How Electric Pressure Cookers Work

An electric pressure cooker consists of three parts, the lid, inner pot and housing. See the diagram to the right. The most important things to know about electric pressure cookers  are the safety valves and smart control box.

How electric pressure cooker works

How electric pressure cooker works

The Inner Pot

The inner pot is a removable cooking pot. It is generally made from aluminum or stainless steel. The aluminum inner pots may be stamped and buffed or anodized, but this metal is unsuitable for the dishwasher. Higher quality stainless steel inner pot are made with sturdy, three-ply, or copper-clad bottom for uniformed heating.

The size of the inner pot determines the size of the housing, and to some degree the price of the cooker. The inner pot capacity typically ranges from 3 liter (3 quart) to 6 liter (6.3 qt).  Over 6L, it becomes difficult to maintain and the cooker becomes prohibitively expensive to some consumers.

The Lid Lock

The lid has a gasket or sealing ring. When the lid is played on the cooker in the sealed position, the lid and the inner pot form an air-tight chamber. The pressure inside this chamber increases when heat is applied to the inner pot. There would be an unsafe operating condition if the lid is not in the locked position when significant amount of pressure is generated inside the chamber. Some electric cookers have the pin lock mechanism to prevent the lid from being accidentally opened while there is significant amount of pressure inside. The pin is essentially a float valve. If there is enough pressure inside the inner pot, the float valve is pushed up by the pressure. Once pushed up, the pin of the float vale serves as latch lock and prevents the lid from the turning movement, even under force.

Instant Pot also extends such safety assurance with a safety power switch. If the lid is not in the desired fully close position, the electronic control system of Instant Pot can detect the situation and will not switch on the power for heating.

Safety Valves

Similar to the conventional pressure cooker, the pin of the float valve can be self-destroyed by excessive temperature or pressure. The float valve without the pin becomes a pressure escape hole, and the pressure inside the chamber is released this hole. Although in such a case the float valve is permanently damaged and possible a lid replacement may be required, this is an effective last line of defense from the safety perspective. The modern electric pressure cookers also use other safety assurance measures before this last line defense kicks in. Instant Pot employs the patented innovative push-down pressure release mechanism to release excessive pressure, even in the unlikely case where the pin of the float valve cannot destroyed. Instant Pot provides a multi-level in-depth defense system to offer unprecedented safety assurance to the consumers.

Normally, the only way the pressure can escape is through a pressure release regulator valve on the lid. The pressure release valve has anti-block shield insider the lid. The pressure release regulator valve is made not to release the pressure under normal operating pressure range when in the seal position. If the pressure increases beyond the safe operating range, the pressure release regular valve will be pushed up, similar to that on the conventional pressure cooker, to release excessive pressure built up inside the chamber. The difference from the conventional pressure cooker is that the pressure release valve only kicks in to release excessive pressure due to possible failure of electronic based sensing circuitry.

The Housing: Sensors, Heating Element & Control Box

Electric pressure cooker functional diagramThe housing unit contains a heating element, pressure and temperature sensors and a control box. The functional diagram of housing unit is shown on the right.

The control box is the heart of the intelligence of the electric pressure cooker. It monitors the temperature and pressure of inner pot with the sensors. It is equipped with a microprocessor to control the timing, heating and complex cooking cycles. This is how a positive feed-back system is formed to achieve precise cooking conditions. If an unsafe operating condition is detected, it will sound audible alarm or cut off the power supply to the heating element.

Pressure sensor controls heating

The control panel, being the user interface of the control box, allows one-key operation to activate pre-programmed cooking cycle for various dishes. For instance, corns, peas, cauliflower and broccoli can be steamed in 1 minute. Frozen corns, peas, cauliflower and broccoli will been done in 2 minutes. Dry beans and bones will take only 30~40 minutes.

Intelligent Pressure Cooking

Electric pressure cookers normally operates at a pressure range of 70-80 kPa (kilopascal) or 10.15~11.6 psi (pound-force per square inch). This translates to the temperature of 115°C~118°C or 239°F~244°F. Initially pressure may reach 105kPa/15.2 psi, due to the heat dissipation delay from the heating element. This is comparable to stove-top pressure cooker reaching 15 psi and then heat being turned down.

By switching on and off the heating element and varying the heat intensity at different temperature and pressure, the best cooking result can be achieved in an intelligent way. The following diagram shows the pressure curves of Instant Pot.

15psi 512x295 How Electric Pressure Cookers Work

Some electric pressure cooker, such as the Instant Pot, has intelligent cooking capabilities to achieve the best result, such as,

  • automatically altering the cooking time and pressure based on the chosen food type , i.e. rice, soup, meat, vegetable, etc.
  • adjusting cooking cycle based on the amount of food in the cooker, by measuring pre-heating duration.

Read about the three generation of electric pressure cooker.

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