The Zimbabwe Bucket Pump An update

Transcription

1 The Zimbabwe Bucket Pump An update Peter Morgan A publication by Aquamor-Zimbabwe. February 2014

2 Introduction The Bucket Pump is a water lifting device which uses a tubular bucket to raise water from a tubular well known as a tube well. These wells are usually drilled with a hand auger. They work best in shallow aquifers, where the soil is soft and easy to penetrate. Where conditions are suitable a well can be hand drilled in a few hours, then cased with a PVC pipe, which is surrounded by a gravel pack. The pipe ascends through a concrete headworks consisting of an apron and water run-off. The pipe is closed off at the top with a lid. The tubular buckets are fitted with a non-return valve at the base. Work on this concept was carried out in Zimbabwe at the Blair Research Laboratory in the early 1980 s. At first the tube-buckets were raised on a rope directly by hand. Later models used a windlass system to raise the bucket. Initially these windlass adapted bucket pumps were hand made using treated gum poles as windlass supports. Later the concept was commercialised, and the pumps were mass produced. Bacteriological studies revealed that the quality of water drawn from tubewells fitted with tubular buckets was a significant improvement on water drawn from wider diameter wells. This was due to the high rate of change of water within the tubular well chamber compared to wider diameter wells. The water in the well chamber was flushed out and rapidly replaced by fresh ground water as water was withdrawn with the bucket. The work on this concept was also performed using a hand operated drilling rig, made with an auger fitted to water pipes, which were turned with wrench spanners or cross bar. This method worked satisfactorily down to shallow depths of up to about 6m. Later V&W Engineering designed the VonderRig, a more sophisticated hand drilling machine. V&W also made the commercial version of the bucket pump. Over the years the Bucket Pump was phased out of the national program, being replaced by the more versatile Upgraded Family Well, which used standard buckets to raise water with a windlass system from wider diameter, brick lined wells. Tens of thousands of these units were built and the concept was endorsed by the Government of Zimbabwe. 2

3 Some background How it works The bucket pump consists of a tubular bucket fitted with a non-return valve at the base and a simple handle at the head. This bucket, supported by a rope or chain is lowered and raised through a tube-well. Tube-wells are normally hand drilled holes which enter the water table and are lined with PVC casing. Gravel packs are introduced at the base of the casing and around the casing. Normally these pumps are fitted to shallow tubewells normally less than 12m deep. They are best used at family level where they can be looked after and maintained properly. The methods used should be low cost, durable and easy to manage. As the bucket descends through the water within the tube-well, it picks up water, which passes through the non-return valve. When the bucket is raised the valve closes, bring up a full bucket of water. This water is poured into a bucket sitting on the well apron. The bucket can be raised and lowered by hand direct or through a windlass system. An important part of the Bucket Pump, as it is with an Improved Family Well, is that a strong concrete Apron and water run-off are built around the tube-well opening. These provide a hygienic environment surrounding the well head. Early Bucket Pump with wooden windlass supports and surrounded by a protective apron. 3

4 In this system there is a rapid passage of water from the aquifer into the tube-well casing and then up within the bucket itself to the surface. This has the effect of flushing water through the system rapidly. The overall effect is that water quality is higher compared to larger diameter wells. The flushing effect of water passing through the Bucket Pump system The high rate of change of water in the casing, where fresh water is constantly entering the base of the casing and being withdrawn from the top, has a significant effect on the final purity of the water (provided that the tube-well is properly sited). Buckets are handled at the surface, and might be expected to take down contaminants into the tube well. However if these contaminants enter they are rapidly diluted as water is flushed through the system - fresh water entering the base of the tube-well to replace water being extracted at the surface. The following table compares E. coli levels in poorly protected traditional wells, bucket pumps and hand pumps fitted to tube-wells. Levels of E. coli are not so different for Bucket Pumps and Hand Pumps (in this case Blair Pumps). Data taken from Rural Water Supplies and Sanitation. Peter Morgan MACMILLAN 4

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6 Demonstration of the flushing effect Supporting evidence for the flushing effect is shown in the following figure which illustrates the results of an experiment where contaminants were added to a tube-well fitted with a Bucket Pump. In the experiment a sample was taken before the contamination was added and analysed for bacteria (Faecal E. coli/100ml sample). The initial sample showed zero bacteria, but reached a peak in the second bucket withdrawn after contamination was added of 180,000 E. coli/100ml sample. This was dramatically reduced in the following samples taken from buckets, showing how fresh water coming from beneath diluted the concentrations of bacteria drawn up in the buckets. Bucket Pumps are best used in family settings where they can be well looked after. In the family setting, the concept of ownership is resolved, and the family itself takes on the responsibility for maintenance and upkeep of the facility. If there is any doubt about security, the lid covering the tube- well can be locked in place and the bucket and rope can be taken indoors at night. It is common practice in some areas, that the windlass is kept inside the house at night. Acknowledgments for the early work Many thanks to the Blair Team of years ago, Ephraim Chimbundi, Fambi Gono, Philimon Ndororo, Joshua Mazanza, Felix Chawira, and Michael Jere. Also for the support of the Ministry of Health. Jan

7 Basic stages of construction This uses the following sequence: 1. Making the bucket 2. Drilling the tube well 3. Building the head-works 4. Putting to use 5. Upgrading In this case a 165mm diameter hole is drilled into the ground manually so that it passes the water table as far as possible. This tube-well is fitted with a 110mm PVC casing surrounded by a gravel pack (10mm granite chips). The bucket is hand-made using a length of 90mm PVC piping with a handle at one and end a non-return valve at the other end. A suitable head-works (apron and water runoff) is built around the PVC pipe. At first the bucket can be raised and lowered directly by hand. Several upgrades are possible, the first being the fitting of a windlass system to keep the rope in a hygienic position and the assist with raising the bucket. The tube well can also be fitted with a Blair Pump or a Bush Pump if necessary if the well provides enough water. It is important to drill the hole as deep as possible into the aquifer. The best drilling time is at the end of the dry season when the water table is at its lowest. However with hand drilling the tube-well can be drilled at any time of the year. The simplest and cheapest version of this system does not use a windlass. But this can be upgraded to use a windlass system. The cap placed over the end of the PVC pipe can be locked in place with a chain and padlock to increase security. 7

8 Making the bucket This is made with a mm length of 90mm class 6 or class 10 PVC pipe with a non- return valve fitted into the base and a simple handle fitted into the top. Start by fitting the brass non return valve. Brass non return valves are cheap and commonly available in hardware stores. The half or ¾ inch or one inch non return valves can be used. The valve is inserted in a concrete plug as follows. A length of the 90mm PVC pipe is cut off to make a mould in which the high strength concrete is poured. This has the same length as the non-return valve. If a metre of pipe is used, a part of this can be used to make the mould. A mix of 2 parts clean sharp river sand (200mls) and one part PC15 ( 100mls Portland cement) is used. 8

9 This is mixed into a paste And added between the valve and the PVC pipe mould This is allowed to cure for 2 days. Then the PVC is cut, allowing the plug of concrete which holds the valve to be released. 9

10 The valve plug is then allowed to dry and the outer surface is then applied with a hard setting epoxy adhesive. The lower end of the mm long PVC pipe is then gently heated over a flame. The plug is then pushed into the pipe. Fitting a handle The cut length of 90mm pipe used to caste the concrete plug is than cut again so it will fit inside the PVC tubular bucket. This doubles the thickness of the bucket at this point. This is bonded with PVC cement or fast setting adhesive. 10

11 Holes are drilled through the double thickness of PVC pipe to hold the wire handle. A hot nail can also be used. A suitable length of 3-4mm wire is cut and bent into shape and fitted in the two holes and acts as a handle The bucket/bailer is now complete. It is good to make a second unit as a back-up. 11

12 Time of filling of the bucket The filling time of the bucket, once it enters the water depends on the size of the valve and the length of the bucket. Also the open space allowed for water passage through the valve. Some flap valves on brass non return valves open wider than others. Also there are other types of non-return valves that might be considered, such as a golf ball sitting on a standard PVC fitting. The following valves were tried and timed to fill a 500mm length bucket (carrying about 2.5litres of water). Type of valve Half inch (12.5mm), brass ¾ inch (20mm), brass One inch (25mm) brass Golf ball type time to fill 500mm bucket 8.6 secs 9.0 secs 3.5 secs 3.0 secs Note that the ¾ inch brass non return valve allowed water to pass through at about the same rate as the half inch valve because the flap on this ¾ inch unit did not open fully. Clearly the most suitable brass valve is the one inch, and if used golf balls are available the golf ball. The golf ball type is slightly leaky, but may last longer. Making the golf ball valve A piece of 90mm PVC casing is cut to the same height as the PVC fitting. The fitting is placed centrally within the casing and filled with a very strong mix of river sand and Portland cement (2:1 or even 1:1). The movement of the ball is restricted by two galvanised steel wires 3 or 4mm thick. 12

13 The golf ball is fitted in place followed by the two shaped galvanised steel rods. 10mm should be allowed between ball and lower rod. Making bucket valve with one inch brass non-return valve This one inch brass non return valve opened fully and allows plenty of water to pass into the bucket. This is probably the best and easiest to make. The 90mm class 10 pipe is cut to the height of the valve. A very strong mix of river sand and Portland cement is used to fill the space. After a day or two the PVC section is cut off and used to thicken the upper wall of the bucket for handle attachment. 13

14 Various buckets and valves Various bucket valves being prepared together with their bucket tubes, in this case each 500mm long. The upper end of each bucket is thickened by adding the piece of casing used to mould the valve, and cut to fit inside the bucket pipe and held with PVC solvent cement. Some epoxy adhesive is added to the dried valve. The lower end of the bucket pipe is carefully heated over a flame. The bucket pipe is then pushed down over the bucket valve. A seal is made. A selection of pipe lengths and valves being tested 14

15 Drilling the tube-well Many rigs, augers and other methods have been used to make hand drilled shallow tube wells. The best available in Zimbabwe is called the Vonder Rig, designed by the late Mr Erwin von Elling. This can drill 165mm diameter holes down to depths above 20m. The same auger bit can be fitted to simpler pipes, cross bars and used without the work table for shallower tube-wells. Vonder Rig in use Also various other methods can be used where the holes drill through softer soils and sands and at shallow depth. The hole is drilled as deep as possible below the water table. Hand augers cannot penetrate hard rock. This subject has been widely studied internationally and local methods used in Zimbabwe will be dealt with in another manual. Two types of equipment used to drill tube wells in Epworth by the Blair Research Team in the early 1980 s. 15

16 Using Vonder Rig auger without a work table For shallower depths a full Vonder Rig may be unnecessary. The excellent earth auger can be welded to a shaft which can be turned directly by hand. The cutters of the Vonder Rig earth auger. In this cases welded to a shaft which can be turned by hand with a cross bar. The soil is cut and lifted up into the auger The cross bar is used to turn the auger. The auger is lifted when 2/3 rd full and emptied and put back into the hole. 16

17 Fitting the PVC pipe and adding the gravel pack Once the tube-well has been drilled as deep as is possible, the 110mm PVC casing and gravel pack are added to the drilling. If the material is easily available, it is best to wrap a piece of stainless steel screen around the bottom end of the pipe first. 10mm granite chips are used as gravel packing. First a 10 litre bucket full of chips is carefully poured down into the tube-well before the casing is lowered. Then the casing is lowered down the tube well. This PVC pipe is sold in 6m lengths. Joints are bonded with PVC solvent cement. In this simplest of arrangements there are no slots made in the casing. The aquifer water enters through the base of the PVC pipe. The tube well drilled. 10li of small granite chips are added to the drilling. Then the casing is lowered on top of the granite chips placed on the bottom of the hole Buckets of 10mm granite are carefully poured down into the annular space between the casing and the PVC pipe 17

18 Now the start of the head works is built. In this case a 1.2m diameter slab has been prepared with central hole. Using a slightly larger diameter, a ring of bricks is laid and corbelled in slightly to hold the slab. The slab sits on three courses of brickwork. A plug of concrete acting as a sanitary seal then placed over the gravel layer which comes to within 200mm of the ground level. The space between the brickwork and the PVC pipe is now backfilled with soil. 18

19 Placing the concrete well slab in position In this case a 1.2m diameter slab with a central hole (diameter about 120mm) was prepared ready to mount over the tube-well. The PVC casing should rise above the slab by about 100mm, and is cut at this point. The exposed casing is protected and surrounded by a concrete ring cast within a mould made from an inverted bucket. A flower pot is used to cover the PVC casing whilst strong concrete is placed in the space between bucket and casing. The outer wall of the raised head works is now plastered with cement 19

20 Making the water run-off and rim of the well slab A double layer of bricks is laid as a foundation for the water run-off channel. This should be about 3m long. Then bricks are stepped up to the level of the slab to form a cascade arrangement which allows waste water to flow down from the slab into the channel The walls of the channel are combined with the walls of the slab rim The bucket is removed and the whole unit neatly plastered and allowed to cure. The area around the tube-well is tidied up. 20

21 The step When the well slab is placed several courses above the ground, a convenience step can be built. The step. A few bricks laid in cement mortar is all that is required Adding chain anchor to the upper concrete ring For units which are owned and supervised by families, experience in the field with upgraded family wells reveals that the family itself often decides to fit a security chain. This type of security can also be fitted to this Bucket Pump arrangement. While the concrete ring is still not fully cured a slot can be cut on each side of the ring and a cut piece of chain link can be inserted and bonded with a strong mix of concrete on each side. This should also be allowed to cure before the unit is put to use. 21

22 Making a l lid for tube-well The opening of the PVC tube-well must be protected and is covered by a lid. The lid can take several forms. Ideally the tube-well outlet should be lockable if the unit is fitted in a family setting which is recommended. The lid can be made in concrete using the bottom section of a bucket as a mould. The bucket base is sawn off, two holes punched through the base and a wire handle fitted. A 9-10li bucket is used. The base of the bucket is used to prepare the lid. Two holes are made and the handle of 3mm wire is passed through as shown. The wires are bent inwards. A 110mm casing 50mm long is cut and the diameter reduced, being held with tape. 22

23 The mould being prepared for concrete. A 3:1 mix of clean sharp river sand and PC 15 cement is made and poured into the mould and levelled. The pipe is added centrally More concrete is then added within the pipe. This is left to cure and harden. The ring can then be removed. The unit is then left for a few days to cure and harden. 23

24 The final head-works showing security chain in position with pad locks fitted Security chain and locks fitted. The bucket and rope (or strap as shown in these photos) can be stored in the tube-well or in the home. With thanks to Oswald Chakauya who helped build the demonstration unit shown in this manual. 24

25 Conclusions This system may mark the simplest and lowest cost option for extracting water from shallow tube-wells. It is best suited for family use, where it can be cared for. The bucket and valve system is cheap and easy to make. Brass non return valves are not expensive and locally available in Zimbabwe and 90mm PVC casing costs between $4.00 -$5.00 a metre. A 500mm length is enough to make a bucket together with an extra mm for the valve mould and upper strengthening of the bucket. The volume of cement required is small, and may come from the single bag of PC15 (Portland cement) required to make the head-works. Some form of epoxy cement is required to cement the valve block and the PVC pipe together and PVC solvent cement. Rope may be used for raising and lowering the bucket, but the material shown here, strong strapping, used in the transport of goods, is popular in the rural areas of Zimbabwe. In any event the rope and bucket should cost less than $ The system is upgradeable. First a windlass system can be added to house the rope and make lifting easier. Such upgrades have been described in earlier works (Technical Manual for upgrading Family Wells, 2010, Peter Morgan and Annie Kanyemba, Aquamor. 2010). In Zimbabwe, a simple direct action lift pump, like the Blair Pump can also be added and even a Bush Pump, although this will be an expensive option for a family. The most interesting feature of this concept is the flushing effect where there is a rapid movement of water through the system which appears to have the overall effect of increasing the quality of water delivered from the bucket, even when it is handled. The water should be clear and taste good. This system will be placed on field trials during 2014 in certain areas of Zimbabwe, with bacteriological analysis being undertaken. As with all these devices, their success can only be judged over time. Only time will tell! Peter Morgan Harare February