chapter 4 hydraulic pumps

7/28/2019 Chapter 4 Hydraulic Pumps

1/40

AU-HYD-10

CD-20-00Page 1 of 40 Pages

Thai-German Institute

- Hydraulic Pump

HYDRAULICPUMP


2/40

AU-HYD-10



- Hydraulic Pump

Type of pumps

Non-positive displacement pump


3/40

AU-HYD-10



- Hydraulic Pump

Centrifugal Pump

Inlet

Outlet

Non-positive displacement pumps

used the centrifugal force appliedto the fluid being pumped.

Non-positive displacement pumps

find more use in lower pressuresystem.


4/40

AU-HYD-10



- Hydraulic PumpIncreasing resistance to flow

at the outlet will cause the

flow output to decrease withoutdamage to the pump.

It dose not acceptable in mostpower hydraulic system.

This may be desirable characteristicin the some application.


5/40

AU-HYD-10



- Hydraulic Pump

Type of pumps

Non-positive displacement pump

Positive Displacement Pump


6/40

AU-HYD-10



- Hydraulic Pump1. As the handle is moved to the left,

a partial vacuum exists since anincreasing volume is being created.

2. This vacuum creates unbalance pressurecondition

3. so that atmospheric pressure canpush the oil into the pumping cylinder.


7/40

AU-HYD-10



- Hydraulic Pump1. Movement of handle to the right,

the fluid is forced through the uppercheck valve to the discharge.

Output of the pump is positivedisplacement because it is not

significantly affected by theresistance to flow.

The resistance to flow will determinethe discharge pressure.


8/40

AU-HYD-10



- Hydraulic Pump1. A pump is one of the most importantcomponent in any hydraulic system.

2. It supplies the flow of hydraulicfluid to the system.

4. The pump converts mechanical powerinto the hydraulic power of fluid flow.

3. If there is no resistance, thenthere is no pressure.


9/40

AU-HYD-10



- Hydraulic PumpPositive Displacement

Hydraulic Pumps

Fixed Displacement Variable Displacement

Gear Vane Piston Vane Piston

External

Internal

Crescent seal Gerotor Seal

Radialpiston AxialPistonBentAxisRadialpiston AxialPiston BentAxis


10/40

AU-HYD-10



- Hydraulic Pump

Gear tip come in close

proximity to the pumphousing effectively sealing.

The pumping chamber is

form by the gear, pumphousing, and side plate.

As the gear teeth unmesh apartial vacuum created allowingfluid into space between the teeth.

The fluid is expelled from the

Space between the teeth asthe gears remesh.

External Gear Pump


11/40

AU-HYD-10



- Hydraulic Pump


12/40

AU-HYD-10



- Hydraulic PumpInternal Gear Pump

Sealing of high pressure chamber from

the pump inlet is achieved by the closeproximity of the crescent to the gear.

and the meshed gear teeth.

Volume on this side decreasedas the gear teeth mesh.

Volume on this side increasedas the gear teeth unmesh.


13/40

AU-HYD-10



- Hydraulic Pump


14/40

AU-HYD-10



- Hydraulic PumpGerotor Pump

The inner Gerotor always has oneless tooth than the outer element.

Clearance seal betweeninlet and outlet.

Volume on this side decreasedas the gear teeth mesh.

Volume on this side increasedas the gear teeth unmesh.


15/40

AU-HYD-10



- Hydraulic Pump


16/40

AU-HYD-10



- Hydraulic PumpUnbalance Vane Pump

The spinning of the rotor causes a

centrifugal force which pushes thevanes out the rotor slots.

Fluid enters as space betweenring and rotor increasees..

and discharge as

space decreases.

Cam ring is eccentric fromthe rotor and shaft centerline.


17/40

AU-HYD-10



- Hydraulic PumpSince centrifugal force is usually insufficient

to overcome high pressure at the outer

tip of the vane on the outlet side..

Pressurized oil is alsosupplied under the vanes.

This cause the pressure underthe vane to be equal to thepressure on the top.


18/40

AU-HYD-10



- Hydraulic PumpBalance Vane Pump

This design has opposing setsof inlet and outlet ports.

The high forces generated at theoutlet ports cancel each other out.

This prevents side loading ofthe pump shaft and bearings.


19/40

AU-HYD-10



- Hydraulic Pump


20/40

AU-HYD-10



- Hydraulic PumpThe variable vane pumpis an unbalance design,..

and creates the changing displacementby moving the cam ring.

Maximum flow rate


21/40

AU-HYD-10



- Hydraulic Pump

By moving the cam to the left,

the differential volume between

inlet and outlet is reduce.

Then pump displacement

is decreased.


22/40

AU-HYD-10



- Hydraulic Pump

When the eccentric between

the cam ring and rotor is zero.

There is no flow rate.


23/40

AU-HYD-10



- Hydraulic PumpAxial Piston Pump

In this design, the piston and cylinderbarrel are parallel to the drive shaft.

The piston reciprocate in their cylinderbore, causing a pumping action.When the cylinder block rotated, pulling oil

from the tank as the piston are retracting.

And pushing oil from cylinderbarrel to the outlet as the pistonsare push back into their bores.


24/40

AU-HYD-10



- Hydraulic PumpAxial Piston Pump


25/40

AU-HYD-10



- Hydraulic PumpVariable Axial Piston Pump

When changes the angle of the swash

plate, which changes the stroke of thepiston in and out of their bores.

Maximum Flow

Maximum stroke


26/40

AU-HYD-10



- Hydraulic PumpVariable Axial Piston Pump

Displacement of the pump

decreases with a decreasesin the swash plate angle.

Reduced Flow

Decreased in strokeof the piston..


27/40

AU-HYD-10



- Hydraulic Pump

Zero Flow

When the angle of the swash

plate is zero then there is noreciprocating motion of the piston.

So that there is no flow atthe outlet port of the pump.

Variable Axial Piston Pump


28/40

AU-HYD-10



- Hydraulic Pump

When the angle of the swash plate

changed to opposite direction, theoutlet flow will reversed in another direction.

Reversed Flow

Variable Axial Piston Pump


29/40

AU-HYD-10



- Hydraulic Pump

The reciprocating motion of the pistons in the

cylinder block is cause by an angle in theconnection from the shaft to the cylinder block.

Bent-Axis Piston Pump

When the cylinder block rotated, pulling oilfrom the tank as the piston are retracting.

And pushing oil from cylinder

barrel to the outlet as the pistonsare push back into their bores.


30/40

AU-HYD-10



- Hydraulic Pump1. As the angle between the cylinder

block and drive shaft changes,2. The piston travel in theirrespective bores changes,

3. Increasing or decreasing thepump displacement change.


31/40

AU-HYD-10



- Hydraulic Pump1. The displacement angle is controlled

by the displacement control valve

mounted on the rear of the pump.

2. If the displacement angle decreased,the flow rate at the outlet port decreased too.


32/40

AU-HYD-10



- Hydraulic PumpThe piston moved in by some form of

mechanical action and moved out bycentrifugal force in the cylinder block .

Porting in the control journal permits

the piston to take in fluid from theinlet as they move outward

And allows the fluid to be discharge asthe pistons are forced inward.


33/40

AU-HYD-10



- Hydraulic Pump1. In this picture show typical radial piston pumpthat has been modified for variable displacement.

2. It work on the same principleas the variable vane pump

3. in that the outer cam is moved left

or right by the displacement control tochange eccentricity with the cylinder block

4. and change piston strokewhich changes displacement.

Displacementcontrol piston


34/40

AU-HYD-10



- Hydraulic Pump

1. Displacement is a theoretical volumeof oil that is transfer from inlet side.

2. to the discharge side in onerevolution of the pump shaft.

Displacement is usually expressed in

in3/rev or cc/rev

DISPLACEMENT


35/40

AU-HYD-10



- Hydraulic Pump

Pressure Rating

Pressure rating is the maximum

pressure that should be encounteredat the pump discharge port.

This rating is specified by the

manufacturer base upon reasonable

service life expectancy.


36/40

AU-HYD-10



- Hydraulic Pump1. If the size of thispump is 20 in3/rev.

Volumetric Efficiency

2. It should deliver 20 in3 of oil foreach revolution of its input shaft.

3. In reality the actual pump output flow rate is

reduce in form of leakage as pressure increasesacross the clearance fits of the pump.

4. This leakage fluid flows back to the

suction side or the housing of the pump


37/40

AU-HYD-10



- Hydraulic Pump

1.If the theoretical flow of the 20 in3/revpump is 108 gallons per minute at 1250 rpm.

2. But the actual flow rate at the outlet portof this pump is 98 gallons per minute.

98 GPM x100 = 90.74%108 GPM

Actual Flow x100 = Volumetric EfficiencyTheoretical Flow

Volumetric Efficiency


38/40

AU-HYD-10



- Hydraulic PumpLeakage in hydraulic pump

1. Leakage between cylinderblock and valve plate

3. Leakage between sliding shoeand swash plate

2. Leakage between cylinderblock and piston

Case drainport


39/40

AU-HYD-10



- Hydraulic Pump

Case Drain Connection

1. In the piston pump pressurized oil whichleaks past the clearance fits of the piston,..

2. running clearance between

valve plate and cylinder barrel,collect in the case of the pump.

3. The leakage oil back to tankthrough a separate drain line.


40/40

AU HYD 10


- Hydraulic Pump

Case Drain Connection

1. In general, the leakage oil provides

a second function in that it lubricates

bearing and other moving parts in the pump.

2.For this reason it is imperative that the housingbe filled with oil prior to start the pump,..

3. And the drain port be oriented upward toassure a permanently oil filled housing.

4. The excessive pressure in the case drainline, cause the oil seal to damaged.Remember: Case drain pressure should

not higher than 5 to 15 psig.

chapter 4 hydraulic pumps

Documents