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**HYDRAULIC SYSTEMS TRAINING**

Presented by: Scott Levy Date

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**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 Mechanics Fluid Flow = Q Volumetric rate gal/hour, L/min Fluid Pressure = P Force per square area Lbs/sq in, Kg/sq m Fluid Velocity = V Distance over time ft/sec, m/sec Fluid Temperature = T °F or °C Fluid Viscosity = ν Fluid resistance to flow cSt (centistokes) 3

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**Basic Hydraulic Fluid Principles**

Fluid Mechanics Relationships Flow – Velocity Q= A * v Where 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 4

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**Basic Hydraulic Fluid Principles**

Hydraulic Fluid Power Fluid 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. Gravity Change in Temperature Source Creates Pressure Fluid Flow Viscous Fluid Has Velocity Sink Turns fluid pressure / energy into leverage 5

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**Basic Hydraulic Systems Overview**

Typical Lift / Ram Circuit (mobile or industrial – open center system) Cylinder Motion Relief Valve Control Valve Cylinder Pump Filter Tank Cooler

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**Basic Hydraulic Systems Overview**

Typical Motor Power Circuit (mobile – closed center system) EH Servo Control Valve Hydraulic Motor Blower Fan Joystick Variable Pump Filter Tank Cooler

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**Hydraulic Motors Overview**

Purpose A 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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**Fixed Positive Displacement Motors**

Hydraulic Motors Fixed Positive Displacement Motors Motor displacement is fixed Torque is proportional to inlet pressure Speed is proportional to flow rate Regulate 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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**Fixed Positive Displacement Motors**

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 Radial Piston Motor Fixed Displacement Bent Axis Piston Motor Fixed Angle Swash Plate Piston Rotating Group Fixed Displacement Axial Piston Motor

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**Fixed Positive Displacement Motors**

Hydraulic Motors Fixed Positive Displacement 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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**Fixed Positive Displacement Motors**

Hydraulic Motors Fixed Positive Displacement 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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**Variable Positive Displacement Motors**

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 Radial Piston Motor Variable Displacement Axial Piston Motor

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**How to Choose & Size a Hydraulic Motor**

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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**How to Choose & Size a Hydraulic Motor Gerotor / Geroler Motor**

Hydraulic Motors How to Choose & Size a Hydraulic Motor Fixed Motor Type Selection Chart Selection Criteria Gear Motor Piston Motor Gerotor / Geroler Motor Vane Motor Low Cost X High Pressure X (cast iron) High Speed / Low Torque Low Speed / High Torque High Efficiency High Reliability / Durability Superior Cold Start Performance Availability Compact Size / Displacement Large Displacements Wide Range of Displacements Tolerant to Contamination Serviceability Bidirectional Motors connected in series w/ one pump

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**How to Choose & Size a Hydraulic Motor**

Hydraulic Motors How to Choose & Size a Hydraulic Motor Step 3 – Determine Motor Displacement How much max horsepower or torque is required to drive the devise? Torque (in-lbs) = 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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**How to Choose & Size a Hydraulic Motor**

Hydraulic Motors How to Choose & Size a Hydraulic Motor Motor Sizing Example A 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 chart Gear type is best selection Reasons – fixed displacement, low cost, tolerant to contamination in an unfiltered system & low pressure.

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**How to Choose & Size a Hydraulic Motor Gerotor / Geroler Motor**

Hydraulic Motors How to Choose & Size a Hydraulic Motor Fixed Motor Type Selection Chart Selection Criteria Gear Motor Piston Motor Gerotor / Geroler Motor Vane Motor Low Cost X High Pressure X (cast iron) High Speed / Low Torque Low Speed / High Torque High Efficiency High Reliability / Durability Superior Cold Start Performance Availability Compact Size / Displacement Large Displacements Wide Range of Displacements Tolerant to Contamination Serviceability Bidirectional Motors connected in series w/ one pump

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**How to Choose & Size a Hydraulic Motor**

Hydraulic Motors How to Choose & Size a Hydraulic Motor Motor Sizing Example Continued Theoretical Motor Displacement Calculation Torque (in-lbs) = Horsepower / Speed (rpm) Torque = (15 hp) / 1500 rpm = 630 in-lbs Δ Pressure (psi) = Max systems inlet – Max motor return to tank pressure Δ 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 Rated pressure (psi) 3625 2000 Theoretical max speed (gpm) 35 30

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**How to Choose & Size a Hydraulic Motor**

Hydraulic Motors How to Choose & Size a Hydraulic Motor Motor Sizing Example Continued Verify 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 flow Flow (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

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**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 Suspension Strut Cylinder Cut Away Telescoping Cylinder Threaded Head Cylinder Welded Cylinder Bolted Cylinder

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**Hydraulic Cylinders Overview**

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 Overview**

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 Overview**

Typical Cylinder Construction Barrel or body Rod Piston & Seal Rod Gland Head Cap Position Sensor Position Sensor Rod Gland Head Barrel Cap Piston Rod

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**How to Choose & Size a Hydraulic Cylinder**

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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**How to Choose & Size a Hydraulic Cylinder**

Hydraulic Cylinders How to Choose & Size a Hydraulic Cylinder 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) * 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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**How to Choose & Size a Hydraulic Cylinder**

Hydraulic Cylinders How to Choose & Size a Hydraulic Cylinder Step 5 – Determine the piston rod diameter & column size continued 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

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Hydraulic Motors

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**How to Choose & Size a Hydraulic Cylinder**

Hydraulic Cylinders How to Choose & Size a Hydraulic Cylinder 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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**How to Choose & Size a Hydraulic Cylinder**

Hydraulic Cylinders How to Choose & Size a Hydraulic Cylinder Cylinder Sizing Example A 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 Type Telescoping dual acting cylinder is chosen Reason – the fully extended length is more than ½ the fully retracted length and hydraulic pressure is needed to fully lower the dump bed.

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**How to Choose & Size a Hydraulic Cylinder**

Hydraulic Cylinders How to Choose & Size a Hydraulic Cylinder Cylinder Sizing Example Continued Cylinder Bore Size Force = Required Force / # Cylinders = 58,350 lbs / 2 Cylinders = 29,175 Lbs Cylinder Bore (in) = [.7854 * Force (lbs) / Pressure (psi)] ½ Cylinder Bore = [.7854 * / 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 / min Flow Rate (gpm) = Fluid Velocity (ipm) * Cylinder Piston Area (sq in) * Flow Rate = 350 in/min * 15.9 sq in * = 24.1 gal / min < 25 gal / min Determine the piston rod diameter & column size From Table 1.1 the Column Strength Factor = 2.0

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**How to Choose & Size a Hydraulic Cylinder**

Hydraulic Cylinders How to Choose & Size a Hydraulic Cylinder Cylinder Sizing Example Continued Determine 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 = [ ] / 10 = 10 in Cylinder ends – Clevis Pivot Mount Piston Rod Diameter = 4.5 in Corrected Length =140 in Thrust Load =38,160 Lbs

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**How to Choose & Size a Hydraulic Cylinder**

Hydraulic Cylinders How to Choose & Size a Hydraulic Cylinder 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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**How to Choose & Size a Hydraulic Cylinder**

Hydraulic Cylinders How to Choose & Size a Hydraulic Cylinder 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.

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