Water engine

The water engine is a positive-displacement engine, often closely resembling a steam engine with similar pistons and valves, that is driven by water pressure. The supply of water is derived from a natural head of water, the water mains, or a specialised high-pressure water supply such as that once provided by the London Hydraulic Power Company. Water mains in the 19th century often operated at pressures of 30 to 40 psi (210 to 280 kPa), while hydraulic power companies supplied higher pressure water at anything up to 800 psi (5,500 kPa).

The term water motor (German: Wassermotor) was more commonly applied to small Pelton wheel type turbines driven from a mains water tap (e.g. Whitney Water Motor), and mainly used for light loads, for example sewing machines.

In the nineteenth century, the terms hydraulic motor and hydraulic engine often implied reference to any motor driven by liquid pressure, including water motors and water engines used in hydropower, but today mentions of hydraulic motors, unless otherwise specified, usually refer more specifically to those that run on hydraulic fluid in the closed hydraulic circuits of hydraulic machinery.

Because water is virtually incompressible, the valve gear of water engines is more complicated than that used in steam engines, and some water engines even had a small secondary engine solely to power the operation of their valves. Closing a valve too quickly can cause very large pressures to result, and pipework to explode (a phenomenon similar to water hammer), and in addition to valves designed to close slowly, many water engines used air chambers to provide some absorption of force by compressing the air in them.

It is unclear when or where water engines were invented, but it is possible that they were first used in the mines in central Germany; certainly such a device was described by Robert Fludd after he had visited Germany around 1600.

During the 19th century water engines were extensively used in the city of London, operating on high-pressure water supplied by the London Hydraulic Power Company via its extensive network of pipes. Even when practical electric motors entered use, water engines remained popular for some years as they possessed several advantages: they were quiet, reliable, cheap to run, compact, safe, and could be relied on to operate reliably in damp or waterlogged conditions unsuited to electrical apparatus, such as powering water pumps in mines, where their ability to continue operating even while completely submerged was a major advantage.

Other applications included usage by the railway companies, where they powered railway turntables, cranes, hoists, etc., revolving stages at the London Palladium and Coliseum Theatre, and powering pipe organs.

The largest possible design of a water engine is the directly acting water-column engine or water column machine (German: Wassersäulenmaschine). Such devices had been in use for pumping purposes in different mining areas since the middle of the eighteenth century and one was used, for example, by Georg Friedrich von Reichenbach in 1810 to pump brine from Berchtesgaden to Reichenhall.