The "bunyip pump" or "gravity bellows pump" is a water-powered pump, which operates on the same principle as a hydraulic intensifier. Low pressure, high volume water flow is used as the driving force to push to the larger of two or more mechanically connected pistons. As the pressure on the drive side increases, a mechanical connection directs the driving force into a smaller diameter piston and bore, creating a greater pressure in a smaller volume of water. Pressure on the drive side is released or reversed to complete the cycle. Check valves on either side of the output piston(s) ensure that flow only occurs toward the output pipe.
Comparison to Ram Pumps[edit | edit source]
Like a ram pump, this pump can be used with a relatively high ratio of output head height vs input drive head. Output to drive height ratios of 1:1 through 60:1 are all practical. However, the larger the ratio between drive and output, the lower the volumetric efficiency. In other words, more water must "waste" through to pump to drive smaller volumes of output as the output head is raised.
Unlike a ram pump, the bunyip pump does not rely on the "water hammer effect", which can create immense pressures, vibration, and noise. True ram pumps require very strong materials in the pump itself and the drive pipe, as well as very stout plumbing connections, to survive this repeated pressure spike. Even when built of very stout materials, the ram effect can destroy conventional check valves, and wear out seals of almost any kind of material.
Also, ram pumps might only properly oscillate under a very narrow range of drive and output pressure conditions. Drive pipes must be of the right length, diameter, and ideally angle to create driving force velocity, and waste check valves must have a suitable weight, return spring tension, or elastomeric properties, or automatic operation might not occur. This can require priming the output back pressure, tuning, monitoring and adjustment (at installation and as conditions change). The bunyip pump, however, can operate under a wider variety of driven flow rates without manual intervention.
Ram pumps connected in series [1], to the same drive pipe, or the same output pipe [2], may suffer from destructive inference that partially or completely negates the operation of one or both pumps. However, two the bunyip pumps can be connected to the same drive pipe [3] with parallel operation pumping output being less than the combined output of both pumps under single operation.
Commercially Available Versions[edit | edit source]
The Bunyip Pump is sold in Australia by Porta's Affordable Pumps. [4]
Porta's Affordable Pump Design[edit | edit source]
In Brett Porta's current design, a car tire is used as a flexible bellows to contain the water in the drive side of the piston. Output side of the piston is a typical stout metal bore sleeve, and rubber seals around the piston. Output water is suctioned into the output piston from the same pool the waste water is jettisoned to, then pushed out to the drive pipe, each operation using its own check valve.
Other designs[edit | edit source]
The Glockemann pump [5] is a different design, using a hybrid bellows and ram to drive the piston.
Other experimenters, including Joe Malovich [6], are using the air bladder from a vehicle air suspension system as the drive side bellows, the output side bellows, or both. [7]
Each of these designs (Bunyip, Glockermann, Malovich) are effectively modifications of the float pump cited in Mother Earth News, "How to Build a Float Pump" by Robert J. Mitchell; January 1, 1977. (https://www.motherearthnews.com/sustainable-living/renewable-energy/how-to-build-a-float-pump-zmaz77zbon/)
Possible improvements[edit | edit source]
The design might improve in efficiency if some drive side water pressure and volume was fed to the output side piston, instead of requiring the output side to suction lift from the waste water pool. This might require an intermediate chamber to temporarily store drive side pressure until the correct portion of the cycle to feed the drive side. This also would reduce the oxygenation of output water caused by the splashing of wasted drive water into the waste pool.
The design might be able to be simplified by replacing the drive side piston seal with a flexible rubber check valve.
If the output side was connected to an accumulator, output flow would be more continuous, instead of pulsating.
References[edit | edit source]
- Intriago Zambrano, J. C., Michavila, J., Arenas Pinilla, E., Diehl, J. C., & Ertsen, M. W. (2019). Water lifting water: a comprehensive spatiotemporal review on the hydro-powered water pumping technologies. Water, 11(8), 1677.
