Introduction to Fluid Power

Methods of transmitting PowerMechanicalElectricalFluid power

Fluid powerTechnology that deals with the generation, control and transmission of power using pressurized fluids.Hydraulics Petroleum oils, Synthetic oils and water.Pneumatics Air

Types of Fluid SystemsFluid transport systemsDelivery of fluid from one location to anotherPumping stations , Cross-country gas lines, etc.Fluid power systemsWork is accomplished by a pressurized fluid bearing directly on an operating fluid cylinder or fluid motor.

History of fluid powerAncient historyProduce power by means of water wheelsAir was used to turn windmills.1650 Pascals LawPressure is transmitted undiminished in a confined body of fluid.1906 Battleship USS Virginia elevating and controlling guns

Advantages of fluid powerEase and accuracy of controlMultiplication of forceConstant force or torqueSimplicity, safety and economy

Advantages of hydraulic power systemsGenerate and transmit large tonnes of forces. Provide reversible, infinitely variable speed and load control.Achieve accurate feed back control of load, position, etc.Offer cushioning for shock loads. Hence the noise and vibration produced are minimal.Wear of the system is reduced due to self-lubrication action of the transmission medium.Power-to Weight ratio is comparatively higher than mechanical and electrical systems.

Disadvantages of Hydraulic Power systemsHydraulic fluid leakage poses many problems to the operations as well as operators.Flammable hydraulic fluids may pose fire hazards, thus limiting the higher level of working temperature.Require special treatments to protect them against rust, corrosion, dirt, etc.

Advantages of Pneumatic power systemsSince the density of air is much lower than liquid, it can be transported.Simple in construction.High degree of controllability.Due to less viscosity, it results in less frictional pressure and power losses.Cheaper than hydraulic.Leakage of pneumatic fluid does not affect seriously, so there is no risk of fire hazard.

Disadvantages of Pneumatic Power systemsDue to high compressibility, it is impossible to obtain a precise control of actuators.Pneumatic systems are suitable only for low load and power applications.

Applications of fluid power

Applications of fluid power

Applications of fluid power

Applications of fluid power

Components of Hydraulic systemA tank (reservoir)A pumpAn electric motorValves Direction, Pressure and FlowAn actuator Linear (Cylinder), Rotary (Motor)Piping

Hydraulic system with Linear actuator

Hydraulic system with rotary actuator

Components of Pneumatic systemAn air tankA compressorAn electric motorValves Direction, Pressure and FlowAn actuator Linear (Cylinder), Rotary (Motor)Piping

Types of Fluid power systemsOpen loopDoes not use feedbackDirection control valvesClosed loopUses feedbackServo Valves

Types of fluid power control systemsElectrical control systemPressure switches, limit switches and relays used to operate electrical solenoids.Fluid logic control systemProgrammable logic control system

ExercisesThe piston diameter of the small cylinder is 25mm and the large cylinder is 100mm. The force needed at the large cylinder piston is 2000N.Calculate the amount of force applied at the small cylinder piston. [Ans: 125N]How far the large piston will move if the small piston moves 100mm. [Ans: 6.25mm]

ExercisesA hand operated hydraulic jack as shown in fig. has a piston pump with a cylinder diameter of 30mm and a stroke of 50mm. The operator makes one cycle (one suction stroke and one delivery stroke) per second in the pump. The ram cylinder of 60mm diameter raises a load of 8000N. Calculate the following:Pressure in the system [Ans. 28.3 bar]Force exerted on the rod of pump [Ans:2000N]Force on the handle given by the operator [Ans: 500N]The number of cycles and time required for hand pump to lift the load by 500mm. [Ans: 40 cycles, 40 seconds]Output power assuming 90% efficiency.[Ans. 90Nm/s]

Exercises