design of centrifugal pumpsCentrifugal pumps

• Centrifugal force is the force of spinning

• A centrifugal pump operates by increasing the velocity, or speed of a liquid.

Design of centrifugal pumps

Pumps are classified according to: • Number of stages.

• Impeller design

Type of centrifugal pumps

• Single or double suction.

Design of centrifugal pumps

• Propeller pumps

The propeller blades whirl the liquid to high speed in a straight line path.  These high-speed pumps have low heads, and can handle large capacities.

Type of centrifugal pumps

• Liquid leaves in the same direction it entered.

• Liquid enters the pump through the blades.

• The area through which liquid enters is larger and can handle larger capacities

Design of centrifugal pumps

• Turbine Pumps

The flow of liquid through a turbine pump is halfway between the flow through a centrifugal pump and the flow through a propeller pump.  As the liquid enters the pump, it circulates around and around, gaining additional pressure each time it passes the turbine blades

Types of centrifugal pumps

The best features of the impeller pump and the propeller pump are combined in the turbine pump.  Turbine pumps generally have a high head and high discharge pressure for their size and speed. 

Design of centrifugal pumpsType of centrifugal pumps

• Turbine pumps generally have a high head and high discharge pressure for their size and speed.

• Propeller pumps have low heads, and can handle large capacities  

Design of centrifugal pumpsSeries and Parallel operation

• When the discharge of one pump is fed into the suction of another pump, the two pumps operate in series.  This increases the discharge head of the system.

• Pumps that discharge into the same line are operating in parallel.  Operating pumps in parallel increases the capacity of the system because the total amount discharged is the combined sum of the amounts discharged from both pumps

Components of centrifugal pumpsWear Rings, Packing Box and Lantern Rings

Wear Rings

• Maximize efficiency by reducing the leaking.• Minimize the cost of pump maintenance.• Replaceable periodically during the pump life.

Packing Box

• Provide a seal to reduce leakage.• Filled with a flexible, low friction and non-abrasive material.• Shaft part is protected by a removable sleeve.

Lantern Rings

• Around the shaft sleeve inside the packing box.• Provides space where the lubricating or seal oil can be supplied

Components of centrifugal pumpsMechanical seals and sealless pumps

• Require less maintenance and hold leakage to a minimum.

• The springs push against the compression ring and compress the o-ring against the shaft and the rotating seal members, which prevents leakage.

• The pump and motor are housed within the same casing.• Rotating magnetic field that causes the rotor to move, or

rotate.• They contain no seals, they are more resistant to leakage

than pumps with a packing box or a mechanical seal.

Components of centrifugal pumpsImpeller Thrust and Balancing Drums

• Any leakage into the collar flows back into the suction through a hole in the impeller, which equalizes pressure between the left and right sides of the impeller

• The total impeller thrust is the sum of the thrust of all the impellers. 

• The pressure acting on the left side of the balancing drum is the pump discharge the right side of the balancing drum is a suction pressure.

• Balancing drum balance the impeller thrust eliminating axial thrust.

Operation of centrifugal pumpsPumps alignment and pump cooling

• Puts a strain on the shaft and may wear or break the shaft or couplings.

• May cause bearings and seals to wear excessively or fail.

• May damage wear rings and permit the impeller to rub against other parts.

• May cause excessive vibration.

• Heavy-duty and hot liquids pumps may be water-jacketed to cool the lubricating oil.

• Shaft and packing are often fitted with water jackets as well.  The cooling water circulates in the water jacket surrounding the packing box.

Operation of centrifugal pumps

• Wear rings : simplify maintenance by protecting the casing and the impeller• Packing Box: Must be always lubricated.

– Ring Packing lubricated by the liquid being pumped– Lantern ring and packing are lubricated by oil.

• Bearings and Couplings

Lubrication

There is almost no friction between the balls and any of the other parts they touch because of the lubrication.

Used in large pumps. Has more surface area than a ball bearing and can support a very heavy shaft.

Used in pumps with a large axial load. The shoes are pivoted to absorb minor variations in the rotation of the collar.

Operation of centrifugal pumps

• Priming: The process of removing the air or gas from the pump and filling the casing with liquid.

Pump Priming

• This pump may be primed by venting the air or gas from the casing

Removing the air or gas from the pump creates a vacuum inside the pump. 

Thanks for coming.

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Hector Nguema Ondo Perez