The âshackleâ is built up by welding together a pulley wheel, two 16mm ... Drum movement restrictor plates (2) Welde
Zimbabwe Bush Pump “C” type Development, description and testing January 2008
Peter Morgan January 2008 1
Zimbabwe Bush Pump “C” type Development, description and testing This experimental design by Peter Morgan, was field tested for the Zimbabwe rural water supply programme during the 2006 to 2008 period. Its development and trials were approved by the WES Technical Task Force, working under UNICEF chairmanship (16th October 2006). Several prototypes were built in the Government workshops of DDF and the Department of Water Development, and also by V&W Engineering. By June 2007, 7 pumps were on trial in Hopley Farm and a further 2 units in the Bulawayo Municipal area. Feedback from these pumps leads to further technical refinements. In early 2008 a single pump was placed at the Chisungu school in Epworth, where it still provides excellent service in 2013, serving over 2000 pupils. 50 pumps have been tested overall. The main reason for initiating this work, was not that any fault could be found with the “B” type pump. Rather in 2006, when the work was initiated, local exchange rates for foreign currency by NGO’s did not favouring the purchasing of pumps in Zimbabwe, where the cost became uncompetitive. Thus it was the economics rather than the engineering aspects that prompted the development of an alternative design in 2006. However by mid 2007, NGO’s were allowed to exchange their foreign currency at more favourable rates, and this made the purchase of the existing standard “B” type pump far more competitive. However by that stage the development of the “C” type pump head has reached an advanced stage and development continued. Eventually each pump must stand on its own merits and whichever is deemed the most suitable should be chosen for future use. There is no reason why the existing standard should change, unless the new model competes very adequately with the old. Cost reductions in the B type cannot be made by modifying the head, but by using reduced diameter rising main. A 40mm GI rising main can be used with the B type provided the uppermost pipe remains at 50mm. This requires only a changing of the uppermost pipe, a reducing socket between 40mm and 50mm pipe and a 50mm to 40mm reducing bush fitted to the cylinder. The advantage of the C type head, is that it is easier to manage and is cheaper to construct. At the time of writing this description, its performance at greater depths is unknown and its longer term durability has not yet been proven. It can be adapted to fit the India Mk II down the hole components, which may give it merit when promoted on the international market. But this can only be followed through when all suitable trials have been completed. 50 “C” type Bush Pumps were manufactured and placed on trial. However as the economic climate in Zimbabwe improved, there seemed little need to consider reverting to the “C” type. Consequently the durable, long tested and internationally recognised “B” type was retained as the National Standard. The development of the “C” type Bush Pump was therefore terminated and went into history. It remains however an interesting development, and worthy of recognition.
Basic characteristics The “C” type is similar to the “B type” Bush Pump in many ways and retains the main features of all Bush Pumps. Namely: 1. 2. 3. 4. 5. 6. 7.
The use of hardwood block (boiled in oil) as bearing Durable steel pump stand Use of large u bolts to attach pump stand to borehole casing Use of steel pipe as pump handle Exposed parts of pump head for ease of maintenance Forgiving nature of pump head in respect of loss of parts Designed principally for galvanised iron pipes and rods.
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Basic aims of experimental design 1. To simplify the pump head further, thus reducing cost and making pump head maintenance easier. 2. To reduce the number of moving and working parts in pump head. 3. To restyle the pump head so that it can accept a wider range of “down the hole components”, specifically 32mm GI rising main. This can reduce the overall cost significantly 4. To provide a pump head which may have international appeal, due to its durability, adaptability, long life of bearing, and ease of pump head maintenance. 5. To experiment with a new concept in hand pump design which used components which have hitherto not been used in this equipment (mainly a rope flexible link).. : BASIC DESCRIPTION The C type Bush Pump uses a drum system which is fitted to a steel pump handle (1.5m X 32mm GI pipe, steel thickness 4mm). A steel box bracket mounted within the drum surrounds and clamps the wooden block which is made of teak and boiled in oil. The teak block serves as a long life bearing. The drum is attached to the pump head with a strong pivot pin, secured with heavy duty lock washer and nut. The link between the drum and the pump rod is made through a “flexible link” and shackle. The flexible link is made of polyester rope, but can be replaced temporarily by other ropes made of various materials. The rope is held firming to the drum by passing it around the handle and then securing under a plate which is held tightly in place by 16mm nuts and bolts. The rope is fed through a “shackle” which incorporates a pulley wheel, around which the rope passes. The shackle is also linked to the pump rods through a rod connector. When the drum is rotated by movement of the handle, the rope lifts and lowers the shackle which is attached through a connector to the string of pump rods. This results in a vertical rod movement of approximately 200mm. There is little lateral movement of the rod which permits smaller, lighter and cheaper steel pipe to be used for the rising main (eg 32mm). This can be a major cost saver. The rope can lift considerable weights but can tear or wear if it meets a sharp surface. It is essential therefore that all surfaces in contact with the rope must be smooth. The rope is easily replaced and the operation of the pump can be continued by the use of a variety of rope-like materials. Alignment of pump stand As with the B type pump head, the alignment of the pump stand is critical to ensure that the rod moves up and down precisely through the 18mm hole in the water discharge unit which lies directly above the rising main. However tests carried out so far indicate that there is some minor variation in the pump head alignment and several tests pumps have shown some wear on the upper plate of the water discharge unit by pump rod. For this reason a small floating washer has been fitted below the rubber buffer compensate for wear at this point. Even after this refinement objects like small stones and sand found their way down the rising main and sometimes jammed the piston within the cylinder. For this reason the well tried and tested concept of the double floating washer system used in the “B” type head was adapted for use in the “C ” type head as well. The lower washer cannot be lifted without disconnecting the water discharge unit plates. And it is far more difficult to through sand and other objects down the rising main, a problem which has plagued the “C” type. As with the “B” type head, a jig should be used to attain the right angle of the pump stand.
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BASIC DESCRIPTION The “C” type pump stand The “C” type pump stand is similar to the “B” type in many ways. The lower channel section is retained at 400mm. The upper channel section has been increased from 350mm to 450mm. The angle of the pump stand has been reduced due to the new method of linking the wooden block to the pump rod. The upper side arms of the pump stand are extended to the same extent as in the B type. The pump stand base plate (support plate) is the same as in the B type pump and the same method of attachment to the borehole casing is used. The 50mm heavy duty socket has been retained on the water discharge unit to hold the steel pipes of the rising main. Compared to the “B” type pump head, the main changes are: 1. A “head drum” is used to pull a “flexible link” which is attached to the pump rod through a special “shackle.” The “flexible link” is made from “nylon type” rope. The preferred rope is 16mm polypropylene rope (poly-steel rope), but can range from 10mm to 16mm in diameter. Polyester rope and other ropes can also be used. 2. The head drum has a diameter of 240mm, and radius 120mm. It has a wooden bearing at its centre. The wooden bearing measures 150mm X 150mm X 100mm. (four can be cut from an existing B type pump block). This single smaller bearing has approximately the same working life as the bearing on the “B type,” as the wear pattern is similar to the B type. This wooden bearing is held in place within a steel box bracket through which four bolts pass. Two bolts on the distal plate and one each on the upper and lower plates of the box bracket. These are tightened against the wood to secure it in place. When tightened these bolts actually penetrate the wood slightly which helps to reduce lateral movement of the block within the bracket and the drum. The bolts require tightening from time to time. The box bracket is welded to the drum rim and the handle and rope holding bolts (see later). All these components are thus welded together to form a strong unit. The drum is also fitted with a rope holding plate and two drum movement restrictor plates, which prevents the handle going over top dead centre. Initially the drum was filled with concrete as a filler, b ut this method has been discontinued. The wooden block can be removed from the box bracket completely for renewal if required. 3. The drum is mounted on the pump stand and swivels around a single pivot pin which is attached to the pump stand (as in the B type) 4. The single pivot pin has the same specifications as the B type. Only one pivot pin is used. This retains the large lock washer. The pin is made of 35mm solid steel bar (preferably bright mild steel - BMS). The use of an easily removable pivot pin is essential for easy removal or replacement of the drum. The drum is removed during fitting of the down the hole components. 5. The steel components of the box bracket surrounding the wooden block are welded to both the handle (1.5m X 32mm GI pipe, 4mm thick steel) and all other steel components within the drum. As the drum rotates through movement of the handle, the nylon type rope unwinds and rewinds around the drum. This raises and lowers the shackle and the rods linked to it. A maximum stroke of 200mm can be achieved. The stroke length can be varied to suit the cylinder length etc by adjusting the attachment on the rope on the drum. 6. The important “flexible link” is 2m long and connects the drum to the rods via the shackle.
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The flexible link can be made of several materials: rope of various types (nylon, hemp, etc, steel cable, belt etc. In the early trials 16mm polypropylene rope (called poly-steel rope in Zimbabwe) was used. Later 12mm polyester rope was used. Professional advise was sought and this confirmed that the polypropylene rope was more abrasion resistant and thus more suitable for this particular application. However the polypropylene rope tends to twist. The white polypropylene rope was later chosen as the best for this application. These ropes can lift considerable weights of 16mm rods, although current trials have not gone beyond 40m. The rope is fed into a pulley wheel arrangement which forms part of the shackle. The shackle holds the pump rod through a rod socket (as in the “B type” arrangement). It is essential that all steel members over which the rope passes are very smooth. 7. The double rope is led from the shackle over the drum and around the handle and then bound and secured under the rope holding plate held in place by the two 16mm U bolts. The ends of the rope are held and clamped securely under the plate. The ends of the rope should be melted down and hardened to avoid fraying. By adjusting rope length, variations in stroke length can be achieved. 8. The “shackle” is built up by welding together a pulley wheel, two 16mm pumps rods, a steel washer and a pump rod connector. The rope is looped through the pulley wheel and the rod screws into the pump rod connector. This is a strong unit and is described in detail below. 9. The shackle sits on a rubber buffer (same as B type – diameter 64mm height 50mm) which itself sits on a small 6mm thick steel floating washer (diameter 65mm) and then the head plate of the water discharge unit. The small floating washer adjusts for any minor variation in the location of the rod within the water discharge unit, which cause wear on the upper plate. 10. The water discharge unit is similar to the B type unit, but with modifications in the sizes of the components. Field testing has established that the lower floating washer is essential in order to reduce the amount of sand and other objects pushed down into the rising main. The upper floating washer supports the rubber buffer and weight of the rods. 11. The lower base plate of the water discharge unit has the same dimensions as the B type unit – external diameter 160mm, internal opening 68mm, thickness 12mm. The main tube is 65mm pipe (length 200mm) as with the B type. The upper plate of the water discharge unit is identical to the lower plate (external diameter 160mm, internal opening 68mm, thickness 12mm). To this is attached a spacer ring with a thickness of 6mm, an external diameter of 160mm and an internal diameter of 100mm. The upper plate of the water discharge unit has a thickness of 6mm plate, a diameter of 160mm with a central 18mm hole drilled in it. The upper two plates and spacer ring are bolted together with 3 X 24mm nuts and bolts. The upper floating washer has a diameter of 65mm and sits on the upper plate of the water discharge unit. The lower floating washer has a diameter of 80mm and is enclosed between the upper and lower plates of the water discharge units. Both upper and lower floating washers are drilled centrally with 18mm holes to accept the 16mm rod. The movement of the rod through the water discharge unit is mainly in the up and down plane. But with minor variations in pump alignment, rope thickness and rod straightness, some wear occurs on the upper plate which necessitates both upper and lower floating washers be fitted. 12. The pump support plate and holder plate (skirt) are the same as in the B type. 13. The pivot pin held by large spring washer can be removed easily with a large spanner and this is followed by the removal of the drum/handle unit during pipe assembly and maintenance. 14. The main U bolts for attachment of the pump stand to the borehole casing are the same as the B type.
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DETAILED DESCRIPTION OF THE DRUM Drum plate The drum has a diameter of 240mm, radius 120mm. It has a wooden bearing at its centre. The wooden bearing is surrounded and supported by a steel box bracket which is also welded to the handle. The drum is made from a sheet of 3mm steel plate 780mm long and 125mm wide. This is formed into a tube by rolling and welded up. Holes for the handle and rope holding bolts are made before rolling. The handle is made from a 1.5m length of 32mm pipe, wall thickness 4mm (40mm pipe could also be used and filled with concrete for greater depths). A squared U bolt with threads is welded through the drum 75mm above the handle and acts as a holding clamp for the flexible link (rope). This secures the nylon rope tightly in place. Measurements of the drum plate Thickness Dimensions Hole for handle
3mm 780mm X 125mm Hole centre 75mm from end of drum plate. Hole diameter 44mm. Placed centrally. Holes (2) for rope holding clamp Hole centres 150mm from end of plate. Hole diameter 18mm Distance apart 75mm. Drum movement restrictor plates (2) Welded on edge of drum opposite to the handle. Wooden bearing This consists of a teak block measuring 150mm X 150mm X 100mm. A 36mm hole is drilled centrally through the 150mm width of the block. The block should be boiled in oil for several hours and left to cool overnight. The block is then left to drain. The block is then fitted within the bearing box bracket, which is made of steel and mounted centrally within the drum. It is essential that the centre of the hole in the wood is dead centre within the drum. The bearing box bracket The teak block is encased in a steel box bracket made of 10mm steel plate (width 65mm). There are four plates welded together to form a box in which the wooden bearing is mounted. The rear (proximal) plate is also attached to the handle with gussets as supports. The four plates are called proximal (attached to handle), distal (fitted with 2 bolts for securing the wooden block, and two side plates (upper and lower). The proximal and distal plates are each made 205mm long (width 65mm). The two side plates (fitted and welded within the proximal and distal plates) are102mm long. These are welded to the distal and proximal plates 152mm apart. The block which measures 150mm X 100mm can then be inserted within this steel box which has an opening of 102mm X 152mm. The block is tightened in position with 12mm bolts which are threaded though nuts welded to the plates. These holes are drilled in the distal plate (2 bolts), and side plates (1 bolt each) and nuts are welded over the holes. Bolts are then screwed through the nuts to hold the block tightly in place. The bolts are tightened onto the wooden block. A standard
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Bush Pump spanner can be used for this purpose. The Standard Bush Pump large spanner is used for the main head bolt (pivot pin). Four bolt configuration Each side plate (upper and lower) has a 14mm hole drilled in it centrally. The distal plate has two 14mm holes drilled in it – these being 75mm apart. A 12mm nut is welded over each hole and fitted with a 12mm nut. The two nuts placed through the distal plate are 40mm long. The two nuts placed through the side plates are 30mm long. These bolts penetrate the wood slightly when tightened. The two bolts tightened through the distal plate will press the block well into the proximal plate and also indent the wood slightly. Gussets For increased strength to the handle the proximal plate is fitted with two gussets. These are triangular shaped 12mm steel wedges (gussets) measuring 65mm X 45mm X 12mm. These placed 46mm apart to accept the 32mm GI pipe handle. These gussets are tack welded at first and then fully welded. These gussets (wedges) are also welded to the rope holding U bolt clamp. The rope holding U bolts and the pump handle are also welded to the drum casing. The pump handle is then introduced through the side wall of the drum held straight and welded to the gussets of the box bracket. Mounting the teak block inside the bearing box bracket. The block is placed in the bearing box bracket centrally Leaving about 1mm space all round. The four bolts are each tightened very securely. The two bolts on the distal plate are tightened first and then the bolts on the side plates are each tightened. The bolts are secured as tight as possible so indents are made in the wood. A tendency for some bolts to loosen has been noted and this is still being examined. However most times the bolt stays tight. it is easy to maintain tightness with a simple spanner which becomes part of routine maintenance of the head. Mounting the bearing box bracket in the drum It is essential that the hole in the block is placed dead centre in the drum. A special jig helps in this alignment. This should be checked before final welding. Once the parts are in place each steel component is tack welded in place and checked again for alignment. The pump handle is then introduced through the side wall of the drum held straight and welded to the box bracket and its two triangular gussets. All steel components are tack welded at first and then fully welded to the box shackle. One gusset (wedge) is also welded to the rope holding U bolt clamp. The rope holding U bolts and the pump handle are also welded to the drum casing. It is essential that the hole in the wooden block is dead centre within drum and also that the wooden block protrudes about 12 - 15mm on each side of the drum. This ensures a wood to steel contact with the pump head, with no rubbing of the drum itself on the pump stand. Thus the drum, handle, block holding U bracket and rope holding U bolts are all welded together. Final adjustments to the wooden block can be made by loosening the holding bolts, relocating and retightening.
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Drum movement restrictor plates To ensure the drum does not override the top dead centre position (which could be dangerous) two extra steel plates are welded to the edge of the drum. These two plates are made of 12mm steel plate and measure 40mm high by 35mm wide. These drum movement restrictor plates are welded to the rim of the drum plate. These plates are placed diametrically opposite to the handle. All surfaces of these plates are rounded off before welding to the drum and the final weld is also made smooth. These plates ensure that the handle cannot move above top dead centre on the stand. Smoothing of drum surface It is essential that all surfaces over which the rope passes are smooth. The drum is polished so that all abrasions and rough surfaces are removed. The pulley wheel on the shackle is also polished to make it very smooth. DETAILED DESCRIPTION OF THE SHACKLE The “shackle” is built up by welding together a pulley wheel, two 16mm pumps rods, a steel washer and a pump rod connector. The diameter of the pulley wheel is 50mm* (60mm has also been tried) and its width 30mm. The wheel is shaped to take the rope, with the hollowed out section being 5mm deep (this is shaped on a lath). Two 16mm pump rods are cut, straight at one end and angled at the other, the longer side being 100mm in length and the sorter side 90mm in length. The 65mm diameter washer is 6mm thick and is drilled with a central hole of 18mm diameter. Two versions of the rod socket are currently on test, one which has a lock washer and one without a lock washer. The rod connector (socket) is 40mm long in the version without a lock washer and 30mm long with the lock washer (which is 10mm thick). The two rods (side arms) are welded to each side of the pulley wheel along the middle line. The distance between the top of the connector or nut and the outer pulley wheel is 20mm. This distance is 25mm between the inner surface of the pulley wheel and the top of the socket (or socket and nut). The rod connector is welded upright and centrally to the washer in its dead centre, directly above the central whole. The two pump rods are welded to the washer and the welding linking the rods. The washer and rod connector is built up to form a strong and rigid unit. A full weld extends the length of the rod connector on either side. The whole unit is welded thoroughly. All surfaces in the pulley wheel are thoroughly cleaned up to make all surfaces along which the rope passes very smooth. This requires taking off all flecks of weld material with a round file and then polishing with paste. The unit can be painted with red oxide. One configuration allows for a lock nut to be placed on top of the rod connector. The second configuration does not use a lock nut. It needs to be established if the lock nut is essential in this unit. It is very possible that the rod will loosen in the shackle, as this depends on the tightness of the fit which will be variable. Tool to tighten the top lock nut A simple tool is required to tighten the rod lock nut in the shackle, if a lock nut is present. This is made of plate as shown in the photos later. The tool can slip in within the shackle and can tighten the nut within the small space provided. Alternatively the locknut can be tapped tight with a screwdriver and spanner. This part is exposed for inspection at all times. A lock nut is desirable, as sometimes the rod
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may become loose in the shackle. What remains is an easy method of tightening the locknut to the shackle. Flexibility of concept The pump head has been designed to accept a wide range of steel down the hole pipes (32mm, 40mm, 50mm, (and with a modified water discharge unit, 65mm pipe as well). These can be fitted to the water discharge unit through steel (GI) reducing bushes. Primarily the new head has been designed to match 32mm GI pipes. This will make it compatible with down the hole components of the India Mk II pump. Because the stroke length can be adjusted, the pump head can also be used with standard India Mk II cylinder, although with reduced water output compared to the longer 75mm Bush Pump cylinder. A combination of an India Mk III cylinder and India Mk II end caps provides extra cylinder length. PVC and HDPE pipes can also be used with this design, but require field testing. Steel pipes are the preferred material for rising main. Rods can be 16mm mild steel or 12mm stainless steel. Bush Pump and Indian Mk II/III cylinders and foot valves can be fitted. The 32mm pipe can be connected through a reducing bush (50mm to 32mm) to the standard 75mm brass cylinder used in Zimbabwe. The same reducing bush is use to connect the pipe to the water discharge unit. 10mm, 12mm and 16mm rods can be used with the system. 12mm rods are best stainless steel as in the India Mk II design. The rod connector in the shackle is modified accordingly. A wider range of cylinders can also be used. This includes the India Mk II cylinders (cylinder length of India Mk II end caps with India Mk III barrel is about 350mm). The length of the existing 75mm “closed top” brass cylinder used on the current Bush Pump can also be shortened from 600mm to 450mm. This requires extra care in fitting and get rod length correct. Choice of rope Several types of rope are available for use. The preferred rope is called white “marine” rope made of polyester. Another type of rope known as poly-steel rope is made of polypropylene. This is more resistant to abrasion than the polyester rope, but it tends to twist during use. The ideal diameter for the polypropylene rope is 16mm, but 12mm and 10mm rope will work, although the working life will be reduced. When polyester rope is used, this will normally be 12mm in diameter. In emergencies any type of rope will do. If a rope fails, local temporary replacement sho uld be easy with any rope strong enough to lift the rods. The choice of preferred rope has oscillated between polypropylene and polyester. Spare rope (2m) should be left with the chosen pump caretaker together with suitable tools (2 spanners). The rope is the main wearing part in the pump head, but is easily replaced by spare ropes or by locally adapted ropes prior to fitting the post appropriate rope type. Wear and tear on the nylon rope. Field evidence has revealed that the polypropylene and polyester ropes are strong enough to lift over 40m of 16mm pump rod and possibly more (possibly 60m). It has however been established that these ropes are sensitive to sharp edges and rough items placed in the path of the rope. It is essential that the
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rope rides over smooth steel components throughout its passage through and around the pump head. The main wear points have been centred around 2 points on the pump head a) the box shackle and b) touching on the drum movement restricting plates. Refinements have been made to both these potential wear points on the rope. The drum movement restrictor plates are placed well to one side of the rope and the rope passes through a pulley wheel in a revised design of the shackle. Adjustment of the rope The rope length is adjusted so that the rope is taught throughout the normal range of pumping. The shackle should just avoid touching the drum when the handle is moved downwards so it touches the ground or concrete apron. Loosening of the wooden block Block shrinkage was noted in several cases in earlier pump trials leading to block movements within the drum. A more recently designed bearing box bracket where bolts are tightened and driven into the wood hopes to overcome the problem of wood shrinkage. Replacement of the teak block Since the block can easily be removed, the teak block can easily be replaced. However it is most likely that the teak block may be long lasting and may outlive several other parts of the pump head. Possible abuse Whilst the flexible link (rope etc) can be cut with a knife, it is easily replaced by any flexible rope of any type strong enough the pull the rods. However in current trials there is no evidence of deliberate cutting of the rope by individuals. Current evidence shows that communities ha ve been prepared to mend or fix a worn or torn rope, so that pumping continued. This is a positive sign. Steel cable can also be used, but is more unsightly and more expensive. Extra lengths of suitable rope could be held in storage. However the nylon rope is not an expensive component and is manufactured in Zimbabwe. This rope is made by Ropes and Nets Pvt Ltd. In Europe it is available on large drums. 12mm white nylon rope appears to cope with this demanding situation better than 16mm poly steel rope. The rope is easily replaced, and this has been demonstrated both at Hopley and in Bulawayo. Forgiving nature of the pump head As with the B type head, all the bolts in the pump head assembly can be removed and the pump can still be made to work by local ingenuity. The working parts of the pump are exposed and available for inspection and repair. The Bush Pump’s reputation to take hard handling and prolonged use, even in a harsh working environment are well established. The universal nature of the pump head may have advantages on the international scene. It may, for instance be used where routine “down the hole” management of the India Mk II pump has become standard practice.
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Ease of handling, maintenance and repair 1. Pump head The revised pump head allows the working parts of the head (drum and rope) to be removed easily for replacement or refurbishing. The main wearing components of the pump head is now the rope. The use of parts which can be replaced, even temporarily by locally available fittings, rope, bolts or steel rods etc, is seen as an advantage in the rural setting. The use of a flexible link which can be made (if needs be) of a variety of materials may have appeal. This means that the head of the pump can be maintained at minimal cost in the rural and other areas. The latest design allows for the block holding bolts to be tightened or the wooden block to be replaced if necessary. Spare drums and shackles should be available and held by those responsible for the maintenance of the unit. 2. Down the hole components The use of 32mm or 40mm GI pipe makes the pipes lighter and thus easier to lift. They are also cheaper than 50mm pipe. The use of 32mm pipe on the India Mk II and its replacement has become a slick and well practiced method of servicing the pump. The use of steel pipe used with the Bush Pump is similar to the use of steel pipe used in the India Mk II. It is only the size and weight of the pipe which differs. The methods of removal and installation have similarities. The India Mk II pump uses 12mm stainless steel rod, whereas the Bush Pump uses 16mm mild steel rod. But the two are interchangeable. It is possible that the larger rod inside a smaller pipe may reduce water output. Stainless steel pump rods suitable for the Bush Pump are not currently made in Zimbabwe. However a conversion of one down the hole system to another would not be difficult either in Zimbabwe. The pump could also be adapted to use Afridev down the hole components although water output would be much reduced. Bearing durability The exceptional durability of the bearing is unique to the Bush Pump, and should last for at least 10 years before replacement is required. 25mm of wear on the wooden block are allowed in this design. The block can be turned over and refitted within the box bracket. But teak blocks which are boiled in oil are essential for a long working life. Teak block replacement is possible on the new units. Strength and durability of the drum The combination of teak and steel within the steel drum develops great strength. It is easily capable of lifting 70 kg of rods and much more. A handle length of 1.5m (32mm) has been chosen as an overall standard. For shallower lifts a shorter handle can be used and can be pumped at a higher rate. For deeper lifts a 40mm handle may be used and this could be filled with concrete. However the long term durability of this drum unit is not yet known, simply because this concept has never been tried before (comment – December 2007). The pump is now almost ready to be used on a second series of trials at greater depths and increased pumping demand. Crucial components The drum, shackle, drum restricting plates and rope components are the most crucial part of this design and these have been improved considerably over the course of the early trials in Hopley Farm and in Bulawayo. The drum and rope can be replaced in a few minutes using a special spanner which can deal
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with M24 and M16 nuts. The drum restricting plates and their possible wear on the pump head still requires close inspection but their latest relocation of the drum appears to have reduced former problems of wear on the pump stand. In a pump head maintenance kit, a spare drum may be available and spare sets of ropes and the two spanners described above. With these parts it should be able to keep the pump head operational for some period of time. This period is yet to be specified from extended field trials. Stages of pump head improvement under trials (Initial design August 2006) Improvements 1. Surround teak block with steel U bracket and bolt 2. Add concrete to drum in 2 stages 3. Block movement restrictor added 4. Refine “flared” rope holes within box shackle to reduce wear on rope (later improved with pulley wheel) 5. Drum plate increased from 2.5mm to 3mm 6. Drum width reduced drum 140mm to 125mm (to allow some protrusion of wooden bearing) 7. White nylon rope replaces blue poly-steel rope 8. Small floating washer added 9. Position of block movement restrictor modified 10. Pulley wheel added to box shackle. 11. Construction and testing of simpler shackle unit (not in box form) 12. Ensure smooth working surfaces on pump head where the rope is attached. 13. Method of restricting lateral movement of block within drum devised. 14. Revision of method of holding drum within a box bracket and 4 tightening bolts 15. Revision of method of holding drum within a box bracket and 4 tightening bolts 16. Flanges linking the box bracket to the rim of the drum introduced 17. A bolt access hole and tube designed to gain access to one of the block tightening bolts from outside the drum. 18. Revert back to poly-steel rope as preferred type 19. Weaker concrete (5:1) mix used as filler in place of strong mix (2:1). This enables the cement to be removed and bolts tightened and even teak bearing replaced. The cement now becomes a filler and has no mechanical properties. 20. Concrete filler abandoned. 21. Box bracket revised in shape so that plates are welded directly to the drum 22. Revision of drum restrictor plate position 23. Addition of lower floating washer within water discharge unit with a spacer ring (as in B type). Experiments with down the hole components The “C” type head has been designed for use with 50mm, 40mm or 32mm GI pipe and 16mm pump rods. However the pump trials include the use of PVC pipe and 16mm pump rod. Time will tell if this PVC steel combination can be successfully accomplished.
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Testing with Zimbabwean “down the hole” components The cost of down the hole components cannot only be reduced by fitting smaller GI pipe. A shorter brass cylinder has been tried at 350mm length as compared to the standard 600mm version. But this has proved to be too short and does not give the flexibility during the fitting stage compared to the 600mm version. The minimum length for the 75mm cylinder should be 450mm. Also the 63.5mm open top cylinder should be retried, although not with the expectation of fitting larger 65mm NB steel pipes. Theoretically the single brass tube concept, expanded above and contracted below (as made by V&W Engineering) should be cheaper to manufacture than the 63.5mm India Mk II/III cylinder. The low cost of the India products is due to high rate of production and not necessarily related to design. A second way of lowering the cost of the brass components of the cylinder/foot valve combination is to reduced the size (and therefore the weight of the brass component) of the heavy duty and highly successful Bush Pump foot valve. This unit (when properly made) is a masterpiece of engineering design and should not be lost to the world of pump development. With refinement the unit could be made smaller. During the 1980’s a smaller model of this unit was available but no sample has been found by the writer. Using an identical design concept a smaller but equally durable unit could be made New casting moulds would need to be made. Also there has been some discussion of testing chromium or nickel plated caste steel cylinders in Zimbabwe (from the Bulawayo side). This could be undertaken. A chromium plated cylinder was manufactured in Zimbabwe during the 1970’s but was discontinued. The writer has a sample. Testing with Indian MK II/III “down the hole” components It is important (for international reasons) that the pump head be tried with India Mk II down t he hole components imported from India at low cost. This would include a special India Mk II/III hybrid cylinder (with foot valve) and 12mm stainless steel rods. There should be closer collaboration between Zimbabwe and India on this aspect. The India Mk II/III cylinder and rods are of high quality and should be tried in Zimbabwe on the “C” type pump head. The Mk II cylinder will work down to a depth of about 60m which covers most of the units fitted in Zimbabwe. If extended trial prove favourable, it would be desirable that the C type head also be tried in countries like Uganda and or Ethiopia. A long life bearing, easily replaced flexible link and robust pump stand may prove desirable in such countries. Testing with Afridev pump “down the hole” components The C type pump head can also be adapted to pumps that use PVC pipes such as the Afridev pump. Pipes from the Afridev pump could be adapted to fit the C type head. The Afridev has a low water output compared to the Bush Pump and user perception would need to be tested. But the 50mm piston can be pulled out of the rising main. Some modifications to the Afridev down the hole components might be considered during this exercise. Further testing The “C” type pump head needs further trials in heavy duty se tting and also at deep settings. The nylon rope changes shape under tension and becomes hardened. Its life in different settings is unknown at the
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moment. Trials on at 60m and 80m settings need to be undertaken as well as endurance trials with long hours of daily service. It is unlikely that the rope link will cope with 100m settings. Drawings High quality drawings should be made of the “C” type head once it has reached near final design. This may be possible in early to mid 2008. It is essential that potential manufacturers of this trial pump are knowledgeable on exact specifications. If this design is found to be acceptable after endurance trials, official drawings can be made and lodged with the Department of Water (GOZ). The “B” type Bush Pump which is still the official standard hand pump for Zimbabwe was field tested for 2 years before it was accepted by the NCU and NAC of the GOZ. It remains the National Hand Pump for Zimbabwe. The new design, whilst being simpler and lower in cost must prove itself in the field, both under endurance testing and also testing at great depth. This is a hard act to follow. As we have seen, the need to consider changing from “B” type to “C” type fell away as economic conditions in Zimbabwe improved. Consequently the development work was brought to a conclusion. The “B” type Bush Pump was retained as the National Standard Hand Pump of Zimbabwe.
Peter Morgan Harare January 2008 Updated June 2013.
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Selected series of photos showing “C” type Bush Pump testing and main parts of the pump
Early “C” type Bush Pump trials in Hopley Farm and Bulawayo
Attachment of rope on the drum (before holding plate added). Attachment of the rope to the box shackle (earlier design) showing rubber buffer and small floating washer.
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Drum with box bracket surrounding the teak block and showing the 6 bolts passing through nuts welded to the bracket. The bolts are tightened hard on the block. Right: showing the rope holding bolt arrangement. Once the hole in the block is centred all steel components are welded together
The box bracket welded to the rim of the drum. On the right the drum movement restrictor plates.
On the left the first prototype of a simpler shackle, probably the most promising final design. In this design with rod socket is 40mm long and there is no provision for a locknut. An alternative uses a 30mm socket and room for 10mm lock nut. The pulley wheel has a diameter of 60mm. A 50mm diameter pulley is also being tested.
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Trials of the “C” type Bush Pump at Chisungu School, Epworth This pump was fitted over a 12m deep well at the Chisungu Primary School in Epworth in January 2008 serving about 2200 pupils and staff. It is still in service in July 2013. During that period seals have been replaced and faulty rods and pipes. The wooden block also became loose and was refitted. The pump operates at a shallow depth and is protected, since it operates within the school environment. In other parts of Epworth Peri-Urban settlement, the National Standard “B” type Bush Pump is used. This is more rugged and able to cope with much heavier duty and deeper settings.
The “C” type Bush Pump in use.
The pump can get busy!
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Parts of the Pump
Overall view
From the side and rear.
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