On This Page On This Page Are You Using the Right Sterilization Cycle? This in-depth guide will ensure that you select the appropriate cycle configuration for your intended application every time. Access Your Copy Steam Sterilization Cycles, Part 1: Gravity vs. Vacuum Written by: Arthur Trapotsis MS Biochemical Engineering, MBA, Consultant Key Takeaways Steam sterilization relies on steam, time, temperature, and pressure, which can be manipulated into different cycle types to meet different sterilization requirements. A gravity cycle uses steam to displace chamber air through the drain. It works well for glassware, vented containers, unwrapped instruments, and waste. A vacuum cycle pulses air out mechanically before sterilization begins. It’s suitable for porous and wrapped loads, including surgical packs and cages with animal bedding. Consolidated can help you identify and program the right cycle type for your facility’s load requirements. Steam sterilization relies on four parameters to eliminate microbes and organisms: steam, time, temperature, and pressure. These parameters can be manipulated into different cycles to meet the sterilization requirements of various types of loads, including red bags, media, glassware, cages, animal bedding, and pipette tips. Although it’s possible to sterilize the vast majority of common laboratory loads using one of three basic cycles — gravity, vacuum (or prevac), and liquid — you’ll want to ensure that your sterilizer offers the appropriate cycles for all of your load requirements. In this article, we’ll explore the first two basic steam sterilization cycles — gravity and vacuum — including how they work and when to use them. Then, in other articles, we’ll discuss additional cycle types, such as liquid cycles, air-overpressure cycles, and a myriad of other, more advanced cycles for specialized applications. Steam Sterilization Basics For a brief overview of how steam sterilization works, we recommend reading our blog post on the subject or watching this short video: eBook Offer: Discover the Top 12 Steam Sterilization Cycles Our definitive guide explains the mechanics behind different sterilization cycles and what types of loads they’re best suited for. Get Your eBook>>> Gravity Sterilization Cycle The traditional gravity sterilization cycle — or simply gravity cycle — is the most common steam sterilization cycle. During a gravity cycle, steam is pumped into a chamber containing ambient air. Because steam has a lower density than air, it rises to the top of the chamber and eventually displaces the air. As steam fills the chamber, the air is forced out through a drain vent. By pushing the air out, the steam is able to make direct contact with the load and begin to sterilize it. At the end of the cycle, steam is discharged through the autoclave’s drain vent. At this point in the gravity sterilization process, the load may still be hot and possibly wet. To address this issue, gravity autoclaves can be equipped with a post-cycle vacuum feature to dry the load. If an autoclave is equipped with this feature, it will run a normal gravity cycle and, once the load is sterilized, a vacuum will pull the steam and condensation through the autoclave’s drain vent. The longer the vacuum system runs during the dry phase, the cooler and dryer the goods will be when you remove them from the chamber. It’s common to use a gravity sterilization cycle on loads such as glassware, biohazardous material (red bag waste), vented containers, and certain types of unwrapped instruments. A Note on Red Bag Waste If your facility routinely sterilizes red bag waste, keep the weight and density of your loads in mind when you set exposure times. Bags can trap pockets of air that slow steam penetration, so waste loads require more time at temperature than glassware or unwrapped goods. The CDC notes that 10 pounds of microbiological waste requires at least 45 minutes at 250°F (121°C) in a gravity displacement sterilizer. Heavier or more tightly packed bags require longer still, which is why Consolidated’s cycle guidelines list gravity exposure times as a range of 30 to 90 minutes. For best results, avoid overfilling bags, which creates more air pockets for the steam to work through, and confirm that the exposure time programmed into your waste cycle is based on the heaviest load your facility actually runs. Vacuum Sterilization Cycle There are certain applications, such as sterilizing porous loads or partially vented containers, where air cannot be easily displaced from an autoclave chamber, rendering gravity air displacement ineffective. These loads — which may include cages with animal bedding, wrapped goods, and surgical packs — require the use of a vacuum sterilization cycle, also known as a vacuum cycle or prevac cycle. A sterilizer configured to run a vacuum cycle will be equipped with a vacuum system. A typical vacuum cycle begins with a series of alternating steam pressure injections and vacuum draws (also known as pulses) to dynamically remove air from the chamber. Using pulses to remove ambient air from the autoclave chamber allows steam to be sucked into areas it would otherwise have difficulty penetrating. As noted in “Principles and Methods of Sterilization in Health Sciences” by John J. Perkins, the absence of air within the chamber allows “steam to penetrate the load almost instantaneously,” resulting in more reliable sterilization and shorter sterilization cycle times. How many pulses a load needs depends on how much air is trapped inside it. A pre-vacuum cycle typically runs anywhere from zero to six pulses at 18 psi and 20 in/Hg, with exposure times from 20 to 90 minutes at 250°F (121°C). Cages packed with bedding, tightly wrapped packs, and other dense, porous loads belong at the higher end of that pulse range, while lighter loads can reach full stream penetration with fewer. If you’re programming a cycle for a load type you haven’t run before, start with more pulses than you think you need and validate down from there rather than the inverse. Once sterilization is complete, you can program a post-cycle vacuum to enhance and expedite the drying process. Consolidated’s sterilizers come with two vacuum system options: a water ejector with optional booster pump and a liquid ring vacuum pump. It’s important to conduct a Bowie-Dick test to confirm whether air actually leaves the chamber. Simply place the test pack in an empty chamber and check the thermochromic paper inside for uniform color change. How often you’ll need to run this test depends on your facility: Healthcare facilities should run a daily test, before the first processed load, while laboratories can set their own frequency according to their standard operating procedures. A vacuum leak test can also confirm the chamber and plumbing’s air-tight integrity, against an industry standard leak rate of 1 mmHg/min or less. Common Vacuum Systems A water ejector system utilizes a simple Venturi effect to create a vacuum within the chamber. A water ejector draws on your building’s water supply, so confirm the dynamic pressure available at the sterilizer before you commit to one. Anything below 45 psig will require adding a booster pump to the system. This is a question for your facilities team or architect rather than something to discover at installation, and our utilities checklist lists the water, steam, drain, and electrical requirements to verify during planning. A liquid ring pump has a higher upfront cost, but uses less water and produces the deepest vacuum of all available vacuum system options. Gravity Sterilization vs. Vacuum Sterilization: Air Removal Process See a visual representation of how both gravity cycles and vacuum cycles remove air from an autoclave chamber in this brief video: <span data-mce-type="bookmark" style="display: inline-block; width: 0px; overflow: hidden; line-height: 0;" class="mce_SELRES_start"></span> Gravity Sterilization vs. Vacuum Sterilization at a Glance Basic Cycles Description Typical Application or Load Type Gravity The most basic sterilization cycle. Steam displaces air in the chamber by gravity (i.e. without mechanical assistance) through a drain port. Glassware, unwrapped goods, waste, utensils, redbags. Pre-Vacuum Air is mechanically removed from the chamber and load through a series of vacuum and pressure pulses. This allows the steam to penetrate porous areas of the load that couldn’t otherwise be reached with simple gravity displacement. Wrapped goods, packs, animal cage bedding, cages, porous materials, redbags. Gravity and vacuum cycles are the two most commonly used sterilization cycles because they can accommodate a wide variety of load types and applications. However, some loads — such as syringes, contact lenses, and certain types of media — require special cycle configurations that employ pressure or temperature ramping. Fortunately, today’s advanced controllers can manipulate sterilization parameters to accommodate these loads. At Consolidated, we recognize that many of our customers need assistance in identifying and creating the proper sterilization cycle for their load type. As such, we hope this article helps you better understand how gravity and vacuum sterilization cycles work and what types of loads they’re appropriate for. We encourage you to read the rest of our steam sterilization cycles series. In the meantime, if you have any questions, we’re always happy to help — contact us today to speak to a specialist. eBook Offer: Discover the Top 12 Steam Sterilization Cycles Our definitive guide explains the mechanics behind different sterilization cycles and what types of loads they’re best suited for. Get Your eBook>>> Frequently Asked Questions What is a gravity sterilizer? A gravity sterilizer is any sterilizer that uses the gravity displacement method for air removal. Gravity sterilizers perform what’s known as a gravity cycle to sterilize loads. How long does a gravity sterilization cycle last for? How long a gravity cycle lasts depends entirely on the load you wish to sterilize. The CDC advises that: Wrapped instruments be exposed for 30 minutes at 250°F (121°C) and 15 minutes at 270°F (132°C), with a dry time of 15–30 minutes Textile packs be exposed for 30 minutes at 250°F (121°C) and 25 minutes at 270°F (132°C), with a dry time of 15 minutes Wrapped utensils be exposed for 30 minutes at 250°F (121°C) and 15 minutes at 270°F (132°C), with a dry time of 15–30 minutes Can a pre-vacuum sterilizer also run gravity cycles? Yes, a pre-vacuum sterilizer can run gravity cycles because its vacuum system sits alongside the standard steam and drain setup rather than replacing it. By comparison, gravity sterilizers can only run vacuum cycles if they’re equipped with a post-vacuum feature. Can you sterilize wrapped instruments in a gravity sterilizer? Yes, you can sterilize wrapped instruments in a gravity sterilizer, though they require a longer exposure than unwrapped items. The CDC recommends they be exposed for 30 minutes at 250°F (121°C) or 15 minutes at 270°F (132°C), with 15 to 30 minutes of drying time. A vacuum cycle, which mechanically removes trapped air, is more suitable for densely wrapped packs, porous textiles, and hollow instruments with lumens. Do gravity sterilizers need a Bowie-Dick test? No, gravity sterilizers do not need a Bowie-Dick test. A Bowie-Dick test confirms whether a vacuum system removes air from the chamber effectively, so it only applies to pre-vacuum sterilizers. That said, gravity units still require monitoring through other methods, including process challenge devices and biological indicator testing. Article Sources Centers for Disease Control and Prevention, “Steam Sterilization, https://www.cdc.gov/infection-control/hcp/disinfection-sterilization/steam-sterilization.html Consolidated Sterilizer Systems, “Steam Sterilization Cycles, https://consteril.com/resources/sterilization-cycles/.” Consolidated Sterilizer Systems, “How Does a Laboratory Autoclave Work, https://consteril.com/how-does-a-laboratory-autoclave-work/.” Thermo Fisher Scientific, “What Is Ambient Air?, https://www.thermofisher.com/blog/mining/what-is-ambient-air/.” The Washington Post, “Why dry air is heavier than humid air, https://www.washingtonpost.com/news/capital-weather-gang/wp/2013/08/05/why-dry-air-is-heavier-than-humid-air/.” John J. Perks, “Principles and Methods of Sterilization in Health Sciences, https://books.google.com/books/about/Principles_and_Methods_of_Sterilization.html?id=-lYpPQAACAAJ.” Consolidated Sterilizer Systems, “Consolidated Smart Options, https://consteril.com/products/smart-options/.” SimScale, “What Is the Venturi Effect?, https://www.simscale.com/blog/what-is-venturi-effect/.” Centers for Disease Control and Prevention, “Minimum cycle times for steam sterilization cycles, https://www.cdc.gov/infection-control/hcp/disinfection-and-sterilization/steam-sterilization-cycle-times.html.” Get The Steam Sterilization Cycles Guide Read this comprehensive 31-page guide about when and how to use the top 12 steam sterilization cycles. This guide outlines how today’s steam autoclaves can be configured with specific parameters suitable for nearly any load and application type. Get the Guide Tweet Like Share
Steam Sterilization Cycles, Part 1: Gravity vs. Vacuum Written by: Arthur Trapotsis MS Biochemical Engineering, MBA, Consultant Key Takeaways Steam sterilization relies on steam, time, temperature, and pressure, which can be manipulated into different cycle types to meet different sterilization requirements. A gravity cycle uses steam to displace chamber air through the drain. It works well for glassware, vented containers, unwrapped instruments, and waste. A vacuum cycle pulses air out mechanically before sterilization begins. It’s suitable for porous and wrapped loads, including surgical packs and cages with animal bedding. Consolidated can help you identify and program the right cycle type for your facility’s load requirements. Steam sterilization relies on four parameters to eliminate microbes and organisms: steam, time, temperature, and pressure. These parameters can be manipulated into different cycles to meet the sterilization requirements of various types of loads, including red bags, media, glassware, cages, animal bedding, and pipette tips. Although it’s possible to sterilize the vast majority of common laboratory loads using one of three basic cycles — gravity, vacuum (or prevac), and liquid — you’ll want to ensure that your sterilizer offers the appropriate cycles for all of your load requirements. In this article, we’ll explore the first two basic steam sterilization cycles — gravity and vacuum — including how they work and when to use them. Then, in other articles, we’ll discuss additional cycle types, such as liquid cycles, air-overpressure cycles, and a myriad of other, more advanced cycles for specialized applications. Steam Sterilization Basics For a brief overview of how steam sterilization works, we recommend reading our blog post on the subject or watching this short video: eBook Offer: Discover the Top 12 Steam Sterilization Cycles Our definitive guide explains the mechanics behind different sterilization cycles and what types of loads they’re best suited for. Get Your eBook>>> Gravity Sterilization Cycle The traditional gravity sterilization cycle — or simply gravity cycle — is the most common steam sterilization cycle. During a gravity cycle, steam is pumped into a chamber containing ambient air. Because steam has a lower density than air, it rises to the top of the chamber and eventually displaces the air. As steam fills the chamber, the air is forced out through a drain vent. By pushing the air out, the steam is able to make direct contact with the load and begin to sterilize it. At the end of the cycle, steam is discharged through the autoclave’s drain vent. At this point in the gravity sterilization process, the load may still be hot and possibly wet. To address this issue, gravity autoclaves can be equipped with a post-cycle vacuum feature to dry the load. If an autoclave is equipped with this feature, it will run a normal gravity cycle and, once the load is sterilized, a vacuum will pull the steam and condensation through the autoclave’s drain vent. The longer the vacuum system runs during the dry phase, the cooler and dryer the goods will be when you remove them from the chamber. It’s common to use a gravity sterilization cycle on loads such as glassware, biohazardous material (red bag waste), vented containers, and certain types of unwrapped instruments. A Note on Red Bag Waste If your facility routinely sterilizes red bag waste, keep the weight and density of your loads in mind when you set exposure times. Bags can trap pockets of air that slow steam penetration, so waste loads require more time at temperature than glassware or unwrapped goods. The CDC notes that 10 pounds of microbiological waste requires at least 45 minutes at 250°F (121°C) in a gravity displacement sterilizer. Heavier or more tightly packed bags require longer still, which is why Consolidated’s cycle guidelines list gravity exposure times as a range of 30 to 90 minutes. For best results, avoid overfilling bags, which creates more air pockets for the steam to work through, and confirm that the exposure time programmed into your waste cycle is based on the heaviest load your facility actually runs. Vacuum Sterilization Cycle There are certain applications, such as sterilizing porous loads or partially vented containers, where air cannot be easily displaced from an autoclave chamber, rendering gravity air displacement ineffective. These loads — which may include cages with animal bedding, wrapped goods, and surgical packs — require the use of a vacuum sterilization cycle, also known as a vacuum cycle or prevac cycle. A sterilizer configured to run a vacuum cycle will be equipped with a vacuum system. A typical vacuum cycle begins with a series of alternating steam pressure injections and vacuum draws (also known as pulses) to dynamically remove air from the chamber. Using pulses to remove ambient air from the autoclave chamber allows steam to be sucked into areas it would otherwise have difficulty penetrating. As noted in “Principles and Methods of Sterilization in Health Sciences” by John J. Perkins, the absence of air within the chamber allows “steam to penetrate the load almost instantaneously,” resulting in more reliable sterilization and shorter sterilization cycle times. How many pulses a load needs depends on how much air is trapped inside it. A pre-vacuum cycle typically runs anywhere from zero to six pulses at 18 psi and 20 in/Hg, with exposure times from 20 to 90 minutes at 250°F (121°C). Cages packed with bedding, tightly wrapped packs, and other dense, porous loads belong at the higher end of that pulse range, while lighter loads can reach full stream penetration with fewer. If you’re programming a cycle for a load type you haven’t run before, start with more pulses than you think you need and validate down from there rather than the inverse. Once sterilization is complete, you can program a post-cycle vacuum to enhance and expedite the drying process. Consolidated’s sterilizers come with two vacuum system options: a water ejector with optional booster pump and a liquid ring vacuum pump. It’s important to conduct a Bowie-Dick test to confirm whether air actually leaves the chamber. Simply place the test pack in an empty chamber and check the thermochromic paper inside for uniform color change. How often you’ll need to run this test depends on your facility: Healthcare facilities should run a daily test, before the first processed load, while laboratories can set their own frequency according to their standard operating procedures. A vacuum leak test can also confirm the chamber and plumbing’s air-tight integrity, against an industry standard leak rate of 1 mmHg/min or less. Common Vacuum Systems A water ejector system utilizes a simple Venturi effect to create a vacuum within the chamber. A water ejector draws on your building’s water supply, so confirm the dynamic pressure available at the sterilizer before you commit to one. Anything below 45 psig will require adding a booster pump to the system. This is a question for your facilities team or architect rather than something to discover at installation, and our utilities checklist lists the water, steam, drain, and electrical requirements to verify during planning. A liquid ring pump has a higher upfront cost, but uses less water and produces the deepest vacuum of all available vacuum system options. Gravity Sterilization vs. Vacuum Sterilization: Air Removal Process See a visual representation of how both gravity cycles and vacuum cycles remove air from an autoclave chamber in this brief video: <span data-mce-type="bookmark" style="display: inline-block; width: 0px; overflow: hidden; line-height: 0;" class="mce_SELRES_start"></span> Gravity Sterilization vs. Vacuum Sterilization at a Glance Basic Cycles Description Typical Application or Load Type Gravity The most basic sterilization cycle. Steam displaces air in the chamber by gravity (i.e. without mechanical assistance) through a drain port. Glassware, unwrapped goods, waste, utensils, redbags. Pre-Vacuum Air is mechanically removed from the chamber and load through a series of vacuum and pressure pulses. This allows the steam to penetrate porous areas of the load that couldn’t otherwise be reached with simple gravity displacement. Wrapped goods, packs, animal cage bedding, cages, porous materials, redbags. Gravity and vacuum cycles are the two most commonly used sterilization cycles because they can accommodate a wide variety of load types and applications. However, some loads — such as syringes, contact lenses, and certain types of media — require special cycle configurations that employ pressure or temperature ramping. Fortunately, today’s advanced controllers can manipulate sterilization parameters to accommodate these loads. At Consolidated, we recognize that many of our customers need assistance in identifying and creating the proper sterilization cycle for their load type. As such, we hope this article helps you better understand how gravity and vacuum sterilization cycles work and what types of loads they’re appropriate for. We encourage you to read the rest of our steam sterilization cycles series. In the meantime, if you have any questions, we’re always happy to help — contact us today to speak to a specialist. eBook Offer: Discover the Top 12 Steam Sterilization Cycles Our definitive guide explains the mechanics behind different sterilization cycles and what types of loads they’re best suited for. Get Your eBook>>> Frequently Asked Questions What is a gravity sterilizer? A gravity sterilizer is any sterilizer that uses the gravity displacement method for air removal. Gravity sterilizers perform what’s known as a gravity cycle to sterilize loads. How long does a gravity sterilization cycle last for? How long a gravity cycle lasts depends entirely on the load you wish to sterilize. The CDC advises that: Wrapped instruments be exposed for 30 minutes at 250°F (121°C) and 15 minutes at 270°F (132°C), with a dry time of 15–30 minutes Textile packs be exposed for 30 minutes at 250°F (121°C) and 25 minutes at 270°F (132°C), with a dry time of 15 minutes Wrapped utensils be exposed for 30 minutes at 250°F (121°C) and 15 minutes at 270°F (132°C), with a dry time of 15–30 minutes Can a pre-vacuum sterilizer also run gravity cycles? Yes, a pre-vacuum sterilizer can run gravity cycles because its vacuum system sits alongside the standard steam and drain setup rather than replacing it. By comparison, gravity sterilizers can only run vacuum cycles if they’re equipped with a post-vacuum feature. Can you sterilize wrapped instruments in a gravity sterilizer? Yes, you can sterilize wrapped instruments in a gravity sterilizer, though they require a longer exposure than unwrapped items. The CDC recommends they be exposed for 30 minutes at 250°F (121°C) or 15 minutes at 270°F (132°C), with 15 to 30 minutes of drying time. A vacuum cycle, which mechanically removes trapped air, is more suitable for densely wrapped packs, porous textiles, and hollow instruments with lumens. Do gravity sterilizers need a Bowie-Dick test? No, gravity sterilizers do not need a Bowie-Dick test. A Bowie-Dick test confirms whether a vacuum system removes air from the chamber effectively, so it only applies to pre-vacuum sterilizers. That said, gravity units still require monitoring through other methods, including process challenge devices and biological indicator testing. Article Sources Centers for Disease Control and Prevention, “Steam Sterilization, https://www.cdc.gov/infection-control/hcp/disinfection-sterilization/steam-sterilization.html Consolidated Sterilizer Systems, “Steam Sterilization Cycles, https://consteril.com/resources/sterilization-cycles/.” Consolidated Sterilizer Systems, “How Does a Laboratory Autoclave Work, https://consteril.com/how-does-a-laboratory-autoclave-work/.” Thermo Fisher Scientific, “What Is Ambient Air?, https://www.thermofisher.com/blog/mining/what-is-ambient-air/.” The Washington Post, “Why dry air is heavier than humid air, https://www.washingtonpost.com/news/capital-weather-gang/wp/2013/08/05/why-dry-air-is-heavier-than-humid-air/.” John J. Perks, “Principles and Methods of Sterilization in Health Sciences, https://books.google.com/books/about/Principles_and_Methods_of_Sterilization.html?id=-lYpPQAACAAJ.” Consolidated Sterilizer Systems, “Consolidated Smart Options, https://consteril.com/products/smart-options/.” SimScale, “What Is the Venturi Effect?, https://www.simscale.com/blog/what-is-venturi-effect/.” Centers for Disease Control and Prevention, “Minimum cycle times for steam sterilization cycles, https://www.cdc.gov/infection-control/hcp/disinfection-and-sterilization/steam-sterilization-cycle-times.html.” Get The Steam Sterilization Cycles Guide Read this comprehensive 31-page guide about when and how to use the top 12 steam sterilization cycles. This guide outlines how today’s steam autoclaves can be configured with specific parameters suitable for nearly any load and application type. Get the Guide Tweet Like Share
5.29.26 Protect Your Sterilizer & Keep Your OR Running With SterilSource → For sterile processing teams at healthcare facilities, providing purified water for their autoclave has historically meant accepting tradeoffs around floor space, budget, and throughput. Ambulatory surgical centers (ASCs) and other, smaller healthcare facilities have felt this most acutely, with many having to choose between installing a bulky reverse osmosis (RO) system that takes up significant […]
5.28.26 Consolidated Sterilizer Systems Introduces SterilSource, a Premium Water Purification System for Healthcare Facilities and Life Science Labs → May 2026, Billerica, MA — Consolidated Sterilizer Systems is proud to announce the launch of SterilSource, a compact wall-mounted water purification system designed to meet the demanding water quality regulatory requirements of healthcare and life science environments. SterilSource is available in three configurations, offering scalable water treatment solutions from basic mineral and contaminant removal to […]
5.14.26 Consolidated Selected as Small Business Manufacturer by the University of California → What Set Us Apart Throughout the RFP process, Consolidated stood out for our: Relationship with UC, which predates this agreement, with many campuses already standardized on our autoclaves Low cost of ownership through non-proprietary parts and third-party service models, including local service Built-in water- and energy-saving features Support for both in-house and generator steam Custom […]
