The condition that the volume of the fluid mass shall remain unchanged requires that there shall be more than one piston, and that the -velocities and areas of the pistons shall be connected by the equation ~l.va=o.
Converging and Diverging Trains of M~hanism.Two or more trains of mechanism may converge into oneas when the two pistons of a pair of steam-engines, each through its own connectingrod, act upon one crank-shaft.
An excellent brake for very large cranes is Matthew's hydraulic brake, in which water is passed from end to end of cylinders fitted with reciprocating pistons, cooling jackets being provided.
It has been shown that this behaviour of dielectrics can be imitated by a mechanical model consisting of a series of perforated pistons placed in a tube of oil with spiral springs between each piston.
I, the lift cylinder is in hydraulic connexion with a pair of short cylinders placed one above the other, the pistons working in them being connected together by a common rod.