Thursday, January 24, 2008

Humidity control

Refrigeration air conditioning equipment usually reduces the humidity of the air processed by the system. The relatively cold (below the dewpoint) evaporator coil condenses water vapor from the processed air, (much like an ice cold drink will condense water on the outside of a glass), sending the water to a drain and removing water vapor from the cooled space and lowering the relative humidity. Since humans perspire to provide natural cooling by the evaporation of perspiration from the skin, drier air (up to a point) improves the comfort provided. The comfort air conditioner is designed to create a 40% to 60% relative humidity in the occupied space. In food retailing establishments large open chiller cabinets act as highly effective air dehumidifying units.

Some air conditioning units dry the air without cooling it, and are better classified as dehumidifiers. They work like a normal air conditioner, except that a heat exchanger is placed between the intake and exhaust. In combination with convection fans they achieve a similar level of comfort as an air cooler in humid tropical climates, but only consume about a third of the electricity. They are also preferred by those who find the draft created by air coolers discomforting.

Air conditioning-History

While moving heat via machinery to provide air conditioning is a relatively modern invention, the cooling of buildings is not. The ancient Romans were known to circulate aqueduct water through the walls of certain houses to cool them. As this sort of water usage was expensive, generally only the wealthy could afford such a luxury.

Medieval Persia had buildings that used cisterns and wind towers to cool buildings during the hot season: cisterns (large open pools in a central courtyards, not underground tanks) collected rain water; wind towers had windows that could catch wind and internal vanes to direct the airflow down into the building, usually over the cistern and out through a downwind cooling tower[2]. Cistern water evaporated, cooling the air in the building.

In 1820, British scientist and inventor Michael Faraday discovered that compressing and liquefying ammonia could chill air when the liquefied ammonia was allowed to evaporate. In 1842, Florida physician John Gorrie used compressor technology to create ice, which he used to cool air for his patients in his hospital in Apalachicola, Florida.[3] He hoped eventually to use his ice-making machine to regulate the temperature of buildings. He even envisioned centralized air conditioning that could cool entire cities.[4] Though his prototype leaked and performed irregularly, Gorrie was granted a patent in 1851 for his ice-making machine. His hopes for its success vanished soon afterwards when his chief financial backer died; Gorrie did not get the money he needed to develop the machine. According to his biographer Vivian M. Sherlock, he blamed the "Ice King," Frederic Tudor, for his failure, suspecting that Tudor had launched a smear campaign against his invention. Dr. Gorrie died impoverished in 1855 and the idea of air conditioning faded away for 50 years.

Early commercial applications of air conditioning were manufactured to cool air for industrial processing rather than personal comfort. In 1902 the first modern electrical air conditioning was invented by Willis Haviland Carrier. Designed to improve manufacturing process control in a printing plant, his invention controlled not only temperature but also humidity. The low heat and humidity were to help maintain consistent paper dimensions and ink alignment. Later Carrier's technology was applied to increase productivity in the workplace, and The Carrier Air Conditioning Company of America was formed to meet rising demand. Over time air conditioning came to be used to improve comfort in homes and automobiles. Residential sales expanded dramatically in the 1950s.

In 1906, Stuart W. Cramer of Charlotte, North Carolina, USA, was exploring ways to add moisture to the air in his textile mill. Cramer coined the term "air conditioning," using it in a patent claim he filed that year as an analogue to "water conditioning", then a well-known process for making textiles easier to process. He combined moisture with ventilation to "condition" and change the air in the factories, controlling the humidity so necessary in textile plants. Willis Carrier adopted the term and incorporated it into the name of his company. This evaporation of water in air, to provide a cooling effect, is now known as evaporative cooling.

The first air conditioners and refrigerators employed toxic or flammable gases like ammonia, methyl chloride, and propane which could result in fatal accidents when they leaked. Thomas Midgley, Jr. created the first chlorofluorocarbon gas, Freon, in 1928. The refrigerant was much safer for humans but was later found to be harmful to the atmosphere's ozone layer. Freon is a trademark name of DuPont for any Chlorofluorocarbon (CFC), Hydrogenated CFC (HCFC), or Hydrofluorocarbon (HFC) refrigerant, the name of each including a number indicating molecular composition (R-11, R-12, R-22, R-134). The blend most used in direct-expansion comfort cooling is an HCFC known as R-22. It is to be phased out for use in new equipment by 2010 and completely discontinued by 2020. R-11 and R-12 are no longer manufactured in the US, the only source for purchase being the cleaned and purified gas recovered from other air conditioner systems. Several non-ozone depleting refrigerants have been developed as alternatives, including R-410A, known by the brand name Puron.

Innovation in air conditioning technologies continue, with much recent emphasis placed on energy efficiency and improving indoor air quality. As an alternative to conventional refrigerants, natural alternatives like CO2 (R-744) have been proposed.[5]

How to Clean your Air Conditioner like a Pro???

Lets get started

1. Start by removing the filter from the front grille. If it is a disposable type simply replace it with a new one. Other types are made in a plastic frame and can be cleaned and reused. To clean a reusable type lay it flat in the sink and sprinkle surface with laundry detergent. Then cover with about one inch of hot water. Just enough so the filter is submerged. Soak for 15 minutes. Remove from water and rinse with warm water. Hang up to dry while proceeding to next step.

2. Next, remove the front grille from the main body of the air conditioner. They usually pivot on 2 spring clips at the bottom. It is usually removed by pulling the grille gently forward while pushing it down at the same time. If there is resistance then look for hidden screws. Look near the top edge of the grille or behind the control knob door. Once removed place the grille aside until later.

3. Carefully remove metal cover of air conditioner to expose inner workings. Once all the screws are removed lift the cover straight up. Do not let it hit the other parts as it can have sharp edges.

This is where the old can comes in handy (ice cube container or muffin tin works well also). Use it to keep track of all the screws you will be removing. An air conditioner will often use a number of different types and sizes of screws. Segregate them from each other or confusion will result when we start reassembly.

4. Check the fan motor for any oil holes or oil plugs. If the motor has oil plugs they are usually rubber. Use caution when removing because the rubber may have become brittle. Often they will break off in the oil holes resulting in a blockage. If this occurs try to remove the broken plug by using a pin, or the tip of a small screwdriver.

Once the fan motor oil holes are exposed add a few drops of oil to each end of the motor body. Use a general purpose (3in1) oil or clean motor oil. A #30 oil is sufficient.

The natural tendency is to over-oil. Too much lubrication is as bad as not enough. Therefore only 3 or 4 drops on both ends of the motor body is sufficient. Add the oil slowly, pausing a few seconds between each drop. If you add it too quickly over-lubrication will result.

5. Use the brush to remove surface dust and dirt from the evaporator (front fins). Use an up and down motion. Do not go side to side or allow the fins to be bent over. The fins are very soft aluminum and can be easily damaged.

Once surface dirt is removed, spray with de-greaser or cleaner. There is a good product on the market called HVAC cleaner. As the name implies it is meant for Heating, Ventilation, and Air Conditioner coil cleaning. If this is not available Fantastic spray cleaner used in kitchens and bathrooms works quite well.

Let stand about 15 minutes or as per instructions on de-greaser can. This will allow cleaner to loosen any hidden dirt. Remove dirt and excess cleaner by slowly pouring warm water into fins. Do not allow the water to enter any electrical connections or components that may be near the coil. As an added precaution cover the motor with one of the cloth rags. to protect it from the water.

Do not use any form of high pressure air or water because this can drive dirt farther into fins. Also, use extreme caution as these coils are filled with high pressure refrigerant.

6. Straighten any bent fins. Use a fin comb if available. If no fin comb then use something soft such as a Popsicle stick. Straightening the fins will increase the efficiency of the air flow through the coils. This adds to the overall cooling effect produced by the air conditioner.

7. Repeat steps 5 and 6 for the condenser (rear fins) coil. A plastic cowling usually surrounds the condenser fins. If so, check the top edge to see if it will lift or open. If it opens this will allow easier access to the condenser fins. Again use caution because the condenser coil is also filled with high pressure refrigerant.

8. Wipe any dirt buildup from both fan blades using a soft rag. Do not bend blades. This would cause a vibration that would harm the motor.

9. Vacuum all surfaces including front and back of grille assembly. Do not forget to vacuum underside of metal air conditioner cover. If the cover contains air holes clean them thoroughly. If necessary use a damp rag. Also use an old rag to remove any debris build-up from the base.

10. Drain any water left in the base and allow it to dry for few hours.

When completely dry plug in air conditioner and test operation. If everything appears okay unplug and reassemble.

Once reassembly is complete, retest operation to ensure replacing the cover has not affected anything. Adding the cover will tend to twist the frame and can cause interior parts to move out of alignment. This can cause the fan to become noisy. To correct for this problem remove the cover and realign to the main body of the air conditioner. Reinstall the cover and test for noises every time 2 or 3 additional screws are added to the cover.

Finally, cover air conditioner with plastic wrap or an old blanket. Store in a warm dry area. Raise it from floor slightly by placing onto a couple of pieces of wood. This will protect the floor from the metal edges of the air conditioner, and also protect the air conditioner from moisture.


Air conditioning does more than cool the air. It truly "conditions" it by removing dust and dirt as the air is drawn through a filter. Air conditioning also lowers the humidity, making the air more comfortable at any temperature. These benefits, however, can be costly. Depending on your region of the country, air conditioning can account for anywhere from 5 to 50% of your household budget. Because an air conditioner is such a sizable investment, you can save money and energy by carefully purchasing and operating your air conditioner.

When shopping for an air conditioner, first consider what system best suits your needs - central air conditioning or room air conditioning. Central air conditioners are located in one part of a building, but they cool the entire building either by blowing cold air through ducts positioned in each room, or by circulating cooled water through pipes to each room where fans blow air across the pipes. Room air conditioners work in the same way, but have a smaller capacity and therefore only cool the immediate area.

Central air conditioners generally provide the greatest comfort but they also cost more than room units. If several rooms need to be cooled, however, a central system is probably the best buy. Central systems generally are not cost-effective as an addition to an existing home unless the existing ductwork can be used.

Room air conditioners are mounted in windows or built into an external wall. Room units are less expensive than central units; however, they only cool the general space in which they are located. There are three types of room units; window models can be installed in most windows; casement window models, used in narrow, vertical windows, usually require the removal of a window panel for installation; and built-in models which are encased in a sleeve installed in the wall.


After selecting the optimum unit type, consider unit size. A bigger unit is not necessarily better, because a unit that is too large will not cool an area uniformly. Also, an oversized unit will cool an area too quickly, causing the air conditioner to frequently turn on and off. This wastes electricity and money. In addition, a unit that is too large will not run long enough to reduce humidity and, instead of feeling comfortable, the air will feel cold and clammy at the normal thermostat setting.

On the other hand, you should avoid purchasing too small a unit. An insufficiently sized unit will run constantly on hot days and still not be able to cool the area adequately.

In sizing an air conditioner for your home, consider the dimensions of the area to be cooled and how the area is used. Based on size alone, an air conditioner generally needs 20 Btu for each square foot of living space. For instance, to air condition a room that is 15 feet wide and 20 feet long, you would calculate: 15 x 20 x 20(Btu) = 6,000. Thus, an air conditioner with a 6,000 Btu capacity would be required.

Calculating Btu requirements becomes more complicated when you consider an area's use. For instance, if you use passive cooling techniques such as shading, ventilation or vegetation, your Btu estimate can be lowered. Likewise, your Btu needs are increased by factors such as the size of the household, frequent use of heat-producing appliances, or summer humidity levels. An appliance dealer will use these factors to adjust your estimated Btu requirement. For most efficient cooling, purchase a unit, with a capacity within 5% of this estimate.

How to Clean a Room Air Conditioner?

A room air conditioner that doesn't cool may need to be recharged with refrigerant--a task you should leave to a professional--but often just needs to be cleaned.

To clean the coils and filter:
* Unplug the unit. You may need to remove it from the window (be careful--it's heavy!)

* Remove the air inlet grill and remove the filter;

* Wash the filter or replace it with a disposable one;

* Vacuum the coils' fins with a soft brush attachment;

* Spray water back through the fins from the fan side (cover the wiring and motor with plastic);

* Check to be sure that the drains are clean;

* Lubricate the motor--check the owner's manual for instructions; and

* Reassemble and reinstall the unit.

Room Air Conditioner Problems and Repairs

Room air conditioners draw a lot of electrical power. If your air conditioner is not turning on, check for a tripped circuit breaker or blown fuse caused by an overloaded circuit. Also check that the thermostat to be sure it is set to cool and to a few degrees below room temperature.

If your air conditioner doesn't cool, you may need to clean or replace the filter, which might be restricting air movement. If that doesn't do it, clean the evaporator and condenser coils.

Room air conditioners can sometimes become very noisy. Check that the fan blades are not bent, and clean them. You may need to tighten the mounting bolts for the blower, which could be rattling in its casing, and lubricate the motor according to the manufacturer's directions. Also check that the unit's mounting bracket is firmly connected to the window or the wall; it too may be loose and rattling.

If you are working on a room air conditioner, clean the drains that allow condensed water to drip away from the unit.

Window Air Conditioner Problems?

Window air conditioners are usually plugged in and forgotten – until they stop cooling properly, or until they exhibit problems. Don’t just plug in your window air conditioner and ignore it. There are things you must do to properly maintain your window air conditioning unit in an effort to avoid problems. Taking proper care of your window air conditioner will ensure the unit will continue to provide the cold air you want when you need it the most. Don’t wait for problems to start before taking the necessary steps to keep your window air conditioner running properly.

The following information provides facts and tips on what you must do to avoid problems with your window air conditioner. Also included are troubleshooting tips for correcting common problems with window air conditioning units.

Preventing Problems

Any item that uses an air filter can’t run properly if the filter is dirty, and window air conditioners are no exception. If you want your window air conditioning unit to run properly and efficiently, it’s imperative that you change or clean the filter once a month.

The filter isn’t the only part of a window air conditioner that requires regular care and cleaning. The condenser coils can become covered in dirt and dust, and they should be cleaned at least once a year. Even if condenser coils don’t appear to be dirty, grime and dust can hide in places not readily visible.

While the air conditioner is unplugged and the condenser coils are dry, vacuum the coils with a crevice tool, blow away dirt and dust with an air compressor, or clean the coils with a soft brush such as an old toothbrush. This is an easy preventative measure that you can do yourself in an effort to avoid problems while lowering your electric bill in the process.

Type of Compressors, Key Features

There are two important components of the window AC – the compressor and the Fan motor. The Compressor consumes 90 percent of the electricity whereas the fan motor consumption is only 10 percent. The compressor is backbone of the air conditioner as this is the component that causes cooling. It compresses the gas causing it to become hot, which is then condensed into a liquid through a set of coils. This cools the air around it. There are two types of compressors used in window ACs – reciprocating and rotary.

Reciprocating compressor - It compresses the air by sliding the piston over the cylinder. Air conditioners fitted with a reciprocating compressor are generally less expensive but are not as efficient and silent as the ACs with the rotary compressor.

Rotary compressor - This compresses air by centrifugal action of high-speed impeller in a confined space. This method reduces the loss in pressure of the refrigerator gas. Rotary compressors are more efficient and silent. Buying an energy efficient compressor will save on your electric bills in the long run.

The rotary compressor is expensive as compared to a reciprocating compressor, however, it makes up for that cost by saving more on power as compared to a reciprocating compressor.


Energy efficiency ratio (EER)
Energy Efficiency Ratio measures the cooling efficiency of the air conditioner as compared to the power it consumes. It is the ratio of the cooling capacity in BTU/hr to its electricity consumption in watts. Models with a higher EER save on your electricity bills but are priced a little higher than ones with lower EER. An EER of nine and above is considered good.

A filter purifies the air that goes through the air conditioner. There are different types of filters that remove dust, germs, bacteria, odour, etc. Deodorising filters remove dust particles and dirt; anti-fungal filters clean the air and remove germs and bacteria thus reducing respiratory problems. The Electrostatic filter releases positive ions, which ionise the negative ions of dust and static electricity giving you a clean, dust free environment. Slide-in and Slide-out filters allow easy maintenance as they can be removed for cleaning without opening or dismantling the entire machine. If you smoke or live in an air-polluted area that is prone to dust, this would be an important feature to consider.

Anti corrosion body
The body and framework of air conditioners is prone to corrosion especially as one part of it is outside and is exposed to rain, moisture, dust, etc. However, if the exterior is made of galvanised steel or is powder coated it helps in protecting the unit from corrosion and extends the life of the body.

Auto restart
If there is a power failure or if the air conditioner has been disconnected, you may have to reset and programme all the cooling functions and features that you originally had. An air conditioner with the auto restart facility starts automatically and restores the original settings when the power is restored. This feature is beneficial in areas where power supply is irregular.

Remote control
Don't need to go into why this is useful but it becomes a must-have if your AC is placed at a height. Of course, most of us cannot imagine an appliance without a remote control, as it would mean having to get up each time to change settings.

The timer lets you to set the air conditioner to begin cooling at any time, whether you are home or not. It is also helpful to shut off during the middle of the night when it gets very cold.

Air conditioners with rotary compressors generally make less noise than a reciprocating compressor. The noise level in a window AC ranges fro 40 to 60 db. The lower the better, however, higher the capacity of the air-conditioner, more the decibels.
These are few things that you need to be informed about before deciding upon a window AC. For more information on the various brands available in the market click here.

Airconditioners (Window)

Rising temperatures, low prices, improved efficiency are making window air conditioners a very attractive proposition. Of course, the manufacturers also realize this and so have bombarded you with dozens of models to pick from. Clearly you're spoilt for choices. Hopefully, this guide will help you make an informed choice.

Before you get into the brand or company you want to buy an AC from, you need to have figured out basics like how much cooling you will want (capacity), how much you are willing to invest on this (budget) and what else you would like your AC to have (additional features – remote control, display, etc).

Most air conditioners are rated in BTU per hour (British Thermal Unit) or by tonnage. One ton is equal to 12,000 BTU per hour. The cooling capacity that you need would depends on a number of factors like number of people in the room, number of appliances in the room, etc. The average ambient temperature of your area during the year: Higher the average temperature of the outside air, the more will be the cooling capacity required. If you live in a cities which have scorching hot summers, you will need an AC with higher cooling capacity.

The cooling capacity required is proportional to the area of the room you wish to cool. A bigger room will naturally require a higher ton AC as compared to a smaller room. Also if you have a bigger family, five or more people and everyone will crowd into one room, then the capacity will have to be higher even though the room may be small. Also, your capacity will need to be higher if any of your walls gets a direct blast of sunlight, so as to negate the heat from the sun. The hottest room in your house is your kitchen, so if the AC room is next to the kitchen then a higher cooling capacity is advisable.

Rooms Size (Sq ft)
Tonnage Capacity
Up to 90 sq ft
0.8 Ton
Up to 120 sq ft 1.0 Ton
Up to 180 sq ft 1.5 Ton
Up to 220 sq ft
2.0 Ton

A one ton window AC starts from as low as Rs 9,700 and can go up to Rs 31,490. You may already have a budget in mind as to how much you would like to spend. Window Air Conditioners range from Rs 9,700 to Rs 31,490. The cooling capacity and features affect the price.

Price range
0.6 Ton - 1.0 Ton
Rs 8,990 - 21,600
1.1 Ton - 1.5 TonRs 13,495 - 24,600
1.6 Ton - 2.0 TonRs 16,200 - 32,990


View Details

Main Features
Cooling Capacity (Tonnes) 1.5
Power Consumption (Watts)1850
Energy Efficiency Ratio (EER) 9.73
Compressor Type Rotary
Refrigerant Gas ---
Number of Fan Speeds Available 2
Maximum Fan Speed (rpm) ---
Air Circulation and Moisture Removal
Air Circulation (High) (CFM)480
Air Circulation (High) (M3/Hr) ---
Moisture Removal (Ltrs/Hr) 2.3
Filter Type Slide-in/out
Deodourising Filter
Anti Fungus or Bacteria Filter
Electrostatic Filter
Minimum Temperature (Degrees Celsius)---
Maximum Temperature (Degrees Celsius)---
Temperature ControlMechanical
General Features
Slide-in Slide-out Chassis
Remote Control
Air Swing
Ventilation Control
Auto Restart
Anti Corrosion Body
Noise Levels (db) 52
Power Requirement
Voltage (Volts)230
Frequency (Hz)50
Running Current (Amps) 8.5
Machine Dimensions
Width (mm)660
Depth (mm)770
Height (mm)428
Approximate Net Weight (Kgs)65
After Sales Service
Warranty Period (Years)1

Toshiba 7-in-1 Filtration Air Conditioners

Toshiba air conditioning presents toshiba 7-in-1 filtration air conditioners. This will keep your home cool, clean comfort can grace every room and breathtaking advanced in air conditioning features mean you can breathe with greater confidence.

toshiba`s 7-in-1 filtration system tackles odours, bacteria, allergens and viruses. It`s self-cleaning protects against the mechanism build up of mould ,the ultimate comfort is at hand using the new one touch comfort option and a range of features such as super quiet, comfort sleep and multiple airflow controls. Its double compact design has made the indoor unit 24% smaller and downsized the outdoor unit by 28%, providing optimum performance when space, style and discretion are in mind.

toshiba`s advanced energy-saving technology exceeds the highest energy-efficiency standards in many markets. When you turn off your air conditioner, an internal fan automatically activates to dry out the coil that removes the moisture which causes mould to form.

Wednesday, January 9, 2008

The electrical & electronic control systems:

The electrical system:

Electricity powers most of the devices in the car. The starting motor requires electricity to crank the engine, the ignition system requires electricity to deliver spark inside the cylinders. The fuel injectioin system, lights, horns, radio, air conditioner and other accessories require electricity to operate. The battery supplies electricity while the engine is off and for cranking the engine. After the engine starts, the alternator recharges the battery and supplies power for the electrical load.

The electronic control systems:

Many devices and systems on the car require a control system for safe and proper operation. A basic control system has three parts. These are inputs, the control unit and the outputs. The inputs are switches and sensors; they provide information to electronic control modules (ECM). Then the ECM signals the output devices or actuators to take the required action. The ECM has a self-diagnostic capability. This means a memory stores information about faults or malfunctions that have occurred and perhaps disappeared. When recalled from the memory this stored information helps the technician to diagnose and repair the vehicle.

Types of Lathe:

Lathes of various designs and constructions have been developed to suit the various conditions of metal machining. But all of them employ the same fundamental principle of operation and perform the same function.

Generally used Lathes are:

  • Speed Lathe
  • Engine Lathe
  • Bench Lathe
  • Tool Room Lathe
  • Capstan and Turret Lathe
  • Special Purpose Lathe
  • Automatic Lathe

The Speed Lathe:

The speed lathe, in construction and operation, is the simplest of all kinds of Lathe. It consists of a bed, a headstock, a tail stock and a tool post mounted on an adjustable slide. There is no feed box, lead screw or conventional type of carriage. The tool is mounted on the adjustable slide and is fed into work purely by hand control. This characteristic of lathe enables the designer to give high spindle speeds which usually range from 1200 to 3600 rpm. As tool is controlled by hand, the depth of cut and thickness of chip is very small.

The headstock construction is very simple and only two or three spindle speeds are available. Light cuts and high speeds necessitate the use of this type of machine where cutting force is minimum such as in wood-working, spinning, centering, polishing. Etc. The “Speed Lathe” has been so named because of the very high speed of the Head stock spindle.

The Engine Lathe or Centre Lathe:

This Lathe is most important member of the lathe family and is the most widely used. The term “Engine” is associated with the lathe owing to the fact that early lathes were driven by steam engines. Similar to the speed lathe, the engine lathe has got all the basic parts for example bed, head stock and tail stock. But the head stock of engine lathe is much more robust in construction and it contains additional mechanism for driving the lathe spindles at different speeds. Unlike speed lathe, engine lathe can feed the cutting tool both in cross and longitudinal direction with reference to the lathe axis with help of carriage, feed rod and lead screw. With these additional features an Engine lathe has proved to be a versatile machine adapted for every type of lathe work.

Engine lathes are classified according to the various deigns of the head stock and methods of transmitting power to the machine. A lathe that receives its power from an overhead line shaft is a belt driven lathe and is equipped with a speed cone and one or more back gears to get a wide range of spindle speeds. A lathe that receives its power from an individual motor integral with machine is called a motor driven lathe. A geared head lathe gets its power from a constant speed motor and all speed changes are obtained by shifting various gears located in headstock. It has no cone pulley.

The Bench Lathe:

This is a small lathe usually mounted on a bench. It has practically all the parts of an engine lathe and it performs almost all the operations, its only difference being in the size. This is used for small precision work.

The Tool Room Lathe:

The Tool room Lathe having features similar to Engine lathe is much more accurately built and has a wide range of spindle speeds ranging from a very low to a quite high speed up to 2500rpm. This is equipped besides other things, with a chuck, taper turning attachment, draw in collet arrangement, thread chasing dial, relieving attachment, steady and follower rest, pump for coolant etc. This lathe is mainly used for precision work on tools, dies, gauges and in machining work where accuracy is needed. The machine is costlier than an Engine lathe of same size.

The Capstan and Turret Lathe:

These Lathes are development of the Engine lathe and are used for Production work. The distinguishing feature of this lathe is that the tail stock of Engine lathe is replaced with a hexagonal turret, on the face of which multiple tools can be fitted and fed into the work in proper sequence. The advantage is that several different types of operations can be done on a work piece without re-setting of work or tools, and a number of identical parts can be produced in minimum time.

Special Purpose Lathe:

As the name implies, they are used for special purposes and for jobs which cannot be accommodated and conveniently machined on a standard lathe. The wheel lathe is made finishing the journals and turning the tread on railroad car and locomotive wheels. The gap bed lathe, in which a section of the bed adjacent to head stock is recoverable, is used to swing extra large diameter pieces. The T-Lathe, a new member of the lathe family is intended for machining of rotors for jet engines. The axis of the lathe bed is at right angles to the axis of head stock spindle in the form of T. The duplicating lathe is one for duplicating the shape of a flat or round template on to the work piece. Mechanical, air and hydraulic devices are all used to co-ordinate the movements of the tool to reproduce accurately the shape of the template. The Missile Lathe, which has a very large swing for accommodating long missile component of very large diameter, is the most modern and latest in Lathe design.

Automatic Lathe:

These are high speed, heavy duty, mass production lathes with complete automatic control. Once the tools are set and the machine is started it performs automatically all the operations to finish the job. The changing of tools speeds and feeds are also done automatically. After the job is complete, the machine will continue to repeat the cycles producing the identical parts even without attention of the operator. An operator will simply look after general maintenance of the machine and cutting tool, load up a bar stock and remove finished products from time to time.

The Lathe

The Lathe


The Lathe is one of the oldest machine tools and came into existence from the early tree lathe which was then a novel device for rotating and machining a piece of work held between two adjacent trees. A rope wound around the work with its one end attached to a flexible branch of a tree and the other end being pulled by a man caused the job to rotate intermittently. Hand tools were then used. With its further development a strip of wood called “lath” was used to support the rope and that is how the machine came to be known as Lathe. This device continued to be developed through centuries and in the year 1797 Henry Maudslay, an Englishman, designed the first screw cutting lathe which is the forerunner of the present day high speed heavy duty lathe, a machine tool which has practically given shape to our present day civilization by building machines and industries.

Function of Lathe:

The main function of lathe is to remove a metal from a piece of work to give it the required shape and size. This is accomplished by holding the work securely and rigidly on the machine and then turning it against cutting tool which will remove metal from the work in the form of chips. To cut the material properly the tool should be harder than the material of work piece, should be rigidly held on the machine and should be fed or progressed in a definite way relative to the work.


Refrigeration cycle of Window Air Conditioner

Preventive Maintenance of Air-conditioner :

Periodic cleaning of the air-conditioner is necessary to prevent breakdown and excessive wear of the unit. A soft cloth or vacuum cleaner can be used to clean the components. The grills, condenser and evaporator coils, fans and dampers should be freed from obstructions. The air seals in the window and cabinet should be checked to see that they have not loosened or deteriorated. Such cleaning and periodic checking give troublefree service in most of the cases.

Air-conditioning Cassettes :

The term “Cassette” came into use in 1875 to describe a flat box used for transporting photographic plates. In more recent times, we have used this term for hi-fi equipments as videos, computers, compact cameras and so on. From 1980 onwards, the ceiling cassette became terminilogy in air-conditioning industries. The cassette air-conditioner has made a bigger impact in Heating, Ventilating and Air-conditioning trade during last 10 years than any other single product in its history. The first ceiling cassette was brought in the market in 1984. By 1985, other two companies Daikin and Hitachi from Japan entered injto this market, type of air-conditioning cassette which is of drawing board size and sufficient to cool a single room. The sale of air-conditioning cassettes in U.K. was of 11 million dollars in 1987 which went to 18 million dollars in 1988.

Cassette system has rapidly established themselves as an economical alternative to other packages or central plant with a better return on capital investment. This is because, cassettes give higher flexibility for retail operations which are frequently on the move or subject to periodic re planning. The popular concept “Shop Within a Shop” has often concentrated high lighting and occupancy loads in relatively small areas with the need for additional spot cooling, conveniently provided by Cassette unit.

Hi-tech electronics provide further refinements in terms of temperature and operating efficiency. This latest unit claims 30% more output on heating, 20% on cooling and 20% less power consumption and continuous capacity control. The next generation of units will need to be more compact, less distraught and overcome the occasional problems of condensate disposal.

A Hitachi Air conditioning cassette creates a musical sound by distributing four way air and requires hardly 28cm space with a virtually flush face side diffuser. Micro computer controls makes the cassette easy to operate and you can choose cooling only, heat pump only and heat pump models with supplementary electric heating element to give the security of additional heat on extra cold days. The Hitachi air conditioner cassette is quiet, light weight, easy to install and economical also to operate.

Installation of Room Conditioner :

Since the window air conditioner uses an air-cooled condenser to cool the hot refrigerant, the cooler the condenser, the more efficient is its operation. If the window unit is exposed to the sun’s rays the heat of radiation and warm air can diminish the efficiency of the exposed condenser and reduce the capacity of the unit. It is thus advisable to install the window unit for a minimum of sun exposure. The order of preferential exposure for optimum performance is : north, east, south and lastly west, of course, the shape of the room relative to air circulation patterns, location of the windows and the location preferred by the occupants often overrule the above consideration. In installing the conditioner, good air pattern in the room should be planned to establish comfortable condition satisfactory to the occupants. The following points should be kept in mind during the installation of conditioner.

1) Whenever the unit is exposed to the sun, a shade should be provided such as an awning.

2) It should be carefully seen that louvers of the outer cabinet are not blocked up or restricted by a brick block or by the wall itself.

3) The air-conditioner should slope toward the outside about 1.5 cm/m. This ensures the flow of condensate water from the evaporator back to the singer ring on the condenser fan blade or to the drain hose.

The Thermostat control


The pressure actuated type thermostat uses a bulb containing gas which expands or contracts with variation in room temperature. This expands or contracts a bellow which, in turn, opens or closes an electrical contact and the compressor operation is automatically controlled to maintain a constant temperature. Thus, if the room air returned to the unit becomes cooler than the thermostat setting, the gas in the bulb contracts, causing the bellows to contract. The electrical circuit opens and the compressor stops. When the room air temperature goes above the thermostat setting, the gas in the bulb expands, the bellow expands, the electrical contracts close and the compressor starts. In this way, the room air-conditioner maintains the temperature desired. The room occupants need adjust the thermostat control to a new position when they wish to change the desired, temperature.

A second type of room thermostat is a bi-metal temperature running device in place of the gas filled sensing tube. If two metals are joined together in a bimetallic strip and then heated, the varying rates of expansion of the metals cause them to bend. This bending in response to heat or cold is used to close or open an electrical contact. This contact is wired in series with compressor relay and its controls compressor operation in the same manner as does the gas-bulb thermostat described above.

Electric Controls :

The electric controls are placed either on the top, side or front of the unit for convenience and style. Most units have two main electrical controls (1) a master control that starts and stops the fans and compressor, the occupant uses this control to choose the operation desired (cool, exhaust, heat or ventilate) and to select fan speed, (2) a thermostat control that adjusts the thermostat to cooler or warmer side.

The master control.

The master control is often called the selector switch or cooling and fan control. It controls the compressor motor, condenser fan motor and evaporator fan motor. When the control switch is in its COOL position, all motors operate and the complete unit functions as an air-conditioning unit. When the control switch is in the VENTILATE position, the evaporator fan works as ventilating fan. In the EXHAUST position, the condenser-blower motor operates drawing stale air from the room as does an exhaust. The damper control must be at its similar position to allow the air to flow either out or in.

The Thermostat control.

The thermostat element in room air-conditioners is usually located in the returned air stream near the filter. The thermostat control is wired in the series with the starting relay that controls the compressor motor. Thus both the thermostat control and master control govern compressor operation.

Air-distribution System :

The evaporator fan used in the room unit is of the centrifugal or propeller type and is surrounded by acoustical insulating material that reduces operating noise. The evaporator fan pulls in fresh outside air through louvers and a ventilation damper. Room air enters at the room end of the air-conditioner through return louvers in the cabinet. The fresh air and room air mix and are drawn through the evaporator cooling coil. The cooled air is then supplied to the room through the discharge grills in the front of the cabinet. A one-ton unit circulates air at 40 m3/min in the room. If 25% fresh air and 75% recirculated room air are used then one ton unit results in 1.3 air changes per hour for a room of 40 m3 volume.

Air should be filtered as soon as possible after it enters the air-conditioner. In the window unit, the air filter is located on the air entering side of the cooling coil. Either permanent or replaceable filters are used. The permanent filter is a metallic mat or plastic foam type. It is coated with odourless mineral oil that helps in catching dust particles. It may be cleaned as needed by washing in soap flakes. Replaceable filters are made of spun glass or similar materials and are also coated with oil or other suitable adhesive. They may be easily removed from the unit and replaced by a new filter.

The fresh air intake to the room conditioner is regulated by a dampered door inside the cabinet. Most units operate with from 0 to 25% fresh air, depending upon the damper-control knob adjustment within the ventilate position. On hot days, the proportion of fresh air intake should be decreased, because the more fresh hot air, the greater the cooling load on the unit.

To exhaust room air, the fan control is set to EXHAUST position. The condenser blower starts operating when this is done. The exhaust damper musrt also be open to permit room air through to the outside and therefore the damper control is also set to its exhaust position. With these controls are in this setting, the room air-conditioner acts as an exhaust fan. In this way, smoke and odours are removed from the room by the condenser fan which draws air through the damper and exhausts it through the louvers in the rear of the unit.

The air system on the outside includes in the condenser fan and dissipates the heat taken from the cooled area to the outside atmosphere. The air system within the cooled area circulates room air over the cooling unit. These two air systems are so arranged that the cooling coils are located on the room side of the window and condensing units on the outside of the window. It is important that no intermingling of hot condenser air and cooled room air takes place. A partition inside the air conditioner separates the room air from the condenser air. The rubber seals and panels at the window prevent exchanges of inside and outside air. Tight installation at the window is of utmost important.