Wood impregnation autoclaves — what they do and how to buy one used

A wood impregnation autoclave is a pressure vessel used in industrial wood preservation. Wood is loaded into the cylinder, air is evacuated, the vessel is pressurised with preservative (typically 8-12 bar), and a final vacuum removes excess fluid. The process drives the protective agent deep into the timber so it can survive outdoor service conditions — without pressure treatment, wood used in ground contact, decking, fencing, poles or sleepers will not reach Use Class 3+ under EN 335.

WeSellMachines lists used woodworking machinery from European manufacturers including Machinenbau Scholz, whose autoclaves are common in preservation plants across Poland, Germany, and the Nordics.

How the vacuum-pressure cycle works

A standard pressure-treatment autoclave runs three phases: an initial vacuum opens the wood cells, a pressure phase (typically 8-12 bar) forces the preservative into the timber, and a final vacuum returns excess fluid to the storage tank. A full cycle usually takes 2-6 hours, depending on wood species, cross-section and the retention level required.

The four points that determine the working capacity of a used autoclave are: cylinder diameter and working length (typically 1.2-3.0 m diameter at 4-15 m length), maximum working pressure, the condition of doors and seals, the vacuum pump capacity, and the control system (manual, semi-automatic, or PLC with stored recipes).

What to check when buying a used autoclave

When an appraiser evaluates a used pressure vessel, the physical and documentary checks that matter are:

Nameplate and pressure-vessel certification. Industrial pressure vessels fall under periodic inspection regimes (UDT in Poland, TÜV in Germany). Confirm the last inspection date and that the certification is still valid — without it the vessel cannot be operated legally.
Cylinder and door condition. Corrosion, deformation, and traces of repair lower value. Wall thickness is measured with ultrasound.
Vacuum pump and pressure system. Pump capacity (m³/h) and stability of achieved vacuum directly drive impregnation quality.
Control system and recipes. PLC-based units store repeatable recipes for different species; older manual controls need an experienced operator.
Parts and service availability. Manufacturers such as Machinenbau Scholz keep archived drawings and service documentation; models without service backup cost more to keep running.

The same checklist is part of the used machinery appraisal method used at WeSellMachines.

Where pressure-treatment autoclaves are used

Industrial autoclaves serve plants that treat:

Construction and structural timber — beams, joists, rafters, shuttering boards, railway sleepers.
Outdoor timber — decking, cladding, pergolas, playground equipment, fence posts.
Joinery elements — windows, external doors, stairs where Use Class 3+ is required under EN 335.
Sawmill output — treatment of sawn timber before or after kiln drying; see the sawmills and band saws category for related equipment.

Manufacturers of wood impregnation autoclaves

The second-hand market is dominated by European builders that maintain service documentation and supply spare parts. Three manufacturers whose units are regularly offered used:

Maschinenbau Scholz (Coesfeld, Germany) — established 1919, builds complete impregnation plants for the full, Lowry and Hamburg methods. Catalogue chambers up to Ø3000 mm and 25 000 mm long, working pressure up to 14 bar, steel or stainless-steel construction. Currently listed: two Scholz autoclaves of 78 m³ each (id 1900).
WTT (Wood Treatment Technology, Denmark) — supplies impregnation, thermal modification and vacuum drying plants; a Ø2500 × 12 000 mm installation operates at a sawmill in Sweden.
WTM Vaglio (Italy) — builds vacuum-pressure impregnation plants, vacuum kilns and steaming chambers, delivering to the European market.

Used listings also feature Bondtech (USA), ETSA and IWT Moldrup (Denmark). Regardless of manufacturer, our appraisal methodology for a used autoclave verifies the pressure-vessel documentation, the condition of the cylinder and includes a leak test.

Available units and pricing

Currently listed on WeSellMachines: two Machinenbau Scholz wood impregnation autoclaves (id 1900) — operational condition, 34 000 EUR per unit, available separately. Scholz is one of the longest-established autoclave builders in Central Europe, known for heavy, simple steel construction and reliable valve assemblies.

Market prices for used autoclaves range from fifteen thousand to several hundred thousand EUR depending on cylinder size, working pressure and manufacturer; an individual valuation requires hands-on inspection and the year of manufacture.

For orientation — listings with public prices (September 2026): complete used impregnation plants on the European market were offered at roughly 30 000–90 000 EUR, e.g. a set of two autoclaves with preservative tanks at 48 000 EUR (Karsin, Poland) and an IWT Moldrup plant at 89 000 EUR. New plants from outside the EU start around 14 500 USD but require verification of pressure certification for the destination market.

Frequently asked questions

What size autoclave does a small sawmill need?

A small sawmill typically needs a vessel 1.2-1.8 m in diameter and 4-8 m long, working at 8-10 bar. The decisive factors are a working vacuum pump (minimum 100 m³/h), access to service, and a valid pressure-vessel certificate. Newer PLC units allow you to store recipes for different wood species.

Does a wood impregnation autoclave need a permanent operator?

Yes. Fully automated lines exist, but a standard autoclave needs operator attention during loading, cycle setup and unloading. The operator selects pressure, cycle time, and monitors the impregnant level.

How do I test the seal of a used autoclave before buying?

The seal test closes the vessel, brings it to working pressure and watches the gauge for 15-30 minutes. A pressure drop above 2-3% indicates leaking doors, gaskets or fittings. An appraiser runs the test twice — once cold and once at working temperature.

How much does a used wood impregnation autoclave cost?

Used autoclave prices start at around 15 000 EUR for small laboratory units, 30 000-80 000 EUR for mid-sized vessels, and reach 200 000+ EUR for industrial units above 2 m diameter. Final price depends on the manufacturer, technical condition, and the date of the last pressure-vessel inspection.

Can I sell my old autoclave through WeSellMachines?

Yes. Submit the form on sell a machine or write to the address listed on the contact page. We need photos of the cylinder, doors, nameplate and control panel; we handle the rest during the appraisal.

Guides — buying used machinery

We describe pre-purchase inspection procedures in the WeSellMachines blog guides:

Buying used CNC woodworking machines — practical guide — how to verify condition and documentation of used woodworking machines.
How to choose used woodworking tools — technical condition assessment criteria.
Used machinery buying guide 2026 — general inspection procedure for second-hand industrial machines.

Contact for autoclave enquiries

Questions on a specific model, help with appraising your used autoclave, or transport arrangements — get in touch. We operate in Poland and Germany and accept assignments from other countries with full technical documentation. Learn more about WeSellMachines and the team behind the woodworking machinery category.