A NEW DEVELOPMENT IN GOLDDREDGING MACHINERY.

Otago Witness, Issue 2842, 2 September 1908, Page 28

A NEW DEVELOPMENT IN GOLDDREDGING MACHINERY.

In our issue of last week 't was 6tated that the pumping plant of the New Perseverance Dredging Company had undergone a successful preliminary trial. The start- ) ing of this plant is being watched with j great interest by' mining men, owing to the I fact that a great departure is to be made [ from the usual method of treating the excesive overburden some 60ft high in this company's claim. Through the courtesy ' of the company's consulting engineer, MiEdward Roberts, M.I. Mech. E., London, . iwe are enabled to give a description' of the . | plant and the proposed method of woi-king it. The advantage of having the current ; of tha river running close to the high ■ 1 bank being worked has always been an , I important factor in this company's opera- ' I tion«, the river carrying away a great < j portion of the finer material. The long ] I elevators fitted to some of the dredges on , adjoining claims have so far only succeeded | ' in placing the dredges altogether beyond j the influence of the river, a"rf hjIU form- 1 mg a high bank between ihr i \c-r and the t clrodgo. So bad ha« this 'j >" n that tho i ■ dredges in some cases cswriot got water j ' enouith to float in, and it has b< < n ncc-s- J

sary to devise means for adding' to fnV| water supply by races or pumping fronß the river into the paddock- The company's dredge engineer, Mr M'Callura, hay* ing seen m Tasmania and Victoria whati had been accomplished in removing gravel by mea°n6 of centrifugal dredging pum^c. sketched out a proposal for removing thd overburden to about 6ft below the waterline by a centrifugal dredge pump, to ba fixed on one of the dredges, and the material thus dredged to be conveyed through pipes with flexible joints, supported on pontoons to the other side of jbhe river, a bucket-dredge to be then used to follow? Tip the first or suction -dredge, and to dredge up the deep and richer gold-bear-ing wash. The project w«s considered' by the directors, who called Mr Robertas inta counsel, and instructed him to proceed to Alexandra to examine the ground, confer with the company's officers, and to report? on the feasibility or otherwise of .the] scheme, and to estimate the cost of carrying it out if be favoured the project. The report, which has been previously pnfclished, being favourable, the company miy about raising the extra capital required bj» means of preferential shares, Mr Roberts was then instructed to design the machinery* and get the work put is hand.

The following is a description of thex plant : — The ' dredging pump is a massive piece of work, having 15in inlet and . delivery. It is of special design, and similan in some respects to a smaller' pump dcV signed by and fitted to * suction dredge? recently built to Mr Roberta's plans foi> the Waimakariri Harbour Board, where it has proved very satisfactory. The suction pipe is attached to a strong girder fram* ing pivoting on bearinfte fixed at the endi of dredge, the outer end of the suction pipe projecting well beyond the end oi j dredge and past, the line ' of the- dredge j side,^ permitting the dredge to work close/ up to the ' bank without .any excessive angling of the dredge. The girder franw ing also carries a shaft with a revolving 1 ' outter at the end projecting beyond the end of suction pipe in order to loosen the ground. The girder framing, with suction pipe and outter, is capable of vertical movement similar to; a dredge ladder and is controlled from the dredge winch. A box or trap is provided to catch extra large stones just before they would enter; the pump. ~~ The gravel and the water after passing through the punxp is carried alonjp the dredge deck through a. line of pipes to the stern, thence around a bend of easy radius to a line of pipes running right across the river. These pipes are supported in a new and original manner from 1 three bowstring lattice girders, each 72ft; long, the ends of which rest on three small pontoons, forming a bridge the river. The small pontoons are held in position, against the current of the river by headlines nutde fast to a small wincn 1 on each pontoon and connected to one strong headline led to a winch fixed on the river bank well ahead. The pipes, are attached to the underside, of the girders and have flexible points immediately under the joints of girders. The pipes and joints -embody . some novel features, for which patent rights have been applied. On the pontoon most remote from the dredge & sluice-box is fitted* to save -the gold from the overburden. The movement of the oipes is controlled from the dredge. AJ breaking-down or giant* nozzle is fixed at the bow of the dredge, the water for which is supplied by an Bin centrifugal pump, which also • does duty as a circulating pump for the condenser. The plant is driven by the boiler *md 20 horse-power (nominal) ' engine formerly used on th© dredge, the engine speed being considerably increased. . ' - During the time the construction of th« new machinery was in progress one of tho dredges was dismantled of 'its bucket (rear and got ready for the reception of the new machinery, this work, as well as the erection of ihe new plant and repairs to the dredge, being carried out by the company's own staff, ably led by Messrs M'CaUum and Baker, Mr M'Oalhcm also; conferring several times with the consulting engineer when the details were being considered. The building of the pontoons was entrusted to Mr John Kne>wstubb, Messre Oossens and Black carried out a large portion of the work, including ßirders and delivery pipes, and Messrs Roberts and Sons (of Bendißo) manufactured tn« pump and suction, piping, framing, etc.

Notes from Cromw 11. (Faou Qdb Owh Cobbespondeitt.) CROMWELL, August 25. • There has been some rain ag&jn tbia „ week, but snow hae fallen on the high country, and consequently the rtverj^dia not rise. There is every appearance of ib keping low for some time yet. The Hartley- and Riley dredge is still creating considerable excitement locally, as the dredgemaster is known to ha-v* taken returns to the bank on Monday Ajul to-day, but what the amount won so far is not known. JFrom what I can gather, there is every prospect of the returns continuing, as there is believed to be another lead on the shore running outside the ground worked previously. ♦ . a Messrs J. Solomon and J. Stokes (ofi Dunedin), direotors of the Alpine Consols Company, arrived here on Monday even* ing, and left again this moroing. Mr is.Butler, the late manager, resigned the. position, and Mr George Good«er has been appointed. The dredge is at present a short distance up from the bottom ot the late Great Central claim, and dredging: was resumed to-day. It is generally ex-, pected that something Rood m the wax <« returns will be made on thie claim.