Types of Autoclave: A Complete Guide to Choosing the Right Sterilizer for Your Lab

If you've ever stood in front of a supplier's catalogue trying to decide between a horizontal or vertical autoclave, or a Class B unit versus a standard gravity model, you've hit the real problem — most pages just list features without explaining why one type fits your lab. Here's how we explain it to walk-in customers at Bionicsro, in plain terms, with the physics behind it.

Quick Answer

Autoclaves differ along two independent axes. Loading design (vertical or horizontal) is the physical build. Sterilization class (N, S, or B) is what load types the cycle is validated to sterilize under EN 13060. A vertical unit can be Class N, S, or B; so can a horizontal unit — check the two separately. A small clinic typically wants a Class B vertical tabletop unit (commonly 18–24 L) for wrapped and hollow instruments. A hospital CSSD or high-volume lab typically wants a horizontal unit with trolley loading, and separately needs to confirm Class B (or equivalent) validation for wrapped loads.

What Is an Autoclave, Really?

An autoclave is a pressure vessel that uses saturated steam to destroy microorganisms, spores included, on instruments, glassware, media, and waste. Water boils at 100°C at sea-level pressure, but trap that steam and raise pressure inside a sealed chamber, and the boiling point climbs well past 121°C. Held there for a validated duration, even heat-resistant spores can't survive.

Reading an Autoclave Diagram

Any autoclave diagram shows the same core parts: a chamber, a jacket or heating element, a pressure gauge, a safety valve, a locking door, and a drain/exhaust line. In gravity-displacement models, steam pushes air out through a lower vent. In pre-vacuum (Class B) units, a vacuum pump actively removes air before steam enters — critical for hollow or porous loads like wrapped surgical packs, where trapped air pockets would otherwise leave a "sterilized" instrument that isn't actually sterile.

Temperature and Pressure — The Numbers That Matter

Two reference cycles are commonly cited: ~121°C at ~15 psi gauge, and ~134°C at ~30 psi gauge. Treat these as indicative reference points, not a spec for any specific machine or load.

Gauge vs. absolute pressure. Gauges read pressure above atmospheric, not total chamber pressure. Atmospheric pressure at sea level is ~14.7 psi. Absolute pressure is gauge plus atmospheric, so ~15 psi gauge is roughly ~29.7 psi absolute (≈2 bar), and ~30 psi gauge is roughly ~44.7 psi absolute (≈3 bar).

Hold times aren't universal. The pressure-temperature relationship is fixed by physics, but the validated hold time depends on load type, packaging, chamber design, and the sterilizer's own validation data (per EN 13060 or ISO 17665). Liquids need slow exhaust; solids tolerate fast exhaust; wrapped or porous loads need the air-removal phase to complete first. Always run the cycle your unit's manufacturer has validated for your load.

Two Ways to Categorize Autoclaves

Most guides muddle "horizontal," "vertical," and "Class B" as if they're on one menu. They're not — they answer two separate questions.

By Loading Design: Horizontal vs Vertical

About the physical build and where the door is. A vertical autoclave loads from the top, has a smaller footprint, and suits clinics and small labs with tight space. A horizontal autoclave loads from the front like an oven, supports trolley-based bulk loading, and suits hospitals, CSSDs, and pharma units running continuous, high-volume sterilization. Horizontal units cost more upfront but process more per cycle, lowering cost-per-load over time. Either design can carry Class N, S, or B validation — check the two specs separately.

By Sterilization Validation: Class N, S, and B

This comes from EN 13060, the standard for small steam sterilizers (compact, typically benchtop units) — it describes load type, not machine size. Larger pass-through or bulk sterilizers are generally validated against other standards (e.g. EN 285), so don't assume N/S/B labelling carries over to a large horizontal unit — ask which standard applies.

• Class N: Gravity-displacement, validated for solid, unwrapped instruments only. No air-removal phase — unsuitable for hollow or porous items.
• Class S: Manufacturer-defined. The manufacturer specifies and tests a particular set of load types beyond Class N — scope varies by brand. Check the IFU rather than assume it matches Class N or B.
• Class B: A fractionated pre-vacuum cycle — pulling air out in multiple pulses before steam injection — plus drying. Validated for the broadest range: solid, hollow, porous, and wrapped instruments, including dental handpieces and surgical packs. If your load includes wrapped or hollow instruments, confirm your unit's IFU specifically covers it.

Buying Guide: Matching Capacity to Your Actual Load

Skip the specs — what are you loading, and how much? Treat the litre figures below as typical ranges, not fixed brackets.

Size by throughput, not just litres. Usable chamber volume is less than nominal capacity once trays and required pack spacing are accounted for — ask for a model's usable loading volume. To size correctly: estimate daily instrument/pack count, divide by how many fit per load, and multiply by validated cycle time to get total daily processing time. If that exceeds your working hours, you need a larger chamber or a second unit. Send us your daily counts and we'll size it against real model specs rather than upselling a bigger unit than you need.

Autoclave Price in the Indian Market

Pricing depends far more on chamber material, control type, and validation documentation than on brand name. A basic vertical unit sits in a modest bracket; a Class B tabletop costs more due to its vacuum system; horizontal autoclaves scale up sharply with size and automation. Rather than quote a flat number that goes stale fast, we'd rather size a configuration to your actual load and give you an accurate quote.

Specification Comparison

(Cost isn't listed under validation class — price is driven by build quality and documentation, not class label alone. Loading design and validation class are separate specs; check both.)

Why Labs Across India Choose Bionics

We manufacture our autoclave range with stainless steel chambers, PID-controlled temperature and pressure, and safety interlocks built for daily use — not just showroom conditions. Every unit ships with calibration documentation, and our technical team helps match chamber size and cycle type to your actual load.

Get in touch with Bionicsro today for a free consultation and a customized quote based on your load volume and space.