c5_basic Hydraulic Circuit

DJJ5123 PNEUMATIC & HYDRAULICS 5.0 BASIC HYDRAULIC CIRCUIT

Hydraulic Circuit

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A hydraulic hydraulic circuit is a system comprising an interconnected set of discrete components that transport liquid.

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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).

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Arrangement Of Components

Cylinder

Flow control valve

Directional Control Valve 4/3

Pressure regulating valve

Accumulator

Check valve

Motor Filter

Tank

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A basic circuit of hydraulic control system to drive a motor two actions 4

The basic components in a hydraulic circuit is as below: -

Components Valve

Description 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.

Tank

Serves to hold the hydraulic oil and cool the hydraulic oil. 5

Sterling hydraulic 

It is designed to control a sequence of operations cylinder with sequence valve. Example; given sequence is A + B + B- A-

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

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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

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6 In the circuit in sequence, sequence valve (a) and (b) must be adjusted at a pressure

sequence valve (a) sequence valve (b)

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Electro hydraulic

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In the electro-hydraulic circuit as shown in the figure below, the directional control valve with double solenoid actuated by limit switches.

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

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At the end of the operation (1), solenoid (c) is energized by limit switches 2 to get the operation (2).

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Then the solenoid (b) is energized by limit switches 3 to get the operation (3).

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Finally, the solenoid (d) is energized by limit switches 1 for operation (4).

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LS1

solenoid (a)

solenoid (b)

1

2

3

4

LS3

LS2

solenoid (c)

solenoid (d)

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Opened cynosure system 

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.

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Advantages: 

It was found that this system is simpler in construction and good for the lower pressure at the time of the movement.

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This reduces vibration and wear and reduce the energy caused by the leakage when the system is neutral condition.

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

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Cylinder

Directional Control Valve 4/3

Pressure regulating valve

Accumulator

Check valve

Motor Filter

Tank 11

Closed cynosure system 

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.

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Advantages: 

The pump only operates when the system requires oil. This method saves engine power when the hydraulic equipment is used.

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

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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.

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If the hydraulic system is used to create a variety of work in the same time of course the 12

Cylinder

Directional Control Valve 4/3

Accumulator Pressure Motor Switch

Check valve

Motor

Filter

Tank 13

FIND THE DIFFERENCES

Cylinder

Cylinder

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

Pressure regulating valve

Accumulator

Accumulator Pressure Motor Switch

Check valve

Check valve

Motor

Motor Filter

Filter

Tank

Tank 14

Methods of Pressure and Flow Control

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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 

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Meter-in

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Flow control valve mounted on the circuit at the input to the hydraulic oil actuators such as cylinders or motors.

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To allow seamless movement speed while entering the cylinder rod, check valve installed as shown in figure below.

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When the pressure reaches the maximum pressure, hydraulic oil will flow into the tank.

cylinder

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Cylinder

One way flow control Valve

Directional Control Valve 4/3

Accumulator

Check valve

Motor Filter

Tank 17

Meter-out 

The control valve is mounted on the circuit at the output of hydraulic oil to the actuators such as cylinders or motors.

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To allow seamless movement speed while entering the cylinder rod, check valve installed as shown in figure below.

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When the cylinder pressure reaches pressure, oil will flow into the tank.

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When the load decreases or small, back-pressure greater than the pressure of the pump output.

the

maximum

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Cylinder

One way flow control Valve

Directional Control Valve 4/3

Accumulator

Check valve

Motor Filter

Tank

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Bleed-off 

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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.

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The speed can be controlled by adjusting the flow control valve.

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If all the oil flowing back to the tank, the cylinder rod will not move due to the pressure drop of the system. 20

Cylinder

Adjustable flow control Valve

Directional Control Valve 4/3

Accumulator

Check valve

Motor Filter

Tank 21

FIND THE DIFFERENCES

Cylinder

Cylinder

Cylinder Adjustable flow control Valve One way flow control Valve

One way flow control Valve

Directional Control Valve 4/3 Accumulat or

Accumulat or

Accumulator

Motor

Motor

Motor

Filter

Filter

Tank

Check valve

Check valve

Check valve

Filter

Directional Control Valve 4/3

Directional Control Valve 4/3

Tank

Tank 22

Problems in hydraulic system

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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.

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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.

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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

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.

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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.

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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.

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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.

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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.

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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 26 can cause wear on pump components and it can damage the pump

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.

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Hydraulic fluid leakage occurs internally and externally component.

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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.

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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.

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e) Other problems i) Problems That Occur At Cylinders 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'. 28

ii) Problems Caused By Fluids

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The problem of water-based fluids and oils 

Easy to rust in a part of the system that is made of iron

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

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Chances are frozen in the cold weather

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Large equipment is necessary

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