Glasgow Main Drainage: the Mechanical
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Proceedings.] MOHTON ON GLASGOW MAIN DRAINAGE. 213 (Paper No. 3 9 8 I .) “ GlasgowMain Drainage : the Mechanical Equipment of the Western Works and of the Kinning Park Pumping- Station.” By DAVIDHOME MORTON, M. Inst. C.E. THE main-drainage works of Glasgow and of the adjoining burghs, including certaindistricts inland, havebeen described generally in the Paper presented by Messrs. A. B. McDonald and G. Midgley Tay1or.l Themap given therewith shows the positions of the severalworks described in thisPaper. Although the Author’s duties included the design of the various stations, and in some cases of the building works, the space at disposal renders it necessary for his remarks to be confined to the mechanical details ; and even these cannot be dealt with by any means as fully as he could wish. PARTICKPUMPING-STATION (Fig. 1, Plate 7). The sewage discharged from the Glasgow and Partick intercepting sewers, the former having a diameter of 6 feet and the latter of 5 feet, is dealt with at this station. The head to beovercome is 35 to 36 feet, including a sufficient allowance for loss of head while passing through screens, etc., and for giving assurance that the in- tercepting sewers will, except during very heavy rain, always have a clear fall into the station. The sewage flows across the station and, after being raised by the pumps, is delivered directly over forebays into the main outfall-sewer, where it joins the high-level sewage passing through the aqueduct over the Kelvin, and flows with it to Dalmuir.There are practically no horizontalpipes: the flow of sewage and the behaviour of the pumps are under easy observation ’ Ante, p. 167. Downloaded by [ York University] on [20/09/16]. Copyright © ICE Publishing, all rights reserved. 214 MORTON ON GLASGOW MAIN DRAINAGE. [Millutesof In Table I of the Appendix are given the quantitiesof sewage to be dealt with at this station. These, as well as the quantities for the various other stations referred to in this Paper, calculatedare on the basis of 70 per cent. of the flow during 24 hours being dealt with in 12 hours, which as a general statement is fairly correct, though the maximum flow during the hours from 10 a.m. to 4 or 5 p.m. often considerably exceeds this. Another matter largelyaffecting the capacity of the pumping- plant is the allowance for rainfall, which is here stated simply as 3 inch of rain in 24 hours, and is added to the rate (70 per cent. in 12 hours multiplied by 2) for sewage alone. The equivalent quantity of rain falling uniformly during 24 hours is relatively unimportant in arriving at suitable proportions for the pumps ; rain does not fall in this manner, and in a city almost wholly paved the result of even a moderate shower is quickly felt in thepumping-station. This t inch of rain in 24 hours, or inoh in 1 hour, is frequently quoted in relation to sewerage, but in most cases it seems doubtful whether it is used in the sense intended by the originators of the allowance. In the discussion on Messrs. Worth and Crimp's Paper on the Main Drainage of London, in 1897,' Sir Alexander Binnie stated that Sir Joseph Bazalgette " had provided for an average flow of sewage in 24 hours of 5 cubic feet, or 31; gallons, together with & inch of rainfall in 24 hours. But the sewers wereconstructed (and that was what so many people forgot) to carry one-half of that total quantity in 6 hours of the day." Attention is also drawn to a quotationby Sir AlexanderBinnie from Sir Joseph Bazalgette immediately following this, to the effect that " it is probable that if the sewers are made capable of carrying off a volume equal to a rainfall of 4 inch per day during the 6 hours of maximum flow, there would not bemore than 12 days in a yearon which the sewers wouldbe overcharged, andthen onlyfor a short period during such days." These statements indicate not merely provision for a flow of sewage equal to 70 percent. in 12 hours, but for 50 per cent. of the total in 6 hours of maximum flow, including, during these 6 hours of maximum flow, an allowance for rainfall at a rate equivalenteither to 6 inch or 1 inch of uniformfall in 24 hours. This last proportion of rainfall is rather seriously different from an allowance of inch during 24 hours, and represents more nearly thequantities which must be carried and pumpedwhen rain coincides with the hours of maximum sewage-flow, if very frequent 1 Minutes of Proceedings Inst. C.E., vol. cxxix, p. 135. Downloaded by [ York University] on [20/09/16]. Copyright © ICE Publishing, all rights reserved. Proceedings.] MORTON GLASGOWON MAIN DRAINAGE. 215 surcharge of sewers or use of storm-overflow weirs is to be avoided. It is also of obvious importance to be able to pump vigorously in the early hours of a rainfall, particularly after drought, so that the sewers may bewell flushed. Then if raincontinues, discharge over the storm-weirs is less objectionable. On the other hand, the flow of sewage during the night is very small and may readily fall toone-third of the avera.ge dry-weather flow; the pumps must therefore be able to continue working at very low speeds without risk of stopping. After a thorough study of all the circumstances it was decided to install at Partick three similar units, makingprovision for a fourth to be added if found necessary (Pig. la, Plate 7). The pumps selected were of the three-throw single-acting plungertype, each with a capacity of 1,800 cubic feet per minute (16,200,000 gallons per 24 hours). It was decided todrive each unitdirectly by a verticalthree-crank triple-expansion engine. Obviously, centri- fugalpumps similar to those employed on otherdepartments of the Glasgow main-drainage works might have been adopted, but having regard to thecontinuous nature of the work, the reciprocat- ingtype was preferred, because of its superior efficiency. When properly designed, this type of pump gives a velocity of flow second only in uniformity to that of the centrifugal pump, and markedly superior to that of any other type or combination of displacement pumps with rotatory motion. Had the actualdry-weather flow of sewage remained as scheduled, probably one engine would have sufficed for the whole day’s work. In practice, however, two are generally required during the 6 or 7 hours of greatest flow, running at about two-thirds of full speed. During the rest of the day one engine suffices, and in the small hours of the night the speed is reduced to 8 or 9 revolutions per minute, the normal full speed being 20 revolutions. Two engines running up to full speed deal with all but the heaviest rainfall, leaving the third as a stand-by for pump-cleaning and repairs. The sewage entersthe station from the City and the Partick intercepting-sewersthrough penstocks, the frames of which are secured by long anchor-bolts built into the walls, so that the doors can withstand a pressure equal to that due to the highest recorded tide.The penstock-chamber is 33 feet wide by 10 feet 6 inches long (in the direction of the flow), to the face of the rough screens which guard the entrance to threescreening-channels. These rough screens are composed of strong wrought-iron frames l1 feet high, the barsbeing vertical and4 inches apart in theclear. Similar horizontal grilles are fitted between the heads of the vertical Downloaded by [ York University] on [20/09/16]. Copyright © ICE Publishing, all rights reserved. 216 MORTOXGLASGOW ON MAIN DRAINAGE. [RIinuteS of screens and a tidal wall 25 feet high (forming the north side of the chamber) to prevent thepassage of large solids to thefine screens in time of surcharge. In front of each screening-channel, on the face of the tidal wall, is placed a penstock 5 feet wide by 7 feet high; the channels are made 7 feet wide and are fitted with fine screens of wrought steel 6 feet 6 inches wide, set at an inclination of nearly 45". These are of plates + inchthick, perforated with l-inch holes so closely drilled thatthe effective passage-area is 50 percent. of the total. The holes are countersunkon the dis- charge side. Power-driven scrapers and rakes travel slowly on the face of the inclined screens, raising the screenings into hoppers, from which they are lifted periodically by light bucket elevators. Two screening-channels usually suffice for the work of the station, and with ordinary attention on the part of the workmen the loss of head can be kept down to a few inches. Behind the screens, dis- tributing-channelscarry the sewage to the pump-wells, of which there are four. In addition there is a deeper well into which the others may be draineddry. All wells are guarded by penstocks fixed inside the walls, so that the pressure tends to force the doors fromtheir frames. All penstocks are provided with small side guide-rollers of gun-metal, whereby the doors are made to run clear of the frames immediately they begin to rise. All are balanced and can be raised or lowered by one man. The main pump-wells are each 12 feet wide by 33 feet long, and the levels in them do not vary more than 2 inches when the pumps are running at full speed. Sludge-pipes 12 inches in diameter are provided to drain off the sludgewhen the main wells are being cleaned, and it is subsequently lifted by an auxiliary steam-pump or by a pulsometer.