POWER POINT PRESENTATION FOR H&P

POWER POINT PRESENTATION FOR H&P By; 1JT12ME058

Objectives • Explain fundamental hydraulic principles. • Apply the laws of hydraulics. • Calculate force, pressure, and area. • Describe the function of pumps, valves, actuators, and motors. • Describe the construction of hydraulic conductors and couplers.

Hydraulics • The term hydraulics is used to specifically describe fluid power circuits that use liquids—especially formulated oils—in confined circuits to transmit force or motion. • Hydraulic circuits: • Hydraulic brakes • Power steering systems • Automatic transmissions • Fuel systems • Wet-line kits for dump trucks • Torque converters • Lift gates

Pascal’s Law • Pressure applied to a confined liquid is transmitted undiminished in all directions and acts with equal force on all equal areas, at right angles to those areas.

Fundamentals • Hydrostatics is the science of transmitting force by pushing on a confined liquid. • In a hydrostatic system, transfer of energy takes place because a confined liquid is subject to pressure. • Hydrodynamics is the science of moving liquids to transmit energy. • We can define hydrostatics and hydrodynamics as follows: • Hydrostatics: low fluid movement with high system pressures • Hydrodynamics: high fluid velocity with lower system pressures

Atmospheric Pressure • A column of air measuring 1 square inch extending 50 miles into the sky would weigh 14.7 pounds at sea level. • If we stood on a high mountain, the column of air would measure less than 50 miles and the result would be a lower weight of air in the column. • Similarly, if we were below sea level, in a mine for instance, the weight of air would be greater in the column. • In North America, we sometimes use the term atm (short for atmosphere) to describe a unit of measurement of atmospheric pressure. • Europeans use the unit bar (short for barometric pressure).

Force • Force is push or pull effort. • The weight of one object placed upon another exerts force on it proportional to its weight. • If the objects were glued to each other and we lifted the upper one, a pull force would be exerted by the lower object proportional to its weight. • Force does not always result in any work done. • If you were to push on the rear of a parked transport truck, you could apply a lot of force, but that effort would be unlikely to result in any movement of the truck. • The formula for force (F) is calculated by multiplying pressure (P) by the area (A) it acts on. • F = P x A

Pressure Scales • There are a number of different pressure scales used today but all are based on atmospheric pressure. One unit of atmosphere is the equivalent of atmospheric pressure and it can be expressed in all these ways: • 1 atm = 1 bar (European) = 14.7 psia = 29.920 Hg (inches of mercury) = 101.3 kPa (metric) • However, each of the above values is not precisely equivalent to the others: 1atm = 1.0192 bar 1 bar = 29.530 Hg = 14.503 psia 10 Hg = 13.60 H2O @ 60° F

Torricelli’s Tube • Evangelista Torricelli (1608–1647) discovered the concept of atmospheric pressure. • He inverted a tube filled with mercury into a bowl of the liquid and then observed that the column of mercury in the tube fell until atmospheric pressure acting on the surface balanced against the vacuum created in the tube. • At sea level, vacuum in the column in Torricelli’s tube would support 29.92 inches of mercury.

Manometer • A manometer is a single tube arranged in a U-shape used to measure very small pressure values. • It may be filled to the zero on the calibration scale with either water H2O) or mercury (Hg), depending on the pressure range desired. • A manometer can measure either push or pull on the fluid column. Examples: • Crankcase pressure • Exhaust backpressure • Air inlet restriction

Absolute Pressure • Absolute pressure uses a scale in which the zero point is a complete absence of pressure. • Gauge pressure has as its zero point atmospheric pressure. • A gauge therefore reads zero when exposed to the atmosphere. • To avoid confusing absolute pressure with gauge pressure • Absolute pressure is expressed as: psia. • Gauge pressure is usually expressed as: psi or psig.

Hydraulic Levers (1 of 2) • Hydraulic levers can be used to demonstrate Pascal’s law: • Pressure equals force divided by the sectional area on which it acts. • (P=F\A) • Force equals pressure multiplied by area. • ( F = P x A)

Hydraulic Levers (2 of 2) • One of the cylinders has a sectional area of 1sq.” and the other 50 sq.” • Applying a force of 2 lbs. on the piston in the smaller cylinder would lift a weight of 100 lbs. • Applying a force of 2 lbs. on the piston in the smaller cylinder produces a circuit pressure of 2 psi. • The circuit potential is 2 psi and because this acts on a sectional area of 50 sq.”, it can raise 100 lbs. • If a force of 10 lbs. was to be applied to the smaller piston, the resulting circuit pressure would be 10 psi and the circuit would have the potential to raise a weight of 500 lbs.

Flow • Flow is the term we use to describe the movement of a hydraulic fluid through a circuit. • Flow occurs when there is a difference in pressure between two points. • In a hydraulic circuit, flow is created by a device such as a pump. • A pump exerts push effort on a fluid. • Flow rate is the volume or mass of fluid passing through a conductor over a given unit of time. • An example would be gallons per minute (gpm).

Flow Rate and Cylinder Speed • Given an equal flow rate, a small cylinder will move faster than a larger cylinder. If the objective is to increase the speed at which a load moves, then: • Decrease the size (sectional area) of the cylinder. • Increase the flow to the cylinder (gpm). • The opposite would also be true, so if the objective were to slow the speed at which a load moves, then: • Increase the size (sectional area) of the cylinder. • Decrease the flow to the cylinder (gpm). • Therefore, the speed of a cylinder is proportional to the flow to which it is subject and inversely proportional to the piston area.

Pressure Drop • In a confined hydraulic circuit, whenever there is flow, a pressure drop results. • Again, the opposite applies. Whenever there is a difference in pressure, there must be flow. • Should the pressure difference be too great to establish equilibrium, there would be continuous flow. • In a flowing hydraulic circuit, pressure is always highest upstream and lowest downstream. This is why we use the term pressure drop. • A pressure drop always occurs downstream from a restriction in a circuit.

Flow Restrictions • Pressure drop will occur whenever there is a restriction to flow. • A restriction in a circuit may be unintended (such as a collapsed line) or intended (such as a restrictive orifice). • The smaller the line or passage through which the hydraulic fluid is forced, the greater the pressure drop. • The energy lost due to a pressure drop is converted to heat energy.

Work • Work occurs when effort or force produces an observable result. • In a hydraulic circuit, this means moving a load. • To produce work in a hydraulic circuit, there must be flow. • Work is measured in units of force multiplied by distance, for example, in pound-feet. • Work = Force x Distance

Bernoulli’s Principle (1 of 2) • Bernoulli’s Principle states that if flow in a circuit is constant, then the sum of the pressure and kinetic energy must also be constant. • Pressure x Velocity IN = Pressure x Velocity OUT • When fluid is forced through areas of different diameters, fluid velocity changes accordingly. • For example, fluid flow through a large pipe will be slow until the large pipe reduces to a smaller pipe; then the fluid velocity will increase.

Bernoulli’s Principle (2 of 2)

Laminar Flow • Flow of a hydraulic medium through a circuit should be as streamlined as possible. • Streamlined flow is known as laminar flow. • Laminar flow is required to minimize friction. • Changes in section, sharp turns, and high flow speeds can cause turbulence and cross-currents in a hydraulic circuit, resulting in friction losses and pressure drops.

Types of Hydraulic Systems • Hydraulic systems can be grouped into two main categories: • Open-center systems • Closed-center systems • The primary difference between open-center and closed-center systems has to do with what happens to the hydraulic oil in the circuit after it leaves the pump.

Open-center Systems • In an open-center system, the pump runs constantly and oil circulates within the system continuously. • An open-center valve manages flow through the circuit. When this valve is in its neutral position, fluid returns to the reservoir. • An example of an open-center hydraulic system on a truck is power-assisted steering.

Closed-center Systems • In a closed-center system, the pump can be “rested” during operation whenever flow is not required to operate an actuator. • The control valve blocks flow from the pump when it is in its “closed” or neutral position. • A closed-center system requires the use of either a variable displacement pump or proportioning control valves. • Closed-center systems have many uses on agricultural and industrial equipment, but on trucks, they would be used on garbage packers and front bucket forks.

Calculating Force • In hydraulics, force is the product of pressure multiplied by area. • Force = Pressure x Area • For instance, if a fluid pressure of 100 psi acts on a piston sectional area of 50 square inches it means that 100 pounds of pressure acts on each square inch of the total sectional area of the piston. The linear force in this example can be calculated as follows: • Force = 100 psi x 50 sq. in. = 5000 lbs.

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POWER POINT PRESENTATION FOR H&P