Pressure cooker type autoclave is a type of autoclave that works on the principle of moist heat sterilization. It can either be gravity displacement autoclave or vacuum displacement autoclave.
Pressure Cooker Type Autoclave Parts
Pressure cooker type autoclave consists of a layer of high-quality stainless steel. The upper layer is covered with a removable lid. Similarly, the lower portion is a hollow chamber.
- Heating Element:- For heating the water.
- Gasket:- For preventing the loss of vapor and heat.
- Steam Releasing Valve:- To replace air present within the autoclave before sterilization and steam after sterilization.
- Pressure Regulating Valve (Stop Cock):- To maintain the vapor pressure within the chamber by releasing excess steam during sterilization.
- Safety Valve:- To release excess steam if the stop cock fails to operate properly.
- Tripod Stand:- To hold the physical objects that you want to autoclave.
- Vacuum Releasing Valve (Optional):- To create a pre-vacuum, prior to its operation.
Working Principle of Pressure Cooker Type Autoclave
The pressure cooker type autoclave works on the principle of moist heat sterilization.
The heating element present at the base of the pressure cooker type autoclave causes the heating of the water. When the water starts to vaporize, it displaces the air present within the chamber. If there is a pump system in the autoclave, then the pump will draw out the air from the chamber.
Once the lid of the autoclave is closed, the vapor begins to exert pressure within the chamber. After about 20 mins, the indicator of the pressure gauge will begin to rise up. When the indicator of the gauge reaches towards 15 psi pressure, the vapor pressure will become greater than that of the weight of the stop cock (pressure regulating valve). Thus, the stop cock will begin to whistle.
After 15 mins of operation, the sterilization will be complete. In case, the stop cock fails to operate properly, the safety valve will whistle.
Pressure Cooker Type Autoclave Procedure
(How to use pressure cooker type autoclave?)
- Place distilled or RO water, sufficient enough to submerge the water immersion heater. But, do not totally submerge the tripod stand.
(Note:- If the water immersion heater is exposed to the atmosphere during operation, it will overheat and get damaged. Similarly, if you supply tap water, the minerals and ions present in the water will react to the internal layer of the autoclave at high pressure and temperature. )
- Put the chemical or biological indicators on to the objects to be sterilized.
- Then, place the objects within the autoclave on a tripod stand.
- Close the lid and tighten the screws to prevent leakage.
- Turn on the power supply.
- Open the steam release valve to release the air trapped within the chamber.
- Observe the indicator of the pressure gauge.
(Note:- When the water begins to boil, the vapor pressure will cause the indicator of the pressure gauge to increase. During this time, the trapped air within the chamber will continue to escape into the surrounding. )
- When the indicator of the pressure gauge stops to increase, close the steam release valve.
- When the autoclave reaches the 15 Psi pressure (121°C), the whistle will blow.
- Continue operating the machine for 15 mins.
- After 15 mins of operation, turn off the machine.
- Then open the steam release valve.
- Once, the indicator of the pressure gauge goes to 0, remove the lead of the autoclave.
(Note:- Do not open the lid of the autoclave at once. Else, the vapor will cause a severe burn on your face and hands. )
Advantages of Pressure Cooker Type Autoclave
- Cheaper than other types of autoclaves
- Easy to operate
- Simple in design
- Easy to clean and maintain
- Useful in multiple applications such as sterilization of autoclavable glassware, plastic ware, culture media, etc.
Disadvantages of Pressure Cooker Type Autoclave
- The size of the autoclave may only range from 20 -25 liters.
- Not suitable to sterilize bulk volume of objects at once.
- Since there will not be any system to control the heating element, the accuracy of the autoclave (in terms of temperature and pressure) tends to be lower. Generally, the pressure goes to about 17 Psi or more.
- Generally, it belongs to class N autoclave.
- Most of the manufacturers do not provide the proper handle system. So, while opening the lid of the autoclave, there can be a chance of steam burn.
During transportation or operation, the pressure cooker type autoclave can undergo different kinds of faults. So, in such cases, you may need to repair the machine.
Since the pressure cooker type autoclave draws too much current, there can be a problem with the power supply. The power cord can burn. Similarly, the 3- pin plug can burn. The indicators, switch, etc, can also be damaged.
In any case, you need to replace the components with new ones.
2. Heating Element
The heating element might be damaged if it does not get sufficient water when being operated. When the rod gets damaged, the rod will become black and deformed.
When the heating element is damaged, it will not heat the water. Sometimes, the heating element operates partially. In such a case, the water might get warm but will fail to boil.
The heating rod should be replaced with a new one having the same rating. If the rod is of high wattage, it will draw more current. So, the system may not be able to handle it. Similarly, if the wattage is low, the water will take more time to heat. So, selecting a proper rod is essential.
3. Vapor Pressure
The pressure of the chamber is displayed by the pressure gauge. So, if the pressure gauge does not show 15 Psi pressure during the phase of sterilization, there can be issues related to the vapor pressure.
The first cause can be the defect in the pressure gauge. This means that, even if the pressure within the chamber has reached the required value, the pressure gauge will fail to show the actual pressure. In such a case, you generally need to replace the gauge with a new one.
Pressure Regulating Valve (Stop Cock)
The second cause can be the defect in the pressure regulating valve. If the valve is broken, the overall weight will decrease. Also, there can be a blockage within the valve. Or, the valve can undergo blockage due to storage for a longer period of time, rusting, etc. In the above cases, the valve will not operate properly.
If the pressure regulating valve is broken, you need to replace it with a new one having the same weight. If you use a valve of low weight, the pressure will not reach 15 Psi. Similarly, if you use a valve of high weight, the safety valve will open or the machine will burst.
In case of blockage, rusting, etc, you may try cleaning. Else, you need to replace it.
Steam Releasing Valve
In case you forget to close the steam releasing valve during operation, the vapor will escape from the valve. Thus, the pressure within the chamber will never rise up.
Vacuum Releasing Valve
In some of the cases, the pressure cooker type autoclave is designed to operate in the form of a vacuum displacement autoclave. In such a case, the vacuum releasing valve should be properly closed, before you operate. Else, the vapor will leak through it.
The safety valve is useful only when the pressure regulating valve fails to act properly.
Sometimes, there can be leakage through it. So, in such a case you need to replace it with a new one.
The gasket is a circular, rubber that is found in the mouth of the chamber or at the base of the lid. This helps to prevent the loss of pressure and heat from the lid. So, if the gasket is not fixed properly, or gets damaged, then the vapor will leak through it.
In such a case, you need to readjust or replace the gasket.
Due to the operation of the machine for a long period of time, the autoclave may rust. The rusting can be either internal or external. If the rusting is external, it degrades the aesthetic looks of the machine. However, if the rusting becomes internal, there can be chances of contamination during sterilization. So, in such a case, it is better to replace the machine with a new one.