Bart Schultz
The driving devices for the pumped discharge from polders have been described in previous contributions to Flevolands Geheugen. This time the lifting devices will be described.
Lifting devices are equipment that lifts and discharges water. The most important lifting devices that are or have been used for the purpose of discharge from polders is the paddle wheel, scoop disc, open Archimedes screw, suction pump, suction pressure pump, centrifugal pump and screw pump. Most of these lifting devices have different designs. They can usually be driven by different types of driving devices.
For several centuries, paddle wheels were the lifting devices for the discharge from polders by windmills, and were later also used in steampower pumping stations. The paddle wheel is a vertical wheel that lifts the water over a culvert between two walls. A guard door is placed in the upper water to prevent the water from flowing back. Such a closure, often also designed as a valve, is fitted to all low-lying lifting devices where there is a risk of siphoning or backflow.
Over the years, many variations and improvements for paddle wheels have been devised and implemented. The paddle wheel is almost certainly a Dutch invention. The first known application in windmills for the discharge from polders dates from the beginning of the fifteenth century. In large windmills, the paddle wheels normally had a diameter of 5.5 to 7.0 metres, and a width of 0.45 to 0.55 metres. The maximum lifting height was 1.5 to 2.0 metres.
The principle of the scoop disc was based on the fact that the water that was raised did not flow out on the outside of the wheel, but was guided by the blades in such a way that the outflow occurred in the middle of the wheel. The scoop disc was already known in the time of Vitruvius. The Englishman Wheler gave it a new shape, which was used in 1629 during the draining of the Naardermeer. A modification of this scoop disc was used in 1744 at two windmills in the Watergraafsmeer. The scoop disc was only applied in a few polders.
The open Archimedes screw consists of a shaft with helical blades in a semi-cylindrical sloping channel, the trainer. Usually three screw threads are used together. The lifting height could be four to five metres when used in windmills. The water is guided to the highest point of the trainer. In order to utilise the advantage of the lower delivery height at low water levels, part of the trainer can be folded down in a number of screws. When used in windmills, the screw was an eminently suitable lifting device, especially at lifting height of a few metres and a constant water level. Later, open Archimedes screws were also used in steampower pumping stations and in electric pumping stations. Open Archimedes screws may also have been used on a limited scale in diesel pumping stations.
The origin of the open Archimedes screw is not known with certainty. Most authors name Archimedes of Syracuse as the inventor. The screw in the form of a barrel mill was already used in Egypt in the third century BC for irrigation. The open screw, as it is mainly used in the discharge from polders, was invented in 1634 by Hulsebosch from Amsterdam, who built a windmill with an open Archimedes screw in that year.
In a number of polders, after improvements to paddle wheel windmills, the transition from paddle wheel windmills to open Archimedes screw windmills was the first significant change in discharge. Due to the greater lifting height that could be achieved with open Archimedes screw windmills, the number of mills per series of windmills could be reduced in a number of cases. In 1829, the first steampower pumping station with an open Archimedes screw was built for a polder at the Mariënwaard estate in Beesd. The second application of steampower pumping using open Archimedes screws was during the draining of the Zuidplas in 1840.
Suction pumps have been used in horizontal and vertical versions. They could be single-acting or double-acting. The latter type was called a suction pressure pump. Suction pumps and suction pressure pumps have only been used on a limited scale in polders, and then only in steampower pumping stations. The most important application of suction pumps by far has been for the draining and discharge of the Haarlemmermeer polder.
The centrifugal pump consists of a volute with an impeller. The suction is done by under-pressure. The water is thrown out by the impeller in a plane, perpendicular to the axis, and also flows off in this plane. Centrifugal pumps have a high speed, which makes direct coupling to the driving device possible. When installed above water, a vacuum pump was often required. The suction height is a maximum of six to seven metres. The suction pipe must be sufficiently far under water to prevent air from being sucked in.
Centrifugal pumps were initially mainly used for higher lifting heights than 2.5 metres. They can be used for both large and small discharges, and for large, small or variable lifting heights. Centrifugal pumps were initially used in steampower pumping stations and later in diesel and electric pumping stations. A distinction can be made between horizontal and vertical installation. A distinction can also be made between closed and open versions. Furthermore, a distinction can be made between a low installation, in which the pump is placed below the polder water level, and a siphon installation, in which the pump is installed above the polder water level, and often also above the level of the receiving water body.
The centrifugal pump was invented in 1689 by Denis Papin. After that, about 160 years passed before centrifugal pumps were used on a large scale for the discharge from polders. The possible first application of centrifugal pumps in polders was in 1864 during the draining of the Holendrechter and Bullewijker polder.
In the screw pump, the screw-shaped body consists of a rapidly rotating impeller or rotor, with blades curved in two directions, which, in addition to a rotating movement, give the water a movement mainly in the direction of the axis of rotation. The blades can be made adjustable when there are varying lifting heights. The screw pump is particularly suitable for small lifting heights and relatively large capacities. A distinction is made between pumps with a horizontal axis and pumps with a vertical axis. Furthermore, the screw pumps with a vertical axis can be distinguished into pumps in a closed design and pumps in an open design. For most screw pumps, an electric engine is used as the driving device.
The application of screw pumps in polders dates back to 1915. They are mainly used for lifting heights of up to 3.0 to 3.5 metres. The vertical screw pump in open design was first used in 1922 for the draining of the Lemsterhop. Since then, these pumps have mainly been used for a capacity of up to 100 cubic metres per minute.
