TSM 363 Fluid Power Systems

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TSM 363 Fluid Power Systems

• Control of Power Distribution- Valve-based
  Controls

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How to Make it Functioning as Expected?
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1. Pressure Controls

• System Pressure Control
• Use of a line relief valve to limit the maximum
  allowable system pressure
• Other Pressure Control Functions
• Unloading
• Pressure reduction
• Load holding
• Sequential control
• Others

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Line Relief Valve

• Line relief valve is a pressure control valve.
• A basic LR valve has a pilot pressure applied.
• There are a few types of LR valves available.

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Pressure Override Characteristics
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Pilot Operated Relief Valves
Function protect a hydraulic system with low
override characteristics. Operation The spring
loaded puppet valve opens when the pressure
reaches the cracking pressure, the flow cause the
back pressure drop, which leads the open of the
spool valve.
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Improved Pressure Override Characteristics
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Application of Relief Valves
1,000 psi
It is recommended that there is always at least
200 psi difference between two line release
(pressure relief) valves in a line.
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Heat Generation in Pressure Relief
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Example Other Pressure Controls-- Sequence
Valves
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Functionality and Operation of a typical
Sequence Valves

• Controls the order of operations in branch
  circuits
• The sequence valve is normally closed. It is set
  to react to a system pressure less than the
  setting of the pressure relief valve.
• Pressure increases resulting from an actuator
  reaching the end of its stroke open the sequence
  valve.

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2. Flow Controls

• Uncompensated Flow Control
• Example metering-in/metering-out using needle
  valves
• Compensated Flow Control
• Example -
• Proportional Flow Control
• Often use of proportional directional control
  valve (discuss in direction control)

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Metering Controls of Flow

• Often us of a needle valve
• Simple, but energy inefficient
• Commonly used in some light load, inexpensive
  systems for load control.

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Typical Metering Flow Control Approaches
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Flow Divider Example of Pressure-compensated
Flow Control
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Functionality and Operation of a Flow Divider
Valve

• Directs flow to two or more branches
• Controls flow and also direction (e.g., priority
  control)
• Common on off-road equipment to divide flow
  between circuits (e.g., power steering and
  front-end load or left and right crawler tracks)

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3. Direction Controls

• Simple direction control
• On-off type direction control
• Multi-direction Control
• Circuits Switching-type direction control
• Proportional direction control
• Direction and flow integrated control

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Simple direction Control
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Simple direction Control
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Multi-direction Control Case 1 Hydraulic
Cylinder Controls
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Multi-direction Control Case 2 Hydraulic System
Priority Controls
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Theoretical Base for All Valve ControlsOrifice
Equation

• Cd is determined experimentally
• Pressure drop is proportional to flow
• Valve Principles Area is a adjusted to control
  pressure and flow rate
• Density of petroleum-based fluids 850-950 kg/m3

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Lecture Summary

• Discussed the basic principles of different
  methods of using valves to control a hydraulic
  system
• Pressure controls
• Flow controls
• Directional controls
• All valved-based controls follows the same
  control principle