A Dragon Spine (water ladder or in Thai rahad) is a low lift pump with sprockets that move a chain of paddles through a slanted trough. Water is lifted as the paddles push the water up the trough. Often sized for one person turning the wheel with push pull handles, but at times up to eight for rotary drives. The pump’s name comes from its resemblance to a dragon’s spine.
The Dragon Spine pump has been used for millennia for irrigation and drainage and is still used by farmers in Southeast Asia. The Dragon Spine pump may have been first made during the Eastern Han Dynasty (25-220). Others suggest it was designed or improved by Ma Jun, an inventor and engineer who lived during the Three Kingdoms period (220-280). In any case the Dragon Spine pump has played a significant role in agriculture.
The body of the water lift is a large wooden trough, rectangular or curved, that can hold water and has sprockets on axles at both ends. The chain of paddles fits to the sides of the trough. The foot of the trough is placed in water and then the foot steps or hand bars rotate the drive sprocket. As the chain of paddles rotates water is lifted.
On larger Chinese Dragon Spine pumps the upper sprocket is normally driven by a long horizontal shaft which is pedaled by from two to eight people working together. The foot pads are spaced on the drive shaft so that one or more of the operators is applying full foot pressure at any moment, smoothing out the torque and keeping the chain of paddles tensioned and running smoothly. Pumps with three workers are often used for this reason.
They can move quite a bit of water. About 1900 F. H. King found that two men standing on crankshaft foot pads could raise water 1 meter (3 feet) at a rate of 2.5 acre inches in 10 hours. This is about 13,000 liters (13 cubic meters) per man in ten hours or 1,300 liters (340 gallons) per person hour. Women as well as men operated the Dragon Spine pumps. The one person pumps use handles to a linkage that convert push pull to turn the drive sprocket (like a steam locomotives piston to drive wheel). Demonstrated in the video https://www.instagram.com/reel/DIsh-B4N9A_/?hl=en.
The Dragon Spine pumps could also be driven by an animal turning a vertical shaft with a horizontal drive from a gear box (like the Persian wheel pump). The Chinese commonly sheltered the draft animal and often the worker with a roof for comfort and long term health and steady work.
In 1986 the FAO included design details for commercial models from the Chengqiao Water Lift and Agricultural Tool Plant, Hangjiang Commune, Putian County. The Dragon Spine pump for 2 men with a 3 m long trough had paddles that were 0.25 m tall x 0.20 m wide and cost of 106 Yuan. A pump for 4 men with a 5.3 meter long trough had similar paddle size and cost 165 Yuan.
Advantages
The Dragon Spine pump is still a useful tool. They can be built and repaired easily at a very low cost. All, or almost all, of the components can be built with local resources. Wood planks traditionally were sawed by hand. The fast growing and strong Paulownia wood was often used. The light weight of the pump made it possible for a woman to move the pump from field to field and then back to the farm and into shelter for the winter.
Disadvantages
The efficiency is constrained by the fit of the paddles in the trough, but there was not much backsplash. These pumps can lift water only a few meters at most. For higher lift as many as eight men might be needed to turn the long chain of paddles.
