Mechanical Advantage Calculation
Determine the mechanical advantage of the Automotive Lift Repair Tampa Florida system by calculating the pressure created in the fluid by the hand pump when a force of 10 lb is applied to the pump piston and the resultant force exerted by the fluid on the piston carrying the load.
Solution
Both pistons’ surfaces are oriented perpendicular to the movement direction. The pump piston has a radius of 0.5 inches, leading to an area of approximately 0.7854 square inches. The pressure from the piston is calculated as force divided by area, yielding a pressure of approximately 12.73 lb/in². This same pressure applies to the load-carrying piston, which has an area of 7.069 square inches. The overall force generated is pressure multiplied by area, resulting in approximately 90 lb. Ignoring frictional losses, this results in a ninefold increase in force, as the load piston’s radius is three times that of the pump piston, making the area proportional to the square of the radius.
Problem
If the diameter of the pump piston were only 0.1 inches, what would the mechanical advantage of the system be?
Example 2
Demonstrate that the work (force multiplied by distance) is equivalent for both pistons.
Solution
The following fundamental relationships apply:
1. Work = Force × Distance
2. Volume = Area × Distance
3. Pressure = Force/Area
4. The change in fluid volume is constant for both pistons.
5. Pressure remains constant across both pistons.
From (1), substitute force with pressure multiplied by area from (3) and substitute distance with volume divided by area from (2). The areas will cancel out, resulting in work = pressure × volume. Since pressure and volume are equal for each piston, the work must also be equal.
Flow Through an Orifice and Other Obstacles
A restriction in a line, such as an orifice or valve, causes a pressure gradient when fluid is in motion. When fluid is at rest, the pressure gradient across the restriction diminishes to zero, as fluid pressure remains constant according to Pascal’s law. When flow occurs through a restriction, useful mechanical energy is transformed into (unusable) heat energy. The heat produced is proportional to both the pressure gradient and flow rate. Notably, no flow occurs through a fully closed valve.
Essentially, any line acts as an orifice, resulting in a pressure drop across it and leading to energy loss. However, these energy losses can be minimized by using appropriately sized lines to prevent high flow velocities, avoiding sharp turns in flow, and following sound design principles.
Automotive Lift Repair Tampa Florida Hydraulic Jacks
The system described earlier is impractical due to its limited range of motion, requiring many pump operations to raise an object to a suitable height. A check valve facilitates flow in one direction only, allowing multiple handle operations to lift the load efficiently. This mechanism operates using a ball that seats against a seal.
Automotive Lift Repair Tampa Florida Hydraulic fluid serves multiple functions, primarily enabling power transmission by transferring forces from one location to another. It also lubricates internal surfaces, making cleanliness crucial; abrasive particles in the fluid can cause excessive wear on the system. Additionally, hydraulic fluid acts as a sealant and coolant. While these fluids can operate up to about 82°C (180°F), cooling is advisable for temperatures exceeding 70°C (160°F). Air coolers use tubing with metal fins to enhance surface area, while water coolers utilize cold water to absorb heat from the hydraulic fluid.
Key characteristics of hydraulic fluid include viscosity and the type and quantity of additives. Additives may include antiwear agents, corrosion inhibitors, and antioxidants. Viscosity is important for maintaining a thin layer of fluid on surfaces to minimize wear, with higher temperatures requiring more viscous fluids. The viscosity index indicates how viscosity changes with temperature; a higher index means less variation. The pour point is the lowest temperature at which the fluid flows freely.
Reservoirs
Automotive Lift Repair Tampa Florida Reservoirs (sump or tank) store a reserve of fluid and also help cool the oil and separate air and contaminants. Fluid can leak from systems, and the position of cylinders can change system volume. Reservoirs may be pressurized (maintained by air pressure) or vented to the atmosphere. Pressurized systems must be sealed, making them more resistant to contamination and condensation. A larger reservoir can aid in cooling the hydraulic fluid. Key components of reservoirs include a filler cap, fluid level gauge, outlet (to pump), inlet with a filter to remove harmful particles, drain plug (which may be magnetic to capture metal debris), inspection plate, and pressure regulator. Baffles can separate inlet and outlet flows for cooling and contaminant separation.
Reservoirs should be tall and narrow to create a fluid column above the pump inlet, reducing the risk of air entering the system and compromising efficiency, as air makes the fluid compressible.
Filters and Strainers
Automotive Lift Repair Tampa Florida Strainers are coarse filters designed to remove larger debris, while filters use a porous medium to eliminate insoluble solids from hydraulic fluid. Common porous materials include cotton, cloth, and resin-reinforced paper, with effective filters capable of removing solids of 10 μm diameter and larger. Filters with fine pores can create a pressure drop of up to 25 psi, so they should not be used at pump inlets to prevent cavitation. Strainers can be used cautiously at pump inlets if pressure drops are minimal. Some filters include automatic bypass valves that activate when the filter becomes clogged, allowing continued flow in the system. Color indicators may signal when bypass conditions occur.
Transfer of Hydraulic Fluid
Automotive Lift Repair Tampa Florida Hydraulic fluid moves through tubes represented as single lines in schematic diagrams. Solid lines indicate working lines carrying the bulk of the fluid, while pilot lines, used for control components, are shown with long dashes. Drain lines are depicted with short dashes and return leakage oil to the reservoir.
Automotive Lift Repair Tampa Florida Hydraulic fluid can be transported using pipes, tubing, or hoses. Pipes are typically made of non-stainless steel (galvanized steel should be avoided due to reactivity with some fluid additives) and are rigid, designed to remain unbent. The schedule number indicates wall thickness; actual thickness and pressure ratings depend on the nominal diameter. Common schedules include 40 (for low pressure), 80 (for high pressure), and 160 (for very high pressure). Larger inside diameters generally operate at lower pressures.