Importance of a Vacuum Pump in an Autoclave

The purpose of an autoclave is to facilitate sterilization.

Sterilization is a process designed to remove or destroy all viable forms of microbial life, including bacterial spores, to achieve an acceptable sterility assurance level.

In today's scenario at least 1 among 10 hospitalized patients acquire HCAI (Health Care Associated Infection). One of the major factors is due to improper sterilization carried out under sub-standard machines which do not comply with cGMP’s and other standard regulations. Infections can also be fatal causing loss of precious lives.

Vacuum pump is a vital component of an Autoclave. It serves many purposes.

To understand the importance of a vacuum pump, it is important to know what exactly the term 'vacuum' means.

Vacuum is the space in which there is no matter or in which the pressure is so low that any particles in the space do not affect any process being carried on there. It is a condition well below normal atmospheric pressure and is measured in units of pressure (the pascal). A vacuum can be created by removing air from a space using a vacuum pump. In simple terms vacuum is space devoid of matter.

Air is the biggest deterrent to steam sterilization. Air must be removed from the chamber and the load for effective sterilization. This is accomplished in a steam sterilizer by a series of vacuum pulses prior to sterilization (pre-conditioning phase / Purge phase). A small amount of air will always be present in the autoclave chamber, but must be minimized. Insufficient air removal is a common cause of sterilization failures.

The process of Sterilization consists of three basic phases, i.e. a). Pre-conditioning / Purge phase, b). Sterilization phase and c). Exhaust phase.

The process commences with the Purge phase, wherein the air in the chamber is evacuated with a vacuum pump and saturated steam is purged. With multiple pulses of Vacuum and Pressure (with saturated steam), the air present in chamber is effectively removed.

Similarly, in the Exhaust phase (post sterilization phase), vacuum pulses aid the removal of steam, condensate and assist in faster drying of the load. During the sterilization phase, condensation occurs due to the release of latent heat as the saturated steam contacts cold surfaces of sterilizers including the different types of load. These surfaces, especially wrapped items, must be dried before they are aseptically removed from the sterilizer. As per EN 285 "the mass of the load shall not increase by more than 1% for textile and 0.2% for metal load after the sterilization cycle". The presence of condensate results in being a breeding ground for bacteria, which can cause contamination of the load.

Vacuum level of 6.9 to 13.8 kPa is recommended for efficient drying. At 6.9 kPa chamber pressure, water boils at 38.7°C. so during the Exhaust phase, while the temperature is reducing gradually from 121°C, applying vacuum pulses helps in evaporating the condensate. This evaporated condensate (vapor) is simultaneously evacuated from chamber resulting in drying of the load. As per EN 285 guideline, the vacuum system shall be capable of evacuating the sterilizer chamber to an ultimate pressure equal to or less than 70 mbar absolute (7 kPa).

The vacuum pump used in PIPL's Autoclave is a liquid ring vacuum pump.

In Liquid ring vacuum pump, the vacuum is generated using liquid seal. The most commonly used sealant is water (with recommended temperature of 150ºC). Vacuum generation occurs with the rotation of an installed impeller in the casing partly filled with liquid.

With high revolutions of the impeller, centrifugal force is generated. This centrifugal force recedes the liquid from the impeller center to the periphery of the casing to form a liquid ring. This phenomenon creates the space within the center of the impeller to generate a vacuum. As the vacuum is generated, the gas is drawn from the suction port. These gasses further move along with impeller vanes in the increased space within the liquid ring (due to the eccentric installation of the impeller). At the end of revolution, the gas is compressed (due to reduced space between the liquid ring and impeller vanes) thus forcing it to discharge through the discharge port.

The vacuum pump can be operated with water recirculation in open or closed loop circuit. It ranges from 1.5 to 3 HP.


Hence, a vacuum pump plays a vital role in conducting effective sterilization in an autoclave.



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