Auto Mech Tech

✳️ Engine Oil Filter

✴️ Introduction

An oil filter is a filter designed to maintains continuous oil flow and removes particles (dirt, oxidized oil, metallic particles) that may appear in the motor oil due to engine wear. Oil filter remove contaminants from engine oil, transmission oil, lubricating oil, or hydraulic oil. Their chief use is in internal-combustion engines for motor vehicles (both on- and off-road ), powered aircraft, railway locomotives, ships and boats, and static engines such as generators and pumps.

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✴️ Major Parts of Oil Filters:
(see picture to know what I'm talking about)

1⃣Tapping plate:
A tapping plate is an entry and exit point on the oil filter. It contains small holes around the edge which allows the free flow of oil into the filter container. The threaded hole at the centre is where the oil flows out and it faces the engine.

2⃣ Antidrainback Valve:
The oil filter part is a rubber valve with a flap that holds oil from flowing back into the filter when the engine is not running. The filter required this because it’s located between toward the middle or bottom of an engine.

3⃣ Filter Medium:
A porous filter medium contains microscopic cellulose fibres and synthetic fibres such as polyester and glass. it helps to increase filtering durability and efficiency. It’s also saturated with resin to offer stiffness and strength. high-performance filters are designed with more synthetic fibres.

4⃣ Pleats:
The folded filter medium creates a greater total surface area. Well, the number of pleats will be determined by the medium’s thickness.

5⃣ Center Steel Tube:
This oil filter part provides structure to the filter and allows filtered oil to return to the engine. The number, size, and position of holes will ensure the effectiveness of the oil flow and not being restricted.

6⃣Relief Valve:
Because oil can be too thick to filter on a cold start, the engine needs to be prevented from starving. An oil filter is designed with a relief valve that opens when enough pressure is produced to force the calibrated spring downward. This allows unfiltered oil into the centre tube through the top.

7⃣End Disc:
An end disc which is made of either fibre or metal is used to stop the unfiltered oil from leaking into the centre tube. This end disc is bonded to each end of the filter medium.

8⃣ Retainer:
A retainer is a bit of metal that acts as a leaf spring. It keeps the filter medium and end disc tight against the tapping plate.

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✴️ Types of Oil Filters:

🔹Full-Flow Oil Filter:
The full-flow oil filter is the most common type used on cars which are also known as a primary oil filter. It is designed to clean and remove impurities from all the oil used by the engine. Full-flow filters are specially designed to work in colder temperature, cold weather cause motor oil to thicken and at cold start is the oil is thick.
These filter types allow the oil to move more freely through the engine than other types. If a filter is too restrictive, the engine may be starved with oil which may cause damage to its part. This is why the full-flow filter is better as it provides sufficient oil needed for the efficient performance of the engine.

🔹Cartridge Oil Filter:
The cartridge is a type of full-flow oil filter that is less complex and easy to use. It’s mounted upright which make it easily accessible for inspection without needing to remove the oil. These filter types are available in both metal and fibre but in most cases fibre which makes it easier to recycle.

🔹Spin-On Oil Filter:
A spin-on filter is another type of full-flow oil filter that contains a steel canister with a paper element. Car owners can easily fix it themself since the installation is simple and it requires minimal tools.

🔹Secondary or By-pass Oil Filter:
In some automobiles, secondary oil filters are used to support vehicles with full-flow filters. It’s designed to purify less than 10% of the engine oil. Contaminants there were not removed by a full-flow filter will then be clear-off by the secondary oil filter. These filter types extend the life of motor oil and ensure additional protection to the engine.

🔹Spinner Oil Filter:
A spinner oil is a type of secondary oil filter that uses centrifugal force to trap contaminants from the engine oil. Some of the filters can generate more than 2,000 force, which is greater than that of gravity. These filter types have the possibility of removing tiniest contaminants from the motor oil.

🔹Magnetic Oil Filter:
Just like the spinner oil filter, a magnetic oil filter is also a type of secondary filter that supports the full-flow version. It is designed to effectively remove metallic contaminants from the motor oil but does not clean dust and grime.

Magnetic oil filters don’t need replacement like the other types. All it needs is regular cleaning to keep it functioning.

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✴️ Reasons to change your oil filter:

🔹To reduce engine wear
🔹To avoid soiling your new oil

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✴️ Signs To Change The Oil Filter

🔹️Lowering Oil Pressure:

When you find the oil pressure has decreased, it is an indication of a problem with the car engine. Low oil pressure can be caused by a leaking oil filter or a blockage, causing oil to enter the engine.

🔹️Engine Overheat:

An oil filter that is not in good condition will hinders the oil supply to run properly to the car engine. Less oil entering the engine will create friction that occurs in the car engine and this will make the car engine overheat.

🔹️Decreased Engine Performance:

When there is a buildup of contaminants due to a faulty oil filter, the engine performance will be greatly reduced and the engine power of the car will be very bad. Decrease in engine performance will stop the driver from getting to the desired driving speed.

🔹️Metal Friction Sounds:

A clogged oil filter will reduce the oil supply to the engine and will make engine components not work properly. Reduced oil supply will usually cause metal friction and this condition will greatly interfere with your driving comfort.

🔹️Exhaust Smoke Looks Dirty:

When you find exhaust fumes that look dirty, then it's a sign that your car's oil filter is in bad condition. The smell of burning oil is also a sign that there is a problem with the oil filter.

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✴️ Replacing your engine oil filter:

☑️Replacement guideline of engine oil filter ...

🔹Severe driving condition
Every 7,500 km/6 months ....Whichever comes first

🔹Normal driving condition
Every 15,000 km /1 year .....Whichever comes first

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✴️ Choosing the right oil filter:

🔹️Choosing the correct oil filter for your vehicle is of the utmost importance. Most oil filters look very similar, but small differences in the threads or gasket size can determine whether or not a particular filter will work on your vehicle.

🔹️The best way to determine which oil filter you need is by consulting your owner’s manual or by referencing a parts catalog.

🔹️Using the wrong filter can cause oil to leak out of the engine, or an ill-fitting filter could just fall off. Either of these situations could lead to serious engine damage.
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✳️ Four Stroke Engine (4-Stroke Engine)

✴️ Introduction

🔹Engines are most widely used all over the world for numerous applications. These are used in different vehicles such as buses, trucks, vans and motorcycles, etc. There are different types of engines, and a 4-stroke engine is one of them.

🔹According to the number of piston strokes, the engines have two major types that are :-
🅰️ 2-stroke engine
🅱️ 4-stroke engine

✴️ What is a 4-Stroke Engine?

🔹A 4-stroke engine is an internal combustion (IC) engine that uses four strokes (intake, compression, power, and exhaust) of the piston to complete a working cycle. It converts the thermal energy of the fuel into useful mechanical work due to the upward and downward movement of the piston. Therefore, it belongs to the category of the reciprocating engine.

🔹A four-stroke engine completes a power cycle after the completion of two revolutions of the crankshaft and 4 strokes of the piston. These engines are most widely used in different vehicles such as light trucks, buses, vans, cars, etc.

🔹In this reciprocating engine, the compression process occurs due to the up and down movement of the piston.

🔹A stroke is a distance a piston travels in the combustion cylinder as it moves from the top dead centre (TDC – the top most point of the working area of a piston) to the bottom dead centre (BDC – the bottom most point of the working area of a piston).

✴️ How does a 4-Stroke Engine work?

⏺️ A four-stroke engine works in the following steps :-
▫️Intake Process
▫️Compression Process
▫️Power Process
▫️Exhaust Process

🔹Intake stroke

▫️The intake stroke is when the air-fuel mixture is introduced to fill the combustion chamber. The intake stroke occurs when the piston moves from TDC to BDC and the intake valve is open.

▫️The movement of the piston toward BDC creates a low pressure in the cylinder. Ambient atmospheric pressure forces the air-fuel mixture through the open intake valve into the cylinder to fill the low pressure area created by the piston movement.

▫️The cylinder continues to fill slightly past BDC as the air-fuel mixture continues to flow by its own inertia while the piston begins to change direction.

▫️The intake valve remains open a few degrees of crankshaft rotation after BDC. Depending on engine design. The intake valve then closes and the air-fuel mixture is sealed inside the cylinder.

🔹Compression Stroke

▫️The compression stroke is when the trapped air-fuel mixture is compressed inside the cylinder. The combustion chamber is sealed to form the charge. The charge is the volume of compressed air-fuel mixture trapped inside the combustion chamber ready for ignition. Compressing the air-fuel mixture allows more energy to be released when the charge is ignited.

▫️Intake and exhaust valves must be closed to ensure that the cylinder is sealed to provide compression.

▫️Compression is the process of reducing or squeezing a charge from a large volume to a smaller volume in the combustion chamber.

▫️The flywheel helps to maintain the momentum necessary to compress the charge.

▫️When the piston of an engine compresses the charge, an increase in compressive force supplied by work being done by the piston causes heat to be generated.

▫️The compression and heating of the air-fuel v***r in the charge results in an increase in charge temperature and an increase in fuel v***rization. The increase in charge temperature occurs uniformly throughout the combustion chamber to produce faster combustion (fuel oxidation) after ignition.

▫️The increase in fuel v***rization occurs as small droplets of fuel become v***rized more completely from the heat generated.

▫️The increased droplet surface area exposed to the ignition flame allows more complete burning of the charge in the combustion chamber.

▫️Only gasoline v***r ignites. An increase in droplet surface area allows gasoline to release more v***r rather than remaining a liquid.

▫️The more the charge v***r molecules are compressed, the more energy obtained from the combustion process. The energy needed to compress the charge is substantially less than the gain in force produced during the combustion process. For example, in a typical small engine, energy required to compress the charge is only one-fourth the amount of energy produced during combustion.

▫️The compression ratio of an engine is a comparison of the volume of the combustion chamber with the piston at BDC to the volume of the combustion chamber with the piston at TDC.
This area, combined with the design and style of combustion chamber, determines the compression ratio.

▫️Gasoline engines commonly have a compression ratio ranging from 6 - 12. The higher the compression ratio, the more fuel-efficient the engine.

▫️A higher compression ratio normally provides a substantial gain in combustion pressure or force on the piston.

🔹 Power Stroke

▫️The power stroke is also known as a combustion stroke.

▫️When the compression stroke is nearly to be complete, a spark plug burns the compressed air-fuel mixture.

▫️As the air-fuel mixture gets ignited, the power is generated so that the piston moves from TDC to BDC by expanding the chemical reaction. Therefore, this stroke is called POWER STROKE.

▫️Due to this burning process, the temperature and pressure of the mixture become very high.

▫️During this process, both the inlet and exhaust valves are closed.

🔹 Exhaust stroke

▫️The exhaust stroke occurs whenspent gases are expelled from the combustion chamber and released to the atmosphere.

▫️The exhaust stroke is the final stroke and occurs when the exhaust valve is open and the intake valve is closed. Piston movement evacuates exhaust gases to the atmosphere.

▫️As the piston reaches BDC during the power stroke combustion is complete and the cylinder is filled with exhaust gases.

▫️The exhaust valve opens, and inertia of the flywheel and other moving parts push the piston back to TDC, forcing the exhaust gases out through the open exhaust valve.

▫️At the end of the exhaust stroke, the piston is at TDC and one operating cycle has been completed.

✴️ Engine Firing Order

➡️ What's The Firing Order ?

🔹️The firing order of an internal combustion engine is the sequence of ignition for the cylinders. In a spark-ignition (e.g. gasoline/petrol) engine, the firing order corresponds to the order in which the spark plugs are operated. Firing order affects the vibration, sound, and evenness of power output from the engine.

🔹️In engines, cylinders don’t fire in the sequence of 1-2-3-4-5-6 and so on as it could cause the crankshaft to deform or break. The order or sequence in which the engine cylinders fire or generate & deliver power is called the engine firing order.

🔹️The firing order heavily influences crankshaft design. In a Diesel engine, the firing order corresponds to the order in which fuel is injected into each cylinder.

🔹️Four-stroke engines must also time the valve openings relative to the firing order, as the valves do not open and close on every stroke.

🔹️Every engine cylinder must fire once in every cycle. This requires that for a four-stroke four cylinder engine the ignition system must fire for every 180 degrees of crank rotation. For a six cylinder engine the time available is only 120 degrees of crank rotation.

🔹️Firing order of various engine configurations:

▫️For 4-Cylinder engines, the possible firing orders are: 1-3-4-2 or 1-2-4-3

▫️For 3 Cylinder engines 1-3-2

▫️8 Cylinder in-line engine 1-6-2-5-8-3-7-4

▫️For a 6-Cylinder engine, firing orders can be: 1-5-3-6-2-4 or 1-5-4-6-2-3

✴️What are examples of a 4-stroke engine?

Four-stroke engines are most commonly used in heavy applications such as trucks, buses, dirt bikes, vans, tractors, and other heavy vehicles.

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🚦BOXER/FLAT/ ENGINE

Flat engines feature cylinders that are arranged horizontally, with the pistons moving left and right rather than up and down.

Boxers are a special type of flat engine that split the cylinders into two even banks around a central crankshaft.

Flat engines have been built with anywhere from two to 16 cylinders.

Boxer engines are inherently balanced, reducing the need for expensive and complicated balancers.

Their horizontal arrangement gives them a low center of gravity, improving power transmission and handling in vehicles that sport these engines.

Power delivery is smooth throughout, and the engines are easier to cool because of their spread-out design; for many years, these engines could get away with simple air-cooling.

However, these engines tend to be rather large, and their spread-out design can make maintenance difficult; cylinder heads are often pushed up against the walls of the engine bay, making a simple task like changing spark plugs a knuckle-bruising job.

They are also more expensive to manufacture, and they often don’t fit well into typical engine bays.

🚦ADVANTAGES

1. Perfect Balance

Owing to its pistons working together to create perfect balance, there will not be another smoother engine system inside a car than this. There would not be any issues related to vibration from the engine. It adds to the boxer engine reliability in the longer run.

2. Added Boost

The perfect balance combined with the size of the boxer engine leads to less load on the crankshaft. Thus, it provides a significant boost in power to the rotational inertia of the car, which offers extreme power without any issues.

3. Unique Design

The horizontally-opposed engine, owing to its unique design gathers a low center of gravity in the car. It offers the driver better handling of the vehicle allowing sports car lovers to race on the track without much understeer.

🚦DISADVANTAGES

1. Size

On one hand, the boxer engines provide an unmatched performance to a sports car. However, the wide configuration makes it a bit hard to work on these mechanically. Besides, the obstruction of airflow they create in the engine area might even lead to their failure at high speeds. The car owner might need an expert with the relevant industry knowledge about car engines.

2. A Bit Complex

The boxer engines are one complex example of automobile engineering, as the two cylinder heads and valve require much maintenance. The owner of the vehicle with this kind of engine needs to take care of the engine to keep it running smoothly.

The slightest neglect in the upkeep of boxer engines can lead to a considerable drop in its performance. It is one of the boxer engine problems, which is resolved by taking care of the engine on time.

3. Maintenance

The offset position of the engine can lead to some rocking with the connection to the connecting rod or crankshaft. However, it all depends on how well is the horizontally-opposed engine maintained by the car owner.

Great ideas🚙🔩👌🏻

Explanation of the Tire Codes ⚙️

AIR COMPRESSOR

An air conditioner compressor is the component in the system that raises the temperature and pressure of the v***r refrigerant that leaves the ev***rator coil. Its important that the compressor raises the pressure of the v***r refrigerant so that it creates a pressure difference, the pressure difference is needed in order for the refrigerant to flow. High pressure fluids flow towards lower pressure fluid. Basically whats happening is the compressor is raising the pressure of the refrigerant so that the refrigerant will flow to the lower pressure refrigerant in the ev***rator coil.
The compressor raising the pressure will also increase the temperature. The direction of heat transfer is from a higher temperature substance to a lower temperature substance, the lower temperature being in the ev***rator coil and the hotter being in the compressor and condenser.

The temperature of the freon being increased is very important, because the refrigerant will get so hot that the hot air outside will be cooler even in the summer when it can be up to 120 degrees! The air being cooler outside allows the heat in the refrigerant to transfer to it when it goes through the condenser coils. The heat in the refrigerant was transferred originally from the heat inside the home at the ev***rator coil. Its important that the compressor increase the temperature so that it can finish removing the heat from inside the home to the condenser.

Air conditioner and heat pump compressors are known as v***r compressors because they are not meant to have any liquid, and liquids are not a compressible fluid. Any liquid that may enter the compressor will result in reduced efficiency and capacity and will typically cause mechanical damage to the compressors internal components.



The main and important types of gas compressors are illustrated and discussed below:

-compressors-types
A positive displacement compressor is the system which compresses the air by the displacement of a mechanical linkage reducing the volume (since the reduction in volume due to a piston in thermodynamics is considered as positive displacement of the piston).[vague]

compressors

A motor-driven six-cylinder reciprocating compressor that can operate with two, four or six cylinders.
Reciprocating compressors use pistons driven by a crankshaft. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines.[1][2][3] Small reciprocating compressors from 5 to 30 horsepower (hp) are commonly seen in automotive applications and are typically for intermittent duty. Larger reciprocating compressors well over 1,000 hp (750 kW) are commonly found in large industrial and petroleum applications. Discharge pressures can range from low pressure to very high pressure (>18000 psi or 180 MPa). In certain applications, such as air compression, multi-stage double-acting compressors are said to be the most efficient compressors available, and are typically larger, and more costly than comparable rotary units.[4] Another type of reciprocating compressor, usually employed in automotive cabin air conditioning systems,[citation needed] is the swash plate or wobble plate compressor, which uses pistons moved by a swash plate mounted on a shaft (see axial piston pump).

Household, home workshop, and smaller job site compressors are typically reciprocating compressors 1½ hp or less with an attached receiver tank.

A linear compressor is a reciprocating compressor with the piston being the rotor of a linear motor.

liquid piston compressor

Main article: Ionic liquid piston compressor
An ionic liquid piston compressor, ionic compressor or ionic liquid piston pump is a hydrogen compressor based on an ionic liquid piston instead of a metal piston as in a piston-metal diaphragm compressor.[5]

screw compressors

Diagram of a rotary screw compressor
Main article: Rotary screw compressor
Rotary screw compressors use two meshed rotating positive-displacement helical screws to force the gas into a smaller space.[1][6][7] These are usually used for continuous operation in commercial and industrial applications and may be either stationary or portable. Their application can be from 3 horsepower (2.2 kW) to over 1,200 horsepower (890 kW) and from low pressure to moderately high pressure (>1,200 psi or 8.3 MPa).

The classifications of rotary screw compressors vary based on stages, cooling methods, and drive types among others.[8] Rotary screw compressors are commercially produced in Oil Flooded, Water Flooded and Dry type. The efficiency of rotary compressors depends on the air drier,[clarification needed] and the selection of air drier is always 1.5 times volumetric delivery of the compressor.[9]

Designs with a single screw [10] or three screws [11] instead of two exist.

vane compressors

Eccentric rotary-vane pump
See also: Rotary vane pump
Rotary vane compressors consist of a rotor with a number of blades inserted in radial slots in the rotor. The rotor is mounted offset in a larger housing that is either circular or a more complex shape. As the rotor turns, blades slide in and out of the slots keeping contact with the outer wall of the housing.[1] Thus, a series of increasing and decreasing volumes is created by the rotating blades. Rotary Vane compressors are, with piston compressors one of the oldest of compressor technologies.

With suitable port connections, the devices may be either a compressor or a vacuum pump. They can be either stationary or portable, can be single or multi-staged, and can be driven by electric motors or internal combustion engines. Dry vane machines are used at relatively low pressures (e.g., 2 bar or 200 kPa or 29 psi) for bulk material movement while oil-injected machines have the necessary volumetric efficiency to achieve pressures up to about 13 bar (1,300 kPa; 190 psi) in a single stage. A rotary vane compressor is well suited to electric motor drive and is significantly quieter in operation than the equivalent piston compressor.

Rotary vane compressors can have mechanical efficiencies of about 90%.[12]

piston

Rolling piston compressor
The Rolling piston in a rolling piston style compressor plays the part of a partition between the vane and the rotor.[13] Rolling piston forces gas against a stationary vane.

2 of these compressors can be mounted on the same shaft to increase capacity and reduce vibration and noise. A design without a spring is known as a swing compressor.

In refrigeration and air conditioning, this type of compressor is also known as a rotary compressor, with rotary screw compressors being also known simply as screw compressors.

compressors

Mechanism of a scroll pump
Main article: Scroll compressor
A scroll compressor, also known as scroll pump and scroll vacuum pump, uses two interleaved spiral-like vanes to pump or compress fluids such as liquids and gases. The vane geometry may be involute, archimedean spiral, or hybrid curves.[14][15][16] They operate more smoothly, quietly, and reliably than other types of compressors in the lower volume range.

Often, one of the scrolls is fixed, while the other orbits eccentrically without rotating, thereby trapping and pumping or compressing pockets of fluid between the scrolls.

Due to minimum clearance volume between the fixed scroll and the orbiting scroll, these compressors have a very high volumetric efficiency.

These compressors are extensively used in air conditioning and refrigeration because they are lighter, smaller and have fewer moving parts than reciprocating compressors and they are also more reliable. They are more expensive though, so peltier coolers or rotary and reciprocating compressors may be used in applications where cost is the most important or one of the most important factors to consider when designing a refrigeration or air conditioining system.

This type of compressor was used as the supercharger on Volkswagen G60 and G40 engines in the early 1990s.

compressors

Main article: Diaphragm compressor
A diaphragm compressor (also known as a membrane compressor) is a variant of the conventional reciprocating compressor. The compression of gas occurs by the movement of a flexible membrane, instead of an intake element. The back and forth movement of the membrane is driven by a rod and a crankshaft mechanism. Only the membrane and the compressor box come in contact with the gas being compressed.[1]

The degree of flexing and the material constituting the diaphragm affects the maintenance life of the equipment. Generally stiff metal diaphragms may only displace a few cubic centimeters of volume because the metal can not endure large degrees of flexing without cracking, but the stiffness of a metal diaphragm allows it to pump at high pressures. Rubber or silicone diaphragms are capable of enduring deep pumping strokes of very high flexion, but their low strength limits their use to low-pressure applications, and they need to be replaced as plastic embrittlement occurs.

Diaphragm compressors are used for hydrogen and compressed natural gas (CNG) as well as in a number of other applications.

three-stage diaphragm compressor
The photograph on the right depicts a three-stage diaphragm compressor used to compress hydrogen gas to 6,000 psi (41 MPa) for use in a prototype compressed hydrogen and compressed natural gas (CNG) fueling station built in downtown Phoenix, Arizona by the Arizona Public Service company (an electric utilities company). Reciprocating compressors were used to compress the natural gas. The reciprocating natural gas compressor was developed by Sertco.

The prototype alternative fueling station was built in compliance with all of the prevailing safety, environmental and building codes in Phoenix to demonstrate that such fueling stations could be built in urban areas.



Dynamic compressors depend upon the inertia and momentum of a fluid.

bubble compressor

Also known as a trompe. A mixture of air and water generated through turbulence is allowed to fall into a subterranean chamber where the air separates from the water. The weight of falling water compresses the air in the top of the chamber. A submerged outlet from the chamber allows water to flow to the surface at a lower height than the intake. An outlet in the roof of the chamber supplies the compressed air to the surface. A facility on this principle was built on the Montreal River at Ragged Shutes near Cobalt, Ontario in 1910 and supplied 5,000 horsepower to nearby mines.[18]

compressors

A single stage centrifugal compressor
Main article: Centrifugal compressor
Centrifugal compressors use a rotating disk or impeller in a shaped housing to force the gas to the rim of the impeller, increasing the velocity of the gas. A diffuser (divergent duct) section converts the velocity energy to pressure energy. They are primarily used for continuous, stationary service in industries such as oil refineries, chemical and petrochemical plants and natural gas processing plants.[1][19][20] Their application can be from 100 horsepower (75 kW) to thousands of horsepower. With multiple staging, they can achieve high output pressures greater than 1,000 psi (6.9 MPa).

This type of compressor, along with screw compressors, are extensively used in large refrigeration and air conditioning systems. Magnetically levitated and air bearing centrifugal compressors exist.

Many large snowmaking operations (like ski resorts) use this type of compressor. They are also used in internal combustion engines as superchargers and turbochargers. Centrifugal compressors are used in small gas turbine engines or as the final compression stage of medium-sized gas turbines.

or mixed-flow compressors

Diagonal or mixed-flow compressors are similar to centrifugal compressors, but have a radial and axial velocity component at the exit from the rotor. The diffuser is often used to turn diagonal flow to an axial rather than radial direction.[21] Comparative to the conventional centrifugal compressor (of the same stage pressure ratio), the value of the speed of the mixed flow compressor is 1.5 times larger.[22]

-flow compressors
Edit

An animation of an axial compressor.
Main article: Axial-flow compressor
Axial-flow compressors are dynamic rotating compressors that use arrays of fan-like airfoils to progressively compress a fluid. They are used where high flow rates or a compact design are required.

The arrays of airfoils are set in rows, usually as pairs: one rotating and one stationary. The rotating airfoils, also known as blades or rotors, accelerate the fluid. The stationary airfoils, also known as stators or vanes, decelerate and redirect the flow direction of the fluid, preparing it for the rotor blades of the next stage.[1] Axial compressors are almost always multi-staged, with the cross-sectional area of the gas passage diminishing along the compressor to maintain an optimum axial Mach number. Beyond about 5 stages or a 4:1 design pressure ratio a compressor will not function unless fitted with features such as stationary vanes with variable angles (known as variable inlet guide vanes and variable stators), the ability to allow some air to escape part-way along the compressor (known as interstage bleed) and being split into more than one rotating assembly (known as twin spools, for example).

Axial compressors can have high efficiencies; around 90% polytropic at their design conditions. However, they are relatively expensive, requiring a large number of components, tight tolerances and high quality materials. Axial-flow compressors are used in medium to large gas turbine engines, natural gas pumping stations, and some chemical plants.

sealed, open, or semi-hermetic
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A small hermetically sealed compressor in a common consumer refrigerator or freezer typically has a rounded steel outer shell permanently welded shut, which seals operating gases inside the system. There is no route for gases to leak, such as around motor shaft seals. On this model, the plastic top section is part of an auto-defrost system that uses motor heat to ev***rate the water.
Compressors used in refrigeration systems are often described as being either hermetic, open, or semi-hermetic, to describe how the compressor and motor drive are situated in relation to the gas or v***r being compressed. The industry name for a hermetic is hermetically sealed compressor, while a semi-hermetic is commonly called a semi-hermetic compressor.

In hermetic and most semi-hermetic compressors, the compressor and motor driving the compressor are integrated, and operate within the pressurized gas envelope of the system. The motor is designed to operate in, and be cooled by, the refrigerant gas being compressed.

The difference between the hermetic and semi-hermetic, is that the hermetic uses a one-piece welded steel casing that cannot be opened for repair; if the hermetic fails it is simply replaced with an entire new unit. A semi-hermetic uses a large cast metal shell with gasketed covers with screws that can be opened to replace motor and compressor components.

The primary advantage of a hermetic and semi-hermetic is that there is no route for the gas to leak out of the system. Open compressors rely on shaft seals to retain the internal pressure, and these seals require a lubricant such as oil to retain their sealing properties.

An open pressurized system such as an automobile air conditioner can be more susceptible to leak its operating gases. Open systems rely on lubricant in the system to splash on pump components and seals. If it is not operated frequently enough, the lubricant on the seals slowly ev***rates, and then the seals begin to leak until the system is no longer functional and must be recharged. By comparison, a hermetic or semi-hermetic system can sit unused for years, and can usually be started up again at any time without requiring maintenance or experiencing any loss of system pressure.

The disadvantage of hermetic compressors is that the motor drive cannot be repaired or maintained, and the entire compressor must be replaced if a motor fails. A further disadvantage is that burnt-out windings can contaminate whole systems, thereby requiring the system to be entirely pumped down and the gas replaced (This can also happen in semi hermetic compressors where the motor operates in the refrigerant). Typically, hermetic compressors are used in low-cost factory-assembled consumer goods where the cost of repair and labor is high compared to the value of the device, and it would be more economical to just purchase a new device or compressor. Semi-hermetic compressors are used in mid-sized to large refrigeration and air conditioning systems, where it is cheaper to repair the compressor rather than buying and installing a new one. A hermetic compressor is simpler and cheaper to build than a semi-hermetic compressor.

An advantage of open compressors is that they can be driven by non-electric power sources, such as an internal combustion engine or turbine. However, open compressors that drive refrigeration systems are generally not totally maintenance-free throughout the life of the system, since some gas leakage will occur over time