An autoclave is a device that is used for sterilization, sterilization in an autoclave means that all life forms of microbes are destroyed using methods such as steam. An autoclave is also called a sterilizing device, which provides sterile conditions using immobile materials, which are as follows: cleaning, decontamination, inspection and monitoring, packaging and preparation, sterilization, storage, delivery. Giving materials and supplies. In the autoclave, heat and pressure are used to sterilize the equipment.
The history of the invention of the autoclave
This device was invented in 1879 and its inventor was Charles Chamberland. In the beginning, the autoclave was a simple device, and over time it became a very advanced device according to the needs and solving the previous problems. The shape of the chambers used in the construction of this device is cylindrical because cylindrical chambers are more resistant to pressure than a box.
Use of types autoclaves are mostly used to sterilize tools and equipment such as culture media, laboratory containers and glassware. The sterilization process with this device is such that in a period of 15 minutes, saturated steam is used at a temperature of 121 degrees Celsius and with very high pressure, this is a very high temperature that is not suitable for many sterilization processes such as milk sterilization because it causes There will be changes in them.
Types of autoclave devices
- We can categorize autoclave devices according to the equipment they sterilize:
- N autoclave device: used for sterilizing instruments that are solid and without coating.
- S autoclave device: it is used for sterilizing instruments that are both solid and uncoated, and coated, and in which a vacuum pump is used and not.
- Autoclave device B: It is used for sterilizing instruments that are solid and uncoated and coated, it has a vacuum pump with a very high power.
- Fast autoclave device: This device is also used in places that require a smaller volume of sterilization, among which we can mention medical and dental centers.
A- autoclave of the type of plate above:
This autoclave is similar to pressure cookers that can be found in abundance in Iranian homes. In these autoclaves, it is closed by screws at the bottom and the pressure gauge is located outside to control the pressure. These devices require an external heat source and are very dangerous, so they should be used by very experienced people. They are produced in sizes of 10, 25, 50, 75 and 100 liters.
B- Autoclave of the facing plate type:
These autoclaves are widely used in laboratories because of their ease of use, but extreme care must be taken in using these autoclaves. These autoclaves are box-shaped and equipped with a water-to-steam conversion unit that is used for sterilization. The autoclave control allows the operator to set the desired temperature and determine the duration of the autoclave. Also, these autoclaves have a device to measure and display pressure/temperature. Front-opening autoclaves may be much larger and are used for sterilizing bulk materials and equipment in hospitals.
Using an autoclave device
Generally, the autoclave works with 220 volts and 50 Hz. Fluctuations of 180 to 220 volts do not cause any problems in the operation of the autoclave. Note that if these changes are more than the above limit, you should put a suitable transformer in it. The type of wire used in its wiring should be 2 mm diameter electric wire.
To drain the autoclave, you need to open the device door and then pull out the tray. Pour water up to the edge of the plate with the max mark. Place the items in the autoclave and close the door. In these cases, if the device does not have enough water, an error message will appear on the screen, and this means that the light related to water is off.
When the autoclave is sufficiently drained, you can adjust the sterilized time. Press the on key. Because the device is already drained. After that, the device performs the steps automatically. If you need to change the sterile time, follow the instructions below.
Press the SET key. The screen will perform the steps automatically. If you need to change the sterile time, do the following procedure.
Press the SET key. The screen will show 15:00. Press SET again to make changes with the up and down keys. Then press SET 3 times to return to temperature mode and be ready to START, and this time is stored in the memory. In this case, the element of the device turns on. HEATER and WATER lights turn on when the temperature of the device reaches 121.5 degrees Celsius. The HEATER light turns off and the sterile time starts working in reverse. If you want to see the sterilization time, press the TIME/DOOR key to show you the remaining sterilization time. After 15 seconds, it automatically returns to the initial state and shows the temperature of the autoclave. When the LED sterile time is over, the heater is turned off and the word “end of sterile” is displayed on the screen. In this case, you must press the power button to turn it off. Open the steam release valve on the lid until the steam is completely removed and the pressure level on the lid drops to zero. Finally, open the autoclave door.
After closing the autoclave, some air remains in the container and must be removed. This is because hot air takes a long time to sterilize compared to steam. For example: steam at a temperature of 134°C needs 3 minutes to sterilize materials, while hot air at 160°C needs two hours in the same conditions. The methods of removing air in the autoclave are as follows:
1- Air removal from the bottom Downward displacement
When the steam enters the chamber, due to its low density compared to the hot air, it is placed on the top of the chamber, and as the amount of steam increases, the hot air is compressed under the autoclave and from The lower part is emptied. Usually, a thermometer is placed in the outlet to control the temperature of the outlet air. We should stop emptying only when the air is out of the chamber. The flow is usually controlled by heater traps or spiral valves.
2- Steam pulsing
In this method, the air in the autoclave chamber is compressed by steam pulses to bring the pan close to atmospheric pressure.
3- Vacuum pumps
These pumps suck air or air/steam from the chamber.
4- Super atmospheric
Vacuum pumps are used in this cycle. After the steam pulse, suction is done and after other pulses, the suction continues. The amount of suction depends on the cycle and type of device.
5- Sub atmospheric
Similar to the super atmospheric cycle, but the chamber pressure is never more than atmospheric until the pressure is raised to the sterilization temperature.
Principles of autoclave operation
Autoclaves work by using the thermodynamic properties of water as a pure substance. In natural conditions (at sea level and pressure of one atmosphere), water boils (in liquid phase) and turns into steam (gas phase) at 100 degrees Celsius. If the pressure decreases, it boils at a lower temperature and if the pressure increases, it boils at a higher temperature. By controlling the water vapor pressure, the temperature of the autoclave chamber may reach temperatures higher than 100°C or vice versa by controlling the temperature to a pressure higher than atmospheric pressure. The following curve shows how water works depending on pressure and temperature conditions.
- This curve shows the operation and relationship between the solid, liquid and gas phases of water depending on the pressure and temperature conditions.
- The sublimation line shows that under certain conditions, if heat is transferred to the solid phase, it can directly change to the vapor phase (section E-E) without changing to the liquid phase.
- The fusion line shows that by transferring heat to water under certain conditions, the solid phase turns into a liquid phase and with increasing temperature, it turns into a vapor phase (part H-H).
- The steam line shows at what temperature conditions water in the liquid phase turns into the vapor phase.
- The point where three lines intersect is called the triple point. In such a situation, three phases are simultaneously in balance.
- This curve shows two distinct lines: saturated liquid lines (to the left) and saturated vapor lines (to the right).
- As the pressure increases, the temperature also increases (cf. p2, p1 and p3 lines), note that p1<p2.
- The left side of the saturated liquid line is water in the liquid phase (diagram A_B). With the transfer of heat, the temperature of the liquid increases from A to B.
- Between the line of saturated liquid and saturated vapor (section B-C) there is a mixture of vapor and liquid phases and the temperature remains constant. By approaching point C, the quality of steam improves. (Quality (X) is the relationship between the total volume of steam and the total volume (volume of liquid and volume of steam). Quality = 1: it means that the steam is saturated and any increase in temperature will make the steam too hot.)
- On the right side of the saturated vapor line, water is completely in the vapor phase (section C_D).
Section view of steam autoclave
The figure below shows the main components of the steam system of an autoclave. The parts that are usually located around the autoclave (the exact location is different in different products), are shown in the upper and lower parts of the view.
Description of autoclave components in view
A brief description of the most common autoclave steam circulation paths is given below. The same number is used to indicate each component in the figure above and its description below. Note that the variety of shapes is related to different designs.
|Safety Valve (Safety Valve):A tool that prevents the steam pressure from increasing more than A certain amount prevents. Manufacturers install these valves in the sterilization chamber as well as the outer shield.|
|Chamber Manometer (Chamber Manometer):Mechanical instrument that measures the steam pressure in the chamber It shows sterilization.|
|External pressure gauge (Jacket Manometer): A mechanical instrument that measures the steam pressure in It shows inside the outer cover of the autoclave.|
|in the autoclave (Autoclave Door): a device that closes the sterilization chamber from the outside environment separates. It usually has a safety device that prevents the door from opening when the pressure inside the chamber is high. It also has seals to prevent steam from escaping from the chamber when the device is working. Autoclave doors may operate manually or electromechanically.|
|Door Handle:A tool that allows the user in some devices opens and closes the door. Usually, it is used to activate in devices with more capacity than motorized systems.|
|Sterilization Chamber (Sterilization Chamber):A space where equipment and materials to be sterilized are placed When the chamber door is closed, the chamber is isolated from the outside and when the sterilization process is in progress, the chamber is filled with steam and pressurized.|
|Chamber Condensation Evacuation Line: A duct that collects the thick liquid that is created by the heat transfer processes between the steam and the equipment being sterilized.|
|Thermometer (Thermometer):A device that shows the temperature of the sterilization steps in the autoclave chamber. gives.|
|The jacket evacuation line It removes the thick liquid formed as a result of heat transfer between the steam and the protective walls.|
|Vapor Exit at the End of the Cycle > At the end of the sterilization cycle, steam is released from the autoclave through controlled methods.|
|Vapor Passage Restriction in liquid sterilization cycle for Liquid Sterilization Cycle):A mechanical device that restricts the passage of steam in a liquid sterilization cycle to reduce the temperature in a controlled manner and prevent boiling of the sterilized liquids.</span >|
|Vapor Evacuation Duct for Sterilization of Liquids >The path that steam takes during sterilization of liquids by passing through the steam restrictor (described above).|
|Vapor Evacuation Line During the Rapid Cycle Sterilization Sterilization Cycle): The path the steam takes when a quick sterilization cycle is in progress.|
|Vapor Feed Line (Vapor Feed Line):A pipe that connects the autoclave with It feeds steam, this tube has controls and attachments that cause steam to reach the autoclave under the conditions specified for the sterilization cycle.|
|Air Admission Valve Filter: A device that allows filtered air to pass at the end of the sterilization cycle. This valve equalizes the pressure of the sterilization chamber with atmospheric pressure.|
|Jacket: A space around the sterilization chamber where steam circulates. Its purpose is to transfer heat to the chamber and minimize the amount of condensed liquid. This space is connected to the chamber and sewer through pipes that are controlled by electric valves. Not all autoclaves have protectors. Some manufacturers replace it by placing electrical resistors around the sterilization chamber.|
|Steam inlet adjustment valve:a mechanical device that controls the steam pressure entering the autoclave. he does. Depending on the type of cycle selected, the pressure and temperature will be different. As the pressure increases, the temperature increases, and the lower the pressure, the lower the temperature.|
|steam supply pipe: the pipe that brings steam from the hot water tank or steam generator to the autoclave.</ span>|
|Vapor Trap (Vapor Trap):A device used for maximum use of heat energy Steam is designed to prevent steam from escaping the system. This valve only allows the thickened liquid formed in the chamber, guard, and tubes of the autoclave to escape.|
|Effluent:It is a pipe for collecting and removing the concentrated liquid produced in the autoclave.< /span>|
Obviously, all laboratories and centers that have autoclave devices should be well aware of how it works and its applications in different fields; But the question is how to ensure the correctness and performance of a device. For example, how can you ensure that the pressure gauge installed on the autoclave or the digital temperature indicator that shows the temperature inside the chamber is working properly and has sufficient accuracy?
Fixing system errors and bugs is done by calibration in accurate and standard measurement laboratories that have the ability to estimate the accuracy and correctness of the mentioned devices.
Novin dynamic precision calibration company has a long history with an experienced and expert staff in performing calibration tasks and having calibrators and standard reference devices with traceability up to the levels of international references. It has an autoclave device for measurement and calibration.