Parul Institute of Engineering & Technology Subject Code : Name Of Subject :Fluid Power Engineering Topic :Rotodynamic Pumps

OUTLINE 1. Different types of rotodynamic pumps 2. The component parts of rotodynamic pumps 3. Maintenance of rotodynamic pumps

Rotodynamic pumps There are three different types of rotodynamic pumps: Axial-flow pumps Centrifugal pumps Mixed flow pumps

Axial-flow Pumps Introduction An axial-flow pump uses a screw propeller to axially accelerate the liquid. The outlet passages and guide vanes are arranged to convert the velocity increase of the liquid into a pressure.As distinct from the centrifugal pump, the axial flow pump absorbs the maximum power at zero flow.

Axial-flow Pumps A mechanical seal prevents leakage where the shaft leaves the casing. A thrust bearing of the tilting pad type is fitted on the drive shaft. The prime mover may be an electric motor or a steam turbine.

Axial-flow Pumps Applicability with The axial flow pump is used where large quantities of water at a low head are required,or example in condenser circulating. The efficiency is equivalent to a low lift centrifugal pump, and the higher speed fs possible enable a smaller driving motor to be used. The axial-flow pump is also suitable for supplementary use in a condense scoop circulating system, since the pump will offer little resistance to flow when idling. With scoop circulation, the normal movement of the ship will draw in water; the pump would be in use only when the ship was moving slowly or stopped. The pump is reversible and this, in conjunction with high capacity flow, makes it suitable for trimming and heeling duties as well.

Axial-flow Pumps The impeller The pump casing is of gunmetal for condenser cooling duties and cast iron for heeling and trimming pumps. The impellers are of aluminium bronze and guide vanes of gunmetal are arranged immediately after the impeller, the pump shaft being of stainless steel.

Centrifugal pumps

Centrifugal pumps - theory and characteristics Centrifugal pump duties are usually for the movement of large volumes of liquid at low pressures, although higher pressures can be achieved with multi-staging. Energy input Energy transformations inside the Dump Velocity and pressure levels Fluid flow

Centrifugal pumps - theory and characteristics A centrifugal pump can be further defined as a machine which uses several energy transformations in order to increase the pressure of a liquid. The energy input into the pump is typically the fuel source energy used to power the driver.

Centrifugal pumps - Priming Centrifugal pumps although suitable for most general marine duties, suffer in one very important respect; they are not self priming and require some means of removing air from the suction pipeline and filling it with the liquid.

Centrifugal pumps - losses When assessing the amount of power needed to operate a centrifugal pump you must always take into account the various losses.

Centrifugal pumps - losses - Friction loss in bearings and glands, surfaces of impeller and casing. Some impellers are highly polished to minimize friction loss. - Head loss in pumps due to shock at entry and exit to impeller vanes and eddies formed by vane edges. - Leakage loss in thrust balance devices, gland sealing and clearances between cut water and casing and bearing seals.

Centrifugal pumps – losses Capacity reduction could be the result of A damaged sealing ring Leaking gland Obstruction (valve partly closed/foreign body) Incorrect rotational speed Excessive vibration may be caused by Loose coupling Loose impeller Bearing damaged Impeller imbalance

Centrifugal pumps-component parts

This is a vertical, single stage,single entry, centrifugal pump for general marine use. The mainframe and casing, together with a motor support bracket, house the pumping element assembly. The volute casing is split in two halves along a vertical plane. Since the suction and discharge nozzles are provided in the rear half of the casing, the rotating element can be taken out by removing only the front half casing without disturbing the rest of the pump.

Centrifugal pumps - component parts The pumping element is made up of a top cover, a pump shaft, an impeller, a bearing bush and a sealing arrangement around the shaft. The sealing arrangement may be a packed gland or a mechanical seal and the bearing lubrication system will vary according to the type of seal. Replaceable wear rings are fitted in the casing around the top and bottom faces of the impeller. The motor support bracket has two large apertures to provide access to the pumping element, and a coupling spacer is fitted between the motor and pump shaft to enable the removal of the pumping element without disturbing the motor or vice versa

Centrifugal pumps - shaft sealing

Centrifugal pumps - maintenance When the pump is due for overhaul, it will be necessary to dismantle it to its component parts to examine them for wear. The following procedures are intended as a general guide only, and your attention should be drawn to the manufacturer's operational instructions regarding specific pump requirements before commencing to dismantle the pump.

Mixed flow pumps In this type, the pressure is developed partly by centrifugal action and partly by the vanes and, as the name implies, the flow is both axial and radial through the impeller.

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