Hydraulic pressure

“ Water-pressure has sometimes been applied to operate machines which are worked continuously and not intermittently, and to continuous working rotary machines. This is unwise, for in applying hydraulic power to the continuous working of shafting or shop tools, the amount of power developed by the hydraulic engine cannot be varied to suit the work to be done, neither can the speed be regulated with sufficient nicety. ”

“ The general features of hydraulic power transmissions are: (1) a central station where the hydraulic pressure is created, usually by means of steam pumping engines; (2) a system of distribution mains; (3) machines for utilizing the pressure. In cases of public supplies there is the further important matter of registration.
When dealing with any practical problem of hydraulic power transmission it is of the first importance to determine the maximum demand for power, its duration and frequency. ”

“ Hydraulic pressure generated by the Stage I pump is used by the servo actuators to gimbal the thrust chamber during Stage I flight.
The Stage II hydraulic system provides hydraulic pressure to the Stage II engine, roll control, and vernier actuators. During sustainer engine firing, the hydraulic system is powered by the turbine pump assembly driven pump. At sustainer engine shutdown the electric motor driven pump starts and supplies hydraulic power to the vernier rocket motor actuators. ”

“ In no previous instance had a pressure exceeding 90 pounds on the square inch been used, but it was now decided to adopt a pressure of 600 pounds’ (Sir W. G. Armstrong, Inst. of Civil Engineers, 1876–7, vol. i. pt. iv.) The storage capacity of the accumulator is not so great as that of a reservoir, but, on the other hand, the higher pressures employed enable the distributing pipes to be made of smaller dimensions than would otherwise be possible, and the pressures are more uniform. By this invention hydraulic machinery was rendered available in almost every situation. ”

“ While still in a molten condition in the mold, the steel used in manufacturing guns and shafting is subjected to hydraulic pressure until the ingot has cooled, thus insuring the solidity of the metal. The upper head of the compressor weighs 125 tons, and the lower one, including the cylinder through which the hydraulic pressure is applied, 135 tons. ”

“ If in the cylinder of a hydraulic press there be put a certain quantity of cobblestones, leaving a clearance between the top of the stone and the piston, and if this space, together with the voids, be filled with water and subjected to a great pressure, the sides or the walls of the cylinder are acted on by two pressures, one almost negligible, where they are in contact with the stone, restraining the tendency of the stone to roll or slide outward, and the other due to the pressure of the water over the area against which there is no contact of stone. ”

“ Consequently, when the piston ascends, it no longer forces the water into M, the air of the reservoir, by the pressure it has received, reacts on the liquid, and raises it in the tube D, until the piston again descends, so that the jet is continuous.
Hydraulic Machine Tools. Probably in no department of engineering has the use of hydraulic power met with more success than in its application to certain machine tools. ”

“ A man exerting his strength on one of these presses can produce a force of upwards of fifty tons. But however great, the pressure is still insufficient. The enormous demand for the cheap side-combs of hoof led to the application of hydraulic pressure. The two portions of the hoof, after being boiled a second time in a number of little troughs, with a steam-jet in each of them to preserve the necessary temperature, the excrescences still adhering are pared off. ”

“ In these cases, an artificial source of water power is created by using a steam engine to pump water to a reservoir at a great elevation, or to pump water into a closed reservoir in which there is great pressure.
Water flowing from the reservoir through hydraulic engines gives back the energy expended, less so much as has been wasted in friction. Where a continuously acting steam engine stores up energy by pumping the water, while the work done by the hydraulic engines is done intermittently,—this arrangement is considered the most useful. ”

“ Fire-mains laid through the streets terminate in deep water at points accessible to the boats, the pumps of which can be connected to them and made to fill them with water at high pressure. In cities where a high-pressure hydraulic supply system is available, a relatively small quantity of the pressure water can be used, by means of Greathead hydrants or similar devices, to draw a much larger quantity from the ordinary mains and force it in jets to considerable heights and distances, without the intervention of any engine. ”

“ There is only one pressure pipe for all the hydraulic pumps. This extends from the tank on the side of the mountain to the 3,000 foot level. It is tapped at the points where are situated the several sets of hydraulic pumps. The water from the pressure pipe enters one part of the pump, where it moves a piston-back and forth, just as the piston of a steam engine is moved by steam. ”

“ With the power pump, when the motive power is stopped, a leak, the size of a pin point, in a valve, will cause a leakage that releases the pressure and makes poor pressing. Be aware of the fact that there is no method of extracting water from the fertilizer so cheap as pressing and the only limit should be the strength of the cloths. Fig. 70 shows how a hydraulic press and pump should be connected.
FIG. 70.—DIAGRAM OF HYDRAULIC PRESS WITH PIPING AND PUMP.
Cooking Killing Stock. ”

“ Here it is proper to mention once for all, that the pressure for the hydraulic machines is obtained not only by natural heads of water, or by forcing-pumps worked by hand, but very frequently by forcing-pumps worked by steam power. ”

“ Thus, with a hydraulic press no larger than a common tea-pot, a bar of iron may be cut as easily as a slip of pasteboard. The exertion of a single man, with a short lever, will produce a pressure of 1500 atmospheres, or 22,500 pounds on every square inch of surface inside the cylinder. ”

“ Hence CD is termed the virtual slope or hydraulic gradient of the pipe. It is the line of free surface level for each point of the pipe.
If an ordinary pipe, connecting reservoirs open to the air, rises at any joint above the line of virtual slope, the pressure at that point is less than the atmospheric pressure transmitted through the pipe. At such a point there is a liability that air may be disengaged from the water, and the flow stopped or impeded by the accumulation of air. If the pipe rises more than 34 ft. above the line of virtual slope, the pressure is negative. ”

“ For instance, there are machines for bending pipe, for curving railroad rails, for punching holes in metal, for pulling wheels off their shafts, for jacking up heavy weights, for baling cotton, paper, and other materials, all of which operate on the same principle as the hydraulic press. Water pressure is supplied sometimes by a hand pump, sometimes by a [100] power-driven pump, and sometimes it is taken from a reservoir in which compressed air imparts the requisite pressure to the water. ”

“ If the base of the material be sand and the fill be so-called quicksand in excess of the voids, pressure will cause the quicksand to set up hydraulic action, and the action of the piston will appear to be similar to that of a piston acting on purely aqueous material. ”

“ As soon as the pressure is relieved the check valve opens and the valve into the chamber closes automatically until a moment later the stream of water has gained sufficient velocity to repeat the performance. Thus an intermittent jet of water is forced into the air chamber and thence through a pipe to a reservoir. The height to which the water will rise depends entirely upon the velocity of the water flowing through the system. The air chamber is necessary to cushion the action of the hydraulic ram and provide a fairly steady pressure upon the water that flows up through the vent pipe. ”

“ Some of the giant nozzles spout streams from 2 to 8 inches in diameter with a pressure of from 50 to 200 pounds per square inch. The powerful streams tear into the gravel banks, washing them away into sluices in which riffle boxes are placed to catch the precious metal. The back pressure of these nozzles is very heavy and the larger ones have to be provided with strong anchorages. Water in motion resists any change of direction and long levers have to be provided to permit the miners to guide the nozzles.
The hydraulic jet is also used for general excavating wherever water power is available. ”

“ When water reached it, it forced the edges apart, one against the plunger, the other against the walls of the recess, with a degree of tightness proportionate to the pressure. On water being released from the cylinder the collar collapsed, allowing the plunger to sink without friction.
The principle of the hydraulic press is employed in lifts; in machines for bending, drilling, and riveting steel plates, or forcing wheels on or off their axles ”

“ This pressure is very great in high-pressure engines, but in models it is generally very low, and seldom exceeds twenty pounds to the square inch. The evaporating capacity of the boiler is according to the requirements of the engine it has to supply. The resistance of the piston to the steam shows the pressure at which it should be supplied. Boilers are generally tested, by means of a [119] hydraulic pump, to stand a pressure at least double that at which it is intended to use them. It is unsafe to generate steam in any vessel that has not been properly tested. ”

“ Large pressure engines have an efficiency of 85%, but small rotative engines probably not more than 50% and that only when fully loaded.
§ 176. Direct-Acting Hydraulic Lift (fig. 171) .—This is the simplest of all kinds of hydraulic motor. A cage W is lifted directly by water pressure acting in a cylinder C, the length of which is a little greater than the lift. A ram or plunger R of the same length is attached to the cage. The water-pressure admitted by a cock to the cylinder forces up the ram, and when the supply valve is closed and the discharge valve opened, the ram descends. ”

“ In any large system where a number of pumping units are required they also allow a sufficient interval of time to start any additional units. Accumulators connected to the mains at a considerable distance from the central station reduce the variations of pressure, and the size of mains required for a given supply of power, and therefore have a most important influence on the economy of distribution. The mechanical efficiency of hydraulic accumulators is very high, being from 95% to 98 %, and they are practically indestructible. ”

“ As long as the gas flows in the normal direction as described there will be no escape to the air. Should the gas in the torch line return into the hydraulic valve its pressure will lower the level of water in the cylinder by forcing some of the liquid up into the two pipes. As the level of the water lowers, the shorter pipe will be uncovered first, and as this is the pipe leading to the open air the gas will be allowed to escape, while the pipe leading back to the generator is still closed by the water seal. ”

“ In the early days of hydraulic mining in California the miners thought that with a vertical pressure of 300 feet they could almost tear the world to pieces, and not a man among them could have been made to believe that any pipe could be constructed that would withstand a vertical pressure of 1,000 feet ”

“ In fig. 910. two centres of motion for the pump-lever are shown. By shifting the bolt into the centre nearest the pump-rod, the mechanical advantage of the workman may be doubled. Two pumps are generally mounted in one frame for one hydraulic press; the larger to give a rapid motion to the ram at the beginning, when the resistance is small; the smaller to give a slower but more powerful impulsion, when the resistance is much increased. A pressure of 500 tons may be obtained from a well-made hydraulic press with a ten-inch ram, and a two and a one inch set of pumps. See Stearine Press. ”

“ But, further, in fluids such as water, air, steam, &c., to which the present division of the article relates, the tangential stresses that are called into action between contiguous portions during distortion or change of figure are always small compared with the weight, inertia, pressure, &c., which produce the visible motions it is the object of hydraulics to estimate. On the other hand, while a fluid passes easily from one form to another, it opposes considerable resistance to change of volume. ”

“ In starting the pump, ‘stand by’ until it has caught suction, and accumulated nearly the correct water pressure, now open the valve on the pulse, or pressure pipe to the controller and open pump throttle wide, thus giving the controller free action.
“Suppose the boiler pressure is 100 pounds, the water pressure will be 10 per cent. higher or 110 lbs. Carrying an even fire, with water at second gauge, feed valves properly set, the load suddenly increases, which pulls steam down to 99 pounds, the water does not remain at 110 lbs. ”

“ After the standing water column has been thrown off by the pressure the air rises through the water reduces its weight, with the result that the water is expelled as fast as the well supplies it, the water outside the pipe, acting as a head, flows into the discharge pipe by the force of gravity. ”