Pneumatic Vacuum Conveying Systems | Pneumatic Powder Transfer System | Negative Pressure Vacuum Pump

Negative pressure (Vacuum) Conveying system:

A negative pressure system is employed to pick up material from multiple sources and deliver the same to one remotely located point.

Basic principle of negative pressure pneumatic conveying system:

The basic principle of operation of a negative pressure system consists of a vacuum pump which is in communication with the conveying pipeline via the separation unit (cyclone separator) and the bag filter unit. Because of the vacuum produced in the system, air is drawn in the conveying pipeline through the air inlet nozzle. The material from the storage hopper or silo is introduced in the conveying line in which a negative pressure is maintained, through suitable feeders. As the material is introduced in the pipeline at negative pressure, the feeders used in this type of system need not be complex in design. A number of storage silos may be connected with the same conveying line, although when one feeder deliver material to the conveying line, usually other feeders are cut out. However, the material is conveyed along the pipelines to the cyclone separator where the major portion of the solid is separated from the air. The relatively clean air from the separator is allowed to pass through the bag filter unit which further cleans the air. The cyclone separator and the bag filter both deliver materials to the receiving hopper where the material is stored for use.

The most notable point in favour of this system is that all air leakage is from the surroundings into the system, so that pollution of the surroundings by the material being conveyed is practically eliminated. Hence this type of system is particularly suitable for toxic, explosive and powder like materials. But a serious limitation of the system is that, as the vacuum pump is located at the discharge end, unless the solid air separation unit and beg filter unit is especially efficient, there is possibility of dust laden air entering the vacuum pump and thereby damaging the life of the same. It is due to this reason that in a vacuum system multiple receiving hoppers cannot be used. Another limitation of the negative pressure system is that in practice only about 0.7 bar pressure drop can be allowed in the whole system and hence long distance conveying and high tonnage of conveying rate is not possible with a negative pressure system.

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1. Reliability analysis

2. Qualitative and Quantitative analysis

3. Failure Mode Effective Analysis FMEA

4. Errors in Measurement - An introduction

5. Terms in Engineering Measurement and Metrology

6. What is 2.5G technology

7. What is 2G technology

8. What is 2G, 3G and 4G technology

9. Difference between GSM and CDMA

10. What is GPRS

Positive pressure Pneumatic Conveying system | Material Conveying with Pneumatic Conveyors | Pneumatic Conveyor Advantages and Disadvantages

Positive pressure:

Positive pressure system is normally employed to pick up material from one source and deliver the same too many position.

Basic Principle of Positive Pressure Pneumatic Conveyors:

The essential component of a positive pressure system consists of a blower which sucks atmosphere air through an air inlet filter and delivers the air at higher pressure to the conveying line. The material which is stored in a storage silo or hopper is fed into the conveying line through a rotary air lock feeder. A basic problem in all the pressure system is how to introduce the material into the conveying pipeline which carries air under pressure. It is feeding device that has to cater for this and hence the special type of rotary air lock feeder is normally used with this type of systems to minimize leakage of air into the storage silo which is at atmosphere pressure. In general, a positive pressure system is not suitable for multiple pick up points because the air leakage through several rotary valves may be considerably high as compared to total air requirements. The material is then carried in suspension along with air through the conveying pipeline and delivered to one or more than one receiving hoppers. Receiving hoppers are nothing but a kind of silo or bin where the material is stored before use. If more than one receiving hoppers are to be served by the same conveying line, diversion valves are used in the pipeline to deliver the supply of material to the desired receiving hopper.

Pneumatic Conveying Cyclone Separators

Separation of solid from the air is usually achieved with the help of a cyclone separator and a bag filter unit which are fitted on the top of the receiving hoppers. A cyclone separator is essentially a cylindrical vessel with its axis vertical and the conveying pipeline is connected with it in such a way that the mixture of solid and air enters the cyclones tangentially and receives a circular motion within the vessel. This produces a vortex flow of the mixture of solid from air is achieved in cyclone separator, still the air contains certain amount of dust particles to be filtered in bag filter unit. The relatively cleaner air is taken out from the separator from the top and led into another cylindrical vessel where a bank of vertical bags, of cotton, cambish or other artificial fibres, are arranged in such a way that the air is made to pass through these bags before going out into the atmosphere. The dust particles carried by air from the cyclone separator are now filtered before being discharged into atmosphere. The filter bags are frequently shaken mechanically to drop the solid particles to the receiving hoppers.

Advantages and Disadvantages of Positive Pressure Conveying System:

An important merit of the positive pressure system is that the blower or fan, which is the heart of the conveying system, is always free from the dust of the material to be conveyed. On the other hand, a serious concern in the case of positive pressure system is the elimination of leakage from the system to the surroundings, a factor which becomes especially important when toxic material is to be conveyed.

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Pneumatic Conveyor Working Principle | Pneumatic Conveyor Advantage and Disadvantage | Powder Transfer System

What is Pneumatic Conveying

The word pneumatic means air, wind or gas etc. The word conveyor means equipment and machinery employed for transporting bulk material on a mass scale. So pneumatic conveying is the process of transporting bulk material on a mass scale. Pneumatic conveying is the process of transporting materials with the help of flowing stream of air or gas. Obviously, the air or gas must flow through a pipe or conduit. In fact, it is also obvious that if a stream of air passes at some velocity through a pipe, and if a powder like material is introduced in the pipe line, it must be carried by the air stream to a distant place.

Pneumatic Conveyors Application:

All materials cannot be transported by pneumatic conveyors. Those materials which are sticky or moist, cannot be carried away by air stream in a pipeline. On the other hand, those materials which are powder-like, free flowing, dry and not friable, are ideally suitable for pneumatic conveying. With the advancement of industries mass scale transportation of such materials are often necessary for different industrial and common applications. For example, cement, flour, powdered milk, powdered ingredients for medicines, explosive powder for ordinance factories, to mention only a few are basically powder-like, free flowing, dry and non sticky substances which are to be transported in a concealed condition in order to avoid contamination and hazards. So, for mass-scale handling of such materials pneumatic conveyors are essential, irrespective of cost factor.

Advantages of Pneumatic Conveying System:

In modern transport technology for handling bulk materials pneumatic conveying is gaining greater popularity day by day despite some disadvantages. The following advantages which a pneumatic handling system enjoys often makes its choice inevitable to achieve economical transportation in the plant.

• A simple technology which enable us to transport various products in a closed system without polluting the environment and being unaffected by the environment and weather changes
• It enjoys flexibility of installation and routing. Pipelines can easily be installed and routed along walls and ceiling to avoid obstruction without major structural modification. This is true for new buildings as well as existing building. Thus, material can also be transported vertically, horizontally or along inclined path
• Materials can be picked up from different points in a plant and can be delivered to a single point or many points in the same plant or in a different plant
• Low maintenance cost and lesser manpower for operation
• Multiple use of the same system can be achieved. The same pipelines can be used to transport variety products
• The system control is easy and can be converted to partial or fully automatic in operation
• It offers maximum security in transportation. Hence valuable bulk materials can be transported
• It offers less danger to operators and is safe for the environment
• It can be integrated into processes and hence great economy can result

Disadvantages and Limitations:

Pneumatic conveyor systems usually suffer from the following a disadvantages and limitations. While selecting a pneumatic conveyor to serve a particular purpose, the designer should give due considerations to the following points:

• Pneumatic conveyors usually involve relatively high energy consumption per ton of material conveyed. The specific energy consumption for a horizontal pipeline is of the order of 1-10 KW-h/ ton-km
• The principal limitation on the use of pneumatic conveyor is imposed by the properties of the material to be conveyed. All materials cannot be and should not be transported by pneumatic means. Before designing the system, the designer has to ascertain whether the material is powder-like, free flowing, explosive or non explosive, abrasive or non abrasive, toxic or non-toxic and so on. Usually, friable materials are not transported by pneumatic conveyors. Thus, a limited number of materials may be transported by this method
• Wear and abrasion are very high in pipeline used for pneumatic conveyors
• Conveying distance for a pneumatic conveyor is limited. Without booster stations, vacuum or low pressure pneumatic conveyors are workable up to 500m in length and for high pressure systems up to 2 to 3 km
• Pneumatic conveyor design requires a high degree of skill. As the flow mechanism in a two phase flow is really complex, mathematical modelling is in most of the cases impractical and the design of the system is based on empirical correlations which must be confirmed by experimental data. Therefore, even the most experienced designer cannot guarantee that the performance of the system will strictly be in accordance with the design specification.

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Types of Pneumatic Conveyor | Vacuum and Positive Pressure Pneumatic Conveying Systems | Dense Phase Pneumatic Conveying System

Classification of Pneumatic Conveying Systems

Pneumatic conveying systems can be classified on different basis of consideration. These basis are listed below:

• On average particle concentration (modes)
• On air pressure (Types of systems)
• On air supply arrangement
• On solid feeder type

Of these, the first two are very important and often influence the choice of the specific design for a given material, loading and delivery condition and the distance to be covered.

Classification based on Average Particle Concentration – Modes of Conveying:

Depending on the mass flow ratio, defined as the ratio of mass of particles conveyed to the mass of fluid used to convey, pneumatic conveying system may be classified into two modes; namely

1. Dilute phase
2. Dense phase

If the mass flow ratio is low, the system is said to operate in dilute phase. Whereas, if the mass flow ratio is high, the system is said to operate in dense phase. If the mode of operation of a system is in dilute phase, the probable range of mass flow ratio is 0 – 15. The dense phase system operates at mass flow ratio over 15.

In a dilute phase system the material is carried through the pipeline by a large volume of air having high velocity but relatively low pressure. The stream of air or gas carries the material in suspension in the pipeline as discrete particles owing to lift and drag forces acting on each particles. The distribution of particles over the cross section of the pipe is fairly uniform. In order to keep the particles in suspension, the air must possess a minimum velocity, called the pick up velocity. The pick up velocity for a particular material depends on many factors, like, the shape, size, specific weight of material and inclination of the pipeline.

If the velocity of air is gradually lowered down below what is required to keep the particles in suspension, the particles gradually settle down and form dunes at the bottom of the pipeline all along the length of the pipe. In this condition the material is about to choke the pipeline and if the pressure is increased these dunes and plugs of materials may move along the pipeline causing a dense phase flow. In a dense phase flow usually the velocity of fluid is much lower than the minimum velocity required for a dilute  phase flow. The distribution of particles over the cross section of the pipe is non uniform. At the lower part of the pipe there is slow moving dunes or plugs of material and the upper part of the cross section of the pipe is filled with certain proportion of finer particles in suspension in a state of dilute phase.

The maximum mass flow ratio achievable for a dense phase flow depends on many factors like the nature of materials and air velocity. It is usually greater than 30

Classification based on Air Pressure:

Based on air pressure, Pneumatic conveying systems may be classified as follows:

• Low pressure systems, in which the operating air pressure is about 1 atmosphere (760 mm Hg). This type of systems may be further sub classified into
• Positive pressure system
• Negative pressure system
• Combined positive – negative pressure system
• Medium pressure system
• High pressure system

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Engine Variable valve Actuating Mechanisms | Valve Train System and Components | Variable Valve Timing Technologies

Valve Actuating Mechanisms:

Each valve must open at the proper time, stay open for the required length of time and close at the proper time. Hence the timing of the valves are controlled by valve actuating mechanisms. Intake valves are just open before the piston reaches the Top Dead Centre (TDC), and exhaust valve remain open after TDC. At this particular instant both valves are open at the same time. This overlap results in better volumetric efficiency and lower operating temperatures.

• Mechanisms with side camshaft
• Double row side valve (T-Head) type
• Single row side valve (L-Head) type
• Overhead inlet and side exhaust valve (F-Head) type
• Single row overhead valve (I-Head) type

• Mechanisms with overhead camshaft
• With inverted bucket type follower operated by single camshaft
• With end-pivoted rocker arm operated by single camshaft
• Inlet valve operated by inverted bucket type follower and exhaust valve by pivoted rocker arm (Double camshaft)
• Double overhead camshaft with inverted bucket type followers
• Double overhead camshaft with separate rocker arms

Valve Train Components:

• Camshaft
• Camshaft drive
• Chain drive
• Gear drive
• Toothed belt
• Valve tappet
• Solid Lifters
• Roller lifters
• Hydraulic lifters
• Followers
• Push rod
• Rocker arm and rocker shaft

Camshaft:

A Shaft with a cam for each intake and exhaust valve. Each cam has a high spot called cam-lobe which controls the valve opening. Camshaft actually controls rotary motion to reciprocating motion.

Camshaft drive:

Cam gear is twice as large as crank gear. This makes the cam turn at 1/2 the speed of the crank

Valve Tappets:

The tappet follows the cam lobe and pushes the push rod. Solid and Roller lifts require adjustable rocker arm. Hydraulic Tappet requires oil to control.

Push Rods:

Metal rod which transfers force from the lifter to the rocker arm

Rocker Arm:

Rocker arm transmit the forces of the pushrod to the valve

Variable Valve Timing (VVT) technologies:

VVT is an engine technology which allows the lift or duration or timing (some or all) of the intake or exhaust valves to be changed during the engine operation

• Phase changing systems
• Profile switching systems
• Variable event timing systems
• Variable lift systems
• Electronic valve actuating systems

VVTi Engines:

VVTi system is a cam phasing system that can be applied on both inlet and exhaust cam shafts. This movement is controlled by engine management system according to need and actuated by hydraulic valve gears.

VTEC Engines:

VTEC stands for Valve Timing Electronic Control, where the system set the optimum valve timing by continuous changing of timing to open or close in Intake and Exhaust valves in response to the engine load, rotation and other operating conditions. This system controls the emission of NOx and HC and the fuel economy is increased.

i-VTEC:

iVTEC stands for Intelligent VTEC. Honda implement this most successful valve actuation system by continuously variable intake valve timing and computer controlled management for optimized torque output and fuel efficiency.

AVTEC:

AVTEC stands for Advanced VTEC. Honda implement this continuously variable phase control system to respond to the drivers power needs independent of engine speed. This system presents 13% better fuel economy and 75% lower emissions than iVTEC.

FIAT Multi - Air Technology:

A new engine air management technology introduced by FIAT which is much better than any VVT technology

Valve Troubles:

• Burning of valve face
• Necking of valve stem
• Valve face wear
• Valve stem and guide wear
• Valve cracking or Breakage
• Noisy valve operation

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What are the Main Parts of an Engine | What is the Function of the Piston in an Engine | What does the Camshaft do

Main Engine Parts:

• Cylinder Block and Crank case
• Cylinder Head
• Sump or Oil Pan
• Manifolds – Inlet and Exhaust
• Gaskets
• Cylinders and Liners (Dry and Wet)
• Pistons
• Piston Rings
• Connecting Rods
• Piston pins
• Crankshaft
• Main Bearings
• Valves and Valve – actuating mechanisms
• Catalytic converter, Muffler and Tail pipe

Functions of Piston:

• To transmit the force of explosion to the crankshaft
• To form a seal so that high pressure gases in the combustion chamber do not leak into the crankcase
• To serve as a guide and a bearing for small end of the connecting rod.

Piston Requirements:

• Should be silent in operation both during warming up and the normal running
• Design should be such that the seizure does not occur
• Should offer sufficient resistance to corrosion
• Shortest possible length
• Light in weight
• High thermal conductivity
• Long life

Methods to avoid Piston Slap:

• Use of Horizontal / Inclined slots
• Use of vertical or T-Slots
• Taper pistons
• Oval pistons
• Use of Special alloys
• Wire-wound pistons
• Autothermic pistons
• Bi-metal pistons
• Offset piston

Special Pistons:

• Pistons with inserted ring carrier
• Cast steel pistons
• Anodized pistons
• Tinned Pistons
• Oil-Cooled pistons
• Two-piece Pistons
• Composite insulated (heat shielded) pistons
• Squeeze cast pistons
• Aeconoguide pistons

Types of Piston Failure:

• Piston scuffing
• Burnt piston
• Damage to ring land
• Damaged piston boss and circlip groove

Functions of Piston rings:

• To form a seal for the high pressure gases from the combustion chamber against leak into the crankcase
• To provide easy passage for heat flow from the piston crown to the cylinder walls
• To maintain sufficient lubricating oil on cylinder walls throughout the entire length of piston travel

Types of Rings:

• Compression Rings
• Plain
• Taper face
• Torsional wrist
• Scraper type torsional twist
• Taper face torsional twist
• Keystone type
• Oil control Rings:
• Bevelled
• Stepped Scraper
• Slotted scraper
• Delayed action scraper
• Double action scraper
• Composite rail scraper

Cause of Ring Failure:

• Rapid Wear
• Scuffing
• Ring Breakage

Connecting Rod:

It’s function is to convert the reciprocating motion of the piston into rotary motion of the crankshaft

Piston Pin:

It connects the piston and the connecting rod. It also called as “Gudgeon pin”.

Crankshaft:

It is the engine component from which power is taken

Crankshaft assembly:

Includes the crankshaft and Bearings, flywheel, vibration damper, sprocket or gear to drive camshaft and oil seals at front and rear

Main parts of Crankshaft:

• Main Journals
• Crank Pins
• Crank Webs
• Counter Weights
• Oil Holes

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