HYDRAULIC
RAM PUMP SYSTEM DESIGN AND APPLICATION
Dr. Abiy Awoke Tessema
Head, Equipment Design
Research, Development and Technology Adaptation Center
Basic Metals and Engineering Industries Agency, P.O. Box 1180, Addis Ababa, Ethiopia
ESME 5th Annual Conference on Manufacturing and Process Industry,
September 2000
Reprinted with ESME
permission by the African
Technology Forum
ABSTRACT
Hydraulic ram pumps are water-lifting devices that are powered by filling water. Such pumps work by using the energy of water falling a small height to lift a small part of that amount of water to a much greater height. In this way, water from a spring or stream in a valley can be pumped to a village or irrigation scheme on the hillside. The main and unique advantage of hydraulic ram pumps is that with a continuous flow of water, a hydram pump operates automatically and continuously with no other external energy source - be it electricity or hydrocarbon fuel. It uses a renewable energy source (stream of water) mid hence ensures low running cost. It imparts absolutely no harm to the environment Hydraulic ram pumps are simple, reliable and require minimal maintenance. All these advantages make hydraulic ram pumps suitable to rural community water supply mud backyard irrigation in developing countries. In this paper, different aspect of designing a hydraulic-rain pump system is discussed. Application and limitation of hydraulic-ram pump is presented. Alternative technologies which compete with hydraulic ram pump, are highlighted. Finally, the Research, Development and Technology Adaptation Center (RDTAC) work on hydraulic-rain pump is presented and discussed.
Introduction
Hydraulic Ram Pump
System
Working Principle of
Hydraulic Ram Pumps
Applications and
Limitations of Hydraulic Ram Pumps
Considerations in
Hydraulic Ram Pump System Design
Hydraulic Rain Pump Design
Considerations
RDTAC's Work on Hydraulic Ram
Pumps
Hydraulic Ram Pump
Development Work of RDTAC
Conclusion
Ram Pumps have been used for over two centuries in many parts of the world. Their simplicity and reliability made them commercially successful, particularly in Europe, in the days before electrical power and the internal combustion engine become widely available. As technology advanced and become increasingly reliant on sources of power derived from fossil fuels, the ram pump was neglected. It was felt to have no relevance in an age of national electricity grids and large - scale water supplies. Big had become beautiful and small-scale ram pump technology was unfashionable. In recent years an increased interest in renewable energy devices and an awareness of the technological needs of a particular market in developing countries have prompted a reappraisal of ram pumps. In hilly areas with springs and streams, the potential for a simple and reliable pumping device is large. Although there are some examples of successful ram pump installation in developing countries, their use to date has merely scratched at the surface of their potential.
The main reason for this being, lack of wide spread local knowledge in the design and manufacture of ram pumps. Hence, the wide spread use of ram pumps will only occur if there is a local manufacturer to deliver quickly; give assistance in system design, installation, and provide an after-sales service.
Hydraulic Ram Pumps are water pumping devices that are powered by falling water. The pump works by using the energy of a large amount of water falling a small height to lift a small amount of that water to a much greater height. In this way, water from a spring or stream in a valley can be pumped to a village or irrigation scheme on the hillside. Wherever a fall of water can be obtained, the ram pump can be used as a comparatively cheap, simple and reliable means of raising water to considerable heights.
The diagram in Fig. 1 shows all the main components of a hydraulic ram pump system. Water is diverted from a flowing river or taken from intake structure of a spring. A drive tank is usually built between the ram pump and the intake to insure constant flow of water to the ram pump. The ram pump lifts part of the water coming through the drive pipe to a higher level at the delivery tank. A pump house is built to protect the ram pump and fittings from theft or accidental damage.
Fig. 1 Components of a Hydraulic Ram Pump Station
WORKING PRINCIPLE OF HYDRAULIC RAM PUMPS
Although hydraulic ram pumps come in a variety of shapes and sizes, they all have the same basic components as shown in Fig. 2. The main parts of a ram pump are Hydram body, Waste value snifter valve, delivery valve, air chamber and relief valve. Ram Pumps have a cyclic pumping action that produces their characteristic beat during operation. The cycle can be divided into three phases; acceleration, delivery and recoil.
Acceleration - When the waste valve is open, water accelerates down the drive pipe and discharges through the open valve. As the flow increases it reaches a speed where the drag force is sufficient to start closing the valve. Once it has begun to move, the valve closes very quickly.
Delivery - As the waste valve slams shut, it stops the flow of water through it. The water that has been flowing in the drive pipe has considerable momentum which has to be dissipated. For a fraction of a second, the water in the body of the pump is compressed causing a large~ surge in pressure. This type of pressure rise is known as water hammer. As the pressure rises higher than that in the air chamber, it forces water through the delivery valve (a non-return valve). The delivery valve stays open until the water in the drive pipe has almost completely slowed and the pressure in the pump body drops below the delivery pressure. The delivery valve then closes, stopping any back flow from the air vessel into the pump and drive pipe.
Fig. 2 Hydraulic Ram Pump
Recoil - The remaining flow in the drive pipe recoils against the closed delivery valve - rather like a ball bouncing back. This causes the pressure in the body of the pump to drop low enough for the waste vale to reopen. The recoil also sucks a small amount of air in through the snifter valve. The air sits under the delivery valve until the next cycle when it is pumped with the delivery water into the air vessel. This ensures that the air vessel stays full of air. When the recoil energy is finished, water begins to accelerate down the drive pipe and out through the open waste valve, starting the cycle again. Throughout the cycle the pressure in the air vessel steadily forces water up the delivery pipe. The air vessel smoothes the pulsing in flow through the delivery valve into an even outflow up the delivery pipe. The pumping cycle happens very quickly, typically 40 to 120 times per minute.
During each pumping cycle only a very small amount of water is pumped. However, with cycle after cycle continuing over 24 hours, a significant amount of water can be lifted. While the ram pump is operating, the water flowing out the waste valve splashes onto the floor or the pump house and is considered' waste' water. The term' waste' water needs to be understood. Although waste' water is not delivered by the ram pump, it is the energy of this water that pumps the water which is delivered.
APPLICATIONS AND LIMITATIONS OF HYDRAULIC RAM PUMPS
For any particular site, there are usually a number of potential water lifting options. Choosing between them involves consideration of many different factors. Ram pumps in certain conditions have many advantages over other forms of water-lifting, but in others, it can be completely inappropriate. The main advantages of ram pumps are:
Use of a renewable energy source ensuring low running cost
Pumping only a small proportion of the available flow has little environmental impact
Simplicity and reliability give a low maintenance requirement
There is good potential for local manufacture in the rural villages
Automatic, continuous operation requires no supervision or human input.
The main limitations are:
Specific situations in which other technologies may prove more appropriate are:
In
terrain where streams are falling very rapidly, it may be possible to
extract water at a point above the village or irrigation site and feed
it under gravity.
If
the water requirement is large and there is a large source of falling
water (head and flow rate) nearby, turbine-pump sets can provide the
best solution. Many ram pumps could be used in parallel to give the
required output but at powers over 2kW, turbine-pump systems are
normally cheaper.
In small-scale domestic water supply, the choice can often be between using a ram pump on a stream or using cleaner groundwater. Surface water will often need to be filtered or treated for human consumption, increasing the cost of a system and requiring regular filter maintenance. Under these conditions, to select a hydram pump, economical considerations compared to other technologies has to be looked at.
CONSIDERATIONS IN HYDRAULIC RAM PUMP SYSTEM DESIGN
The following factors need to be considered in hydraulic Ram pump system design.
Area suitability (head and flow rate)
Flow rate and head requirement
Floods consideration
Intake design
Drive system
Pump house location
Delivery pipes routing
Distribution system
For these considerations reference 1 is a good guide.
HYDRAULIC RAM PUMP DESIGN CONSIDERATIONS
Manufacturing
considerations - A choice between casting and welding method of
manufacture has to be made. Cast ram pumps are less susceptible to
corrosion and have longer life. On the other hand, cast ram pumps are
costly and cannot be made in a simple rural setting workshop. Usually,
for low and medium sized ram pumps welding method of manufacture is
preferred because of simplicity and less cost.
Maintenance
and service life considerations - The critical parts that require
frequent maintenance are bolts, studs and nuts. Therefore, it is
usually preferable to have stainless steel bolts, studs and nuts, even
though they are costly and difficult to source.
Material
availability
General considerations
Shape of hydram has little effect on performance
Valve design considerations. The correct design of valves is a critical factor in the overall performance of ram pumps. Hence, this needs special consideration.
Strength considerations. This determines thickness of hydram body and air chamber.
Others - such as size of air chamber, size of valves, tuning devices need special considerations. Reference 2 is a good guide for design of hydraulic rain pump dimensions.
RDTAC'S WORK ON HYDRAULIC RAM PUMPS
Adami-Tulu Hydraulic Ram Pump Maintenance - During performance follow up of hand pumps developed by RDTAC and installed around Ziway, a station of hydraulic ram pumps which were installed about forty years ago were discovered. Five hydraulic ram pumps in this station were used to supply water to a ranch located about 20 km away. However, the then status of the pumps was that only one out of five pumps was operational. The following parts of the hydram pump station were in need of maintenance.
Drive
pipe - The drive pipes of the hydram station were 6" galvanized
steel pipe. These drive pipes, due to long years of service, have been
corroded and leak at many points. The drive pipes were replaced by new
galvanized steel pipes. Flanged connections were made for ease of
maintenance.
Threaded parts of the hydram body (see Fig. 3). - The threaded parts of the hydram body were out of use due to corrosion. As a result, this required re-threading of the hydram body for fixing valve parts securely.
Fig. 3 Hydraulic Ram Pump Body
Bolts,
studs and nuts - These elements are the ones which had been replaced
often during the service life of hydrams. Hence, the studs were made
out of stainless steel and others were electro-galvanized for longer
maintenance free operation.
Waste
valve perforated disk (see Fig. 4) - This part
is made of bronze to prolong its life against corrosion. However, it
was discovered that it is damaged mostly due to wear. The part needed
to be cast out of bronze, machined and drilled. The bronze casting was
made by subcontracting it to private foundries. Casting of the part
without cavitation (porosity) had been a difficult task. The valve
needed to be re-cast again and again to get it to acceptable quality
standard.
Waste
valve-retaining ring (see Fig. 4) - Some of the retaining ring was
broken due to repeated fatigue loading and corrosion. Hence, they were
replaced as new.
Rubber parts - Besides bolts and nuts, these parts were the ones which needed to be replaced often. When found, all the delivery and waste valve rubber parts were damaged due to wear and tear. To manufacture them, a rubber mold was designed and manufactured. Addis Tyre Enterprise made the rubber valve parts to the required standard using the molds.
Fig. 4 Waste Valve, Retainer Ring and Rubber Parts of Adami-Tulu Hydraulic Ram Pump
Other - Parts such as diversion canal gate, header pipes, intake valves were re-designed and manufactured.
The hydram pumps after renovated successfully are shown in Fig. 5.
Fig.5 Renovated Adami-Tulu Hydraulic Ram Pumps
HYDRAULIC RAM PUMP DEVELOPMENT WORK OF RDTAC
Design - The design of hydraulic ram pump developed by RDTAC is shown in Fig. 2. The pump was 4" drive pipe designed to supply 80 litre/mm at a head of 45 m. This is sufficient for a village of 500 people and their cattle. In the design, casting technology was preferred for the main parts of the hydraulic ram pump for resistance to corrosion and long term maintenance free operation. Parts which are more prone to failure as a result of corrosion were made out of stainless steel or bronze based on experience obtained from the Adami-Tulu hydram maintenance project. Bolts and nuts were designed to be electro-galvanized. Parts of the hydram, the body, elbow and air chamber were made in separate pieces to facilitate easy handling during transportation and machining operation. Provisions for stroke and weight adjustment has been incorporated. The waste valve was designed for simple and less costly manufacturing method.
Fig. 6 RDTAC's Hydram installed At Adami-Tulu
Manufacturing - The hydraulic ram pump parts were manufactured in the RDTAC workshop, RADEL Foundry Pvt. Ltd. Company, Addis Tyre Enterprise and Gelan-Metal Products Factory. RADEL made all the casting parts. Addis Tyre Enterprise has made all rubber parts by moulds manufactured in RDTAC. Gelan Metal Products Factory performed electro-galvanization on bolts, studs and nuts. All the machining and welding of the hydraulic ram pump parts were made in RDTAC.
Installation - The hydraulic ram pump was installed in the pump house of Adami-Tulu hydraulic ram pump with the permission of the Abernosa Ranch (see Fig. 6). Existing civil work such as diversion canal, drive tank and pump house at Adami-Tulu was used for the project. This has resulted in considerable financial, time and labor saving. A delivery pipe of 2" was installed for 0.8 km from the pump house to a reservoir tank which is located in Dodicha Woreda (Oromia Region, Arsi Zone).
Performance - By now, the hydraulic ram pump successfully provides water for drinking and backyard irrigation. See Fig. 7.
Fig.7 Water Supply System at Dodicha Woreda, Arsi Zone, Oromia Region from RDTAC's Hydram
The following conclusions can be made from RDTAC's project work on Hydraulic Ram pumps.
There
is broad prospect of utilizing the country's abundant surface water
run off potential for various purposes or requirements using locally
designed and manufactured hydraulic ram pumps and other similar
appropriate technologies.
To
disseminate hydrams at potential sites throughout the country, there
is a need to create awareness through training and seek integrated
work with rural community, government institutions like water, energy
and mines bureau of local regions and non-governmental organizations.
Hydraulic Ram
pumps made by casting have many advantages, but they could be
expensive. In addition, considering the cost of civil work and pipe
installation, the initial investment could be very high. To reduce
cost of hydrams made by casting, there is a need for standardization.
Standardizing hydram pump size will also have an advantage to reduce
cost of spare parts and facilitate their easy access when they are
needed.
The use of appropriate means of treating river water should be looked at in conjunction with any development project of domestic water supply using hydrams.
Acknowledgement
RDTAC would like to take the opportunity to express its sincere appreciation to the Ethiopian Science and Technology Commission for the unreserved assistance and encouragement rendered.
REFERENCES
1. Jeffery, T. D., "Hydraulic Ram Pumps - A Guide to Ram Pumps Water Supply System", Intermediate Technology Publications, 1992.
2. Teferi Taye, "Hydraulic Ram Pump", Journal of the Ethiopian Society of Mechanical Engineers, Vol. II, No. l, July 1998.
Go back to the updated ATF site or to the main ATF home page at MIT.