centrifugal pumps unlike the reciprocating displacement pump. the simple centrifugal pump, which does not have a positive suction action,consists of a rotating impeller within a stationary pump casing.The fully shrouded.single entry impeller is the type most widely used.

The impeller is mounted on a shaft driven by a prime mover.it consist of a number of vanes backward from the direction of the rotation between the shrouding.

Water enters the rotating impeller through the entry,known as 'eye',at the centre. Due to the circular motion given it is thrown hy certrifugal force to the open periphery of the impeller where it leaves tangentially and enters the space in the casing.and then directed to the outlet branch.

Centrifugal pumps are non-positive and fairly low pressure units. Here a closed discharge valve.will not cause excessive pressure to build up.

centrifugal pumps can be divided into volute, diffuser, mixed-flow, axial flow and turbine or regenerative types.

centrifugal pumps find their widest application for dealing with large volumes with medium-to-low heads and Viscositis.Centrifugal or radial flow pumps give regular delivery,and are quiet in operation.

Axial-flow and semi-axial-flow rotary pumps are frequenLly used for large volumes and low heads,as they are simple.occupy little space and are low in capital cost.

Vertical pumps are in general use.because floor space is usually more valuable than height in engine rooms.

 Centrifugal units require to be primed if the liquid level is below the pump. Small integral reciprocating displacement priming pumps are sometimes provided,hut there is a wider use of water-ring pumps for priming purposes, because of their simplicity.

Various other means. such as internal recirculation,steam ejectors,etc. are also used in appropriate cases. 

In general. reciprocating pumps are suitable for delivering small quantities at high pressure, rotary pumps are used for moderate quantities at moderate pressure,and centrifugal pumps are more suitahle for large quantities at low pressure.

Centrifugal pumps,however,can he designed with a number of impellers in series to attain a high final delivery pressure. They are popular because they are very simple.

in construction,and can produce smooth,constant,non-pulsating discharge.

A pumps  is a device which adds the energy to a liquid or gas,causing an increase in its pressure and perhaps a movement of the fluid.

A basic pumping system consists of a suction branch, a pump and a discharge branch. the pumps employed on board ship fall into two broad classes:positive displacement pumps and centrifugal pumps.

positive displacement pumps  are those where the volume of the pump chamber is alternately increased to draw the liquid in from the suction pipe and then decreased to force the liquid out into the delivery pipe.

the liquid or gas is displaced from the suction to the discharge by the mechanical variation of the volume of a chamber or chambers.

This kind of pumps can be subdivided into two main clawes: reciprocating pumps.in which a plunger or piston is mechanically reciprocated in a liquid cylinder.

And rotary pumps,where the liquid is fored through the pump cylinder or casing by means of screws or gears.under reciprocating are the direct acting,power, and crank-fly- wheel types.

while under rotary are the gear, Vane,screw and piston types. Reciprocating and rotary positive displacememt pumps are self-priming,and can deal with liquid from a level below the pump.

The typical pumps employed in steering gear hydraulic system are rotary-piston pumps,classified either axial or radial type. The pistons in an axial pump operate along the axis of the pump drive shaft.

The cylinder block has a series of cylinder bores with pistons that move in and out.As the block rotates. each piston moves in and out of its cylinder, the length of stroke depending on the angle of the cylinder block with reference to the drive plate or swash plate according to the designs.

As each piston moves outward.oil is drawn into the cylinder bore through the valve plate.On the return stoke,the oil is forced out through the valve plate under pressure.

gear pump is a represent of the rotary pump family and is commonly used on hoard a ship.it consists of two or more meshing gears(spur,single or double helical teeth) enclosed in a close-fitted housing. these are used extensivelv for pumping fuel oil. lubricating oil and hydraulic oil.

When gears are unmeshed on the inlet side. a pressure drop occurs that helps the atmospheric pressure acting on the surface of the oil in the reservoir to force it up the pipe to fill the void,the oil is then transferred around the periphery of the pump housing.

As the gear teeth mesh again on the outlet side,they form a seal that prevents oil from backing up to the inlet, the oil in the void is then be forced out into the discharge line.

pump casting foundry in china, there is much more to casting than selecting a process and making the appropriate pattern in pump casting process in china. During the past two decade since china entry into WTO.  China pump castings suppliers  manufacturers research and production experiences have provided scientific principles for better pump casting techniques.

For china pump casting foundry, the important considerations are the rate at which a pump casting mold cavity is filled, pump casting gate placement, pump casting riser design, the use of chill block of pump casting, and padding in pump casting process.

Filling the pump castings mold cavity. The velocity with which the molten metal fills the pump casting mold is determinded by the cross-sectional area of the gating system and mold-puring rate is the key factory for pump casting foundry foundrymanship.

Too slow a mold pouring rate means solidification before filling some parts of the mold. Allowing surface oxidation. Too high a pouring rate caused by too large gating system causes sand inclusion by erosion, particularly in green sand pump casting molding, and turbulence. These two all easy to cause pump casting defects

The minimum cross section in the gating system is called a choke. In the strict sense. The choke is the section in the gating system, when the gate system is choked at the bottom of the sprue.

It is called a nonpressurized system. This system is somewhat less reliable than a pressuried in which the choke is at the gate of pump casting molding system.

The first metal in the pouring basin and down the sprue usually has some turbulence that carries slag into the runner.To avoid slag in the pump castings, pump casting specialists suggested that the runner should extend past the last gate to trap the initial slag.

By the time the gates become operative. The liquid level should be high enough so that no slag can enter the pump casting cavity.

The runner should be laid out to minimize turbulence. That is it should be as straight and as smooth as possible. The gate is made to enter the cavity at the parting line of the pump casting mould.

pump casting specialists arrange gating may also be made at the top or bottom of the cavity. The parting lines gate is the easiest for the pump casting pattern maker to make;

However, the metal drops into the cavity, which may cause some erosion of the sand and some turbulence of the metal and finally cause for example like pump impeller casting defects

etc. For nonferrous metals, this drop aggravates the dross and entraps air in the metal of pump castings.

Top-gating is used for simple pump casting parts in gray iron, but not for nonferrous alloys pump casting materials, since excessive dross would be formed by the agitation.

Bottom gating provides a smooth flow of metal in the pump casting mold, however. If does have the disadvantage of an unfavorable temperature gradient. It cools as it rises, resulting in cold metal in the riser and hot metal at the gate.

Risers are designed by pump casting specialists and placed so as to ensure filling the cavity during solidification. They also act to relieve gas pressure in the pump casting mold and to reduce pressure on the lifting surface of the pump casting mold in china pump casting foundry

The volume of metal in the riser should be sufficient to retain heat long enough to feed the shrinkage cavity and to equalize the temperature in the pump body casting mold, avoiding casting strains.

The raiser requirements vary with the type of pump casting materials being poured. Gray cast iron pump casting parts, for example, needs less feeding than some alloys because a period of graphitization occurs during the final stages of solidification. Which cause an expansion that tends to counteract the metal shrinkage.

Many nonferrous metal pump casting part require elaborate feeding systems to obtain sound pump casting. The feed metal must be located above the highest point of the casting.

Chill Blocks are metal blocks placed in the pump body casting mold for localized heat dissipation. They may be placed at an intersection or joint where there is a comparatively large volume of metal to cool. thus relieving a hot spot or maintaining a more uniform cooling rate and better microstructure.

They may also be placed at the far surface of a pump body casting mold. Away from a riser or sprue. This will help the far end of the mold to freezed rapidly. Promoting directional solidification.

Chill blocks are also used by pump casting foundry at points where it is desirable to have localized hardening, as in the case of pump impeller casting process or pump bowl casting process.

Padding consists of adding to or building up a section to obtain adequate feeding of isolated section like some pump body casting and pump bowl casting, to feed central or outside boss of the pump body casting or pump bowl casting.

Can use risers with padding. Can provided a yield of say 45% of the metal poured. By the rule of thumb. The total thickness of pad and casting should not be less than one fifth of the metal feeding distance. This rule is not absolute but a good generalization in pump casting process.

pump casting process