Hydraulic ram pumps and Sling Pumps

Emergency water supply in cold regionsWater treatmentLow temperatures affect the rates ofchemical reactions and biologicalprocesses.SedimentationWhen treating water to removesediments by settlement, the size of thesettlement tank required can becalculated as a surface area.Area (m 2 ) =x■■Design Flow Rate (m 3 /s)Settlement Velocity (m/s)Jar tests are used to determine theSettlement Velocity;The Design Flow Rate iscalculated from the size of thepopulation.1 2Measurecleardepth,in metres1. Fill the jar with water whichhas just been stirredvigorously.2. Measure the amount of time ittakes, in seconds, for some ofthe jar to become clear.Settlement Velocity= clear depth + time takenNote: If coagulant needs to be added to thewater then several jar tests can be performedsimultaneously, using different quantities ofcoagulant. The minimum amount to produce arealistic sedimentation velocity is determined.Figure 2. Jar tests for sedimentation treatmentSince settlement velocity depends onthe viscosity (thickness) of the water, it isimportant to use water at the correcttemperature. (Increased water viscosityimplies a slowing of the process by afactor of 1.75 for water at 1°C comparedto water at 20°C.)Tests should be undertaken usingthe outside temperature to avoidunderestimating the size of settlementtank required.Slow sand filtrationThe rate of flow will be slower in a coldclimate both because the biologicalaction of the ‘schmutzdecke’ layer isreduced and because of increasedwater viscocity.ChlorinationThis reaction rate is seriously affected bytemperature (for every 6°C drop intemperature, the necessary contacttime increases by a factor of between1.5 and 3.5). Operators can use jar tests(for example using the Horrocks’ methodas described in Technical Brief No.46) todetermine a suitable contact time andamount of chlorine to be added providedthat the tests are done using watersamples at outside temperatures.Water distributionsystemsThe forces exerted by water expandingas it freezes and becomes ice, are theequivalent of a static head of waterabout 25km high! Protection of pipesand valves against frost is essential.Immediate measuresWater is more likely to freeze if it is notmoving, so:■■for a temporary supply, pipes shouldbe drained when water is not flowing.For a gravity flow system, continuousflow can be maintained by leavingsome distribution taps permanentlyopen.In a pumped system, the water canbe recirculated along dual pipearrangements that allow water tocontinue flowing.Longer-term measures■ If possible, pipes should be burieddeeper than the depth of maximumfrost penetration and lagged withinsulation.■Care should be taken to locatedistribution points as close aspossible to where people live,and preferably indoors. As wellas preventing problems of tapsfreezing, exposure is a serioushealth risk, especially for the elderly,and shelter will avoid the need forpeople to queue in the open.Pipe materialsUsing suitable materials will reduce theprobability of pipes splitting if the waterfreezes inside.■Medium Density Polyethylene(MDPE) remains ductile even at verylow temperatures (to -60°C).■PVC is more brittle at lowtemperatures and is therefore moreeasily damaged than MDPE.PumpsHandpumps and mechanical pumps canbe protected by a pump-house, whichwill reduce the likelihood of waterfreezing inside the pumps and causingdamage.Mechanical pumpsTo avoid running and maintenanceproblems:■■Make sure that the correct grade ofengine oil is used. (Oil more suitableto warmer climates may be so thickat low temperatures that it canprevent the engine from starting.)Use diesel suitable for cold regions.‘Gelling’ can be prevented bykeeping pumps indoors. (Diesel islikely to gel if transported from awarm region to a mountainous areawhere it is cold.)Handpumps■ A lift pump is less likely to suffer fromfrost damage because the cylinder isunderground.■A small hole (approximately 3mm indiameter) cut in the riser pipe nearthe base will let the pump drain atnight. (Note, however, that this willreduce the efficiency of the pumpand limit the maximum depth fromwhich water can be extracted).119