c5_basic Hydraulic Circuit

(1)

DJJ5123 PNEUMATIC

& HYDRAULICS

5.0 BASIC HYDRAULIC

CIRCUIT

(2)

(3)

Hydraulic Circuit



A hy

draulic circuit is

a system comprising an

interconnected set of discrete components that

transport

liquid.



The purpose of this system may be

to control where fluid

flows (as in a network of tubes of coolant in a

thermodynamic system) or to control fluid pressure (as in

hydraulic amplifiers).

2

(4)

3

3 Cylinder

Cylinder

Directional Control Valve 4/3 Directional Control Valve 4/3 Accumulator

Accumulator Pressure Pressure regulating regulating valvevalve

Check valve Check valve Motor Motor Tank Tank Filter Filter Arrangement Of Components Arrangement Of Components Flow

(5)

4

(6)

5

The basic components in a hydraulic circuit is as below:

-Components Description

Valve It serves to regulate the pressure in the circuit and control the direction of the oil flow.

Motor Serves to produce the power to do the job for rotational movement.

Filter Serves to filter the hydraulic oil from impurities.

Pump Serves to distribute the quantity of hydraulic oil to the entire system.

Cylinder Serves to produce the power to create straight movement. Accumulator It serves as a storage system pressure, vibration absorbers and

stabilizer system pressure.

(7)

Sterling hydraulic

 It is designed to control a sequence of operations cylinder with sequence valve.

Example; given sequence is A + B + B-

A- Based on the figure below, directional control valves actuated by hydraulic power.

 When the directional control valve is actuated, the cylinder A and B will move according

to the following sequence:

-i. Rod Cylinder A (clamping) moves out ii. Rod Cylinders B (drilling) moves out iii. Rod Cylinders B move in

iv. A cylinder rod moves in

(8)

7

sequence valve (a)

(9)

 _{In the electro-hydraulic circuit as shown in the figure below, the directional}

control valve with double solenoid actuated by limit switches.

 By pressing the switch, solenoid (a) is energized for operation (1).

 _{At the end of the operation (1), solenoid (c) is energized by limit switches 2}

to get the operation (2).

 _{Then the solenoid (b) is energized by limit switches 3 to get the operation (3).}  _{Finally, the solenoid (d) is energized by limit switches 1 for operation (4).}

8

Electro hydraulic

(10)

9

solenoid (a) solenoid (b) solenoid (c) solenoid (d)

1 LS2 2 LS3 3 LS1 4

(11)



Opened cynosure system or open-centre system, the pump will

move continuously even directional control valve is in a neutral

position. Hydraulic oil will continue to flow from the pump

through the directional control valve then drains back into the

tank.



Advantages:



It was found that this system is simpler in construction and good for the

lower pressure at the time of the movement.



This reduces vibration and wear and reduce the energy caused by the

leakage when the system is neutral condition.



In addition, it has a circuit that is simple and easily constructed.

₁₀

(12)

11

Cylinder

Directional Control Valve 4/3 Accumulator Pressure regulating valve

Check valve Motor

Tank Filter

(13)



_{In a closed cynosure system or closed centre system, the pump will stop when the}

directional control valve is in a neutral condition. Directional control valve will block

the flow of oil from the pump. This will cause the hydraulic pump to stop pumping

oil. The pump will be switched off by disconnecting the supply current to the motor

that turns the pump. The switch is controlled by oil pressure.



_Advantages:

 The pump only operates when the system requires oil. This method saves engine power

when the hydraulic equipment is used.

 Oil stored at high pressure for quick action. This method saves operating time (operating

time).

 _{Delay action hydraulic system can be reduced by providing a high-pressure oil for}

immediate action against the open centre system in which the oil must be held before the oil pressure can be raised or lifted for operation.

 _{If the hydraulic system is used to create a variety of work in the same time of course the}

12

Closed cynosure system

(14)

13

Cylinder

Directional Control Valve 4/3 Accumulator

Pressure Motor Switch

Check valve Motor

Tank Filter

(15)

14

Cylinder

Directional Control Valve 4/3 Accumulator Pressure regulating valve

Check valve Motor

Tank Filter

Cylinder

Pressure Motor Switch

Check valve Motor

Tank Filter

(16)

Methods of Pressure and Flow Control



The circuit control rod speed depends on the position of a flow

control valve in the hydraulic circuit. This is because the speed

control for rod of the cylinders depending on the requirements of

a job. There are 3 ways to control the speed of the rod when it

came out, namely:

-a.

Meter-in

b.

Meter-out

c.

Bleed-off

(17)

Meter-in



Flow control valve mounted on the circuit at the input to

the hydraulic oil actuators such as cylinders or motors.



To allow seamless movement speed while entering the

cylinder rod, check valve installed as shown in figure

below.



When the pressure reaches

the maximum cylinder

pressure, hydraulic oil will flow into the tank.

(18)

17

Cylinder

Check valve Motor

Tank Filter

(19)

Meter-out



The control valve is mounted on the circuit at the output

of hydraulic oil to the actuators such as cylinders or

motors.



To allow seamless movement speed while entering the

cylinder rod, check valve installed as shown in figure

below.



When the cylinder pressure reaches the maximum

pressure, oil will flow into the tank.



When the load decreases or small, back-pressure greater

than the pressure of the pump output.

(20)

19

Cylinder

Check valve Motor

Tank Filter

(21)

Bleed-off



Adjustable flow control valve mounted on the circuit at

the input of the hydraulic oil between the cylinder and

flow control valve as shown in the figure below.



The speed can be controlled by adjusting the flow

control valve.



If all the oil flowing back to the tank, the cylinder rod

will not move due to the pressure drop of the system.

(22)

21

Cylinder

Check valve Motor

Tank Filter

(23)

22 Cylinder Directional Control Valve 4/3 Accumulat or Check valve Motor Tank Filter

One way flow control Valve

FIND THE DIFFERENCES

Cylinder Directional Control Valve 4/3 Accumulator Check valve Motor Tank Filter

One way flow control Valve Cylinder Directional Control Valve 4/3 Accumulat or Check valve Motor Tank Filter Adjustable flow control Valve

(24)

Problems in hydraulic system

(25)

a) Effects of overload burden

 _{Most pumps are used or operated under maximum capacity to make it}

durable. What will happen when used continuously to the maximum level. It will affect the durability of the pump bearings.

 _{For example, if a pump is designed to pump at a pressure of 150 bar and have}

a lifespan of 4800 hours of bearings. If the pump is used to pump the fluid with a pressure of 300 bar, it will affect the durability of the pump.

 _{The above calculation shows that by doubling the pressure from 150 bar to}

300 bar, the life of the pump will be reduced from 4800 hours to 600 hours. During pump operation the things that can cause increased pressure must be taken into account. Increasing pressure on the pump may be caused24

(26)

b) Effects of over speed

 _{By increasing the maximum speed of the pump, the pump will decrease the}

life of the bearing. Let the pump as in the first example to twice its speed is doubled, the following calculation shows a reduction in the life of the pump. Let the ordinary life of the pump is 4800 hours.

 _{By doubling twice the speed of the pump, pump life expectancy will drop by}

half of the original life span. Therefore the maximum speed of the pump must be observed to require the durability of the pump.

(27)

c) Pump Cavitation Effects

 Pump cavitation is a problem that occurs due to improper maintenance of the

pump. Cavitation occurs when fluid does not fulfil all pump room. This means there is space occupied by the air that will affect the operational efficiency of the pump.

 Cavitation occurs when the speed of the fluid produced by the pump too fast while

the inlet to the pump blockage. When the pump continues to operate that way the cavitation in pumps. If the problem continues, the area will be filled by the steam cavitation fluid produced due to the difference in pressure and temperature.

 This cavitation problems will be complicated due to the cavitation pressure drop

will cause it to be filled by existing air contained in the fluid.

 _{The pump will suffer damage when cavitation in the oil (low pressure) met with a}

high-pressure fluid. Damage is caused by vibration resulting pump. Pump vibration can cause wear on pump components and it can damage the pump 26

(28)

d) Leak in the system

 In most people, the hydraulic system is often dirty and leaking. With the design

and installation and maintenance perfect, generally leak system can be controlled and often eliminated. If all circuits leak, we would not dare to fly.

 _{Hydraulic fluid leakage occurs internally and externally component.}

 _{Excessive internal leakage will reduce system efficiency and generate heat that can}

damage the fluid. Little internal leakage is in the component as a lubricant compensator control and others.

 _{External leaks are not only dirty but also dangerous. The fluid can damage}

components. High costs not only fluid lost to be replaced but added downtime and performance also deteriorated.

(29)

e) Other problems

i) Problems That Occur At Cylinders

28

Problems Description

External L eaks Oil out through the end caps, gaskets.

Internal Leaks Oil flows through the clearance between the piston and the cylinder when pressure is applied

'Creeping' When subjected to pressure, the piston will return to

the original condition. This is due to a internal leak. Creeping also occurs to the directional control valve on the cylinder 2-way.

'Sluggish' Due to the existing air in the cylinder. Air can be

compressed, so sluggish going to happen. The inappropriate viscosity of the fluid used also lead to 'sluggish'.

(30)

ii) Problems Caused By Fluids

 The problem of water-based fluids and oils

 _{Easy to rust in a part of the system that is made of iron}

 Cause wear to the bearings, cylinders and other components because of lack of

lubrication

 _{Chances are frozen in the cold weather}  Large equipment is necessary