Date HYDRAULIC SYSTEMS TRAINING Presented by: Scott Levy.

Date

HYDRAULIC SYSTEMS TRAINING

Presented by: Scott Levy

2

Introduction to Hydraulic Systems

What are hydraulics?

Answer – The study of the mechanical properties of fluids

What is Fluid Power?

Answer – The use of fluid motion under pressure to transfer power & energy from a source to a sink (receptor).

Commercial Definitions:

Hydraulics – The transmission of power from a power generation source to a sink using an engineered incompressible hydraulic fluid for the sake of creating leverage or motion.

Pneumatics - The transmission of power from a power generation source to a sink using pressurized air (compressible) as the fluid for the sake of creating leverage or motion.

THIS COURSE WILL ADDRESS HYDRAULIC FLUID POWER

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Basic Hydraulic Fluid Principles

Elements of Fluid MechanicsFluid Flow = Q

Volumetric rate gal/hour, L/minFluid Pressure = P

Force per square area Lbs/sq in, Kg/sq mFluid Velocity = V

Distance over time ft/sec, m/secFluid Temperature = T

°F or °CFluid Viscosity = ν

Fluid resistance to flow cSt (centistokes)

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Fluid Mechanics RelationshipsFlow – Velocity

Q= A * vWhere Q= Volumetric Flow Rate, A= Cross sectional Area & v= Fluid Velocity

Fluid flow in a system is additive

Bernoulli’s Law for incompressible fluids

H = z + p/ρg + v2/2g (fluid is flowing with a significant difference in height between source & sink)Where H=total head pressure, v= fluid velocity, g= force of gravity, z= the height of the fluid source, p=fluid pressure & ρ=fluid density

p0 = p + v2/2 (fluid height is insignificant)Where p0 = total system pressure, p= static pressure v= flow velocity

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Hydraulic Fluid PowerFluid power depends on a viscous fluid flowing under pressure from a sink to a source. The systems efficiency is dependent on fluid density, temperature and pressure loss due to decreased fluid velocity.

Fluid Flow

Viscous Fluid Has Velocity

Source

Creates Pressure

Sink

Turns fluid pressure / energy into leverage

Gravity

Change in Temperature

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Basic Hydraulic Systems Overview

Typical Lift / Ram Circuit (mobile or industrial – open center system)

Pump

Tank

Relief Valve

Control Valve

Cylinder

Filter

Cooler

Cylinder Motion

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Basic Hydraulic Systems Overview

Typical Motor Power Circuit (mobile – closed center system)

Tank

Hydraulic Motor

Blower Fan

Filter

Cooler

Variable Pump

EH Servo Control Valve

Joystick

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Hydraulic Motors

Hydraulic Motors Overview

PurposeA hydraulic motor converts hydraulic energy from pressure into rotary motion and torque to drive an implement or system.

Types Fixed positive displacement – gear, piston, geroter / geroler & vane types Variable positive displacement – piston

Typical Applications Wheel Motors – drive mobile equipment wheels (skid steers, tractors, lifts) Fan Drives – hydraulic fan drives (engine cooling, industrial equipment, drive train cooling,

gen sets, grain driers) Industrial Machinery – (conveyers, machine tools, cutters, cranes, augers, winches) Agricultural Equipment – Harvesters, Trenchers, Lawn Mowers, Forestry Equipment

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Hydraulic Motors

Fixed Positive Displacement MotorsMotor displacement is fixedTorque is proportional to inlet pressureSpeed is proportional to flow rateRegulate torque and speed with either valves, variable displacement pump or pump speed.

Gear Motors Inlet flow / pressure rotates a gear set causing the output shaft to rotate and create torque Advantages

Low cost – initial and rebuild Good availability / many suppliers Cast iron motors have high pressure capability Tolerant to contamination Compact - desirable packaging

Disadvantages Lower efficiency compared to other types Lower torque per unit displacement compared to piston or Geroter / Geroler types

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Hydraulic Motors

Fixed Positive Displacement Motors

Fixed Displacement Piston Motors Axial Piston, Radial Piston & Bent Axis Types Swash plate is fixed on an angle to achieve a specified displacement Number & size of pistons in rotating group determine flow, torque and speed capabilities Advantages

High efficiency / Performance Higher torque capability per unit displacement Radial type packages well for wheel

motor applications Bent axis type available for improved

packaging Good serviceability

Disadvantages Higher cost Not as tolerant to contamination

Fixed Displacement Bent Axis Piston Motor

Fixed Displacement Axial Piston Motor

Fixed Displacement Radial Piston Motor

Fixed Angle Swash Plate

Piston Rotating Group

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Hydraulic Motors


Fixed Displacement Vane Motors Fluid flow over vanes produce rotational speed and torque High speed and pressure capability Number & area of vanes determine flow, torque and speed capabilities Advantages

High efficiency / Performance Higher speed capacity Reliability & durability Forward or reverse rotation Superior cold start performance Good power output per motor size

Disadvantages Lower torque capability Higher cost than gear motors

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Hydraulic Motors


Fixed Displacement Geroter / Geroler Motors Spool valve, disc valve & valve in star types Low speed and high torque capability Works on the “Orbit Principle” – star, drive and output shaft Gerotor & Geroler have similar performance characteristics for equal frame sizes. In the Geroler type,

the drive gear rides on roller bearings in the star for reduced friction, improved mechanical efficiency and useful life.

Advantages High efficiency Higher torque capacity Reliability & durability – only three main components Compact with high power density Can be connected in series with same pump source High systems pressure capability Low speed constant with change in load

Disadvantages No high speed applications High cost than other motors

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Hydraulic Motors

Variable Positive Displacement Motors

Variable Displacement Piston Motors Axial Piston, Radial Piston & Bent Axis Types Swash plate angle is variable – manual, hydraulic, EH or electric control Number & size of pistons in rotating group determine flow, torque and speed capabilities Advantages

High efficiency / Performance Higher torque capability per unit displacement Radial type packages well for wheel

motor applications Bent axis type available for improved

packaging Good serviceability

Disadvantages Higher cost Not as tolerant to contamination

Variable Displacement Axial Piston Motor

Variable Displacement Radial Piston Motor

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Hydraulic Motors

How to Choose & Size a Hydraulic Motor

Step 1 – Document Motor Requirements What is the application (wheel drive, fan, auger, winch, machine tool, turf care, etc.) Space requirements - packaging What torque is required for driving the application component? What hydraulic system pressure is available to the motor? What hydraulic system flow is available to the motor? What speed range is required for the motor? Does the motor have to stall or reverse direction? What is the hydraulic oil cleanliness levels? What are the cost factors? How many motors will be run in series off of the same source? What is the ambient temperature range of operation? What hydraulic fluid will be used?

Step 2 – Choose the Motor Type Fixed or variable displacement? If fixed displacement – use the motor type selection chart to determine which type of fixed displacement

motor best meets the requirements.

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Hydraulic Motors


Fixed Motor Type Selection Chart

Selection Criteria Gear Motor Piston Motor Gerotor / Geroler Motor Vane Motor

Low Cost X X

High Pressure X (cast iron) X X

High Speed / Low Torque X X X

Low Speed / High Torque X

High Efficiency X X X

High Reliability / Durability X X

Superior Cold Start Performance X

Availability X X

Compact Size / Displacement X X X

Large Displacements X

Wide Range of Displacements X X

Tolerant to Contamination X X X

Serviceability X X X

Bidirectional X X

Motors connected in series w/ one pump X

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Hydraulic Motors


Step 3 – Determine Motor Displacement How much max horsepower or torque is required to drive the devise?

Torque (in-lbs) = 63024 Horsepower / Speed (rpm)

What max displacement is required?Displacement (cubic in/rev) = 2π* Torque (in-lbs) / Δ Pressure (psi)* Mechanical Efficiency (%)Mechanical efficiency varies from 80-90% depending on the type of motor.

What flow is required at the motor?Flow (gpm) = Motor Displacement (cubic in / rev)* Speed (rpm) / 231* Volumetric Efficiency (%)Volumetric efficiency varies from 85-95% depending on the type of motor.

Step 4 – Determine the motor that meets the requirements Find a supplier that makes a motor of the type and size determined Determine the best model motor to meet all or as many of the requirements for the

application that is at least equal to or larger than the displacement calculated. Compare the selected motor specifications to the motor requirements and qualify it for the

application. Recalculate the motor torque and flow with the selected motor’s specs to ensure the torque

and system flow requirements are satisfied.

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Hydraulic Motors


Motor Sizing ExampleA hydraulic motor is needed to power a blower fan for a combine separation system. The fan speed will vary from 0 to 1500 rpm and the fan requires 15 hp at max speed and load conditions. The system pump supplying flow is a variable displacement axial piston pump with a max flow of 30 gpm. What type of motor and displacement will satisfy these requirements?

Requirements:• Pressure available at the motor inlet = 2000 psi• Max pressure for motor return to tank = 100 psi• Clockwise rotation only• Only one motor in the system• System is unfiltered• Low cost is important• Ambient temp range 0 °F to 110 °F.• Hydraulic fluid – Hydraulic Oil w/viscosity at 15 cST

normal operation, 10 cST min

Motor Type – See selection chartGear type is best selection

Reasons – fixed displacement, low cost, tolerant to contamination in an unfiltered system & low pressure.

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Hydraulic Motors


Fixed Motor Type Selection Chart

Selection Criteria Gear Motor Piston Motor Gerotor / Geroler Motor Vane Motor

Low Cost X X

High Pressure X (cast iron) X X

High Speed / Low Torque X X X

Low Speed / High Torque X

High Efficiency X X X

High Reliability / Durability X X

Superior Cold Start Performance X

Availability X X

Compact Size / Displacement X X X

Large Displacements X

Wide Range of Displacements X X

Tolerant to Contamination X X X

Serviceability X X X

Bidirectional X X

Motors connected in series w/ one pump X

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Hydraulic Motors


Motor Sizing Example ContinuedTheoretical Motor Displacement Calculation

• Torque (in-lbs) = 63024 Horsepower / Speed (rpm)Torque = 63024 (15 hp) / 1500 rpm = 630 in-lbs

• Δ Pressure (psi) = Max systems pressure @ inlet – Max motor return to tank pressureΔ Pressure = 2000 psi – 100 psi = 1900 psi

• Displacement (cubic inch / rev) = 2π* Torque (in-lbs) / Δ Pressure (psi)* Mechanical Efficiency (%)Gear pump mechanical efficiency = 85%Displacement = (2π * 630 in-lbs) / (1900 psi * 0.85) = 2.45 cubic in/rev or 40.1 cc/rev

Gear pump supplier chosen is Sauer Danfoss Group 3 frame size 44• Specs vs. Requirements

Requirement / Spec Requirement Specification

Displacement (cubic in / rev) 2.45 2.69

Max speed (rpm) 3000 1500

Min speed (rpm) 800 800

Rated pressure (psi) 3625 2000

Theoretical Flow @ max speed (gpm) 35 30

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Hydraulic Motors


Motor Sizing Example ContinuedVerify actual motor torque

Torque (in-lbs) = Δ Pressure (psi)* Mechanical Efficiency (%) * Displacement (cubic in/rev) / 2π Torque = (1900 psi * 0.85 * 2.69) / 2π = 691 in-lbs > 630 in-lbs

Verify actual motor flowFlow (gpm) = Motor Displacement (cubic in / rev)* Speed (rpm) / 231* Volumetric Efficiency (%)Volumetric Efficiency = 88%Flow = (2.69 cubic in/rev * 1500 rpm) / (231 * 0.88) = 19.8 gpm < 30 gpm available at the pump.

THE PUMP SELECTED MEETS ALL THE REQUIREMENTS

21

Hydraulic Cylinders

Hydraulic Cylinders Overview

Purpose

A hydraulic cylinder converts hydraulic energy from pressure into linear motion and force to actuate, move or lift an implement or object.

Types Dual Acting / Single Acting Multi-stage Telescoping Pressurized struts – Mobile Applications Head & Cap Arrangements

• Welded – Medium duty applications / size• Threaded – Light duty applications / size• Bolted – Heavy duty applications / size

Cylinder Cut Away

Suspension Strut

Telescoping Cylinder

Bolted Cylinder

Threaded Head Cylinder

Welded Cylinder

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Hydraulic Cylinders


Typical Applications Construction Equipment – (implements, dump trucks, suspension struts, stabilizers, steering systems) Lifts – (scissors lifts, aerial lifts, cranes, fork lifts, lift gates) Industrial Machinery – (presses, rams, loading docks, injection molding machines) Agricultural Equipment – (tractor implements, bailers, combine heads, sprayers) Mining Equipment – (hoist, bucket, suspension struts, steering system, grader blades)

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Hydraulic Cylinders


Single vs. Dual Acting Cylinders Single acting cylinder only actuates the rod

• The rod extends under pressure and contracts under force or weight• Typically used in applications where load is lifted hydraulically and gravity returned• A spring in the system can be used to achieve contraction

Dual acting cylinder actuates the rod and the head ends• Both extension and contraction occur under hydraulic pressure• Typically used in applications where motion is not in the direction of gravity

Single Acting Cylinder Dual Acting Cylinder

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Hydraulic Cylinders

Typical Cylinder Construction Barrel or body Rod Piston & Seal Rod Gland

RodBarrel

Rod Gland Cap


Head Cap Position Sensor

Piston

Position SensorHead

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Hydraulic Cylinders

How to Choose & Size a Hydraulic Cylinder

Step 1 – Document cylinder requirements What is the application (lift, press, steering, hoist, implement, ram, crane etc.) Space requirements – packaging & end attachments What is the max collapsed length What is the max extended length What max force or weight is necessary to actuate the attached object? What hydraulic system pressure is available to the cylinder? What hydraulic system flow is available to the cylinder? How many cylinders will be used to move the load What max time is required to go from min length to max extended length? What are the cost factors? What is the ambient temperature range of operation? What hydraulic fluid will be used?

Step 2 – Choose the cylinder type Dual or Single Acting? Single Stage or Multiple Stage Telescoping?

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Hydraulic Cylinders


Step 3 – Determine cylinder bore size Force = Required Force / # Cylinders Cylinder Bore (in) = [.7854 * Force (lbs) / Pressure (psi)] ½

This is the minimum bore size required. To decrease the time to fully extend the cylinder, the bore size can be increased.

Find a Cylinder of the type chosen with the next larger bore size available

Step 4 – Determine if the flow rate required for max extension . Flow Rate (gpm) = Fluid Velocity (ipm) * Cylinder Piston Area (in) * 0.00433 Cylinder Piston Area = π * [Cylinder Bore (in) / 2] 2

Fluid Velocity (ipm) = [Extended Cylinder Stroke (in)] / [Max Extension Time (sec) / 60] Is Flow Rate equal to or less than the required flow rate? If not, the cylinder bore size has to

be increased to ensure the max time to full extension is satisfied within the flow rate available.

Step 5 – Determine the piston rod diameter & column size Determine the column strength factor from Table 1.1 Corrected Length = Actual Stroke * Column Strength Factor Cylinder Thrust (lbs) = Max System Relief Pressure (psi) * Cylinder Piston Area

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Hydraulic Cylinders

Determine the appropriate piston rod diameter using Table 1.2

Determine the stop tube length if necessary Internal stops are sometimes required to limit rod

stroke to prevent rod buckling Stop Tube Length (in) =

[Corrected Length – 40 in] / 10


Step 5 – Determine the piston rod diameter & column size continued

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Hydraulic Motors

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Hydraulic Cylinders


Step 6 – Choose the type of cylinder ends for attachment

Step 7 – Determine a cylinder that meets the requirements Find a supplier that makes a cylinder of the type and size determined Determine the best model cylinder to meet all or as many of the requirements for the

application that is at least equal to or larger than the bore and rod diameter calculated. Compare the selected cylinder specifications to the cylinder requirements and qualify it for

the application. Recalculate the cylinder load capability and time for full extension with the selected cylinder’s

specs to ensure that these requirements are satisfied.

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Hydraulic Cylinders


Cylinder Sizing ExampleA cylinder is needed to lift and lower a dump truck bed. The design calls for two cylinders. The maximum load that the cylinders have to lift is 58,350 Lbf. The maximum stroke is 70 inches. The maximum time to fully extend the cylinders into the full dump position is 12 seconds. The system relief pressure is set to 2400 psi and the max available flow rate is 25 gal/min. The empty dump bed weight is not enough to fully retract the cylinder.

Requirements:• Max fully extended length – 125 inches• Max fully retracted length – 42 inches• Clevis Pivot Mount• System is filtered• Ambient temp range 0 °F to 110 °F.• Hydraulic fluid – Hydraulic Oil w/viscosity at

15 cST normal operation, 10 cST min

Cylinder TypeTelescoping dual acting cylinder is chosen

Reason – the fully extended length is more than ½ thefully retracted length and hydraulic pressure is needed to fully lower the dump bed.

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Hydraulic Cylinders


Cylinder Sizing Example ContinuedCylinder Bore Size Force = Required Force / # Cylinders = 58,350 lbs / 2 Cylinders = 29,175 LbsCylinder Bore (in) = [.7854 * Force (lbs) / Pressure (psi)] ½

Cylinder Bore = [.7854 * 29175 / 2400] ½ = 3.09 inches

Standard multistage cylinder has bores – 4.5” 1rst stage, 3.5” 2nd stage & 2.5” 3rd stage and is capable of supporting up to 30,000 Lbs static load.

Determine if the flow rate required for max extension.Cylinder Piston Area = π * [Cylinder Bore (in) / 2] 2

Stage 1 piston Area = π * [4.5 (in) / 2] 2 = 15.9 sq in (largest section)Fluid Velocity = [Extended Cylinder Stroke (in)] / [Max Extension Time (sec) / 60]

Fluid Velocity = [ 70 in ] / [12 / 60] = 350 in / minFlow Rate (gpm) = Fluid Velocity (ipm) * Cylinder Piston Area (sq in) * 0.00433

Flow Rate = 350 in/min * 15.9 sq in * 0.00433= 24.1 gal / min < 25 gal / minDetermine the piston rod diameter & column sizeFrom Table 1.1 the Column Strength Factor = 2.0

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Hydraulic Cylinders


Cylinder Sizing Example ContinuedDetermine the piston rod diameter & column size From Table 1.1 the Column Strength Factor = 2.0 Corrected Length = Actual Stroke * Column Strength Factor = 70 in * 2.0 = 140 in Cylinder Thrust (lbs) = Max System Relief Pressure (psi) * Cylinder Piston Area

Cylinder Thrust = 2400 psi * 15.9 sq in = 38,160 lbs Use Table 1.2 to determine the minimum rod diameter

Stop Tube Length (in) = [Corrected Length – 40 in] / 10 = [140 -40] / 10 = 10 in

Cylinder ends – Clevis Pivot Mount

Corrected Length =140 in

Thrust Load =38,160 Lbs

Piston Rod Diameter = 4.5 in

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Hydraulic Cylinders


Cylinder Sizing Example Continued

Determine a cylinder that meets the requirements The supplier chosen is Prince – PMC/SAE 62 a 3-stage telescoping cylinder with 5”x4”x3” rod sizes and

5.5”x4.5”x3.5” bore sizes.

Requirement / Spec Requirement Specification

Minimum Bore Size (in) 3.09 5.5 / 4.5 / 3.5

Minimum Rod Size (in) 4.5 6 / 5 / 4

Max extended Load (lbs) 38,160 50,000 lbs

Max Closed Length (in) 42 38.58

Max Extended Length (in) 125 146.78

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Hydraulic Cylinders


Cylinder Sizing Example Continued

Determine a cylinder that meets the requirements Cylinder time to full extension

Recalculate the cylinder load capability and time for full extension with the selected cylinder’s specs to ensure that these requirements are satisfied.

35

Thank you.

Date HYDRAULIC SYSTEMS TRAINING Presented by: Scott Levy.

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