Vacuum Degassing Explained for Industrial Processes

Author: Vacuum_Technologies_Limited URL: https://vacuum-technologies.shop/blogs/news/future-of-vacuum-automation-components

Useful links: https://www.vuototecnica.co.uk/companie.php

A batch of resin that foams in the mould, a coating with pinholes, or a process liquid that cavitates in service often has the same underlying cause: dissolved or entrained gas. Vacuum degassing explained simply is the controlled removal of those gases by reducing the pressure around a material until bubbles expand, rise and break free. In production, however, the result depends on far more than connecting a pump to a vessel.

What vacuum degassing does - Link:https://www.vuototecnica.co.uk/product/416/en/11.06.pdf

Gas can be present in a liquid, paste or powder-containing mixture in two forms. Entrained air exists as visible or microscopic bubbles introduced during mixing, filling, pumping or transfer. Dissolved gas is held within the material at a molecular level and may not be visible until pressure or temperature changes.

When absolute pressure falls, gases become less soluble in the product. Existing bubbles also expand. Given sufficient time and a suitable flow path, the gas migrates to the surface and is drawn from the chamber through the vacuum line. This is why a product may initially rise dramatically under vacuum before settling.

The objective is not always to remove every trace of gas. Many applications require a repeatable residual gas level that prevents defects or protects downstream equipment. The required vacuum level, dwell time and vessel design should therefore be based on the product and process specification, rather than an assumption that deeper vacuum is automatically better.

Vacuum degassing explained: pressure, time and temperature

Three variables govern most degassing results: absolute pressure, exposure time and product temperature. Absolute pressure matters because it determines how strongly bubbles expand and how readily dissolved gases are released. A gauge reading alone can be misleading. Engineers should specify and measure absolute pressure when comparing a process requirement with pump performance.

Time matters because gas must travel through the product. A low-viscosity liquid may clear quickly in a well-designed vessel. A viscous adhesive, silicone, resin or slurry may retain bubbles for much longer, particularly if the material is deep, cold or poorly mixed. Simply fitting a larger pump does not always shorten the cycle. Once the chamber has reached its target pressure, gas release and bubble movement can become the limiting factors.

Moderate heating can reduce viscosity and improve gas release, but it also changes vapour pressure. Water, solvents and volatile constituents may boil at reduced pressure. That may be useful where evaporation is part of the process, but it can also alter the formulation, overload the pump or contaminate the system. The operating window must balance degassing performance against product stability.

The typical industrial degassing arrangement - https://www.vuototecnica.co.uk/product/416/en/11.06.pdf

A basic system consists of a sealed vessel, vacuum pump, isolation valve, vacuum gauge or sensor, and housework sized to avoid unnecessary restriction. For controlled production, it may also include a receiver, condensate trap, filter, pressure regulator, automated valves and a programmable control sequence.

The vessel is often more important than it first appears. It needs sufficient freeboard to contain product expansion and foam. A vessel filled too close to the lid can pull material into the line when bubbles rise. Internal geometry should encourage a shallow product depth or provide agitation where the product permits it. Sight glasses, level sensing and a controlled vent valve help operators avoid spills and achieve repeatable cycles.

Pump selection depends on the gas load and what may leave the product. Dry-running vane, claw, screw and diaphragm pumps are commonly considered where oil contamination is unacceptable or vapours are expected. Oil-sealed rotary vane pumps can achieve good vacuum levels but require effective protection from vapour, condensate and product carry-over. Liquid ring pumps can tolerate wet gases in suitable duties, though their utility and operating costs must be considered.

In smaller handling or intermittent automation applications, a pneumatic vacuum generator may be practical. For extended degassing cycles, a mechanically driven pump is usually the more economical choice, especially where compressed-air consumption is significant. The correct answer depends on duty cycle, target pressure, contamination risk and available utilities.

Protect the pump, not just the product

Degassing systems often fail because the pump is treated as a simple suction source. Vapours can condense in the pump, particulates can damage internal components, and foam can be carried into hoses. A correctly selected inlet filter, knock-out pot or condensate trap can extend service life considerably.

The protection device must match the application. Fine filtration is useful for dry powder contamination but can rapidly block if exposed to sticky material. A large-volume separator may be necessary for foaming resins or liquids. If aggressive chemicals are present, material compatibility across seals, hose, vessel and trap is as important as pump capacity.

Choosing the right vacuum level (options) https://www.vuototecnica.co.uk/product/417/en/11.07.pdf

Very deep vacuum can be beneficial, but it is not a universal cure. It may cause excessive foaming, remove volatile ingredients, flash-boil moisture or create a long recovery period between cycles. Conversely, a mild vacuum may release enough entrained air without upsetting a sensitive formulation.

Start with the quality issue being solved. For example, a casting compound may need reduced bubble content to prevent voids and improve electrical insulation. A coating may need degassing to avoid surface craters. A lubricating or process fluid may require dissolved air removal to reduce oxidation, inaccurate dosing or cavitation downstream. Each case has a different practical endpoint.

Record the target absolute pressure, time at pressure, material temperature, batch volume and observed behaviour. These process values provide a better basis for repeatability than relying on an operator's judgement of whether the material looks clear. For critical work, use calibrated sensors and interlocks to prevent a cycle starting with an open valve, full trap or inadequate vacuum level.

Common problems during degassing

Slow pump-down is frequently blamed on an undersized pump, but leaks and restrictions should be checked first. Damaged lid seals, worn hose, loose fittings and undersized valves can all prevent the vessel reaching its intended pressure. A simple blank-off test can help distinguish pump performance from system leakage.

Persistent bubbles may indicate a viscosity problem, inadequate dwell time or unsuitable vessel geometry. If bubbles form but do not rise, reduce product depth, adjust temperature within the formulation limits, or use compatible slow-speed mixing. High-speed agitation can introduce more air than the vacuum system removes.

Foaming is different from ordinary bubble release. It can be caused by surfactants, solvents, moisture or a pressure reduction that is too rapid. A staged vacuum profile often helps: pull down to an intermediate pressure, allow the foam to collapse, then continue gradually. Automated control is particularly valuable where batch-to-batch consistency matters.

Unstable gauge readings can arise from active gas release rather than a leak. As gas evolves from the product, chamber pressure may rise temporarily even with the pump running. Look at the pressure trend alongside the product behaviour before changing equipment. If the system is processing a large vapour load, consider whether a condenser or trap is needed ahead of the pump.

Where degassing is used

Vacuum degassing is common in resin casting, encapsulation, adhesives, sealants, coatings, inks, composites and silicone processing. It is also used in food and pharmaceutical production where air removal supports filling quality, shelf-life objectives or controlled processing, subject to the required hygienic design and validation standards.

In fluid systems, degassing can support accurate dispensing and reduce cavitation risk. In manufacturing cells, it may be integrated ahead of dispensing heads, moulding stations or coating equipment. The best arrangement is usually one that considers transfer, mixing and filling together. Removing air in one vessel has limited value if the next pump, valve or filling step reintroduces it.

Specify the system around the material

Before selecting hardware, establish the batch volume, viscosity range, operating temperature, desired cycle time, target absolute pressure and likely vapours. Also identify whether the material is abrasive, corrosive, flammable, food-contact or sensitive to oil contamination. These details determine the suitable pump technology, seal materials, filtration and vessel configuration.

Vacuum Technologies Shop can assist with matching pumps, valves, gauges, filters, hosework and fittings to the actual duty rather than supplying components in isolation. For replacement work, check the existing connection sizes, electrical or pneumatic control requirements and material compatibility before ordering.

A well-designed degassing system does not need unnecessary complexity. It needs a vessel that contains the product behaviour, a pump that suits the real gas load, and controls that make the result repeatable. Start with a representative material trial, measure the process rather than guessing, and build the specification from what the product genuinely requires.