tailieunhanh - Mechanical Science HandbooksMechanical Science Handbooks 20000 Part 8

Tham khảo tài liệu 'mechanical science handbooksmechanical science handbooks 20000 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | HYDRAULICS DOE-HDBK-1018 2-93 Miscellaneous Mechanical Components HYDRAULICS Many machines and processes use a fluid for developing a force to move or hold an object or to control an action. The term hydraulic refers to a liquid. A number offluids can be used for developing the force. In a hydraulic system oil water or other liquids can be used. Oil is the most common. EO Given the appropriate information CALCULATE the pressure or force achieved in a hydraulic piston. EO DESCRIBE the basic operation of a hydraulic system. Introduction Although any liquid can be used in a hydraulic system some liquids have advantages over others. Oil is a liquid often preferred as the working fluid. Oil helps to lubricate the various sliding parts prevents rust and is readily available. For practical purposes oil does not change its volume in the hydraulic system when the pressure is changed. Pressure and Force The foundation of modern hydraulic powered systems was established when a scientist named Blaise Pascal discovered that pressure in a fluid acts equally in all directions. This concept is known as Pascal s Law. The application of Pascal s Law requires the understanding of the relationship between force and pressure. Force may be defined as a push or pull exerted against the total area of a surface. It is expressed in pounds. Pressure is the amount of force on a unit area of the surface. That is pressure is the force acting upon one square inch of a surface. The relationship between pressure and force is expressed mathematically. F P x A where F force in lbf P pressure in lbf psi A area in ME-05 Page 10 Rev. 0 Miscellaneous Mechanical Components DOE-HDBK-1018 2-93 HYDRAULICS Example 1 In a hydraulic system the oil pressure at the inlet to the cylinder is 1500 psi and the area of the piston over which the oil pressure acts is two square inches. Calculate the force exerted on the piston. Solution Since F P x A the force of the oil on the piston is calculated as