Combination air/vacuum valves — often called air release and vacuum break valves — are small components that play a big role in protecting the integrity and performance of pressure filter vessels.

For systems using pressure filter vessels, these valves are critical to prevent air-related issues that can lead to mechanical damage, process inefficiency, or even safety risks.

1. Preventing Air Lock and Loss of Flow

During system filling or start-up, air can become trapped inside the vessel or connecting pipework. Because air is compressible, trapped pockets can block water from flowing evenly through the filter media.

A properly sized combination air/vacuum valve automatically releases trapped air from high points, ensuring:

• Full water flow through the vessel
• Correct filtration rates
• Even fluidisation of the media bed during backwash

Without air release, filters can suffer from air binding, channeling, or reduced filtration performance.

2. Protecting Against Vacuum Damage (Implosion Prevention)

When a vessel drains, backwashes, or shuts down suddenly, a rapid drop in internal pressure can create a vacuum.
If air cannot enter the vessel fast enough, the pressure differential between the inside and outside can cause the vessel to implode.

What “Implosion” Means for Pressure Filter Vessels

Implosion occurs when the pressure outside the vessel becomes greater than the pressure inside — and the vessel walls collapse inward.

For pressure filter vessels, this can happen if:

• The drain or dump valve opens quickly
• The system is elevated and siphons water out
• The air/vacuum valve is missing, undersized, or blocked

Example:
If internal pressure drops below the atmospheric pressure during rapid draining, caused by a broken pipe or a valve has been opened, the vessel experiences a negative pressure or vacuum which can be detrimental to the structure of the vessel, usually ending in deformation or collapse or the FRP shells, domed heads, or internal laterals — permanently.

The vacuum relief side of a combination valve prevents this by allowing air to enter the system rapidly, equalizing the pressure and protecting the vessel structure.

3. Ensuring Efficient Backwashing

During backwash cycles, water moves in and out of the vessel at high velocity. Without air control, this can lead to erratic flow or vacuum lock.

A combination air/vacuum valve ensures:

• Air is released as the vessel fills (preventing air binding)
• Air is admitted as it drains (preventing vacuum formation)

The result is a smoother, faster, and more efficient backwash cycle — maintaining consistent cleaning performance and extending the life of the filter media.

4. Preventing Water Hammer and Pressure Spikes

Air pockets in a pipeline or vessel can suddenly compress and expand when pumps start or stop, causing water hammer. These high-pressure surges can damage valves, fittings, and vessel internals.

By continuously venting air pockets, the combination valve helps:

• Reduce sudden pressure spikes
• Minimise stress on equipment
• Extend the lifespan of the filtration system

5. Maintaining Process Accuracy and Efficiency

Air accumulation inside a pressure vessel reduces the effective filtration area and can distort pressure readings. This can lead to:

• False differential pressure readings
• Shorter filter run times
• Inconsistent filtration performance

Continuous air release maintains accurate pressure balance and consistent filter operation.

Summary: Why Every Pressure Vessel Needs a Combination Air/Vacuum Valve

A combination air/vacuum valve is not just an accessory — it’s essential protection for your pressure filter vessel.
It ensures reliable operation, prevents costly damage, and maximises system efficiency during every fill, drain, and backwash cycle.

Proper air management is one of the simplest and most effective ways to safeguard your filtration investment.