Performance evaluation of hydraulic ram pumping systems for small-scale farmers: a case study of West Pokot county, Kenya

Water is a basic commodity essential for human, industrial, and agricultural development (Januddi et al. 2018). The need for water has been the key motivation that drives humankind to venture ways of ensuring easy access to it through various pumping mechanisms (Mishra et al. 2018). The first self-pumping machine (hydram) that did not require external energy was invented in 1796 by the Montgolfier brothers (Mohammed 2007). These pumps were modified and utilized until the late nineteenth century after the invention of oil and electric-driven pumps (motorized pumps). Recently, the need for sustainable technology and renewable energy, especially in developing countries, has revived the interest in hydram technology (Kherde et al. 2020).

The effect of climatic change and global warming has adversely affected the water supply for domestic and agricultural use. The small-scale farmers who depend on rain-fed agricultural systems have incurred losses due to unreliable rainfall patterns (Ochieng et al. 2016). These farmers are unable to irrigate their farms due to their limited financial capabilities to acquire and operate oil or electric-powered pumping systems. The solution is to look for an alternative that is cheaper and more self-efficient, the hydraulic ram pumping system (Hussin et al. 2017). Therefore, a more reliable and cost-effective system for irrigation during unfortunate events and also to act as a water supply is required. The most appropriate system will be hydraulic ram pumps.

The hydram pumping system is not a new technology in West Pokot County, Kenya. The farmers have embraced the technology because the area is endowed with a good river network system with a good potential drive head for the pumping systems. The pumping systems in West Pokot are mainly used to supply water from the flowing rivers and streams for the purpose of domestic use and small-scale livestock farming. Unfortunately, the locals lack the technical know-how capacity of the hydram technology and therefore have fabricated and installed hydram pumps that were performing with low efficiencies. Therefore, this study investigated the existing hydraulic ram pumping systems in West Pokot County, Kenya, to assess these systems' design and performance characteristics. A low-cost hydram was designed and fabricated using locally available materials. The pump was tested by varying the drive and delivery head and its performance was assessed. The major limitation of the study was the behaviour of the existing pumps for different drive and delivery heads where they were installed. Similarly, the designed pump was observed for a limited number of drive and delivery heads with the assumption that the pump will simulate the actual site conditions.

Dhanwat et al. (2021) observed that hydram technology is the cheapest and most economical pump that can easily be fabricated since it consists of simple components which are readily available in the market suggesting that this technology is appropriate and sustainable for remote locations.

According to Mahmud & Rahman (2020), for a better output performance of a hydram pump, the drive length should be designed sufficiently to suit the site conditions. This is because the performance of the hydram strongly depends on the drive length. Since losses in the system can easily be predicted, one needs to effectively design the pump to suit the site conditions to ensure higher efficiencies are being achieved (Shende et al. 2015).

Inthachot et al. (2015) investigated the effect of different valves and pressure chamber sizes on pump performance. An off-shelf valve achieved an optimum efficiency of 30%. The larger pressure chamber achieved a higher efficiency. An overall optimum efficiency of 44% was achieved in the field. Iddi et al. (2018) found out that a larger pressure chamber with an additional weight on the drainpipe results in higher pump efficiency, while a smaller pressure chamber without additional weight achieved even higher efficiencies. According to Sethi et al. (2015), higher efficiency is obtained at higher drive heads with a lower delivery head than at lower drive heads. They concluded that the terrain conditions have an impact on the efficiencies of the pump.

The evaluation focused on the design and performance criteria of the eight pump systems. On design criteria, the following components were assessed: materials used for the system, the size of pump and pipe components, and the site conditions (stream flow rates, drive, and delivery head). The performance criteria included the efficiency of the system, failures, and breakages.

The existing pump was locally designed and fabricated by artisans. The process of determining the design and performance criteria of the eight existing hydram systems was as follows:

• Direct interview and interrogation of the owners of the sites.

• Observations and basic measurements.

The key components of design criteria that were necessary for this study were:

• Size of the pump which was determined by measuring the pressure chamber, the impulse, and the delivery valve. Tools used were the measuring tape and rope.

• Size of the drive and delivery pipes (both diameter and length) were measured using measuring tapes and rope.

• The drive and delivery heads were measured using GPS/GIS android applications.

• Stream flows were measured using a time–volume basis approach, by using a container of known volume and the time taken to fill the container measured.

• The material used for fabricating the system was determined through observation and interrogations.

The key components of performance criteria that were necessary for this study were:

• The pump efficiency was calculated after measuring the delivery flow rate using the time–volume basis approach. This was measured for a period of 1 hour for 3 days to establish the consistency of the results obtained.

• Amount of water delivered was determined by interrogating the individual owners.

• Failures and breakages were determined through observations and interrogation of the individual owners.

The drive head and the delivery head were the key parameters for investigation. The variation of both heads significantly affects the quantity of water delivered by the pump (Than et al. 2019).

Table 1 shows the drive heads and delivery heads used for the experimentation of the fabricated hydram.

The investigation of the existing eight hydram pumping systems showed that 87.5% of hydram pumps are made up of steel. The majority of the pumps were of size 80/40 mm configuration (i.e., the inlet pipe size 80 mm and outlet pipe size 40 mm) and 80/25 mm configuration (i.e., inlet pipe size 80 mm and outlet pipe size 25 mm) that constitute 50 and 37.5%, respectively, of the investigated pumps in West Pokot.

It was observed that 25% of the pumps were in working conditions, while 75% of the pumps were not working, of which 12.5% resulted from the failure of a pressure chamber, and 37.5% resulted from the failure of the valves.

These pumps had lower efficiencies of less than 30% due to inadequate design of the system meaning, their designs are not tailor-made to ensure pumps will be working as per site conditions (such as the drive head and the anticipated delivery heads) and pumping requirements that are the flow rates, build-up pressures, and the water velocities within the pump as a result of site conditions.

An average pressure of 92.5 kN/m² was obtained in set-up 3 while an average of 58.7 kN/mm² was obtained in set-ups 1 and 2. Therefore, it is observed that pressure in the hydram increases with an increase in delivery and drive heads. The pressures in the hydram are due to the water hammer effect that results to pressure waves that cause the intermittent closure and opening of impulse and delivery valves that enables water to be delivered. Optimum efficiency of 54% was obtained in set-up 1 and a minimum of 51.4% in set-up 3. The drop in efficiency results from the increase in the delivery/drive head ratio, thereby the hydram pumps lesser water with a great amount of water wasted as a result of an imbalanced delivery head-to-drive head ratio.

The existing systems exhibited low efficiencies of less than 30%, with 25% of the investigated pumps working. The major cause of failure was the imbalance of the pressure within the pump as a result of an improper design of the valves and pressure chamber. The efficiency of the pump depends on the proper design of the valves and the pressure chamber, since these are key controllers of the pressures and the velocities of the system, which thereafter affects the pump's efficiency (Kimaro 2018).

The site conditions, drive and delivery heads, and stream flows are key components when installing the pumps (Asvapoositkul et al. 2019). The existing systems failed due to inadequate designs of the head ratio to flow ratio. The higher head ratio results in high-pressure build-up in the pump. This pressure is due to the water hammer effect of the pump that causes a portion of water to be pumped to the delivery tank (Inthachot et al. 2015). The higher pressure generated in the pump can destroy the pump components, that is the valves, pressure chamber, and pipes. Therefore, a pressure chamber should be designed to absorb the pressure within the pump (Mishra et al. 2018).

The prototype pump designed and constructed was able to achieve a higher efficiency of 54% compared to an efficiency of less than 30% for the existing systems, this was possible by ensuring the components of the pump have been designed to perform well under the prevailing site conditions (Januddi et al. 2018). According to Iddi et al. (2018), pressure chamber design with weight alterations can significantly improve the pump's efficiency. When the delivery head and supply head varied, it was observed that both the amount of water supplied and water wasted through the waste valve increased linearly as in Figures 9 and 10, respectively. This is because when the supply head increases, the velocity and momentum of the water in the drive pipe also increase the pump flow rate, delivery power, and pump efficiency.

Hydraulic ram pumps have great potential in providing alternative pumping solutions to rural populations for domestic and agricultural use. The investigation carried out showed that hydram technology is well utilized in West Pokot County, Kenya. This is because it is cheaper and easy to fabricate and install as compared to motorized pumping systems. The investigated systems, however, performed with low efficiencies of less than 30%. The study, therefore, tries to sensitize and improve the locals' designed systems by providing a simplified designed prototype that they can use to develop new systems and also highlights how they can improve their existing systems. From the study, the pump was able to achieve an optimum efficiency of 54% with an optimum delivery flow rate of 12.938 L/min, further studies can be carried out to improve the efficiency of the pump by modifying the pump, that is the valves and pressure chamber.

The work reported here was undertaken as part of the Building Capacity in Water Engineering for Addressing Sustainable Development Goals in East Africa (CAWESDEA) project which is part of the IDRC-funded programme on Strengthening Engineering Ecosystems in sub-Saharan Africa. CAWESDEA Project is led by Global Water Partnership Tanzania in collaboration with Makerere University (Uganda), Moi University (Kenya), and the University of Dar es Salaam (Tanzania). We acknowledge the support from CAS Consultants Limited for hosting the research reported herein.

All relevant data are included in the paper or its Supplementary Information.

The authors declare there is no conflict.