Clean Steam for Autoclave Sterilization

Application: Biopharmaceutical Autoclaves, Steam Sterilization
Media: Clean Steam (Pure Steam), Plant Steam, Clean Steam Condensate
Valve Requirement: Sanitary Pressure Reducing Valves (PRV), Sanitary Safety Relief Valves, Sanitary Steam Traps, Sanitary Subcooled Condensers

Autoclaves play an essential role in biopharmaceutical manufacturing by sterilizing equipment and components that cannot be sterilized in place. From laboratory glassware and reusable stainless steel containers to process sampling and instrumentation components, autoclaves use saturated clean steam to achieve validated sterilization conditions. Reliable operation depends on more than simply supplying steam to the chamber. Steam pressure must be accurately controlled, condensate must be removed efficiently, and the chamber and jacket must be protected against overpressure.

What Is an Autoclave?

An autoclave is a sealed, steam-jacketed pressure chamber used to sterilize equipment and components that cannot undergo Steam-in-Place (SIP).

Autoclaves range from small benchtop units to large, room-sized systems. Typical items sterilized in an autoclave include:

• Production and laboratory glassware
• Reusable stainless steel drug or product-additive containers
• Stainless steel cleanroom equipment
• Process sampling components
• Instrumentation components
• Other equipment that cannot be sterilized in place

Items are loaded onto shelves inside the chamber. Once the pressure door is closed and sealed, clean saturated steam is introduced into the chamber. Similar to SIP, autoclave sterilization is a validated process. Temperature and pressure data are recorded to verify that the entire load reaches the specified sterilization temperature for the required amount of time.

How Clean Steam Is Used in an Autoclave

Autoclaves commonly have two separate steam circuits:

Jacket Steam

Steam continuously supplies the jacket surrounding the chamber, keeping the autoclave hot and ready for the next sterilization cycle.

Once the jacket reaches its specified temperature, the steam demand is relatively low because only enough energy is needed to maintain temperature.

Chamber Clean Steam

A separate clean steam supply feeds the sterilization chamber. Steam demand is much higher at the beginning of the cycle because the system must heat the chamber and the entire mass of equipment being sterilized from room temperature to sterilization temperature. Once the required temperature has been reached, steam demand decreases substantially. This changing steam demand makes pressure and flow control particularly important.

Controlling Clean Steam Pressure

Clean steam is normally distributed through a biopharmaceutical facility at a higher pressure than required by the autoclave. A sanitary pressure reducing valve (PRV) reduces the clean steam distribution pressure to the pressure—and corresponding saturated steam temperature—required by the autoclave. Closed-loop temperature control is typically managed by the autoclave’s PLC, which controls steam flow to maintain the required jacket and chamber temperatures.

Why Autoclave Steam Control Is Different

Autoclave steam flow control presents a unique challenge for the upstream PRV. Instead of traditional sanitary rising-stem control valves, autoclaves commonly use Y-type sanitary poppet valves that rapidly pulse open and closed to control the amount of steam entering the system. Every time the poppet valve closes, steam flow stops abruptly. The upstream PRV responds immediately, causing its diaphragm, stem and plug assembly to move toward the seat. Repeated cycling can cause the PRV plug to strike its metal seat with considerable force. Over time, this repeated impact can damage the PRV body.

Protecting the PRV

For autoclave applications using rapidly cycling downstream poppet valves, Steriflow recommends specifying the PRV with a polymer seat rather than a metal seat. A PEEK soft seat helps cushion the repeated plug-to-seat contact and protect the PRV body from damage. The Steriflow MK96 Sanitary Pressure Reducing Valve is available with seat options suitable for clean steam autoclave applications.