FLUID SYSTEMSLesson 5

Fluid Systems

Water under pressure is used in many applications such as hydroforming (the process of using water

under high pressure to shape metal components)

and water jet cutting (the process of using water under high pressure and at a high cut speed to cut manufactured products

Volume flow rate

The volume per second of a fluid flow; symbol qv.

The equation is , where qv is the volume flow rate, V is the volume, and ∆t is the time interval

Example 1

The volume flow rate needed to cut a material component is 3.3 L/min, and the time interval required is 18 s. Calculate the total volume of water used during this process.

qv= 3.3 L/min = 0.055 L/s ∆t = 18 s V =?

V = ∆t x qv

V = (18 s) x (0.055L/s) V = 0.99L Therefore the total volume of

water needed is 0.99 L.

The speed of a fluid flowing through a pipe can also be an important piece of information.

Whether plumbing a house, or putting out a fire. The flow rate can be vital information.

The formula to find the speed can be derived from equation for flow rate: the total volume in a pipe of length l is Al, where A is the cross sectional area of the pipe.

Thus

Formulas

Example 2

Calculate the speed of water in a pipe of radius 0.21 mm if the volume flow rate of water is 6.0 x 10-6 m3/s

qv= 6.0 x 10-6 m3/s r = 0.21 mm = 2.1 x 10-4 m A = πr2

A = π(2.1 x 10-4 m)2 A = 1.385 x 10-7 m2

v = ?

v = 43 m/s

Therefore, the speed of the water is 43 m/s

Fluid System Schematic Diagrams The initial source of energy for the systems

can be an electric motor or other device that drives a pump for liquids (liquids) or a compressor (gases). The pump or compressors transforms mechanical forces into fluid forces. The final output of the system is the actuator, a device that transforms fluid forces back into mechanical forces.

All of the components in a fluid system must form a circuit in which the fluid can flow.

Symbols are used to draw circuit diagrams of fluid systems. The following symbols are commonly used in fluid system diagrams.

Transmission lines – the pipe through which the fluid travels

-continuous line - flow line   -dashed line - pilot, drain

Circular

-large circle - pump, motor

-small circle  - Measuring devices

-semi-circle - rotary actuator

Diamond  - Fluid conditioner (filter, separator,

lubricator, heat exchanger)

one square  - pressure control function 

two or three adjacent squares  - directional control

Triangle -solid - Direction of Hydraulic Fluid

Flow

-open - Direction of Pneumatic flow

Shut-Off Valve

Single acting cylinder -returned by external force

-returned by spring or extended by spring force

Miscellaneous Symbols Spring   Flow Restriction

Double acting cylinders -single piston rod (fluid required to

extend and retract)

-double ended piston rod

Directional control valve (3 ports / 2 positions)

-Normally closed directional control valve with 3 ports and 2 finite positions

 

-Normally open directional control valve with 3 ports and 2 finite positions.

Manual Control -general symbol (without showing

the control type)

-pushbutton

-lever

-foot pedal

Mechanical Control -plunger or tracer

-spring

-roller

-roller(one direction only)

Questions

During hydroforming, a force of magnitude 1.8 x 106 N is applied to a piece of steel 12 cm x 14 cm. Calculate the pressure, in pascals and kilopascals on the piece of steel. T(1) C (1)

In a water jet cutting process, a stream of water with the speed 1.6 x 102 m/s drills a hole of radius 0.28 mm with a force of magnitude 1.2 x 102 N. The process lasts for 16 s. Calculate. The pressure, in pascals of the water on the metal . T

(1) The volume flow rate of the water T (1) The total volume of water used in the process, in

cubic meters. T (1)

What are the main uses of valves in a fluid system? C (1)

Name and draw the circuit for the type of device that controls : C (2) A hand-held sprinkler The hand pump used to inflate a tire.

Would you recommend a hydraulically operated or a pneumatically operated robot that needs to respond quickly and efficiently to all types of loads and must operate at many temperatures. T (1) C (1)