In this article we will see the turbine pumps which is a specific type of centrifugal pumps that are using radially-oriented teeth turbine like impeller for fluid movement. They are often known as vortex, periphery or regenerative pumps.
All roto dynamic pumps (i.e. Centrifugal pumps) have got a problem of limited suction i.e. the depth from which water can be lifted. This puts a restriction on usage of these types of pumps for lifting / sucking water from depths greater than 6 to 8 m. The theoretical suction lift of roto dynamic pumps at sea level and 30 °C temperature is 10.33 m but due to friction losses, vapour pressure, etc., the highest permissible is recommended to 8.40 m but safe value is 6.6 m, therefore to lift water more than 6.7 m depth, the pump should be installed very close to the water level, keeping that, the deep well pumps are developed which include:
- Turbine pumps
- Submersible pump
- Jet pump
In this design, the pump is installed, submerged in water and its motor is installed at ground or surface level. The power for driving the pump is transmitted through a rigid shaft running into the well. The pump having impeller of either Francis or semi axial flow type. Since these impeller resemble to those of turbine, such pumps are generally called vertical turbine pumps.
Turbine pumps has got three distinct sections,
- Bowl assembly
- Column assembly
- Head assembly
Pump Bowl Assembly of Turbine Pumps
The core of the vertical turbine pump is the bowl assembly. The casing of the impeller and diffuser type is optimized for the efficient delivery of head and capability that your device needs. The fact that the vertical turbine pump is multi-stage to ensure optimum stability both for the initial selection of the pump and for potential system modifications. The pump can be initiated without the priming with the submerged impellers.
It consists of several identical stages and has got one rotating impeller housed in a stationary bowl. The pump has a radial flow impeller, the water enters axially and comes out radially. If the water is to enter another stage of the pump i.e. an another impeller vertically above the first impeller its direction should be made axially upward. This is done with the help of a stationary guide impeller known as bowl, which has got guide, vanes for this purpose. Such guide bowls are provided after each rotating impeller stage. One set of impeller and stationary bowl is known as bowl assembly.
The discharge from bowl assembly is co-axial with the shaft and contained by a vertical column pipe or discharge pipe through which water is delivered.
Design Features of Turbine Pumps
- Suction bell – Allow smooth entry of liquid into impeller eye, minimum vortex formation
- Suction bell bearing – Provided for shaft stability
- Sand collar – Prevents solids from entering suction bearing
- Impeller – Semi-open or enclosed for appropriate service conditions
- Taper lock – Carbon or alloy steel for fastening impellers
- Keyed – Impeller fastened on to shaft by key and split ring
- Pump shaft – Heavy duty stainless steel, Monel and other alloys for high strength and corrosion resistance
- Intermediate bowl – Cast iron materials
- Stages – Flanged and bolted together for ease of maintenance
- Sleeve type bearing – Provided at each stage to assure stable operation away from critical speed
Coupling Arrangements in Turbine Pumps
- Rigid Flange coupling
- Adjustable Coupling
- Adjustable Spacer coupling
Pump / Line shaft options in Turbine Pumps
- Packed box with sleeve open line-shaft
- Water flush enclosed line-shaft
- Oil lubricated enclosed line-shaft
Sealing Flexibility in Turbine Pumps
- Single seal
- Outside mounted seals
- Tandem seals
Column Assembly of Turbine Pumps
Column assembly connects the bowl assembly with head assembly and forms a medium for lifting the water up. It comprises of column pipes, shaft assembly and its enclosing tube in case of oil lubricated type of pump. The latter element is not required in water lubricated design.
Since the entire length of shaft is to rotate in the column pipe, it is supported by various equi-spaced bearings known as spiders.
Head Assembly of Turbine Pumps
The head assembly consists of
- Base from which the column, shaft assembly, and bowl assembly are suspended
- Discharge-head-elbow which directs water into delivery piping system
- Driver or Prime mover which may be Diesel engine or Electric motor
Uses of Vertical Turbine Pumps
Vertical turbine pumps find their application in various field where centrifugal pumps cannot be used either due to their limited suction capacity or due to medium capacity demands. They are suited for medium capacity demands but are generally suitable for medium and large capacities at low or medium heads. They are the best pumps for pumping water to cities and towns from rivers or deep tube wells. Vertical turbine pumps are available from 70 LPM to 600000 LPM at heads of 5 to 300 m with bowl diameter 75 mm to 1.5 m and casing pipes of equivalent internal diameter.
Materials of Vertical Turbine Pumps
Usually, pumps are constructed from various components. The most critical elements to remember are the basic components that compose the pump pieces exposed to the pumped media and the atmosphere. The selection of these products should take into account fluid properties, pressure ratings, and operational environmental conditions.
- Cast iron offers a high resilience, toughness and abrasion resistance to high pressures.
- Plastics are cheap and provide substantial corrosion resistance and chemical attack.
- Steel and stainless steel alloys guard toward corrosion from chemicals and rust and have higher tensile stresses.