Accumulators, pressurized, hydraulic

Accumulators, pressurized, hydraulic, 2.2 Accumulators, pressurized, pneumatic, 2.2 Articles, pressurized, hydraulic, 2.2 Articles, pressurized, pneumatic, 2.2... 

Accumulated pressure has been bled from hydraulic drives. 

Blowout preventers are opened and closed by hydraulic fluid stored under a pressure of 3000 psi in an accumulator, often referred to as a Coomy unit. 

Water hammer (also known as hydraulic shock) occurs in two distinct ways when the flow of liquid in a pipeline is suddenly stopped, for example, by quickly closing a valve [13], and when slugs of liquid in a gas line are set into motion by movement of gas or condensation of vapor. The latter occurs when condensate is allowed to accumulate in a steam main, because the traps are too few or out of order or in the wrong place. High-pressure mains have been ruptured, as in the following incident. 

Most hydraulic systems have built-in sources of air. Leaky seals in gas-pressurized accumulators and reservoirs can feed gas into a system faster than it can be removed, even with the best of maintenance. Another lesser-known but major source of air is air that is sucked into the system past actuator piston rod seals. This occurs when the piston rod that is stroked by some external means while the actuator itself is not pressurized. 

An accumulator is a pressure storage reservoir in which hydraulic fluid is stored under pressure from an external source. The storage of fluid under pressure serves several purposes in hydraulic systems. 

In some hydraulic systems, it is necessary to maintain the system pressure within a specific pressure range for long periods. It is very difficult to maintain a closed system without some leakage, either external or internal. Even a small leak can cause a decrease in pressure. By using an accumulator, leakage can be compensated for and the system pressure can be maintained within acceptable range for extended periods. Accumulators also compensate for thermal expansion and contraction of the liquid due to variations in temperature or generated heat. 

Oedema refers to an accumulation of interstitial fluid to a point where it is palpable or visible. In general this point is reached with a fluid volume of 2-3 liters. Oedema formation is the result of a shift of fluid into the interstitial space due to primary disturbances in the hydraulic forces governing transcapillary fluid transport and of subsequent excessive fluid reabsorption by the kidneys. Deranged capillary hydraulic pressures initiate oedema formation in congestive heart failure, and liver cirrhosis whereas a deranged plasma oncotic pressure... 

Hydraulic pressure stimulation (fracturing) of oil and gas wells has now accumulated 40 years of history and experience. The actual practice and application of this technique supports a multi-billion dollar service industry which annually utilizes in excess of 130 million pounds of chemical additives. This chapter will describe the fracturing fluids that are used and some of the additives, their purpose, and the principles that make their use effective as well as necessary. Information presented will update a body of review literature that covers the prior years of fracturing(1). Chemicals are added for specific purposes which are identifiable by their descriptive title. Veatch02) has compiled a thorough general list of the additives added to fracturing fluids. 

In a typical fixed-bed carbon column, the column is similar to a pressure filter and has an inlet distributor, an underdrain system, and a surface wash. During the adsorption cycle, the influent flow enters through the inlet distributor at the top of the column, and the groundwater flows downward through the bed and exits through the underdrain system. The unit hydraulic flow rate is usually 2 to 5 gpm/ft2. When the head loss becomes excessive due to the accumulated suspended solids, the column is taken off-line and backwashed. 

Boundary layer formulation. Many membrane processes are operated in cross-flow mode, in which the pressurised process feed is circulated at high velocity parallel to the surface of the membrane, thus limiting the accumulation of solutes (or particles) on the membrane surface to a layer which is thin compared to the height of the filtration module [2]. The decline in permeate flux due to the hydraulic resistance of this concentrated layer can thus be limited. A boundary layer formulation of the convective diffusion equation can give predictions for concentration polarisation in cross-flow filtration and, therefore, predict the flux for different operating conditions. Interparticle force calculations are used in two ways in this approach. Firstly, they allow the direct calculation of the osmotic pressure at the membrane. This removes the need for difficult and extensive experi-... 

High pressure drop causes disruptions to the system hydraulics. Because of the high pressure drop, the lead membranes tend to operate at very high fluxes while the lag membranes operate at low flux. This increases the rate of membrane fouling for both the lead and lag membranes. Lead membranes foul faster because more water is forced to the membrane module faster and the rate of contaminant accumulation in the boundary layer on the membrane surface increases. The lag membranes, on the other hand, experience low flows since most of the water is removed through... 

Crestal pressures of GEA pre-Cretaceous hydrocarbon accumulations are also plotted. Most of these points lie within the envelope of LOT/FIT fracture pressures, apparently suggesting that hydrocarbons have been released as a result of hydraulic failure of... 

Figure 286. Phantom drawing of a modern roller press showing important design criteria such as self-aligning roller bearings, cooled rollers, multiple-screw feeder with central (vertical) feed position, hydraulic pressurizing of floating roller with gas accumulator, automatic grease lubrication, and double output-shaft gear reducer. (Courtesy of Kdppern, Hattingen, FRG)...

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