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HYDRAULIC SYSTEM FOR BEGINNERS


When I have entered in my industrial life, I have observed that approximate every machine is dependent on hydraulic system. I was very interested to gain knowledge about the hydraulic function and maintenance of hydraulic system.

I have searched on web and I have also interacted to my seniors for gaining the practical maintenance knowledge about this system.

I have decided now to post one blog over this system so that I can help you and also other person, who is interested, to understand the hydraulic machineries from very starting.

I have decided to post here the basic of the hydraulic system but later I will post each and every topic about hydraulic system.

Purpose

The main purpose of this post is to understand the following points
  1. Hydraulic system working principle
  2. Various components used in hydraulic system
  3. Various types of actuators and valves utilized in hydraulic system
  4. Role of viscosity in hydraulic system
  5. Factors affecting the viscosity
  6. Working of each components used in hydraulic system

Theory

All hydraulic system work on the principle of Pascal’s law and according to which any increase or decrease in pressure of in-compressible fluid will be transmitted equally in all the direction in static fluid .
Let us understand the various necessary components used in hydraulic system

Reservoir tank

Reservoir tank will act as buffer for holding the of flowing media or hydraulic oil, pump will take fluid from this reservoir and after completion of desired tank, hydraulic fluid or hydraulic oil will be transported to this tank via drain line. Buffer plates are also utilized in hydraulic tank reservoir in order to settling the foreign particle and removing of air from oil.

Pump

Hydraulic pump is used to force the hydraulic oil through the system. There are basically three types of hydraulic pump utilized in hydraulic system
Gear Pump 
Vane pump
Piston pump

Electric Motor

Electric motor is used to drive the hydraulic pump

Valves

There are various types of vales used for three basic functions
  1. Relief valve, Pressure reducing and pressure sequence valve- for controlling the pressure and used to avoid the unwanted pressure for safety purpose
  2. Flow control valve – for controlling the flow rate
  3. Direction control valve – for controlling the direction
  4. Flow control valve and direction control valve
Pressure relief valve, Pressure reducing valve and pressure sequence valve

Actuators

Actuators utilize the oil pressure to convert in mechanical energy to do some useful work. There are two basic type of actuators are applied.
  1. Hydraulic cylinder             
  2. Hydraulic motor

Hydraulic pipe

Hydraulic pipes are used for carrying the pressurized fluid

Accumulator

Accumulator is used for providing the compressible nature in in-compressible circuit. It receives fluid pressure when fluid pressure will be higher than the required pressure and will deliver hydraulic pressure when pressure will be lower in hydraulic circuit.

Fluid viscosity

Viscosity is the most important characteristics of hydraulic fluid in respect of performance of hydraulic system. When we go for selecting the hydraulic fluid, first we focus on viscosity of hydraulic fluid or hydraulic oil. 

Viscosity of hydraulic fluid must match with the range of temperature during system operation otherwise we will not achieve the desired life of various components utilized in hydraulic system. During the selection of correct hydraulic oil, we must think the following points as mentioned below.
  1. Optimum and allowable viscosity range of fluid for satisfactory operation of hydraulic system.
  2. Maximum temperature expected during operation.
  3. Viscosity at lowest ambient-temperature
Once we will have information of above points, we will secure the correct viscosity fluid with the help of curve for viscosity and temperature curve.
Viscosity of fluid is defined as term for measurement of resistance of fluid during flow. Fluid which will have higher viscosity will be thick and will have higher resistance to flow. Viscosity depends on the temperature, when viscosity increases then lubrication characteristics will be improved and problem of oil leakage will be reduced.

There are various processes for measuring the viscosity of fluid and out of them there is one method where there will be a container along with an orifice at bottom. We will have to measure the total time required for flowing a definite quantity of hydraulic fluid through that orifice. 

Once we will come to know the required time for flowing that decided quantity of fluid through that orifice, we will convert this time in viscosity with the help of following formula. Unit of viscosity is usually taken as centi-stock (CST)
V= 0.875 T – 993 / T
Where, viscosity is in CST and time is in second

Hydraulic circuit

Let us discuss one hydraulic circuit as mentioned below;
This circuit is designed for a maximum pressure of 300 PSI, but we will operate on 100 PSI for safety purpose and for easily connections. We will set pressure relief valve at 125 PSI more as compared to other valve setting as if it is set too low then it will cause the heating of oil, let us understand the hydraulic circuit as mentioned below

If system pressure will require more pressure then setting pressure of relief valve , in that case relief valve will be opened and oil will flow through relief valve to tank and hence relief valve act as safety valve for hydraulic system components. 

While if pressure is below as compared to set pressure of relief valve then in that case relief valve will be in closed condition and oil will not flow to tank via relief valve but also it will go to directional control valve and then to actuators .

Find interesting points about hydraulics 

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