7.3 ENERGY LOSSES AND ADDITIONS  Objective: to describe general types of devices and components of fluid flow systems.

7.3.1 Pumps  A mechanical device that adds energy to a fluid.  An electric motor or some other prime power device drives a rotating shaft in the pump.  Then, the pump takes this kinetic energy and delivers it to the fluid, resulting in the fluid flow and increased fluid pressure.

7.3.2 Fluid Motors  Examples: fluids motors, turbines, rotary and linear actuators.  Take energy from a fluid and deliver it to in the form of work, causing the rotating of the shaft or the linear movement of a piston.  The difference between a pump and a fluid motor is that, when acting as a motor, the fluid drives the rotating elements of the device. The reverse is true for a pump.

Types of fluid motor: i. Gear pump (can be a motor also) act as a motor by forcing a flow of fluid through the device.

ii.Hydraulic motor Used as a drive for the wheels of constructions equipment and trucks and for rotating components of material transfer systems, conveyors, agricultural equipment, special machine, and automation equipment. The design incorporates a stationary internal gear with a special shape. The rotating components is called gerotor, that has one fewer teeth than the internal gear. The external gear rotates in a circular orbit around the center of the internal gear. High-pressure fluid entering the cavity between the two gears acts on the rotor and develops a torque that rotates the output shaft. The magnitude of the output torque depends on the pressure different between the input and output sides of the rotating gear. The speed of rotation is a function of the displacement of the motor (volume per revolution) and the volume flow rate of fluid through the motor.

Hydraulic motor

Fluid power cylinder

7.3.3 Fluid Friction  A fluid in motion offers frictional resistance to flow.  Part of energy in the system is converted into thermal energy (heat), which is dissipated through the walls of the pipe in which the fluid is flowing.  The magnitude of the energy loss is dependent on the properties of the fluid, the flow velocity, the pipe size, the smoothness of the pipe wall, and the length of the pipe.

7.3.4 Valves and Fittings  Elements that control the direction or flow rate of a fluid in a system set up local turbulence in the fluid, causing energy to be dissipated as heat.  Whenever there is a restriction, a change in flow velocity, or change in direction of flow, energy losses occur.  In a large system the magnitude of losses due to valves and fittings is usually small compared with frictional losses in the pipes. This is known as minor losses.