Hydraulic systems operation

Maintaining hydraulic fluid within allowable contamination limits for both water and particulate matter is cmcial to the care and protection of hydraulic equipment. Filters will provide adequate control of the particular contamination problem during all normal hydraulic system operations if the filtration system is installed properly and filter maintenance is performed properly. Filter maintenance includes changing elements at proper intervals. 

HM Highly refined mineral oils with 32 Hydraulic systems Operation of general hydraulic May also be used for the... 

Several classes of synthetic oils, such as phosphoric acid esters, polyglycols and silicones, are used as hydraulic lubricants. They are mostly used as fire-resistant lubricants, of importance for coal mines, steel mills and foundries, especially when hydraulic systems operate close to hot areas, e.g. furnaces. Polychlorinated biphenyls, PCBs, are the most fire resistant but are no longer used because of their high and persistent toxicity. Silicones have very poor lubricity and are very expensive, whereas polyglycols with high flash points do not fiilly meet more stringent fire-resistant requirements. At present, therefore, synthetic hydraulic lubricants are almost exclusively based on trialkyl or triaryl phosphates, or their mixtures, available with a wide range of viscosities and adequate low-temperature properties required for hydraulic lubricants. 

Line Pressure. The pressure under which an air or hydraulic system operates. 

Earlier industrial hydraulic systems operated at pressures of 100 bar or less, and usually performed satisfactorily with minimal attention to filtering. Often a simple strainer on the pump discharge, or a filter with a cut-off of 25 to 50 pm, provided adequate protection. Some systems, in fact, dispensed with a filter entirely, instead withdrawing oil periodically for batch filtration and return to the system. 

Modern subsea trees, manifolds, (EH), etc., are commonly controlled via a complex Electro-Hydraulic System. Electricity is used to power the control system and to allow for communication or command signalling between surface and subsea. Signals sent back to surface will include, for example, subsea valve status and pressure/ temperature sensor outputs. Hydraulics are used to operate valves on the subsea facilities (e.g. subsea tree and manifold valves). The majority of the subsea valves are operated by hydraulically powered actuator units mounted on the valve bodies. 

Hydrostatic drives allow for selection of any travel speed up to the maximum without a concurrent variance in engine speed. The engine can be operated at the governed speed to provide proper operating speeds for auxiliary elements, eg, the threshing section of a combine. A frill range of travel speeds is available to adjust to terrain or crop conditions. Industrial applications for hydraulic systems and hydrostatic transmissions include the following (16) ... 

In nearly all mechanical power applications in the oil and gas industry it is necessary to transmit the power generated by a prime mover to an operation (e.g., drawworks of a drilling rig, or a production pumping system). The transmission of rotary power to such operation elements is carried out by a power transmission system. Mechanical power transmission is typically carried out by power betting systems, chain systems, gear systems and by hydraulic systems, or some combination of these three [1,5]. 

To minimize the loss of useable energy lost to its conversion to heat energy, care must be taken in the design, installation and operation of hydraulic system. As a minimum the following factors must be considered ... 

Fluid flow is also critical for proper operation of a hydraulic system. Turbulent flow should be avoided as much as possible. Clean, smooth pipe or tubing should be used to provide laminar flow and the lowest friction possible within the system. Sharp, close radius bends and sudden changes in cross-sectional area are avoided. 

Hydraulic fluid contamination may be described as any foreign material or substance whose presence in the fluid is capable of adversely affecting system performance or reliability. It may assume many different forms, including liquids, gases, and solid matter of various composition, sizes, and shapes. Solid matter is the type most often found in hydraulic systems and is generally referred to as particulate contamination. Contamination is always present to some degree, even in new, unused fluid, but must be kept below a level that will adversely affect system operation. Hydraulic contamination control consists of requirements, techniques, and practices necessary to minimize and control fluid contamination. 

Water Water is a serious contaminant of hydraulic systems. Hydraulic fluids are adversely affected by dissolved, emulsified, or free water. Water contamination may result in the formation of ice, which impedes the operation of valves, actuators, and other moving parts. Water can also cause the formation of oxidation products and corrosion of metallic surfaces. 

Chlorinated solvents, when allowed to combine with minute amounts of water often found in operating hydraulic systems, change chemically into hydrochloric acids. These acids then attack internal metallic surfaces in the system, particularly those that are ferrous, and produce a severe rust-like corrosion. 

The condition of a hydraulic system, as well as its probable future performance, can best be determined by analyzing the operating fluid. Of particular interest are any changes in the physical and chemical properties of the fluid and excessive particulate or water contamination, either of which indicates impending trouble. 

All samples should be taken from circulating systems, or immediately upon shutdown, while the hydraulic fluid is within 5°C(9°F) of normal system operating temperature. Systems not up to temperature may provide non-representative samples of system dirt and water content, and such samples should either be avoided or so indicated on the analysis report. The first oil coming from the sampling point should be discarded, since it can be very dirty and does not represent the system. As a mle, a volume of oil equivalent to one to two times the volume of oil contained in the sampling line and valve should be drained before the sample is taken. 

A hydraulic system must have a reserve of fluid in addition to that contained in the pumps, actuators, pipes and other components of the system. This reserve fluid must be readily available to make up losses of fluid from the system, to make up for compression of fluid under pressure, and to compensate for the loss of volume as the fluid cools. This extra fluid is contained in a tank usually called a reservoir. A reservoir may sometimes be referred to as a sump tank, service tank, operating tank, supply tank or base tank. 

Clean hydraulic fluid is essential for proper operation and acceptable component life in all hydraulic systems. While every effort must be made to prevent contaminants from entering the system, contaminants that do find their way into the system must be removed. Filtration devices are installed at key points in fluid power systems to remove the contaminants that enter the system along with those that are generated during normal operations of the system. 

A valve is defined as any device by which the flow of fluid may be started, stopped, regulated or directed by a movable part that opens or obstmcts passage of the fluid. Valves must be able to accurately control fluid flow, system pressure and to sequence the operation of all actuators within a hydraulic system. 

The wide application of hydraulic systems has undoubtedly been stimulated by the increasing use of fully automatic controls for sequences of operations where the response to signals must be rapid and the controls themselves light and easily operated. These needs are met by hydraulic circuits that, in addition, provide infinitely variable speed control, reversal of high-speed parts without shock, full protection against damage from overhead and automatic lubrication. 

Over the years the performance standards of hydraulic equipment have risen. Whereas a pressure of about 1000 psi used to be adequate for industrial hydraulic systems, nowadays systems operating with pressures of 2000-3500psi are common. Pressures above 5000psi are to be found in applications such as large presses for which suitable high-pressure pumps have been developed. Additionally, systems have to provide increased power densities, more accurate response, better reliability and increased safety. Their use in numerically controlled machine tools and other advanced control systems creates the need for enhanced filtration. Full flow filters as fine as 1-10 micron retention capabilities are now to be found in many hydraulic systems. 

Operational behavior in hydraulic systems (lubrication performance, temperature range and seal compatibility, for example) ... 

The use of hydraulic systems for the setting, operation and control of machine tools has increased significantly. Hydraulic mechanisms being inter-linked with electronic controls and/or feedback control systems. In machine tools, hydraulic systems have the advantage of providing stepless and vibration-less transfer of power. They are particularly suitable for the linear movement of tables and slideways, to which a hydraulic piston may be directly coupled. 

The third class of hydraulic fluids discussed in this profile is the polyalphaolefins. Polyalphaolefins are synthetic hydrocarbons that are made by oligomerizing alphaolefins such as 1-decene (see Chapters 3,4, and 5). Aliphatic hydrocarbons are the principal components of both mineral oils and polyalphaolefins, but the array of hydrocarbons with differing molecular weights is much narrower in polyalphaolefins than in mineral oils. Certain polyalphaolefins maintain good operational characteristics at low temperatures and have been proposed for use in hydraulic systems in U.S. military aircraft (Kinkead et al. 1992b). 

Mineral Oil Hydraulic Fluids. Populations with potentially high exposures to mineral oil hydraulic fluids include all occupations that maintain hydraulic equipment including automobile, truck, and tractor mechanics, mechanics employed by heavy industry and mining operations to repair and maintain hydraulic equipment, and other maintenance workers involved with the repair and maintenance of hydraulic systems. The number of workers with potentially high exposures to mineral oil hydraulic fluids is expected to be very large. 

Other common uses include gaskets and seals for hydraulic systems in harsh environments, such as mining operations, where abrasion is a constant hazard. We take advantage of the... 

The pressure is measured by means of a hydraulic system, either in one reference vessel of the 16-vessel rotor or simultaneously for all vessels of the 8-vessel rotor. The operational limit is 86 bar, sufficient for synthetic applications. In addition, a pressure rate limit is set to 3.0 bar s 1 by the control software provided. Protection against sudden pressure peaks is provided by metal safety disks incorporated into the vessel caps (safety limits of 70 bar or 120 bar, respectively) and by software regulations, depending on the rotor used and the vessel type. 

Ideal designs have a depth between 0.6 and 1.5 M (Neculita et al. 2007) to reduce short circuiting. Vertical upflow is better than downflow (Tsukamoto et al. 2004). A hydraulic retention time of at least 3-5 days is optimal (Kuyucak et al. 2006). There are no reports on systems operating for extended periods (more than 3-4 years). Failures due to plugging, short circuits, and exhaustion of organic carbon are widely reported (Neculita et al. 2007). 

Mechanical and hydraulic systems for control of the knife are now used. The latter allows easy selection of the rate and direction of knife movement and the system is particularly suited to remote control or automatic operation. 

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