Introduction: The Hand Water Pump
Hand pumps are a type of human operated positive displacement pump. They are a common sight in many rural areas where piped water connections do not exist. Hand pumps have a simple and robust design, require little maintenance, and are easy to operate, this has led to their widespread application throughout the world.
Hand Pump
History of the Hand Pump
The invention of the hand operated piston pump occurred in Europe and dates back to the 1400s. Over the following centuries, most villages, towns, and cities, gained access to a reliable water supply via a hand pump or traditional water well. Usually, hand pumps were installed over existing water wells, thus their adoption represents more of an improvement over existing infrastructure, rather than a totally new form of infrastructure.
Medieval Piston Pump Diagram
As hand pumps were often installed near the centre of a community to make access easy for local residents, they were often dubbed ‘parish pumps’; this is because churches and parishes were the local meeting point in most communities, so it made sense to install water pumps nearby. Another name widely used for this type of well pump is the ‘pitcher pump’.
Hand Pump / Parish Pump / Pitcher Pump
Contamination of water from a hand pump (or any well water source) is possible because water is drawn from the soil. Cholera is one such bacteria that is able to spread through the consumption of contaminated water. John Snow proved the spread of cholera through water after an outbreak in 1854 occurred in Broad Street, London. Suspecting that contaminated water was the source of the outbreak, he removed the handle from the local water pump and the number of cholera cases reduced shortly thereafter. Because of his correct assumption and the method by which he came upon it, John Snow is today considered the founder of Epidemiology (the study of how bacteria and viruses occur and spread).
John Snow – the founder of Epidemiology
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Hand Pump Components
A hand pump consists of relatively few parts, these typically include those listed below, but the number and type of parts depend upon the individual pump design.
Suction Inlet – a long hollow pipe that connects the pump cylinder the water supply.
Cylinder – a hollow cylinder that encases the piston, foot valve and piston valve.
Discharge – a hollow pipe that allows water to flow from the cylinder to the point of consumption.
Piston – an assembly that allows for the installation of a non-return valve and retaining cage.
Piston Rod – a solid metal bar connecting the piston to the handle/lever.
Handle/Lever – used to give the operator mechanical advantage; sometimes called a ‘force rod’.
Foot Valve – a non-return valve located at the base of the cylinder.
Hand Pump Components
Theory of Hand Pump Operation
The purpose of a hand operated well pump is to lift a fluid from a lower elevation to a higher elevation, in a safe and efficient manner. The mechanical advantage gained using the hand pump handle/lever depends upon the strength of the user and the length of the handle; this can be explained when looking at the moment of a force calculation:
Moment = Force x Distance
M = F.d
Where:
Moment = turning effect of a force around a pivot point.
Force = force applied by the operator.
Distance = distance from the pivot point.
Hand Pump Mechanics
Increasing the length of the handle increases the distance from the pivot point and thus the resultant moment. Increasing the force applied also increases the moment. Notice that it is possible to increase the moment applied by increasing the distance the force is applied from the pivot point; this can be seen with the following two examples:
Example 1 – more force applied closer to the pivot point.
Force (F) = 10
Distance (D) = 5
Moment (M) = Force.Distance
Moment (M) = 10 x 5 = 50
Example 2 – less force applied further from the pivot point.
Force (F) = 5
Distance (D) = 10
Moment (M) = Force.Distance
Moment (M) = 5 x 10 = 50
Notice that the resultant moment of force is equal for both examples. It can be seen that a longer handle would yield a greater mechanical advantage if the force is kept constant (is not changed). In practical terms, this means that a longer handle will allow weaker people to operate the pump because less strength (force) is required to achieve a given moment of force.
Note – the examples do not use units, although force is usually given in newtons (N), distance in metres (m), and moment in newton metres (Nm). The units used depend upon if using standard units (SI units) or imperial units (pounds, inches etc.).
Simple Explanation: How Hand Pumps Work
The below video is an extract from our Mechanical and Electrical Engineering Explained Online Video Course.
Positive displacement pumps must be primed before the process fluid can be pumped. The term ‘priming’ refers to removing air from the system in order to allow the process fluid to flow. When referring to a well hand pump, air is removed from the system and displaced by water.
Water is drawn into the cylinder as the pump lever is pressed downwards. Pressing the pump lever downwards causes the piston to move upwards and the foot valve to open; the piston non-return valve is closed as the piston moves upwards.
Once the piston has reached its highest point of transit, the operator pulls the pump lever upwards. Pulling the pump lever upwards causes the piston to move downwards and the foot valve to close; the piston non-return valve is open as the piston moves downwards. The result from this movement is that water from the underside of the piston non-return valve is moved to the topside of the piston non-return valve. When the piston next moves upwards, it moves the water that is now present on its topside upwards also.
Repeating this push and pull movement on the hand pump lever results with more liquid being drawn into the cylinder and the water level within the cylinder rising. As the water level rises, it reaches the height of the discharge pipe and begins to flow out of the pump.
Additional Resources
https://en.wikipedia.org/wiki/Hand_pump
https://innovationdiscoveries.space/water-hand-pump-parts-types-working-principle
https://engineeringinsider.org/water-hand-pump-parts-types-working