Autoclave Buying Guide: Portable vs Vertical vs Radial-Locking Autoclaves

What does an autoclave do?

An autoclave sterilises with saturated steam under pressure. When water is heated in a sealed vessel, the pressure rises and so does the boiling point. At about 15 psi above atmospheric pressure, steam reaches 121°C. Steam at this temperature passes its heat into the load very efficiently and kills bacteria, fungi, viruses and heat-resistant bacterial spores, which dry heat at the same temperature cannot reliably do.

The standard laboratory cycle is 121°C at 15 psi for at least 15 minutes once the whole load has reached temperature. Larger or denser loads, such as big media bottles or waste bags, need longer. Autoclaves are used for:

• Culture media, buffers and other heat-stable liquids
• Glassware, pipette tips, surgical and dental instruments
• Decontaminating biological waste before disposal
• Pharmaceutical microbiology, food and dairy testing, and teaching labs

Materials that are damaged by moisture or heat, such as powders, oils and some plastics, need a different method. For dry-heat sterilisation of glassware, see our guide Hot Air Oven vs Incubator vs BOD Incubator.

Types of laboratory autoclave compared

The three designs below all sterilise at 121°C. The main differences are capacity, how the lid closes and how often you can run a cycle.

Portable autoclave (PT-455). The PT-455 portable autoclave is a pressure-cooker type unit with a jointless SS 304 vessel of 25 litres (300 x 300 mm). It is compact and easy to move, and suits clinics, dental practices, small microbiology labs and teaching labs that sterilise a few flasks or instrument trays at a time.

Vertical autoclave, wing-nut locking (PT-457). The PT-457 vertical autoclave is electrically heated and is the usual choice for hospitals, pathology labs, pharma microbiology, food and dairy labs and colleges. It has a double-walled body with an SS 304 mirror-finish outer, SS 304 lid and interior, silicone gasket, SS basket and analog dial gauge. It runs at 15–20 psi and 121°C and comes in five sizes from 40 to 150 litres.

Vertical autoclave, radial locking (PT-458). The PT-458 has the same build and the same five sizes as the PT-457. The difference is a radial locking lid, which opens and closes faster than tightening a ring of wing nuts. If your lab runs several cycles a day, that time adds up.

Key specifications to check before buying

Use this checklist when you compare quotations or write a tender specification.

• Capacity. Size the autoclave for your largest load in one cycle, not your average one. Liquids need room for steam to circulate, so do not plan to pack the chamber full. The PT-457 and PT-458 come as 300 x 550 mm (40 L), 350 x 550 mm (50 L), 400 x 600 mm (75 L), 450 x 600 mm (100 L) and 500 x 750 mm (150 L).
• Material of construction. Look for SS 304 for the chamber, lid and basket. It resists corrosion from steam and condensate and is easy to clean.
• Safety fittings. A vertical autoclave should have a pressure gauge, a steam release valve, a water outlet valve and a spring-loaded safety valve. The PT-457 and PT-458 have all of these.
• Locking. Wing nuts are simple and robust. Radial locking is quicker. Choose based on how many times a day the lid is opened.
• Control. An analog gauge works fine for routine use. If you want accurate, repeatable timed cycles with less operator attention, choose the digital version (PT-457A or PT-458A) with a PID temperature controller, timer and pressure switch.
• Optional extras. The PT-457 can be ordered with a low-water indicator, pressure switch, radial locking, pedal lift or digital PID controller with timer. Spare parts such as gaskets, controllers and ISI heaters are listed under PT-459.
• Power supply. The vertical models run on 220 V, 50 Hz. Check that the socket and wiring at the installation point can handle the heater load.
• Procurement route. Government buyers can order through GeM. See laboratory equipment on GeM.

Common mistakes when buying an autoclave

• Buying too small. A 25 litre portable unit is fine for a clinic but will be the bottleneck in a lab preparing media every day.
• Ignoring cycle frequency. If the autoclave is opened many times a day, radial locking saves staff time and wear on the threads.
• Using an autoclave for things it should not sterilise. Oils, powders and sealed containers need dry heat or another method. Never autoclave tightly closed bottles, because pressure can build up and break them.
• Not planning for validation. Pharma and hospital labs must show that every cycle reached temperature for the full time. If your quality system is strict, choose the digital PID version with timer from the start rather than upgrading later.
• Forgetting spares. Gaskets are consumables. Order a spare gasket with the autoclave so a worn seal does not stop work.

Maintenance tips

• Fill to the correct water level before every cycle, and use distilled or demineralised water to reduce scale on the heater.
• Drain and wipe the chamber regularly. Do not let water stand inside for days.
• Check the silicone gasket for cracks or flattening, and replace it when it no longer seals.
• Test the safety valve as recommended, and keep the pressure gauge in good working order.
• Let the pressure fall to zero before opening the lid. Open slowly, keeping your face away from the steam.
• Verify sterilisation regularly. Use chemical indicator tape on every load and run a biological indicator containing Geobacillus stearothermophilus spores at a set interval, as your quality system requires.

Equipment in this guide

Portable Autoclave PT-455View details →Vertical Autoclave, Electrically Heated PT-457View details →Vertical Autoclave with Radial Locking PT-458View details →

Frequently asked questions