Autoclave Systems and Wood Treatment

Editor’s note: This post was originally published on 6/14/18 and has been updated for accuracy and comprehension.

What are the three steps in the autoclave pressure treated wood process?

The three steps in the autoclave pressure treated wood process are:

  1. The vacuum process removes air from the wood.
  2. The wood is completely coated with preservative.
  3. Atmospheric pressure resets the wood.

Wood is beautiful, but it has always had one downfall – durability and resilience.

Fungus, dirt, insects and water damage are all real threats that deteriorate the structural integrity of wood.

Enter vacuum impregnation and autoclave systems for wood treatment.

Thanks to these technologies, cheaper woods can last long and look great.

Here’s what you need to know about pressure treated wood and how an autoclave system makes all the difference.

Old methods of wood treatment weren’t as effective

In the past, getting pressure treated wood involved baking or boiling.

It doesn’t work as well as an autoclave system because it lacked the increased pressure from the tank.

The intense pressure helps the steam to penetrate the finest cracks and crevices found along the wood.

Autoclave systems for pressure treated wood evolve into more efficient processes

There are three main steps in the autoclave wood-treatment process.

  1. The vacuum process, during which air is squeezed from each wood vessel.
  2. Nozzles are placed throughout the interior of the system coat the wood until it’s completely covered.
  3. Atmospheric pressure resets the wood.


This version of treatment/impregnation allows the head areas and other cavities or vulnerable areas to be completely covered during the wood-treatment process.

It’s safe and efficient because the process eliminates waste and noxious fumes.

Equipment used in the wood treatment process

A lot of machinery is needed for the wood treatment process.

Here’s a deep dive into what’s necessary to efficiently and effectively treat wood in an autoclave.

1. Tram cart

The wood is loaded onto this wheeled cart. You may also hear it referred to as a “tram car.”

2. Autoclave

The untreated wood from the tram cart goes into an autoclave (or ASME Code tank).

3. Storage tanks

The preservative used for treating the wood will most likely be in a concentrated form. 

For a water-based preservative, you’ll mix the concentrate with water, and, for oil-based, you’ll mix it with oil. 

Three storage tanks are required. One each for: 

  • Wood-preservative concentrate.
  • Water or oil.
  • Diluted, or “work solution,” wood preservative. 

Additional storage tanks may be necessary depending on the strength of the preservative where the preserved wood will be used.

4. A System to mix the wood preservative 

We’ve already talked about the need to mix the wood-preservative concentrate. 

But that’s not all that goes into the work solution.

You’ll also have to add additional biocides, depending on the wood preservative you’re using.

You’ll need the proper equipment to measure the biocides and deliver them to the right storage tank.

5. Pumps

You’ll need a fair amount of pumps to get the job done.

Vacuum pump 

A vacuum pump or an eductor are the primary ways a vacuum is created in the wood treatment process.

Pressure pump or air compressor

These tools are responsible for the air pressure in the autoclave while the wood is being preserved.

(You’ll use one or the other – not both.)

Transfer pump

The transfer pump has two jobs.

It fills the autoclave with the preservatives for treating the wood.

And it’s put back into action at the end of the process when it drains the extra preservative back into the proper storage tank.

Additional pumps that may be needed

Any additional pumps will depend on the material you’re using to treat the wood.

For example, you may need a biocide transfer pump, a storage tank mix pump, a water transfer pump, an oil transfer pump, a heat exchanger circulation pump, and/or a cooling tower water pump.

6. Piping valve system

It’s no surprise that a variety of valves and piping are needed to move the various liquids through the process and between pumps and the autoclave.

7. Automation software and instrumentation

When treating wood for various uses, you’ll need different solution strengths.

It’s crucial that each solution is mixed to the precise ratios so the end process can perform as it should.

If you’re working with more than one solution strength, you’ll need an automated system to help you out.

The automation also handles the process inside the autoclave.

More equipment you may need

Your pressure treated wood process may require some additional systems, including:  

  • A wastewater-treatment system. Any water not used in the preservation process has to be treated before it can be discarded.
  • An air-scrubber system. The air that comes from the autoclave when the pressure is released has to be cleaned before it can go back out into the environment.
  • Boiler, heat exchangers, condensers and cooling towers. For industrial wood products, these pieces of equipment are necessary.

Trust wood-treatment experts

Autoclave systems have made the wood-treatment process safer and more efficient.

With a top-notch autoclave for timber impregnation, you’re able to provide your customers with the highest-quality treated wood for all of their needs.

That’s in addition to benefits like increased productivity and profits for your business.

Author: Jeffrey Lippincott

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