Centrifugal pumps of various designs are available nowadays. Centrifugal pumps of various designs create maintenance flexibility. Back pull-out and split casing pumps are Centrifugal pumps of various designs. They are the incredible machine ever produced by man. Centrifugal pump is part and parcel of our life. Our life existing without the use of a centrifugal pump is beyond imagination. Sometimes the high-pressure head is required at other times a high flow of the fluid flow is required. To cater to all these need centrifugal pumps of different design configurations are required. Depending on their flow pattern, centrifugal pumps are categorized as follows:
1) AXIAL FLOW PUMPS:
Axial flow centrifugal pumps are the pumps where the flow is produced parallel to the pump shaft. It is called a propeller pump. It is used for low-pressure head and high flow services. The propeller-type impeller is used in an axial flow pump. The fluid flow produced by the impeller moves in the pump axially and discharged perpendicularly to the pump shaft. The Schematic explains the axial flow in the pumps.
2. RADIAL FLOW PUMPS:
Radial flow centrifugal pumps are the pumps where the flow is produced perpendicular to the pump shaft. It is used for high-pressure head and low flow services. In these pumps, radial flow is produced by the curved vane closed impeller or open impeller in the pump. When the impeller rotates in the pump casing the fluid is sucked in the eye of the impeller then it rotates along with the curved vanes and builds up the pressure head and the fluid is discharged perpendicular to the pump shaft through the pump.
3. MIXED FLOW PUMPS:
Mixed flow centrifugal pumps are the pumps where the flow produced is mixed flow as some axial and some radials. To produce mixed-flow, the volute type pump casing and open mixed-flow impellers are used. It is used for medium or high flow rate and medium pressure head. The Schematic indicates the mixed flow pump.
Centrifugal pumps various design and application
(1) Centrifugal Pump back pulls out design:
Centrifugal pumps of the back pull-out designs are mainly used in refineries, petrochemicals, chemical, and power plants. These are maintenance-friendly pump designs. They can be dismantled very quickly from the location for maintenance of pumps. Rotating assemblies that include: bearings, impellers, impeller wearing rings, shaft, shaft sleeve, and shaft gland packing or mechanical seal. In these designs, pump casing removal from suction and discharge piping is not required. Spacer couplings create more maintenance flexibility. Shifting of pump prime mover from its foundation is not required.
The use of back pull out design centrifugal pumps have the following advantages:
1) Pump rotating assemblies are dismantled quickly for maintenance.
2. Repair of the rotating assemblies is administered at the repair shop.
3 Quick reassembly of the pump after maintenance.
4 No time is spent in the alignment of the pump because the prime mover is not disturbed from its position.
5 No piping tension is working on the pump because the piping is not disturbed during the removal of The rotating assembly of the pump.
6 Total time-saving in the maintenance of the pump to reduce downtime which is extremely important in an energy-intensive plant. Fig indicates back pull-out pump.
(2) Centrifugal pumps monoblock designs:
Monoblock pump designs are similar in construction to the back pull-out centrifugal pumps, they’re not having coupling between pump and motor. In these pumps, the impellers are directly mounted on the motor shaft end. The impeller is boxed up with the pump casing. Pump and motor assembly are mounted on a single baseplate. These pumps are sturdy in construction. They require little space for installation. They’re mainly used in the agricultural sector. In air conditioning and domestic water system.
The use of monoblock pumps have the following advantages:
1 The pump has no separate coupling hence is dismantled quickly for repairing the rotating assembly.
2 No dismantling of suction and discharge piping is required for removal of pump rotating assembly.
3 No coupling is used for connecting pump and motor, hence there’s no power transmission loss.
4 No time is spent on the alignment of the pump as the pump and motor are one unit.
5 Pump maintenance time is minimum.
(3) Horizontal split casing/ Axially split casing pump:
In Horizontal split casing centrifugal pumps, the casing of the pump is manufactured in two parts. The lower part of the pump casing includes: suction and discharge ports and bearing housings. This part of the pump casing houses the rotating assembly of the pump. The impeller is mounted centrally on the shaft of the pump.
The upper part of the pump casing is mounted with a vent valve for air removal and a connection for cooling water for shaft-packing cooling. The upper part of the casing and the lower part of the casing are boxed up together along with the rotating assembly.
Horizontal split casing or axially split volute casing pumps are being used for dirty and contaminated fluid but not for viscous fluids. They’re mainly used for various water services, namely pure, raw, and sewage water services, in various departments like public water supply, irrigation, power plants, fire fighting, chemicals, and petrochemical plants.
The use of horizontal split casing pumps have the following advantages:
1 suction and discharge piping are in the lower part of the casing hence not to be dismantled for pump maintenance.
2 Rotating assembly can be removed very quickly for repairing, by just opening the upper half of the pump casing.
3 Low maintenance cost is involved.
4 Less downtime in repairing.