Hydraulic lock, sometimes referred to as hydrolock, is a condition that affects all engines and motors that use fluids, and can even affect steam engines in some cases, where steam condenses and water remains inside the compression chamber. It mostly occurs on starting up, but can occur during operation as well, for instance when a car drives through a puddle and water enters the piston chambers, flooding the engine. When fluid enters the compression chamber (over the clearance volume) it restricts the travel of the piston, leading to damage. Because fluids are incompressible, any attempt to turn the engine over when it is in a state of hydraulic lock causes severe damage to the moving parts, bending rods and shafts or even splitting chambers open if the pressure is very high inside. Possible causes of hydraulic lock include over priming an engine, thereby drawing excess fluid into the induction system faster than it can escape, clogged drains and other mechanical failures due to low levels of maintenance, as well as failure to drain systems that have been inoperative for a time before restarting them. Causes of hydraulic lock in moving vehicles are generally down to driving through puddles that are deeper than the air intake for the engine – some makes position the intake in the wheel arch, which acts as an invitation for hydraulic lock in even the shallowest puddles. It is a good idea to know where your intake is on your vehicle, as an expensive issue can easily be avoided by knowing for sure whether or not your car will make it through a puddle. If the engine is revving and the vehicle is moving at any speed, water can enter more than one piston chamber and damage all the piston rods, potentially causing shocks through the engine that can cause much more serious damage. If water enters the engine while it is idling, or off, there is a chance it can be salvaged before any damage occurs. If water does enter your car engine ensure that all the fluid is drained from the engine before attempting to restart it. This means removing all of the pistons and checking for signs of damage in the components involved. Reducing the possibility of hydraulic lock is the best course of action, so it is vital to ensure any maintenance plan includes checks for broken seals, that could allow fluid into compression chambers and that drainage valves are operational and not clogged. In certain contaminated environments it may be the case that pollutants frequently enter drainage valves, and these site-specific concerns need to be taken into account when planning maintenance. When using equipment that has been in storage, it is vital that the equipment is drained fully and the compression chambers are inspected, to ensure there is no residual fluid inside. Checking the angles at which an engine sits is also important, as if the drainage systems are inoperable due to the angles involved then hydraulic lock can occur quickly, even when all other conditions are right. It is also very important that all persons operating machinery that is at risk of hydraulic lock, are aware of the warning signs and know not to over prime an engine while attempting to start it. If an engine has been primed too much, it should be left to drain and stabilise before any further attempts to start it are made, as this is one of the main man-made causes of hydraulic lock and is easy to avoid. Hydraulic lock cannot be eliminated entirely, as it has many potential causes. It is possible, however, to effectively reduce the incidence of the causes with good maintenance and staff training.