Fluid power pressure

Applied pressures selected from ISO 2944 Fluid Power Systems - nominal pressures. 

Fluid power encompasses most applications that use liquids or gases to transmit power in the form of mechanical work, pressure and/or volume in a system. This definition includes all systems that rely on pumps or compressors to transmit specific volumes and pressures of liquids or gases within a closed system. The complexity of these systems range from a simple centrifugal pump used to remove casual water from a basement to complex airplane control systems that rely on high-pressure hydraulic systems. 

If a fluid power system is properly designed and used, it will provide smooth, flexible, uniform action without vibration, and is unaffected by variation of load. In case of an overload, an automatic release of pressure can be guaranteed, so that the system is protected against breakdown or excessive strain. Fluid power systems can provide widely variable motions in both rotary and linear transmission of power and the need for manual control can be minimized. In addition, fluid power systems are economical to operate. 

The terms force and pressure are used extensively in the study of fluid power. It is essential that we distinguish between these terms. Force is the total pressure applied to or generated by a system. It is the total pressure exerted against the total area of a particular surface and is expressed in pounds or grams. 

A formula is used in computing force, pressure, and area in fluid power systems. In this formula, P refers to pressure F indicates force, and A represents area. Force equals pressure times area. Thus, the formula is written ... 

Fluid power equipment is designed to reduce friction as much as possible. Since energy cannot be destroyed, some of the energy created by both static pressure and velocity is converted to heat energy as the fluid flows through the piping and components within a hydraulic system. As friction increases, so does the amount of dynamic and static energy that is converted into heat. 

If we change the applied force and place a 200-pound force on the output piston. Figure 40.12, making it the input piston, the output force on the input piston will be one-tenth the input force, or 20 pounds. Therefore, if two pistons are used in a fluid power system, the force acting on each piston is directly proportional to its area, and the magnitude of each force is the product of the pressure and the area of each piston. 

Selection and care of the hydraulic fluid for a machine will have an important effect on how it performs and on the life of the hydraulic components. During the design of equipment that requires fluid power, many factors are considered in selecting the type of system to be used-hydraulic, pneumatic, or a combination of the two. Some of the factors required are speed and accuracy of operation, surrounding atmospheric conditions, economic conditions, availability of replacement fluid, required pressure level, operating temperature range, contamination possibilities, cost of transmission lines, limitations of the equipment, lubricity, safety to the operators, and expected service life of the equipment. 

Although most fluid power motors are capable of providing rotary motion in either direction, some applications require rotation in only one direction. In these applications, one port of the motor is connected to the system pressure line and the other port to the return line. The flow of fluid to the motor is controlled by a flow control valve, a two-way directional control valve or by starting and stopping the power supply. Varying the rate of fluid flow to the motor may control the speed of the motor. 

It is impossible to design a practical fluid power system without some means of controlling the volume and pressure of the fluid, and directing that flow to the proper operating units. This is accomplished by the inclusion of control valves in the hydraulic circuit. 

Flow control valves are used to regulate the flow of fluids. Control of flow in hydraulic systems is critical because the rate of movement of fluid-powered machines or actuators depends on the rate of flow of the pressurized fluid. 

The safe and efficient operation of fluid power systems, system components and related equipment requires a means to control pressure within the system. There are many types of automatic pressure control valves. Some of them merely provide an escape for excess pressures some only reduce the pressure and some keep the pressure within a pre-set range. 

Some fluid power systems, even when operated normally, may temporarily develop excessive pressure. For example, when an unusually strong work resistance is encountered, system pressure may exceed design limits. Relief valves are used to control this excess pressure. 

Pressure regulators, often referred to as unloading valves, are used in fluid power systems to regulate pressure. In hydraulic systems, the pressure regulator is used to unload the pump and to maintain or regulate system pressure at the desired values. 

Three types of lines are used in fluid power systems pipe (rigid), tubing (semi-rigid), and hoses (flexible). A number of factors are considered when the type of line is selected for a particular application. These factors include the type of fluid, the required system pressure, and the location of the system. For example, heavy pipe might be used for a large, stationary system, but comparatively lightweight tubing must be used in mobile applications. Flexible hose is required in installations where units must be free to move relative to each other. 

Threaded connectors There are several different types of threaded connectors. In the type discussed in this section, both the connector and the end of the fluid line are threaded. These connectors are used in some low-pressure fluid power systems and are usually made of steel, copper, and brass is available in a variety of designs. 

Welded Welded joints connect the subassemblies of some fluid power systems, especially in high-pressure systems that use pipe for fluid lines. The welding is done according to standard specifications that define the materials and techniques. 

Some fluid power systems are equipped with manifolds in the pressure supply and/or return lines. A manifold is a fluid conductor that provides multiple connection ports. Manifolds eliminate piping, reduce joints, which are often a source of leakage and conserve space. For example, manifolds may be used in systems that contain several... 

The amount needed for the ion-exchange and steam-generating building will be insignificant. Since we are dealing with pellets, not powders, no special hoods are needed The fluid power lequired to move air, assuming a pressure drop of 3 in H20, is 7.3 hp. Less than 7 kilowatts are required to power fans. 

Accumulator A vessel containing fluid stored under pressure which acts to serve as a source of fluid power. 

Thus, for Newtonian fluids, the pressurization capability of the optimized JMP is eight times that of the SMP, and for non-Newtonian fluids, the ratio exhibits a minimum at n = 0.801 and rises to 11.59 at it — 0.25 whereas, the flow rate at fixed pressure rise for Newtonian fluids is 81 2 — 2.83 times in JMP as compared to SMP, and for non-Newtonian fluids with n = 0.25 it rises to 7.25. Clearly, the JMP configuration is about an order of magnitude more efficient then the SMP one. Moreover, the specific power input in a JMP configuration for Newtonian fluids is one-half that of the SMP, and for n — 0.25, it is one-fifth the corresponding ratios for specific power dissipated into heat are, one-quarter and 1/25, respectively. 

The Strain Distribution Function of a Power Law Fluid, in Pressure Flow between Parallel Plates Consider two infinitely wide parallel plates of length L gap II. Polymer melt is continuously pumped in the x direction. Assuming isothermal steady, fully developed flow, (a) show that F(c) is given by... 

Some of the historical perspective is extracted (no pun intended) from a previous paper of the author ( 1 ) and is expanded with a chronological development of solubility phenomena based upon an additional compilation of recent work on naphthalene-supercritical solvent systems. The new data on flavor extraction and fractionation point out the most unique feature of supercritical fluid solvents, viz., their often-demonstrated selective dissolving power properties, a selectivity that is achieved because the dissolving power of supercritical fluids is pressure-dependent and can, therefore, be adjusted. 

Protection against overpressure is essential for the safe operation of fluid power and process plant. Automatic pressure-relief valves are commonly used for this purpose. They work on the principle of a force balance. When the valve is shut the hydrostatic force tending to open it varies linearly with system gauge pressure, and the return force tending to keep the valve closed is (very nearly) a constant. If system pressure is too high then the hydrostatic force will surmount the return force opening the valve and venting the system. 

---