autoclave service and repair

Jacketed vs. Non-Jacketed

rectangular autoclaves steam autoclaves by priorclave

Does our lab really need a jacketed autoclave? 

Most labs never even ask themselves this question. They’re painfully aware of the shortfalls of the autoclaves they’ve used: high purchase price, high utility bills, frequent maintenance downtime. But they rarely know that the root cause of most of that misery wasn’t the autoclave, per se, but its steam jacket. Fortunately, most labs and industrial settings do not need a jacketed autoclave. A non-jacketed autoclave will perform well for them—at a far lower cost and with much less hassle.

Steam Jacketed Autoclaves Explained

Every steam autoclave is fundamentally the same: It floods a sealed pressure chamber with steam and holds it at a specific temperature for a given period of time. This combination of moist heat, sustained high temperature, increased chamber pressure, and time consistently kills spores and microorganisms, disinfects pathogenic waste, processes liquids, and sterilizes culture media, pipette tips, glassware, surgical instruments, and the like.

Many modern autoclave sterilizers—especially larger models—rely on a “jacketed” design in order to speed up this process. These units require an independent steam generator for their sterilizing steam. That steam is first routed through the “steam jacket,” which is a rectangular steel shell surrounding the rectangular pressure chamber. It then enters the sealed chamber. This nested arrangement makes it possible to reach the sterilization temperature (relatively) quickly. At the end of the sterilization cycle, the jacket can then be flooded with cold water to speed cooling.

The result is an autoclave that is ideal for high-throughput 24/7/365 operation. It’s the preferred sterilization approach for hospitals and may be a good fit for medical or pharmaceutical labs with demanding schedules or a need for terminal sterilization.

But this comes at a cost.

The High Cost of Steam Jackets

Steam jacketed autoclaves are expensive to purchase, maintain, and operate.

This starts with the manufacturing process. The jacketed design is complicated. It relies on specialized interdependent components, many of them proprietary. The jacketed pressure vessel at its heart is essentially double-walled, with the inner pressure chamber made of thick reinforced steel. All of this increases both material and labor costs and results in a heavier unit that is more costly to build, ship, and install.

Once installed, a jacketed autoclave requires a fair bit of tender loving care. Quarterly maintenance visits typically require factory technicians and usually mean purchasing proprietary components. On top of that, jacketed autoclaves rely on independent steam generators. These constitute an entirely separate point of failure with their own maintenance schedule and upkeep.

Finally, these are, by their nature, resource consumptive sterilizers. They trade a small increase in throughput for a sizable increase in resource consumption and often must idle hot.

A Non-Jacketed Alternative

But this isn’t the only way to approach sterilization. Steam jackets are vital in high-throughput settings—but very few labs qualify as “high throughput.”  If you run fewer than five cycles per work day and focus on the following load types, then you have better options.

Autoclave Cycles

Non-jacketed autoclaves have several key design advantages that make them less expensive to own, operate, and maintain.

First and foremost, non-jacketed autoclaves have no jacket. Because they don’t need a jacket, they don’t have to use rectangular pressure chambers. Cylindrical pressure vessels (favored in non-jacketed steam sterilizers) cope better with high pressure and temperature and thus can be safely fashioned from thinner steel with fewer reinforcing ribs. Because the entire system is less massive, there is no need for an expensive external steam source. Instead, non-jacketed autoclaves can rely on extremely efficient in-chamber heating elements.

Diagram of a jacketed vs non-jacketed autoclave

Non-jacketed autoclaves tend to take longer to run complete sterilization cycles. Part of that is because having an independent steam generator means jacketed autoclaves benefit from “instant on-demand” steam. (The in-chamber heating elements in non-jacketed sterilizers need to come up to temperature first thing in the morning, much like the break room coffee maker.)

Additionally, because there is no jacket to flood with cold water, most non-jacketed autoclaves rely on “natural” cooling. This is often augmented with fans and can be further accelerated with the addition of a vacuum pump. Vacuum operations means that for many loads (e.g., pipette tips, red bag waste, porous, and other “dry” loads) non-jacketed autoclaves perform as fast as jacketed ones. But liquids, culture media, and other “wet” loads will take longer in a non-jacketed autoclave.

Nonetheless, even in labs that largely run “wet” loads, a non-jacketed autoclave can be an astoundingly good value. In general, compared to similar-sized jacketed models, non-jacketed autoclaves cost 10% to 30% less to purchase. They’ll use 70% less electricity and 95% less water on a daily basis. They have far fewer moving parts that might fail, can often be repaired with readily available standard components, and generally need less than half as much regular maintenance.


Does Your Lab Need a Jacketed Autoclave?

If you are a hospital, high-throughput application, or require terminal sterilization for human use (as is the case in pharmaceutical production), you may still need a jacketed autoclave.

But if your facility runs five (or fewer) cycles per work day, values sustainable operations, wants to conserve natural resources, and needs to save money, then you probably don’t.