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Class #4

Hydraulic Fluid Properties

ME 4232:

FLUID POWER CONTROLS LAB

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Notes

Lab 2 Regrades

Regrading Policy Undergraduate Research Position:

Compressed Air Energy Storage Testbed

Upcoming Labs:

Lab 7: Bleed Off Circuit

Lab 8: Check Valves: Direct & Pilot Operated

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Agenda

Feedback: Interesting / Challenging

Check Valves Roles of Hydraulic Fluid

Fluid Properties

Viscosity

Viscous Friction

Leakage

Bulk Modulus

Inertia

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FeedbackInteresting

Ingenious Component

Designs

Freedom in Lab = Learning

Understandable Labs

Practical Applications Power of Hydraulics

Variety of Configurations

Matlab for Data Analysis

In Class Activities

Analogies to Electrical

Confusing/Challenging

Learning Matlab

Circuit Diagrams

Understanding Circuit

Operation

Frequency of Labs &Reports

Lab Handout Wording

Cavitation TA Language Challenges

Want Lecture Schedule

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Check Valves

Allows flow only one direction

Main uses are: by-pass components

cylinder locking

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Pilot Operated (open) Check Valve

Allows reverse flow when

pilot pressure is turned on

Enables cylinder locking

Consider force balance to

calculate what pressures

needed to open the check

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Cartridge Valves

Assemble Components

into Circuits in a

Manifold Manifold = metal block

with internal passages

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Cartridge Valves (screw in)

Check Valve Pilot Operated Check Valve

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Cartridge Valve (Screw In)

Relief Valve Pilot Operated Relief Valve

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Roles of Hydraulic Fluid

Primary:

Transmit Power

Secondary:

Lubrication

Sealing

Heat Transfer / Cooling

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Hydraulic Fluid Properties

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Viscosity Index

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Pipe Resistance

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Friction Factor Moody Diagram

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Example: 3 MW Wind Turbine, 35 MPaHydraulic Fluid: ISO 46

= 46 cSt

= 870 kg/m3

Pipe: 100 m long, 20 cm diameter, perfectly smooth

Find:

1. Determine the flow rate and average fluidvelocity.

2. Calculate the Reynolds number. Laminar or

Turbulent?

3. Find the friction factor.

4. Calculate the viscous pressure drop.

5. How does this compare to the pressure

difference due to gravity?

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Hydraulic Connectors

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Example

Q1: Assuming the leakage past the spool is small, find the pressureP

Q2: How long does L need to be for the leakage to be < 0.01% of the

pump flow?

Fluid Properties:

= 870 kg/m3

= 46 x 10-6 m2/s

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Efficiency vs Viscosity vs Temperature

For hydraulic components (e.g. pumps,

motors, actuators) with moving parts,there is always a trade-off between

Volumetric efficiency [leakage]

Mechanical Efficiency [friction]

Total efficiencies for pumps and motorsgiven by:

Optimal viscosity exists for a givencomponent (and system)

Optimal viscosity

However, viscosity changes dramaticallyby temperature!

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Bulk Modulus

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Research Topic:

Fluid Compressibility in Digital Hydraulics Major Form of Energy Loss

Widely Varying Bulk Modulus Models

Goal: Understand the Role of Fluid Compressibility on the

Performance and Efficiency of Switch-Mode Circuits

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Bulk Modulus Models

Bulk Modulus:

Many Models Available in Literature

dPV

dV

Basic: Akers et al.1 1 1 1 1

T a a a

e T T a T a

V V V V

V V V

e

P

R P

o

e

o

PR

P

R PP P

11

1 1111

e

o o

P

P P R c P P P

Merritt

Hayward

Cho et al.0 5 10 15 20 25 30 35

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

2

Pressure (MPa)

BulkModulus

(GPa)

Bulk Modulus vs. Pressure for R = 0.020

Yu et al.

Cho et al.

Hayward

Merritt

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Experimental

Validation

Vary: Entrained Air, Pressure, Vswitched

Measure: Density, Bulk Modulus, Efficiency

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Bulk Modulus Calculation

Based on Sonic Velocity:

Cross-correlation of Pressure Waves

2

2

e c

T