Introduction to Hydraulics Powerpoint.pptx

An introduction to the principles and applications of Hydraulics

1. Principles of Pressure Don’t assume the the science of hydraulics encompasses any devise operated by water just because the term hydraulics is derived from the Greek word for water.

2. Principles of Pressure

3. Principles of Pressure There’s a distinction between devices that use impact or momentum of a moving liquid and those that use the pushing on a confined fluid or in other words, pressure.

4. Principles of Pressure A hydraulic device which uses the impact or kinetic energy in the liquid to transmit power is called a hydrodynamic device. When the device is operated by a force applied to a confined liquid, it is called a hydrostatic device.

5. Principles of Pressure We will only focus on hydrostatic systems and equipment.

6. How Pressure is Created Pressure results whenever there is a resistance to fluid flow or to a force which attempts to make the fluid flow. May be flowing with a pump or gravity.

7. How Pressure is Created Around the time of Pascal, Torricelli proved that if a hole is made in the bottom of a tank of water, the ater runs out fastest when the tank is full and flow rate decreases as the water level lowers. As the “head” of water above lessens, so does the pressure.

8. How Pressure is Created In water pressure increases with depth. Pressure is equal at a particular depth due to the weight of the water above it.

9. How Pressure is Created Around the time of Pascal, Torricelli proved that if a hole is made in the bottom of a tank of water, the ater runs out fastest when the tank is full and flow rate decreases as the water level lowers. As the “head” of water above lessens, so does the pressure.

10. How Pressure is Created Torricelli expressed the pressure at the bottom of the tank as “feet of head” or height of the water column. Today we use psi. We can can calculate pressure if we know how much a cubic foot of liquid weighs.

11. How Pressure is Created

12. How Pressure is Created The term “head” is still used to describe pressure, no matter how it is created. Boilers still “work up a head of steam” when pressure is created by vaporing water in comfinement.

13. Atmospheric Pressure Atmospheric pressure is the pressure of the air in our atmosphere due to its weight. At sea level, a column of air one square inch weighs 14.7 pounds. Thus the pressure is 14.7 psia. At higher altitudes the pressure is less. Why? What happens at lower altitudes?

14. Atmospheric Pressure

15. Atmospheric Pressure Any condition where pressure is less than atmospheric pressure is called a vacumn or partial vacumn. A perfect vacumn is the complete absence of pressure or zero psia.

16. The Mercury Barometer Atmosheric pressure is also measured in inches of mercury (in. Hg) on a device known as a barometer. Toricelli invented the mercury barometer and it was the barometer that got Pascal thinking about pressure.

17. Atmospheric Pressure Torricelli filled a tube with mercury, inverted it, and noticed that the column in the tube fell a certain distance. He reasoned that atmospheric pressure on the surface of the liquid was supporting the weight of the column of mercury with a perfect vacumn at the top of the tube.

18. Atmospheric Pressure

19. Newcomer’s Engine http://en.wikipedia.org/wiki/Newcomen_steam_engine

20. Measuring Vacuum Since vacuum is below atmospheric, use the same units, psi or psia, or as inches of mercury. Most vacuum gages are calibrated in inches of mercury. A perfect vacuum, which will support a column of mercury 29.92 inches high is stated as 29.92 in. Hg.

21. Measuring Vacuum Zero vacuum reads zero on a vacuum gage. Where in maintnance would we use a vacuum gage? What reading would we expect?

22. Summary of Pressure and Vacuum Scales

23. Summary of Pressure and Vacuum Scales An atmoshpere is a pressure unit equal to 14.7 psi. Psia (pounds per square inch absolute) is a scale which starts at perfect vacuum (0.0 psia). Atmospheric pressure at sea level is 14.7 psia on this scale.

24. Summary of Pressure and Vacuum Scales Psi (pounds per square inch gauge) is calibrated in the same units as psia but ignores atmospheric pressure. Gauge pressure may be abbreviated psig. To convert psia to psig: Gauge Pressure + 14.7 = Absolute Pressure Absolute Pressure -14.7 = Gauge Pressure

25. Summary of Pressure and Vacuum Scales Atmospheric pressure on the barometer scale is 29.92 in. Hg. Comparing this to the psia scale, it is evident that: 1 psi = 2 in. Hg (approximately) 1 in. Hg = 0.5 psi (approximately)

26. Summary of Pressure and Vacuum Scales An atmosphere is equivalent to approximately 34 ft. of water or 37 ft. of oil. Why the difference?

27. How Flow is Measured Flow is the action in the hydraulic system that gives the actuator its motion. Pressure gives the actuator its force, but flow is essential to cause movement. Why? Pumps create flow in the hydraulic system.

28. How Flow is Measured Two ways to measure flow. Velocity is the average speed of the fluid’s particles past a given point or the average distance th particles travel per unit of time. Usually, measured in feet per second (fps), feet per minute (fpm), on inches per second (ips).

29. How Flow is Measured Two ways to measure flow. Flow rate is a measure of the volume of fluid passing a point in a given time. Large volumes are measured in gallons per minute (GPM). Small volumes are measured in cubic inches per minute.

30. Difference between Velocity and Flow Rate A constant flow of one gallon per minute either increases or decreases in velocity when the cross section of the pipe changes size.

31. Flow Rate and Speed Speed of an actuator always depends on the actuator’s size and the rate of flow into it. 1 GPM = 231 in 3 /minute

32. Flow Rate and Speed Remember this?

33. Flow and Pressure Drop

34. Flow and Pressure Drop This difference in pressure or pressure drop is required to overcome friction in the line.

35. Flow and Pressure Drop

36. Fluid Seeks a Level When there is no pressure difference on a liquid, it simply seeks a level.

37. Fluid Seeks a Level

38. Fluid Seeks a Level

39. Fluid Seeks a Level In circuit design, the required pressure must include the pressure needed to overcome friction and gravity. Good designs can minimize these “drops” to the point where they become almost negligible.

40. Laminar and Turbulent Flow Ideally, when particles move through a pipe, they move in straight, parallel flow paths. This is called laminar flow and occurs at low velocity in straight piping. Friction is minimized.

41. Laminar and Turbulent Flow

42. Laminar and Turbulent Flow Turbulence is when particles do not move smoothly parallel to the flow direction. Turbulence is caused by abrupt changes in direction, cross section, or by too high velocity. The result is greatly increased friction, which generates heat, increases operating pressure, and wates power.

43. Laminar and Turbulent Flow

44. Laminar and Turbulent Flow Let’s talk about drafting behind a truck.

45. Bernoulli’s Principle A working hydraulic system has two forms of energy. Kinetic: the fluid’s weight and velocity Potential: pressure

46. Bernoulli’s Principle Daniel Bernoulli, a Swiss scientist, showed that in a system with a constant flow rate, energy is transformed from one form to the other each time the pipe cross section size changes.

47. Bernoulli’s Principle Why is this the smallest reading?

48. Bernoulli’s Principle A venturi in an engine carboretor uses the Bernoulli’s Principle.

49. Bernoulli’s Principle

50. Bernoulli’s Principle Bernoulli’s Principle is and important factor n the design of spool-type hydraulic valves. Fluid velocity is always changing. If the maximum flow rate of the valve is exceeded, preesure changes as a result of Bernoulli’s Principle can produce unbalanced axial forces in the valve and could overpower the valve’s actuator and the valve will malfuntion.

51. Bernoulli’s Principle

52. Hydraulic Symbols Hydraulic circuits and their components are depicted in various ways in drawings. Three types: Pictorial representation of the components’ exteriors. A cutaway showing internal construction A graphic diagram which shows function Combination of any of the three

53. Hydraulic Symbols In industry graphic symbols and diagram are most common. We’ll cover the basic symbols. Ask for a handout here.

54. Lines Hydraulic pipes, tubes, and fluid passages are drawn as single lines. Three basic types: Working line (solid) carries the main stream of flow in the system. Pilot or sensing line (long dashes) carries fluid that is used to control the operation of a valve or other component. Drain lines (short dashes) carries leakage oil back to the reservoir.

55. Lines

56. Rotating Components A circle is the basic symbol for ratating components. Energy triangles are placed in the symbols to show them as energy supplies (pumps) or energy receivers (motors). If it is unidirectional, there is only one triangle. Reversible components have two triangles.

57. Rotating Components

58. Rotating Components

59. Rotating Components

60. Rotating Components

61. Cylinders

62. Valves Infinite positioning pressure and flow valves. Finite positioning directional control valves.

63. Valves

64. Valves

65. Valves

66. Reservoir Tank Several symbols can be drawn for one tank to avoid a confussing mess of lines. Vented or unvented.

67. Reservoir Tank