London Main Drainage: the Penstock Chamber at Old Ford, 1861. At Old Ford, the northern high-level, the middle-level, and the Hackney-brook sewers meet in what is called the penstock chamber. A penstock is simply a gate to regulate the passage of water through an aperture...the name of penstock has been given to the very large gates which will regulate the ebb of the drainage waters coming down from a large part of the northern district of London...The waters, having arrived in it from the high and middle level sewers, will pass through the large arched passage in the foreground of the Sketch until they are separated by a cutwater, which is the termination of the solid masonry between the two great drains which carry it to the outfall sewer at Abbey Mills...it will be observed that the abutments of the larger arch are beyond the side walls of the arched passage. Between those abutments and the side walls there is a communication to another system of drainage below the floor of the great passage. From "Illustrated London News", 1861.