Hydraulic controls

Faults in the cycle of control operations due to current failure are eliminated by the so-called closed circuit current principle , i. e. when the solenoids are deenergized, the automatic shutoff valve closes and the pump by-pass valve opens. 

The electrical operation of the control units permits of placing the accumulator at any distance from the pumps. In plants having a wide hydraulic mains system, it is also possible to install a number of accumulators at various locations and place the pumps in a common room. This arrangement ensures small cross-sections of pipes furthermore shocks and heavy pressure drops when several presses work simultaneously, are eliminated. 

The fittings required for an air-loaded accumulator include a hand-operated shutoff valve arranged directly on the pressure-water connection, hand-operated stop valves for the air bottles, a safety device which stops the pump motor when a given pressure is exceeded, as well as a control panel with relays and appertaining pushbutton switches for the solenoids, a circuit breaker, a transformer, the indicator lamps for water level and electric current. 

One or more small multi-stage high-pressure compressors which are directly driven by motors of about 5 to 25 H.P., are used to pressurize the accumulator. The initial filling occupies a few days, whereupon the compressor will have to be used from time to time only to replenish air when losses due to small leaks or to absorption have occurred. 

Designing and calculating a control is preceded by the preparation of a hydraulic circuit diagram, based on the rule that one inlet- and one outlet valve each or one double-acting slide-valve each is required for one reciprocal motion of the plunger. Consequently, a four-valve control is to be provided for the advance and return motion or the up-and-down motion of the piston of a horizontal or vertical press respectively. Examples of this are the controls for the press and the die-carrier shifting device, illustrated in Fig. 92. 

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Figure 10.36 Electro-Hydraulic Control Umbilical Bundle...

Merritt, H.E. (1967) Hydraulic Control Systems, John Wiley and Sons, New York. 

Another example of the importance of the VI is the need for a high viscosity index hydraulic oil for military aircraft, since hydraulic control systems may be exposed to temperatures ranging from below — 65°F at high altitudes to over 100°F on the ground. For the proper operation of the hydraulic control system, the hydraulic fluid must have a sufficiently high VI to perform its functions at the extremes of the expected temperature range. 

Hydraulic control values can utilize a variety of actuators that activate their function. Normally these actuators use manual, electrical, mechanical or pneumatic power sources. 

Phytostabilization Soils, sediments Metals and metalloids (As, Cd, Cr, Cu, Pb, Zn, U, Se) Hydrophobic organics (PAHs, PCBs, dioxins, furans, pentachlorophenol, DDT, dieldrin) Phreatophyte trees to transpire large amounts of water for hydraulic control Grasses with fibrous roots to stabilize soil erosion Dense root systems are needed to sorb/bind contaminants... 

Hedgcore, H. R. and Stevens, W. S., 1991, Hydraulic Control of Vertical DNAPL Migration In Proceedings of the National Water Well Association of Ground Water Scientists and Engineers Conference on Petroleum Hydrocarbons and Organic Chemicals in Ground Water Prevention, Detection and Restoration, pp. 327-338. 

Air injection systems, by their very nature, start with no initial hydraulic control because flow is away from the injection point. Contaminants are sometimes spread laterally by water displacement until control is established. 

The most important criterion to assure that hydraulic control of the contaminated area is maintained during the remediation program is the proper layout of injection and extraction wells. This is important obviously to minimize and exclude the significant spreading of contaminants into clean areas and to ensure the focus of bioremediation efforts in the areas of highest concentration of contaminants. Important parameters to be considered are as follows ... 

Extraction wells are usually necessary to maintain hydraulic control of the plume and to ensure that the plume does not migrate into clean areas or accelerate migration toward sensitive receptors. Placement of extraction wells is especially important with systems that use nutrient injection wells or infiltration galleries. These sources of fluids can alter natural groundwater flow patterns, which may cause contaminant migration in an unintended direction or rate. If the natural groundwater system has a sufficient concentration of electron acceptors and nutrients, to achieve remediation at an acceptable rate, it may not be necessary to add any additional materials. 

Extraction wells should be located where hydraulic control is achieved at the boundary of the contaminant plume. Cones of depression created by recovery wells should intersect so that the overall hydraulic gradients ensure capture and recovery. 

Monitoring wells should be located within the plume at horizontal and vertical locations to monitor progress. Perimeter wells should be placed to ensure that extraction wells achieve the desired hydraulic control and prevent further migration. 

An idealized configuration of extraction, injection, and monitoring wells is shown in Figure 9.8. The design area of influence for extraction and injection points will determine the number of wells required. The area of influence of neighboring extraction wells should overlap sufficiently to achieve hydraulic control. 

Wherever contaminated groundwater must be recovered or prevented by migrating by hydraulic control, the expense of a valid field investigation is always recouped. Efficient hydraulic control or recovery is based on the principle of handling (and treating) the smallest volume of water containing the highest concentration of dissolved chemicals as possible. 

Decoking by Drilling. For this method of decoking, a hydraulically controlled, rotating drill stem is mounted in a well below the coke drum. At the end of the cycle, the bottom from the coke drum is removed and a hole is drilled upward through the coke bed. The drill is then removed from the stem and knocker-bars are mounted in its place. The knocker-bars swing out from the drill stem when it is rotated, hit the coke, and break it loose from the drum. The coke falls out and is recovered (5,40). 

Liquid foodstuffs, for example milk products must be submitted to homogenisation treatment in order to improve their long-term physical stability ("shelf life"). The liquid is pumped at very high pressure by a multiplex reciprocating piston pump through the narrow clearances of a hydraulically controlled homogenisation valve (Fig. 1.4-4, C, bottom). 

The pump consists of dual reciprocating pistons which are hydraulically controlled. Oil is distributed by the system to the two pistons which are 180° out of phase (as with the Altex and Waters systems). A fixed volume of hydraulic fluid is delivered to the control system for every revolution of a special gear pump. The latter is controlled by a motor having a constant speed and a tachometer feedback circuit. Other compensating circuits... 

Three general classes of optimization models for groundwater plume containment design are described in the literature, including hydraulic control models, advective control models, and concentration control models. All three classes of optimization models require that the groundwater flow... 

Ahlfeld, D. P., and Heidari, M. (1994), Applications of optimal hydraulic control to ground-water systems. Journal of Water Resources Planning and Management, 120(3), 350-365. 

Mulligan, A. E., and Ahlfeld, D. P. (1999a). Advective control of groundwater contaminant plumes Model development and comparison to hydraulic control. Water Resources Research, 35(8), 2285-2294. 

Riefler, R. G., and Ahlfeld, D. P. (1996). The impact of numerical precision on the solution of confined and unconfined optimal hydraulic control problems. Hazardous Waste and Hazardous Materials, 13(2), 167-176. 

The June mini-pilot tests showed that the flow from individual wells varied from less than 1 to 16 cfm at a vacuum of approximately 70 inches of water. The hydrocarbon vapor concentrations ranged from 188 to 4,630 ppmv (Table 2). Based on the June vapor flows and hydrocarbon concentrations, 13 wells were selected for continued SVE operation to maintain hydraulic control. These included wells 1-2, 1-5, and 1-7 from circuit 1, wells 2-1 and 2-6 from circuit 2, all wells except well 3-3 in circuit 3, and combination monitor/SVE well MW-9 (Fig. 6). 

Hydrocarbon recoveries were enhanced during this (fourth) quarter of SVE system operation, and PSH thicknesses in both the monitor and the SVE wells decreased. DBS A continued operating both the SVE and AS systems using a variety of configurations to focus on areas with the highest hydrocarbon vapor concentrations or to maintain hydraulic control. Because the systems had been constructed with separate controls located at the equipment compound and at the wellhead, the SVE and AS systems at each location could be operated independently of each other. 

The extension of SVE techniques to low-permeability soils was based on monitoring the vapor recovery rate and using the results of mini-pilot tests to adjust SVE system operation. The periodic mini-pilot tests provided information from individual SVE wells, including air flow, well vacuum, and hydrocarbon concentration in the extracted vapors, that was used to balance the flows. Wells with low hydrocarbon concentrations were shut off to focus remedial efforts on the most contaminated locations, and during some periods, wells with high flows were shut off to allow a more balanced flow from low flow wells or to provide hydraulic control along the periphery of the perched groundwater contaminant plume. 

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