Hydraulic Systems Notes

HYDRAULIC

WELCOME TO BASIC HYDRAULIC TRAINING

INTRO

HISTORY OF HYDRAULIC

• In 1795, Joseph Bramah invented the first hydraulic press.
• This press demonstrated that a low force acting over a long stroke on a small diameter piston could develop pressure in a fluid.

HYDRO LIC FLUID-LIQUID REFER TO POWER

• Hydraulic system: A system that uses a fluid under pressure to drive machinery or move mechanical components.
• The power of liquid fuel in hydraulics is significant, making them common in heavy equipment.
• Pressurized fluid acts on every part of a containing vessel, creating force or power to lift heavy loads.

Typical application fields for hydraulics

• Construction machinery
• Excavators
• Elevating platforms
• Lifting & conveying devices
• Agricultural machinery
• Injection moulding
• Presses machine

Advantages of hydraulics

• Transmission of large forces using small components
• Precise positioning
• Start-up under heavy load
• Smooth operation
• Low noise system
• Frictionless operation

Disadvantages of hydraulics

• Pollution of the environment
• Sensitivity to dirt
• Danger resulting from excessive pressures
• Temperature dependence (change in viscosity)
• Slow movement
• Costly preventive maintenance (e.g., oil changing)

Basic Principle of Hydraulic

Design Of A Simple Hydraulic Circuit

Pressure due to external forces

• If a force acts on an enclosed liquid, a pressure $P$ is produced throughout the liquid.
• The same pressure applies at every point in the closed system.

PASCAL’S LAW

• Pascal’s Law: The property of a liquid to transmit pressure equally throughout itself.
• Discovered by Blaise Pascal.
• Mathematical expression: $P = \frac{Force(lbs)}{Area(in^2)}$ (PSI)

COMPONENT

SYMBOL OF HYDRAULICS SYSTEM’S COMPONENTS

• Tank
• Filter
• Pump
• Accumulator
• Valve
• Actuator
• Motor

TANK

• Function: To contain or store a system’s hydraulic fluid.
• Components:
  • Four walls (usually steel)
  • Dished bottom
  • Flat top with mounting line
  • Four legs
  • Suction, return, and drain lines
  • Drain plug
  • Oil level gauge
  • Filler/breather cap
  • Cleanout cover
  • Baffle plate
  • Inlet Filter
  • Clean Out Access Plate
  • 3 Micron Air Breather with Water Removal Element
  • Baffle Plate
  • Pump Inlet line
  • Return line
  • Drain line
  • Temperature / Sight Gauge
  • Drain Plug

TANK Functionalities

1. Storage of hydraulic fluid.
2. Release of trapped air.
3. Precipitation of contaminants.
4. Accommodation of system leaks.
5. Provision of a surface for cooling the fluid.

PUMP

• Hydraulic pumps are used in hydraulic drive systems.
• Types: Hydrostatic or hydrodynamic.
• Hydrostatic pumps: Positive displacement pumps.
• Hydrodynamic pumps: Can be fixed or variable displacement.
  • Fixed displacement: Flow through the pump per rotation cannot be adjusted.
  • Variable displacement: Construction allows displacement adjustment.

PUMP Types

1. Gear
2. Vane type
3. Piston
4. Screw

GEAR PUMPS

• Generate pumping action by causing gears to mesh and unmesh.
• External Gear Pump
  • Both meshing gears have teeth on their outer circumferences.
  • Sometimes referred to as gear-on-gear pumps.
• Internal Gear Pump
  • Consists of one external gear which meshes with the teeth on the inside circumference of a larger gear.
  • Sometimes referred to as a gear-within-gear pump.

INTERNAL GEAR PUMP

• Important feature: very low noise level.
• Primary use: industrial hydraulics (presses, machines for plastic and tools) and vehicles in enclosed spaces (electric fork-lifts).
• Function: As the gear rotor and internal gear rotate, the space between them increases, causing the pump to “suck”.
• Important parameters:
  • Operating pressure: up to 300 bar (dependent on size)
  • Range of speed: 500 to 3000 rpm (dependent on size)

External Gear Pump

• Inlet
• Outlet
• Idler Gear
• Driven Gear
• Volume increases as gear teeth unmesh
• Volume decreases as gear teeth mesh

VANE PUMP

• Vane pumps generate a pumping action by causing vanes to track along a ring.
• Components:
  • Rotor
  • Vanes
  • Ring
  • Port plate with kidney-shaped inlet and outlet port.
  • Increasing Volume Inlet side
  • Decreasing Volume Outlet side
  • Eccentricity between rotor and cam ring
  • Basic pumping elements of a vane pump

VANE PUMP Functionality

1. Stroke movement limited by a ring with a circular internal form.
2. Volume changes within the displacement chambers due to the off-center position of the ring.
3. Process of filling the chamber (suction).
4. Vane pumps generate pumping action by causing vanes to track along a ring.

PISTON PUMPS

• Definition: A hydraulic pump that uses pistons driven by a rotating swash plate or cam to move fluid through a hydraulic system.
• Highly efficient but costly.
• Pump displacement is based on swash plate angle
• Stroke
• Outlet
• Inlet

PISTON PUMPS parts

• Case Drain
• Rotation
• Outlet
• Inlet
• Swash Plate
• Cylinder Block
• Piston
• Pre-Load Spring
• Spherical Washer
• Shoe Retractor Plate

SCREW PUMP

1. Hydraulic machine with a screw as the working member; used for pumping liquids, including high-viscosity fluids.
2. Also referred to as worm pumps, are a type of rotary pump.
3. Housing contains a driving screw and one or two driven screws.
4. Points of engagement travel longitudinally along the shaft during rotation, forcing out the liquid between the turns.
5. Potential energy is transmitted to the liquids, increasing pressure within it.

VALVE

FIVE METHOD TO ACTUATE THE VALVE

• MECHANICAL
• MANUAL
• PNEUMATIC
• HYDRAULIC
• ELECTRIC

Manual operation Methods Of actuation

• General symbol with spring return and bleed port
• By manual push button and spring return
• By hand lever
• By hand lever with detent setting
• By pedal and spring return

Mechanical Actuation Methods of actuation

• By stem or push button
• By spring
• By roller stem

Directional Valve:Symbol Development

• Draw valve symbol

Directional Valve:Symbol Development

• Valve switching positions are represented as squares.
• The number of squares shows how many switching positions the valve has.
• Lines indicate flow paths; arrows show the direction of flow.
• Shut-off positions are identified by lines drawn at right angles.
• Connections (inlet and outlet ports) are shown by lines outside the box and are drawn in the initial position.

Directional Control Valves

• Classified according to the number of ports and switching positions.
• Examples:
  • 2/2 Way Directional Valve
    • Number of ports
    • Number of switching position
  • 3/2 Way Directional Control Valve Normally closed
  • 3/2 Way Directional Control Valve Normally open
  • 4/2 Way Directional Control Valve
  • 4/3 Way Directional Control Valve

Port Designation

• P: Pressure port
• T: Return port
• A, B: Working ports
  • 2/2 - way valve
  • 4/2 - way valve
  • 3/2 - way valve
  • 4/3 - way valve

Pressure Relief Valve

PRESSURE VALVE

• Definition: A fluid component that monitors pressure in a hydraulic system.
• Protects the system from damage due to overpressure.
• The position of the valve within the square indicates whether the valve is normally open or normally closed.

Flow Control Valves

Flow control valve

• Definition: A fluid component that controls the rate of fluid flow.
• Allows control of other system variables like actuator speed.
• Throttle
  • set
  • adjustable
• Orifice
  • set
  • adjustable

Non Return Valves

• Out
  • Free Flow
  • In-line
  • In
  • Light Spring
• Spring
  • For Back Pressure
  • Symbol
• Poppet.
• Free Flow
  • Right Angle
  • Sub-plate Mounted

FUNCTION Non Return Valves

• Used to stop flow in one direction and allow free flow in the opposite direction (check valve).

Check Valve

• Symbol
• Outlet Port
• Inlet Port
• Poppet
• Spring

Check ValveFree Flow

• Symbol
• Outlet Port
• Inlet Port
• Free Flow

Check ValveNo Flow

• Symbol
• Outlet Port
• Inlet Port
• No Flow

Basic Check Valve

• A check valve is a one-way valve.
• Ball Type
  • No Flow
  • Free Flow

ACCUMULATOR

1. Holds system under pressure
2. Provides hydraulics when pump off/lost
3. Compensates for leakage/makeup volume

• Bladder-type accumulator
• Gas Valve
• Bladder
• Shell
• Port
• Anti-Extrusion Valve
• Nitrogen Gas
• Bladder accumulator operation
• System Pressure Less Than pprecharge
• System Pressure at pmax
• System Pressure at pmin

HYDRAULIC ACTUATOR

• Converts hydraulic power into useful mechanical work.
• Produces linear, rotary, or oscillatory mechanical motion.
• Cylinder
• Motor

HYDRAULIC CIRCUIT

The advantages and disadvantages of hydraulic system’s basic circuit

• Opened center system
• Closed center system

Opened center system

1. Pump-inlet and motor-return are connected to the hydraulic tank via the directional valve.
2. Uses pumps which supply a continuous flow.
3. Flow is returned to tank through the control valve's open center, meaning when the control valve is centered, it provides an open return path to the tank and the fluid is not pumped to a high pressure.
4. Actuation of the control valve routes fluid to and from an actuator and tank. The fluid's pressure will rise to meet any resistance, since the pump has a constant output.
5. Excess pressure returns to tank through a pressure relief valve.

Closed center system

1. Motor-return is connected directly to the pump-inlet. A charge pump (small gear pump) supplies cooled and filtered oil to maintain pressure on the low pressure side.
2. Generally used for hydrostatic transmissions in mobile applications.
3. Advantages: No directional valve, better response, can work with higher pressure.
4. Disadvantages: Requires large charge pumps for high pressures and motor speeds. High oil temperatures are a major problem at high vehicle speeds, reducing transmission lifetime.
5. Used as an alternative to mechanical and hydrodynamic (converter) transmissions in mobile equipment.

The advantages and disadvantages of hydraulic system’s basic circuit open vs close

Steering Hydraulic’s System

• For sequence A+ B+ B- A- movement.
  1. Cylinder’s A extent, then
  2. Cylinder’s B extent, then
  3. Cylinder’s B retract, then
  4. Cylinder’s A retract.

Steering Circuit

• For sequence A+ B+ B- A-
• Cylinder A, Gripper
• Cylinder B, Drilling

Flow control at hydraulic system’s actuators

• To control the speed of actuator
• Prevent sudden movement.
• Divided to THREE types:-
  1. Meter - Out
  2. Meter - In
  3. Bleed – Off

Litar Meter – Out pulling

• Restricts fluid as it leaves an actuator port.
• Works well with both hydraulic and pneumatic actuators.
• Cylinder-mounting attitude is not important because outlet flow is restricted.
• Actuator cannot run away and can never move faster than the fluid leaving it allows.

Litar Meter – In pushing

• Restricts fluid as it enters an actuator port.
• Works well with hydraulic fluids.
• Only works on resistive loads because a running-away load can move the actuator faster than the circuit can fill it with fluid.

Litar Bleed -Off

• Found only in hydraulic systems.
• Little or no advantage with pressure-compensated pumps.
• A needle valve’s inlet is teed into a line going to the cylinder, and its outlet is connected to tank.
• Only works with one actuator moving at a time because all pump flow goes to the currently operating function.
• Only works with resistive loads because it controls fluid into the actuator.

Meter In Flow Control Circuit vs Meter Out Flow Control Circuit

CONSTRUCTION AND LIMITATION OF HYDRAULIC SYSTEM

MAIN PROBLEMS IN HYDRAULIC SYSTEM.

• a. Effects of overload burden
• b. Effects of flow rate exchanger
• c. Cavitation/Hollowing
• d. Leaking in the system
• e. Cylinder (actuator) problems

Effects of overload burden

• Most pumps are used below their maximum capacity to ensure durability.
• Overloading the electric motor that drives the pump causes it to overheat.
• It will affect the durability of the pump bearing

CALCULATION OF PUMP LIFESPAN

• A hydraulic pump is designed to work at 150 bar with life expectancy of 4800 hours. If the pump was often to run at 300 bar, that affected its bearing. So estimate the new lifespan of the pump for this situation.
• FORMULA’S:
  • $T1 = Jangka \ hayat \ lama \ (asal) \ pam$
  • $P1 = Had \ tekanan \ pam \ lama \ (asal) \ pam$
  • $T2 = Jangka \ hayat \ baharu \ pam$
  • $P2 = Tekanan \ baharu \ yang \ dikenakan \ pada \ pam$
  • $\frac{T<em>1}{T</em>2} = (\frac{P<em>2}{P</em>1})^3$

Contoh pengiraan Hayat Pam as above:

• As an example, if a pump is designed to pump at a pressure of 150 bar and has a bearing life of 4800 hours. If the pump is used to pump fluid with a pressure of 300 bar, it will affect the durability of the pump.

Effects of flow rate exchanger.

• Increasing the speed from the maximum pump speed will reduce the bearing life of the pump.
• Doubling the original pump speed from 2000 rpm to 4000 rpm will reduce the pump life by half from the original life.
• Solution: $T1 \cdot V1 = T2 \cdot V2$
  • Where:
    • $T1 = Jangka \ hayat \ lama \ (asal) \ pam$
    • $V1 = Kelajuan \ pam \ lama \ (asal) \ pam$
    • $T2 = Jangka\ hayat \ baharu \ pam$
    • $V2 = Kelajuan \ baharu \ pam$

Cavitations/Hollowing

• DEFINITION: An unwanted condition that occurs in hydraulic pumps due to excess air in the pump.
• Cavitations occurs:
  • When the suction is greater than the pressure levels, which causes air bubbles to collapse at the outlet.
  • This eroding of material is caused by local pressure peaks and high temperatures
  • Motion energy (pressure energy) is required for an increase in flow velocity of oil at a narrowing.
  • Because of this, pressure drops at narrow point may move into the vacuum range.
  • Then bubbles are formed.
• Affects: pressure drops, noise, vibration, temperature rise.

Leaking in the system

• Hydraulic fluid leakage occurs:
  • Internal:
    • Reduces system efficiency and
    • Generates heat
  • External:
    • Dirty
    • Damages components
    • Costly due to fluid loss and reduced performance.

Other problems

Masalah Yang Berlaku Pada Silinder

1. External Leakage
   • Oil comes out through the wiper.
2. Internal Leakage
   • Oil flows through the gap between the piston and cylinder when pressure is applied.
3. ‘Creeping’
   • When pressure is applied, the piston will return to its original state. This is also due to internal leaks. Creeping occurs on 2-action cylinders.
4. ‘Sluggish’
   • Caused by air in the cylinder. Air can be compressed, so sluggish will occur. The use of inappropriate viscosity will also cause this 'sluggishness'.

Hydraulic fluids

An ideal fluid would have these characteristics

1. Thermal stability
2. Hydrolytic stability
3. Low chemical corrosiveness
4. High anti-wear characteristics
5. Low tendency to cavitate
6. Long life
7. Total water rejection
8. Constant viscosity, regardless of temperature, and
9. Low cost.

Influential factors

• Each of the following factors influences hydraulic fluid performance:
  • Viscosity
    • Maximum and minimum operating temperatures, along with the system's load, determine the fluid's viscosity requirements.
    • The fluid must maintain a minimum viscosity at the highest operating temperature.
    • However, the hydraulic fluid must not be so viscous at low temperature that it cannot be pumped.
  • Foaming
    • When foam is carried by a fluid, it degrades system performance and therefore should be eliminated. Foam usually can be prevented by eliminating air leaks within the system.
  • Corrosion
    • Two potential corrosion problems must be considered: system rusting and acidic chemical corrosion. System rusting occurs when water carried by the fluid attacks ferrous metal parts.
  • Oxidation and thermal stability
    • Over time, fluids oxidize and form acids, sludge, and varnish. Acids can attack system parts, particularly soft metals. Extended high-temperature operation and thermal cycling also encourage the formation of fluid decomposition products.

Cont. Influential factors

• Each of the following factors influences hydraulic fluid performance:
  • Seal compatibility
    • In most systems, seals are selected so that when they encounter the fluid they will not change size or they will expand only slightly, thus ensuring tight fits. The fluid selected should be checked to be sure that the fluid and seal materials are compatible, so the fluid will not interfere with proper seal operation.
  • Fluid life, disposability
    • There are two other important considerations that do not directly relate to fluid performance in the hydraulic system, but have a great influence on total cost. They are fluid life and disposability.
  • Fire-resistant fluids
    • The overwhelming majority of hydraulic components and systems are designed to use oil-based hydraulic fluids. No wonder; these fluids rarely present significant operating, safety, or maintenance problems. Unfortunately, there are circumstances where using oil-based fluid should be avoided. One common fluid power application is in an environment with potential ignition sources - an open flame, sparks, or hot metal. In these environments, a leak spraying from a high-pressure hydraulic system could cause a serious fire and result in major property damage, personnel injury, or even death.

Masalah Disebabkan Oleh Bendalir

1. Synthetic-based fluids are classified as chemical compounds that can cause damage to oil seals made of natural rubber. It causes the natural rubber to become soft and expand.
2. Water-based fluids are fire resistant because when the fluid is touched by a source of ignition the steam released from the water will separate air from some of the flammable lubricant and also separate the lubricant from the hot surface thereby preventing fire. Disadvantages of water and oil based fluids
   • Easy to rust in parts of the system made of iron.
   • Causes wear on shafts, cylinders and other components due to lack of lubrication.
   • May freeze in cold weather areas.

(Samb. )Masalah Disebabkan Oleh Bendalir

3. Mineral oil (petroleum based)
   • Mineral oil may be the most widely used oil as a hydraulic fluid.
   • This oil is relatively cheap, easily available and can be obtained with various viscosity grades as appropriate.
   • As long as the reasonable operating temperature (40% C for optimum fluid life), mineral oil is stable.
   • At higher temperatures the oil undergoes chemical destruction, with the formation of acids, varnishes, resins and sludge causing the oil to lose its lubricating properties.