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The word electrohydraulic has two meanings for two highly different operations. It can stand for an electrical control device that makes precise adjustments in a hydraulic system. Also, it can mean a chemical reaction that is created by firing short, powerful electrical impulses into or directly beneath the surface of a body of liquid.
Electrohydraulic devices were first developed for weapon-control systems and missile launch platforms during World War II. Because the heavy weapons needed to be aimed precisely and because hydraulics are inherently unsuited for precision movements, a new kind of actuator was developed to give the weapon handlers improved control over the hydraulic systems. After the war, development on these hydroelectric devices continued, with a new two-stage mechanical feedback (MFB) servo valve being manufactured during the early 1950s. The MFB valve, which first saw service in the aerospace industry before moving into the industrial sectors, offered greater control and precision in hydraulic devices, and would be the standard of the industry for several decades.
Perhaps the most well-known electrohydraulic device is an automobile's power steering unit — also called an electrohydraulic actuator. The unit combines high power with a high degree of accuracy to adjust for the minute movements of the steering wheel in a vehicle. This type of technology, where electrical components are used to increase the accuracy of hydraulic movements, can be applied to almost any situation where hydraulics is used.
The second meaning of the word electrohydraulic is quite different from the first, and relates to electrical impulses being fired into a liquid. These electrical impulses, once they hit the water, are transformed into powerful mechanical shock waves that radiate outward from the point of generation. The impulses are not contained by the water, however, and can be likened to the blast wave created by a moderate amount of high explosive materials. In fact, electrohydraulic reactions of this type are often used in place of explosives as they are generally deemed more environmentally friendly.
First uses of electrohydraulic blasting — also known as the submerged arc discharge process – can be seen as early as the mid 1940s, and by the 1950s and '60s it had come into its own as a viable alternative to using high explosives. The process of electrohydraulic metal forming, for instance, is used by engineers to mold sheet metal into the desired shape by firing an electrical discharge between to submerged electrodes while the metal is kept in contact with the fluid. This causes the metal to be formed into a die, and was originally attained by using explosives to achieve the same result. Other uses for the process include the breaking of rock formations under water and the extraction of crude oil from the ground.