Vacuum Pressure Impregnation Systems for Wood Treatment

Vacuum pressure impregnation is a wood preservation process that removes air from wood cells using vacuum and then forces preservative solution deep into the structure under pressure.

The typical cycle includes:

• Initial vacuum
• Filling with preservative
• Pressure application (commonly 100–200 psig)
• Solution discharge
• Recovery vacuum
• End of cycle

The vacuum stage expands the wood’s cellular structure and removes trapped air. This creates space for deeper preservative penetration once pressure is applied.

In North American pressure-treating plants, consistent vacuum stability directly impacts penetration depth, cycle time, and final product quality.

Wood treatment processes introduce demanding conditions:

• High moisture content air
• Condensable vapors
• Resinous preservative components
• Variable startup loads
• Chemical exposure (CCA, ACQ, and other preservatives)

Dry vacuum technologies can struggle when exposed to liquid carryover or chemical vapors. Seal degradation, overheating, or fouling often reduce reliability in this environment.

Liquid ring vacuum pumps use operating fluid to create compression. For this reason, they:

• Tolerate entrained liquid without internal damage
• Condense vapors during operation
• Operate without metal-to-metal contact
• Require no internal lubrication
• Deliver stable performance during startup and recovery

The key factor is operating envelope stability. When the vacuum system is engineered for condensable vapor handling and chemical compatibility, downtime risk decreases and lifecycle cost becomes more predictable.

Wood preservation impregnates the wood to stabilize its dimensions, increase its resistance to water and chemicals, and reduce cracking.

The structure of wood is similar to a sponge, with cell cavities and cell walls, which represent the actual wood. Wood treatment coats these walls with preservatives to protect them from decay caused by wood-destroying fungi and insects. 

The preservative penetrates deep into the wood with pressure and vacuum. The vacuum removes the air from the cavities to create space for the preservation solution. The solution is then forced deep into the wood under high pressure.

• Initial Vacuum - Once the wood is sealed in the autoclave, vacuum is applied using a single stage NASH vacuum pump. This removes some surface moisture and expands cell structure for easier penetration. Removal of air at this point accelerates, and makes the following stages of treatment more effective. The length of the vacuum cycle varies with the type of wood. 
• Filling - The preservative is introduced from a storage tank, initially by vacuum, and finally by a multistage high-pressure solution transfer pump. 
• Application of Pressure – Autoclave pressure is raised between 100 and 200 psig and held until desired penetration is achieved. The time required varies with the size and type of lumber, the solution pressure, and the efficacy of the preconditioning. 
• Discharging the Solution – Any solution not absorbed by the wood is returned to the storage tank for reuse. In some cases, solution removal may be assisted by using compressed air.
• Recovery Vacuum – Another round of vacuum is used to help the bonding of the active principles of wood. 
• End of Cycle – The autoclave returns to atmospheric pressure and the wood is removed.

NASH liquid ring vacuum pumps offer the following features and benefits for wood treatment applications:

• Ability to handle, process carryover or recycled gases - increases operating efficiency and reduces operating costs
• Long design life – highest reliability
• No internal lubrication required -  less maintenance and downtime
• No metal – to – metal contact – simple operation and wear-free performance
• Cool running – incoming vapor is condensed and smaller, less costly equipment to service application
• Only one moving part – simple and trouble-free operation
• Proven energy-efficient design – lower operating costs
• Over a century of engineering and application experience – peace of mind

Vectra XL

NASH Vectra XL, VectraPak, and SC liquid ring vacuum pumps are the wood preservation industry’s preferred systems that deliver innovative solutions to harsh industrial environments while exceeding customer-specific requirements.

Our Vectra XL liquid ring vacuum pumps are designed for the rigorous, nonstop demands of harsh industrial environments. These systems are held to the highest standard of reliability and manufactured to achieve optimum performance and unprecedented production efficiencies. Vectra XL liquid ring vacuum pumps are a revolutionary line of economical pumps that are of great value to customers.

NASH Vectra single stage liquid ring vacuum pumps provide a high vacuum, meet high combustible range standards, and are ATEX certified. Our vacuum pumps are available in ductile iron and stainless steel and accommodate a variety of mechanical seals.