Project Final (Avas)

8/8/2019 Project Final (Avas)

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INTRODUCTION

A Gear pump uses the meshing of gears to pump fluid by

displacement. They are one of the most common types of pumps

for hydraulic fluid power applications. Gear pumps however are

also widely used in chemical installations to pump fluid with a

certain viscosity. There are two main variations; external gear

pumps which use two external spur gears, and internal gear pumps

which use an external and an internal spur gear. Gear pumps are

fixed displacement , meaning they pump a constant amount of fluid

for each revolution. Some gear pumps are designed to function as

either a motor or pump.

Power transmission pumps in fluid power systems are usually

hydrostatic or positive displacement units, which convert

mechanical power into fluid power, the most common types being

gear pumps. In these pumps fluid is transfered through the machine

in discrete volumes e.g. a gear tooth cavity. The pump size andspeed determines the fluid flow rate.

Gear pumps are sources of flow so that when they are connected to

a hydraulic motor, the outlet pressure will rise so that the flow can

cause the motor to rotate against the load torque. Hydrostatic

motors convert fluid power into mechanical power so that rotation

of the output shaft can take place against an opposing torque load.

Generally speaking pumps can be run as motors but a number of factors influence this possibility, some of which are:



• Not all pumps are reversible in direction of rotation because

of their internal and external sealing arrangements.

• Pumps are designed to operate at relatively high speeds andcan be inefficient at low speeds particularly during starting.

• Motor applications often require significant shaft side load

capacity. Pump rotating components are generally not

designed to carry such shaft side loads and consequently

cannot be directly coupled to the output drive where side

loading exists.

Major aspects in the selection of pumps and motors

The selection of pumps can be determined by a number of factors,

which need to be considered by the user. These factors include:

• Cost

• Pressure ripple and noise

• Suction performance

•

Contaminant sensitivity• Speed

• Weight

• Fixed or variablea displacement

• Maximum pressure and flow, or power

• Fluid type.



Literature surveyed

As the gears rotate they separate on the intake side of the pump,

creating a void and suction which is filled by fluid. The fluid is

carried by the gears to the discharge side of the pump, where the

meshing of the gears displace the fluid. The mechanical clearances

are small—on the order of a thousandth of an inch (micrometres).

The tight clearances, along with the speed of rotation, effectively

prevent the fluid from leaking backwards

The rigid design of the gears and housing allow for very high

pressures and the ability to pump highly viscous fluids.

Many variations exist, including; helical and herringbone gear sets

(instead of spur gears), lobe shaped rotors similar to Roots Blowers

and mechanical designs that allow the stacking of pumps. The

most common variations ..are EXTERNAL GEAR PUMP &

INTERNAL GEAR PUMP.



External Gear Pump

External gear pumps are a popular pumping principle and are often

found in lubrication pumps in machine tools, in fluid power

transfer units, and as oil pumps in engines.

External gear pumps can come in single or double (shown, left)

pump configurations with spur (shown), helical, and herringbone

gears. Helical and herringbone gears typically offer a smoother

flow than spur gears, although all gear types are relatively smooth.Large-capacity external gear pumps typically use helical or

herringbone gears. Small external gear pumps usually operate at

1750 or 3450 rpm and larger models operate at speeds up to 640

rpm. External gear pumps handle viscous and watery-type liquids,



but speed must be properly set for thick liquids. Reduced speeds

with high-viscosity liquids results in greater efficiency.

The design of external gear pumps allows them to be made to close

tolerances. Tighter internal clearances provide for a more reliable

measure of liquid passing through a pump and for greater flow

control. Because of this, external gear pumps are popular for

precise transfer applications involving polymers, fuels, and

expensive liquids.

How External Gear Pumps Work

External gear pumps are similar in pumping action to internal gear

pumps in that two gears come into and out of mesh to produce

flow. However, the external gear pump uses two identical gears

rotating against each other -- one gear is driven by a motor and it in

turn drives the other gear. Each gear is supported by a shaft with

bearings on both sides of the gear.



1. As the gears come out of mesh, they create expanding volume

on the inlet side of the pump. Liquid flows into the cavity and is

trapped by the gear teeth as they rotate.

2. Liquid travels around the interior of the casing in the pockets

between the teeth and the casing -- it does not pass between the

gears.

3. Finally, the meshing of the gears forces liquid through the outlet

port under pressure.

Because the gears are supported on both sides, external gear pumpsare quiet-running and are routinely used for high-pressure

applications such as hydraulic applications. With no overhung

bearing loads, the rotor shaft can't deflect and cause premature

wear.

Advantages

High speed.

Medium pressure.

No overhung bearing loads.

Relatively quiet operation.

Design accommodates wide variety of materials.

Disadvantages

Four bushings in liquid area.

No solids allowed.

Fixed End Clearances.



Disadvantages

Four bushings in liquid area.

No solids allowed. Fixed End Clearances

Applications

Industrial and mobile applications

Fuel and lubrication

Metering

Mixing and

blending (

double pump)

Hydraulic applications

OEM configurations

Precise metering applications Low-volume transfers

Light or medium duty



Materials Of Construction / Configuration Options

A composite external gear pump performs well in corrosive liquid applications

A composite external gear pump performs well in corrosive liquid

applications.

As the following list indicates, rotary pumps can be constructed in

a wide variety of materials. By precisely matching the materials of

construction with the liquid, superior life cycle performance will

result.

External gear pumps in particular can be engineered to the exact

need of corrosion-resistant pumps. By using readily-available

materials such as Ryton®, Ultimet®, Viton®, stainless steel, and

other materials, external gear pumps can be constructed to perform

very well in corrosive liquid applications. For example, compositeexternal gear pumps can handle Acetone, Sulphuric Acid, Tomato

Juice, Zinc Chloride, and hundreds of other corrosive liquids.



External Gear

Externals (head, casing, bracket) - Iron, ductile iron, steel,

stainless steel.

Internals (rotor, idler) - Steel, stainless steel. Bushing - Carbon, bronze, silicon carbide.

Shaft Seal - Packing, lip seal, component mechanical seal,

magnetically-driven pump.

Composite External Gear

Externals (head, casing, bracket) - Ryton bracket and casing,

stainless steel internal pressure relief valve.

Internals (rotor, idler) - Ryton gears, PTFE gears, hardened

stainless steel shaft, and PTFE shaft.

Bushing - Carbon graphite, silicon carbide.

Shaft Seal - Packing, lip seal, component mechanical seal,

magnetically-driven pump

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