Advantages and Disadvantages of Pump Types - Essay Example

?Pumps Pumps Introduction The pump is rotodynamic and is made up of an impeller whose rotation effects cause increased fluid pressure in the pipe system (Addison, 2011). These pumps are mainly usually used to propagate fluids in a piping system at high pressure. The process involves acceleration of the fluid by the pumps impeller hence making to flow out to a volute chamber hence exiting into the piping system. These pumps are commonly used for large discharge in small piping (Turton, 1994). A centrifugal pumps works on the basis of Bernoulli’s principle, that is; it converts kinetic energy to potential energy which can be measured as fluid pressure which is static. Identify typical applications stating the advantages and disadvantages for each of the following pump types: i. Single stage horizontal vertical split centrifugal This is a horizontal, single-stage, double volute axially split case centrifugal pump. The suction nozzle and the discharge nozzle which are cast intergrally and the nozzle is configured side by side. APPLICATIONS The single stage horizontal split centrifugal pump is used for different purpoases in different fileds, some of which are: i. The single stage horizontal split centrifugal pumps are broadly used in the fire systems. ii. They are used to a greater extent in oil refining. iii. Petrochemical. iv. Sugar Industry water supply system. v. Paper Industry water supply system. vi. They are used in pipelines for long distance pumping of fluids. vii. Power Generation. viii. They can be used in cycling use of water in air-conditioning ix. They are used in mining industry. x. They are also used in pressurized water transportation in the waterworks. ADVANTAGES The single stage horizontal split centrifugal pumps have the following distinct advantages: i. Horizontally split casing, double volute minimizes thrust loads and therefore allow for operation over a wide range of capacities. ii. It is a high efficiency design compared to the other designs. iii. It has enclosed impellers and double suction which provides the hydraulic balance and therefore eliminating the axial thrust. iv. It is capable of a clockwise or counter clockwise rotation. v. It has a compact structure which therefore makes it to be space efficient. vi. The pump has an axial which is small in size with little vibration and therefore low noise. vii. They are normally easy to service viii. Horizontal Split Case, can be mounted vertically which also contributes to the efficient use of space and allows flexibility while fitting the pump. DISADVANTAGES i. These pumps are non-self-priming and therefore they are prone to cavitation which therefore necessitates manual priming making its use tedious. ii. There is a high tendency of corrosion inside this pump which is caused by the fluid properties of the fluid pumped. iii. There is a risk of impeller wear which is worsened by presence of suspended solids in the fluid being pumped. iv. There may occur overheating as a resukt of low flow of the fluid in the pump and this usually affects its efficiency v. There is a tendency for leakage to occur along the rotating shaft. b) Horizontal split double suction centrifugal These are pumps that usually have a horizontal pump shaft and with the impeller usually located at the center of the shaft and with a self-contained combination bearing housing with a seal chamber on both impeller sides. Without causing disturbance to the motor or the pipe-work, the split case construction ensures the pump can be set apart in a horizontal plane along the drive shaft.  APPLICATIONS The horizontal split double suction pumps are typically designed for liquid transfer and for circulation of the cold clean or for slightly polluted water. The most common applications include; i. They are used for general purpose pumping ii. The horizontal split double suction centrifugal pumps can be used for air conditioning. iii. They can also be used in cooling towers. iv. The double suction pumps can be used in irrigation and drainage pumping stations. v. They can also be used for industrial water supply systems and also for firefighting applications vi. They can be used for boiler feed and also for condensate systems ADVANTAGES i. These pumps have a low axial load and radial load on the shaft which increases the seal and bearing life, also minimizes vibration and also provides quick operation of the pump. ii. The horizontal split double suction centrifugal pumps usually have an overall higher efficiency. iii. Their spiral housing which is axially spitted ensures easy maintenance without disconnecting the pipes iv. The fully enclosed and single piece casting with a double inlet impeller practically does not result in any axial thrust. v. They have a high operating reliability because of the maintenance parts and service parts. DISADVANTAGES i. The horizontal split double suction centrifugal pumps takes more space than the end suction pumps and they are also more expensive. c) Vertical in - line centrifugal These are mostly close coupled pumps which are designed for easy installation and can also be mounted either horizontally or vertically directly into the pipeline. MAIN APPLICATION AREAS i. The vertical in-line centrifugal pumps are used in heating and air conditioning. ii. They are also widely used in the pressure boosting systems. iii. They can be used in industrial processing systems iv. The vertical in-line centrifugal pumps are also suitable for general circulating water systems. ADVANTAGES i. These pumps can be installed either vertically or horizontally ii. The vertical in-line centrifugal pumps can be easily installed without causing disturbance to the piping system. iii. The impeller is usually mounted on a motor shaft which then minimizes run out. iv. The in-line pump adaptors are interchangeable with the same series of pump sizes. v. The close coupled nature of the vertical in-line centrifugal pumps helps to eliminate the need for extra space, rigid base or alignment. vi. This pump creates a floor space saving as compared to the horizontal end suction pump vii. The piping is made simpler since its piping does not have to change direction as it usually does with an end suction pump. DISADVANTAGES i. Due to its vertical orientation, the weight of the pump and motor is usually directed to a small concentrated point below the casing as opposed to horizontal pumps which normally have the weight of the pump and motor spread across a wider area on the bedplate. ii. Any leakage out of the vertical in-line centrifugal pump seal usually tends to collect around top of the casing , where it can result in corrosion of the casing rather than draining off readily as in the case of the horizontal end suction pumps d) Axial split multi - stage centrifugal In the axially split multi-stage centrifugal pumps, the rotor balance is not disturbed when the rotor is installed. MAIN APPLICATIONS i. These axially split multi-stage centrifugal pumps are used in nuclear safety related high pressure services. ii. They are also used for refined product pipelines. iii. They are used for boiler feed. iv. They are used for liquefied petroleum gas (LPG) pipeline and CO2injection. v. They can also be used for water injection. ADVANTAGES i. They have an exceptional hydraulic coverage. ii. Axially split casing ensures ease of maintenance of the pump. iii. Axially split casing means that the rotor balance is not disturbed while the rotor is being installed. iv. The double volute casing also reduces the axial load to the pump so that the lifetime of the parts inside is prolonged. v. It is relatively less expensive for the multiple stages than radial spilt pumps. DISADVANTAGES i. The axial split multi-stage centrifugal pumps are typically limited to 4000 F operating temperature due to thermal expansion considerations because: There is always a great difference in the case metal thickness between the upper half and the lower half of the pump. ii. The typical working pressure is limited to 3600 PSIG maximum due to difficulty in the bolting with a flat, and irregular gasket and due to the non-symmetrical volute and suction areas between the upper half and the lower half casing. ii. Deep well vertical turbine centrifugal This is a vertical axis centrifugal or a mixed flow type pump that comprises stages which accommodate rotating impellers and also stationary bowls processing guide vanes. It is a specialized centrifugal pump that is designed to move water from a well or a reservoir that is deep underground. MAIN APPLICATIONS i. The deep well vertical turbine centrifugal pumps are generally used where the pumping water level is below the limits of the centrifugal pump. ii. They can also be used to provide plant make-up water and fire water for industrial plants. iii. They are also used in wells that have been bored to provide agricultural or turf irrigation iv. They are also used in thermal and nuclear power plants v. They are frequently used for condensate extraction vi. They are also used in flood control by dry docks. ADVANTAGES i. The vertical well turbine pump is usually self-priming. ii. The outward flow through the impeller usually reduces the pressure at the inlet therefore allowing more water to be drawn in through the pump suction pipe. DISADVANTAGES i. The vertical well turbine pumps generally have a higher initial cost. ii. They are also more difficult to install and to repair. iii. The pressure head developed by a single impeller is relatively less. f) Gear type positive displacement This is mostly a spur gear pump which normally consists of a driven gear and another that runs freely contained within the pump housing. In this pump the rotation of these gears creates a partial vacuum through the meshing of the gear teeth, drawing the fluid into the inlet side of the pump. They can be further classified into internal and external gear pumps. TYPICAL APPLICATIONS i. The internal gear pumps are ideal for pumping high viscosity fluids and where suction conditions call for minimal inlet pressure requirements ii. They are ideal for high pressure applications such as hydraulics. iii. The internal gear positive displacement pumps are used in Barge, Tanker and Terminal Loading/Unloading. iv. The gear type positive displacement pumps are used in fuel and lubricating. v. The external gear type positive displacement pumps are used in precise metering. ADVANTAGES i. The gear type positive displacement pumps have a high pressure capability. ii. They also have a good resistance to contamination which may affect pump operation. iii. They are designed in short packaging and therefore ensure economical use of space. iv. They can be used to handle viscous and watery-type liquids v. The internal gear pumps usually have a constant and even discharge regardless of the varying pressure conditions vi. They have a Positive suction, non-pulsating discharge DISADVANTAGES i. In the internal gear positive displacement pumps there is an overhung load on the shaft bearing. ii. In the internal gear type positive displacement pumps low speeds are usually required iii. No solids are allowed in the external gear type positive displacement pumps. g.) Reciprocating injection positive displacement These pumps are also known as ‘recip pumps’. They are used to convert mechanical input power into hydraulic output power through a high displacement of the fluid being pumped. MAIN APPLICATION AREAS The reciprocating injection positive displacement pumps are generally employed for: i. Light oil pumping ii. Feeding small boilers condensate return iii. Pneumatic pressure systems iv. Oil drilling operation ADVANTAGES i. The total efficiency of reciprocating pumps is about 10% to 20% higher than a comparable centrifugal pump. ii. They are constant flow machines thus they can produce the same flow rate at a given speed regardless of the discharge pressure. DISADVANTAGES i. The discharge from reciprocating injection positive displacement pumps is pulsating and only changes when the speed of the pump is changed. ii. They usually have high installation and high maintenance costs. iii. They also have non uniform torque. Operation of a Centrifugal pump Centrifugal pumps are made of two parts classified as the impeller and casing, the casing is stationary and can also be referred to as the rotor and the impeller is the rotating part of the pump also known as the rotor. Fluid to be propagated is drawn to the pumps centre where it is flung by the rotating blades outward. The pump casing is stationary and it serves in directing the fluid to the outlet which is usually common for centrifugal pumps, this prevents the fluid from going out of the pump in many directions. The pumps main functions of the pump are controlled by the impeller, the rotating blades and the casing. The blades in the pumps which usually rotates energizes the fluid hence creating a velocity and the fluid is then redirected by the casing to produce high pressure under which the fluid is conveyed.. The principle of these pumps is that; the fluid is drawn from the pumps periphery and is then expelled at the center axis Horizontal overhung centrifugal refinery pump These are types of centrifugal pumps which mainly use a direct motor drive for its operation and it is applied in cases where fluid is to be conveyed at very high speeds especially in refineries. This type of pump is best suitable in refineries since it can propagate fluids which are dirty and are of low viscosity at high speeds. The main features of these pumps are: Positive head suction during operation Weld less It has a mechanical lip/seal It can be used to transfer very dirty fluids It shows high head properties of up to 38m Its flow rate range from 6-75m It’s easy and quick to maintain The pump is made up of the following parts as shown in the figure below: A-Motor B-Inspection lantern C-Mechanical seal D-Impeller E-Delivery duct F-Intake duct The impeller of the pump shown above is integral with other parts such as the shaft and also the motor thus it is rotates at a speed which is synchronous to that of the motor and shaft which enables suction at the intake and discharge at the delivery duct. The pump is installed such that the shaft is placed in an horizontal position in that it form a positive suction arrangement. The pumps are generally constructed using materials which are rugged and are resistant to corrosion which includes: stainless steel and plastics. The pump is constructed as shown in the figure below. Construction of a horizontal over hung pump Installation of a horizontal centrifugal pump Reciprocating pump A reciprocating pump is made up of the following parts; a cylinder, a suction pipe, suction valve, delivery pipe and delivery valve. The piston of the pump is displaced at an angle of 180 degrees when during the suction stoke, this leads to creation of a vacuum inside the cylinder hence making the suction valve to open making the fluid to enter into the cylinder. The piston is again displaced to 360 degrees during delivery stroke which leads to an increase in pressure in the cylinder making the suction valve to close hence triggering the opening of the delivery valve forcing the fluid into the pipe for delivery. The efficiency of this pump is enabled by fitting the air vessels on the delivery and suction pipes and they should also be as close as possible to the cylinder. The pumps are mainly made of stainless steel, plastic or cast iron. Assembly diagram of a reciprocating pump Rotary positive displacement pump These pumps use the principle of rotation to enhance the movement of fluids. This rotation movements of the pump components creates a vacuum is drawn in the liquid hence enabling the liquid to be transferred at very high pressure. These pumps suck in air from the system making then the most efficient types of pumps, this is because it reduces the time taken to remove the air from the piping system and it also enables fast flow of fluid in them. Rotary displacement pumps have the drawback which is as a result of their pumping nature. Due to their nature of pumping the space between the rotating part of the pump and the casing is made small hence slowing down the rate at which the motor rotates. Due to their low rotation speeds these motors when operated at high speed fluid in them may cause corrosion on the outer parts of the pump (Findeisen, 2000). This leads to slipping of the fluid hence reducing the efficiency of the pump. These pumps are made of screws or vanes made of stainless steel. Positive rotary pumps are divided into three main groups which include: Gear pumps: These pumps are made up of two gears which are placed side-by –side such that their teeth are enmeshed. These pumps operate such that the gears move in an opposite direction which leads to creation of currents. These currents trap the fluid between the gears teeth, the gears and the pump casing. The fluid is then released on the delivery side of the rotary pump and the processing of creating a teeth mesh is repeated again. Screw pumps: These pumps are made of two screws whose threads are placed in an opposing position. This ensures that the screws turn in opposite direction, one screw turns clockwise and the other turns in an anticlockwise direction. The screws are mounted on the shafts which have gears hence the making the gear mesh to enable transfer of fluid. Moving vane pumps: These pumps are made of a cylindrical rotor put in a housing casing of similar shape. Diagram of rotary pump Screw type rotary pump The other types of positive displacement pipes include: Radial flow pumps: They operate at very high pressures and the fluid in them moves at very low flow rates. Axial-flow pump: The fluid in these pumps enters and then leaves the pumps in the same direction. Mixed-flow pump: The fluids in these types of pumps experience both radial an axial types of acceleration hence the name mixed –flow pump. Rotary vane pumps Rotary gear pumps Rotary screw pumps The above three pumps are described in the rotary displacement pumps section. The types of seals used in centrifugal pumps are: O-rings Gaskets The installation of the above seals is shown on the diagrams below. The choice of the pump to be used was made using the motor profiles below which obtained from the manufactures data sheet A pump that contains the best of the above characteristics combined was chosen, and it was rotary pump which was best fit for the activity specified. Works Cited Addison, H. (2011). Centrifugal and Other Rotodynamic Pumps. Read Books. Findeisen, D. (2000). System Dynamics and Mechanical Vibrations: An Introduction. Springer. Turton, R. K. (1994). Rotodynamic Pump Design. London: Cambridge University Press. Read More