THE ROWER PUMP
by Richard Cansdale.
First published in Developing World Water in 1988
ONE of the images that has almost come to symbolise the African drought is that of a woman scooping dirty water out of a hole in a 'dry' river bed. Although to many this spectacle may suggest the total absence of water, the local people know that often the opposite may be nearer to the truth since rivers with deep sandy beds frequently hold a reservoir of underground water throughout the dry season.
Various techniques may be used to extract water from sandy river beds using either filter
units or well screens. When the rivers are flowing such systems tend to be regarded as filters since the water drawn through the bed will be substantially cleaner than the river water itself but as soon as the rivers dry up the ability to abstract clean water from deep in the bed becomes a most valuable technique. In 1982 the World Bank funded a training course to teach agricultural development workers in Kano State, Nigeria how to install well screens deep in the sandy river beds. Most of these wells - known locally as 'wash bores' - would be connected to petrol-engine pumps for irrigation but hand pumps were also needed by low income farmers for irrigation and also for their families' domestic requirements. Unlike the majority of hand pumps which draw water from directly below them, these would have to be 'off-set'; i.e. placed on the bank several
metres away from the intake.
Two years previously a most unusual hand pump had been developed in Bangladesh. The pump's most striking features were its inclined cylinder, a piston operated by pulling and pushing directly on the piston rod itself and an open discharge through the end of the cylinder. The pump, known as the Rower Pump on account of the similarity of its action to that of an oarsman rowing a boat, was claimed to be both easy to operate and very simple to maintain and in view of this several were tested in Nigeria. It soon became clear that the Nigerian farmers liked the pump but they wanted one with a much greater discharge. Furthermore, the leather cup seals as used in Bangladesh were of variable quality and had an unacceptably short life. With no other suitable hand pumps available it was decided to up-grade the original Rower Pump and offer a really robust version for which there seemed to be a clear need.
When the first Bangladesh Rower Pump was examined at the Consumer Association Testing
Laboratory its simplicity caused both astonishment and incredulity that it could survive their
rigorous testing procedures, yet it came through with flying colours. On further examination one can see why it was so successful. The elimination of the pivot and with it all mechanical linkages has immediately removed one of the prime causes of pump failure. The only regular point of wear is between the cup seals and the inner cylinder wall and although rubbing can occur between the piston rod and the pump mouth, damage is prevented by a steel bell mouth.
The upgraded version - now known as the SWS Rower Pump - differs from the original Bangladesh model mainly in the choice of materials. In Bangladesh the cost is kept to an
absolute minimum by using only locally available materials but since the SWS model is normally air freighted to remote places and durability is of crucial importance it was decided to use only top grade materials; stainless steel for the piston rod, bell mouth, nuts, bolts etc. and high pressure ABS plastic pipe and fittings for the pump body. Although ABS is somewhat dearer than PVC its resistance to fracture and better tolerance of sunlight is of greater importance. High density rubber seals were used in place of leather cup seals and the valve components injection moulded in an acetyl compound.
In Bangladesh the most popular size Rower Pump has a 50mm cylinder. This is normally
connected to tube wells and one has been operated by the author when the water table was as much as eight metres below ground level without too much effort. For very low lifts a 75mm model may be used. This is a single length of pipe the bottom end of which is placed in open water. It is quite portable and may be carried from field to field on the farmer's shoulder. SWS’s first version fell mid-way between these two, having a cylinder internal diameter of 65mm and is ideal for lifts of up to 3.7 metres. Since 1987 SWS has also offered a 52mm version for lifting up to 6.0 metres.
A particular feature of Rower Pumps is the large volume of water that may be pumped with relatively little effort. The broad cylinder combined with a long sweep of the piston permits a discharge of up to two litres per stroke, easily filling a 10 litre bucket in 20 seconds.
Although pump installation is very easy - it simply needs to be half buried in the ground -
the correct height and angle at which it is placed is critical for its easy operation so the open spout should be level with the operator's knee height and the cylinder placed at 30o from the horizontal. Pumping is achieved by the operator straightening the legs, pulling with the arms and leaning backwards. With so many of the body's strongest muscles involved the pump may be worked for long periods without fatigue. Initially very small children may not find the pump too easy to work but the T-handle is broad enough to allow two children to work together in unison.
During the design phase of this pump much emphasis was being given to the need for VLOM (Village Level of Maintenance) hand pumps. So from regular discussions with engineers at the Consumer Association, the original designers and the project in Nigeria which was testing the first prototypes, the new Rower Pump was able to incorporate features which would ensure durability and simple maintenance.
The foot valve is perhaps the best example of this since its seal is none other than a flat disk
cut from an old vehicle inner tube which may be replaced in moments. In any case a recent study tour concluded that many SWS Rower Pumps had not required any maintenance in more than a year's trouble-free operation.
Suitability For Village Water Supply
Self-priming hand pumps are regarded by some as unsuitable for domestic water supplies due to the possibility of them becoming polluted with contaminated water during priming; in addition the upward pointing spout of the Rower Pump has received some criticism since it does little to protect the pump from contamination. Unfortunately there are countless situations - on the banks of streams, beside spring fed water holes etc. - where conventional deep well hand pumps are simply not an option making the need for a reliable suction mode pump even more important. An unattended Rower Pump can hold its prime for weeks but when priming is necessary one cupful of water is sufficient to lubricate the piston for quick and easy priming.
The upward pointing spout has been the cause of some concern although this is perhaps the price one has to pay for simplicity. A variety of delivery fittings and closure plugs are currently being tested although recent research suggests that Rower Pumps are no more prone to contamination than other conventional models.
In Bangladesh more than 10,000 Rower Pumps had been installed by the end of 1985 and of
these most were used for both irrigation and domestic water supply. The SWS model has been sent to more than twelve African countries, including Zaire, Sudan Nigeria, Zimbabwe, Zambia and Kenya. Local Assembly and manufacture is the aim once continued demand is assured but without doubt Rower Pumps have found a niche where they have an important role to play in the development of rural water supplies.