Types of Pumps - Centrifugal Pumps
Types of Pumps
Types of Pumps
Based on the operating principles, Pumps are broadly classified into two main categories. Pumping is done by providing an external force and that force could be Centrifugal or Positive displacement. Pumps are so classified into Centrifugal Pumps and Positive Displacement Pumps.
Centrifugal force is the force that is created during a rotary movement. The force displaces the fluids away from the center. A simple example that is normally taught about Centrifugal force in school days is when you swing a rope tied with a stone at the end, our hand will feel a force that tries to take away the stone from your hold. This is exactly opposite to the Centripetal Force.
Centrifugal pumps are designed to utilize the Centrifugal Force effectively to transport the fluids. Hence intake to the Pumps from a reservoir or tank is fed exactly in the center of the pump body and the fluid travels through a constricted Casing and is gradually expanded to accommodate more flow.
Fluid intake is normally called as Suction and the output is termed as Discharge. There will be an opening in the center of the Casing for Suction. The Casing also contains the Impeller that rotate at high speed to create the Centrifugal force that actually pumps the fluid. The Casing by itself is Volute shaped. The Fluid that enters the Suction also rotates along with the Impeller at high speed and gains energy. The fluid with added energy leaves the impeller and enters the space around it.
Impeller is the actual moving part of a Pump. It rotates at high speed and creates Centrifugal Force. Impellers are designed depending upon the required discharge pressure and flow. Impellers are driven mostly by a Motor but there are cases where a turbine is directly used instead of a Motor.
A shaft directly connects the Impeller with Motor or Turbine. Impeller is tightly fitted on one side of the Shaft and on the other side is connected to the drive which can be either a Motor or a Turbine. Shafts are generally fully polished metal rods that fit in exactly at the center opening of the Pump Casing. The material of construction varies from Mild Steel to SS depending upon the requirement.
Sealing the Shaft with Casing is normally done by a mechanical Seal but in older models gland ropes are also used to seal the opening. In both the cases sealing has to be perfect and should not offer friction to the rotating Shaft. In spite of this, to avoid temperature is inevitable. Wherever required cooling provisions are provided to avoid increase in temperatures that could affect the pump performance. Oil Seals and in some cases Gear boxes are also provided to accommodate the requirements.Gear boxes alter the speed of the Motor to suit the design speed of he Pump using Gears of different sizes that are immersed in lubricating oil.
Applications of Centrifugal Pump
- Centrifugal Pumps are generally used where huge flow of Fluid is required.
- Constant Flow requirements
- Low Pressure requirements.
- These Pumps cannot be used for high Viscous fluids.
- They are normally optimized for operation at Ambient Temperatures.
High capacity Centrifugal Pump
- Keep the Suction open before starting the Pump.
- Keep the Discharge Valve closed while starting the Pump.
- Start the Pump.
- When the Motor load changes from Star to Delta, start opening the discharge Valve and the opening could be throttled in accordance to the pressure and flow requirement.
- Ensure free flow of Cooling water to the glands if there is a provision.
- Ensure that the Gear boxes are filled with required quantity of Oil.
- Look for any abnormal sound in any part of the pump or Motor.
- Ensure that all the bearing are properly greased in regular intervals.
- Measure the current at full flow and keep record of it. Increased current or Amperage means there is some friction in any part.
- Check the foundation bolts in regular intervals.
- Check whether the coupling spiders are in good shape.
- Check for oil spillages or puddle of oil around the Pump which would indicate that the Pump is leaking somewhere.
Centrifugal Pump Operated by Turbine
For Corrosive Fluids
Centrifugal Pumps come in various Material of Construction.
Pumps with SS body and SS Impeller or and Plastic Impellers or Pumps with Plastic Body and Plastic Impellers are more suitable for handling corrosive fluids.
Pumps with Sturdy design are suitable for Raw Sewage Pumping.
Multistage Centrifugal Pump
Types of Centrifugal Pumps
1) Horizontal Pumps
2) Vertical Pumps
3) Multistage Centrifugal Pumps.
These are the most common Pumps used in industries. They are easy to operate and maintenance is also easier.
When the fluid that is required to be Pumped is in a Sump deep enough, then to increase the efficiency of the Pump, a submersible pump is opted. In this type of Pump, the Casing is connected by a long shaft and is immersed into the Fluid. In the ground level, the shaft is connected with a Motor and all the operation could be carried out from the ground level itself.
Multistage Centrifugal Pumps:
When more pressure is desired, Multistage Centrifugal pumps are used. There will be number of impellers connected in series by a single shaft and the combined power of all the impellers generate high pressures.
Centrifugal Pump Operation
- Check the Oil level every day and if there is any reduction, fill the gap.
- Check whether the cooling water flow is sufficient.
- Make sure that the surrounding area is kept clean and easily accessible for emergencies and maintenance.
- Maintain a log sheet that contains the Pump running hours, Current load, Flow and pressure.
- Calculate efficiency of the pump and and ensure that it matches with the standard Pump Performance curve provided by the Supplier.
- Make sure that the Coupling Guard is in place and covers the part completely.
- Check for any vibration and abnormal sound everyday.
- Check and ensure that the output pressure is constant and not fluctuating too much.
- Do not operate the Pump for more than 4 hours continuously or as advised by the Pump supplier. For this purpose a stand by Pump will always be there and the service can be switched to the other Pump after every 4 hours of continuous operation.
- Touch the Pump Casing, Mechanical Seal, Gear Box, Motor and the discharge line several times a day and try to understand the pulse of the Pump. This almost like getting friendly with the Pump and your daily care and knowledge will help you in identifying any abnormality if it occurs.
As per the recommendations of the Pump supplier, the Pump has to be dismantled completely and overhauled at fixed intervals.