ELEVATING WITH LOW PRESSURE.

Otago Witness, Issue 2647, 7 December 1904, Page 47

ELEVATING WITH LOW PRESSURE.

TO THE EDITOE. ' Sib, — In our letter to the Witness we mentioned, in regard to success in elevating with low pressures, that it was due to a difference in measurements from the elevators in general use, and it has occurred to us that, in justice to Mr Dayey, as consulting engineer to ""Notes and Queries," it is only fair to give the fullest information on the subject of. our experience and experiments. We have been forced to come to the conclusion, through observation and ex» perience, that there are claims lying idle, supposed to be unworkable, which could be safely and profitably worked were it generally known that, under certain conditions, elevating can be carried "on at a pressure of 4ft to lft of lift. Of course it stands to reason that an elevator lifting one in ten can swallow a much greater bulk of stuff in a given time than one that is doing,' say, 1 in 5, and this we freely admit; but where, as in our district, stones are large and numerous, this point is not so important ss in a -district where the gravel is fine; and it seems a pity, that. "as we said before, gold should be lying itntouched, solely, through a misapprehension of the power necessary to raise it. We have been led to make these remarks to explain the reason for our appearing in print at all_, and would most emphatically disclaim any intention of trying to "teach our grandmother." In regard to the points we are about to mention,* we have never had an opportunity of discussing them with an engineer, bxyfc hove been repeatedly told that our conclusions do not coincide with those of engineers, except, as you have often mentioned, in regard to the absolute necessity of having the pressure pipes as large as possible,, to obtain the full power there is in the water. The first and main point is in regard to the size of the uptake, together with a very long and gradual taper from the smallest part of ilifi throat $o the spot Wjhero

9 is blocked. This happened several times to the objector's own elevator, and he had over 160 ft of .pressure to a lift of .18ft, witlra first-rate up-to-date plant, only the uptake was llin and the jet 2iin. . Now, with a long taper, and a small uptake, the whole mass is in motion upwards, iind the fact of its tapering considerably lessens the friction. That this principle is sound we believe from the fact that we have been elevating for five years, and have never blocked the discharge pipe. Another- point which is most important is to see that the jet is shooting exactly up the centre of the pipe. We received a letter from Mr Strahle saying that his elevator would not lift 6ft, and from his description it was evident that his jet was crooked. A very slight deviation is sufficient to seriously handicap the power. A small elevator we made for a neighbour .some days ago, and set up 'by him, would not work well till we examined it and found the jet was not true. On being adjusted, it worked well. With the foregoing proportions there is no need to let air into the pipe should the water rise above the mouth, as it will always clear itself. One difficulty, which is rather a serious one to those accustomed to a branch pipe and giant nozzle for blowing everything to the intake, is that under extreme low-pressure conditions it is not advisable to weaken the main cdlumn to such an extent as this necessitates, unless the pressure pipes are very large, and the water supply abundiant, say 7 heads and over. This difficulty, however, can easily be overcome by a little adaptability in method; such a plan as we adopt would do in many places. This is to run a flat, temporary tail face, made of wood 18in wide and 6ft long, from the intake right up to the foot of the face; as the face recedes, we put down another section, and branch ones if necessary. This kind or race will carry an immense amount of gravel with very little fall, and has the advantage oi requiring but little water compared with the giant nozzle, while it carries a regular ceaseless stream of gravel to the elevator, without any scraping or shovelling. It can be put in any direction, and lifted or put down in a few minutes. The sides are made of flat stones, tough sods, or boards weighted; down. We might mention that we have always been very Jh9j\ si WBit*Ljs£ had » ev e« asm .«?* $kva-

users of elevator plants will read' your letter with interest. — I know I did.J