Air-Induced Efficiency Loss in Industrial Processes

How to find air-induced efficiency loss in industrial processes

Your fluid line is losing throughput or responding poorly, but routine checks have found no clear restriction or equipment fault. This guide explains how air-induced efficiency loss in industrial processes develops, how entrained bubbles differ from dissolved air and how fluid compressibility can quantify the problem. It also shows what to inspect around pumps, suction piping, tanks and sampling points before choosing corrective action.

Recognizing air-induced efficiency loss in the line

Air can consume useful pump volume before it becomes obvious at the surface. A centrifugal pump may continue running while delivering less fluid. In a hydraulic system, compressed bubbles absorb energy that should move an actuator, producing slow response, unstable motion or cycle times that change with load and temperature.

At PAPEC, we treat these symptoms as possible aeration signals rather than assuming the pump is undersized. Entrained air reduces pump capacity and changes fluid elasticity, affecting pressure control, actuator timing and repeatability. Bubble collapse in a high-pressure zone can also produce cavitation and erosive wear.

Watch for performance that changes after startup, during a production-rate increase, after recirculation or when the reservoir level falls. Noise and pressure pulsation may accompany lower delivery. In pulp, paper and coating operations, aeration may also coincide with pinholes, streaks or poor adhesion. These signs do not prove that air is the cause, but they identify conditions worth measuring.

Record symptoms against flow, pressure, temperature, tank level and production rate. A fault that appears only under high flow can point toward suction restriction or turbulence, while a fault following a pressure drop can indicate dissolved air leaving solution. This operating context makes an air measurement more useful than an isolated sample.

Entrained bubbles, dissolved air and cavitation

Entrained air consists of bubbles dispersed through the liquid. Because those bubbles are compressible, part of each pump stroke or pressure change compresses gas instead of moving liquid. The mixture becomes less stiff, pump delivery falls and control response becomes less predictable.

Dissolved air consists of gas molecules distributed among the liquid molecules. Its effect remains comparatively small while it stays dissolved. According to TECHNIA, gas leaves solution when fluid pressure drops below its gas-saturation pressure. It then forms entrained bubbles that can affect pump and system performance.

Likely low-pressure locations include pump inlets, restrictions, throttled valves and the downstream side of an orifice. Fluid can therefore look acceptable in a reservoir yet form bubbles as it moves through the process. The gas did not necessarily enter through an external leak; it may already have been dissolved in the fluid.

Aeration must also be distinguished from vaporous cavitation. Aeration involves gas entering the liquid or leaving solution, while vaporous cavitation occurs when pressure falls below the liquid’s vapor pressure. Both can create collapsing cavities and surface damage, but their corrective actions differ. Increasing suction head may address a vapor-pressure problem, but it will not identify an atmospheric leak, poor return-line arrangement or high dissolved-air load.

Interpret any reported air content with the fluid’s pressure history. Gas compresses as pressure rises and expands as pressure falls, so measurements taken at different pressure references are not directly comparable.

Why compressibility measurement reveals hidden air

A clear sight glass cannot show every microbubble, and surface foam does not reveal the full gas load moving through a line. Density, optical and acoustic readings can also change with solids, ash, salts, glycol, surfactants or polymers, making air-related shifts difficult to separate from normal process variation.

PAPEC uses fluid compressibility as the most direct method for measuring entrained air, dissolved air and foam in liquids and aerosols. A known fluid volume is captured and exposed to a controlled pressure change. The volume response shows how much compressible gas is present. Fluid-sampling research from the Norwegian University of Science and Technology describes this compressibility principle for direct entrained-air measurement.

Sampling practice still matters. A restrictive valve or narrow sample line can create a pressure drop that releases dissolved gas before the sample reaches the instrument. The result can include air created by the sampling path rather than present at the process location. Preserve process conditions as far as practical, avoid unnecessary throttling and use consistent pressure references.

One measurement establishes air content at a specific place and operating state. Comparisons can show where it changes. Measure before and after pumps, restrictions, mixers, cleaners or heat-producing stages, then repeat under the conditions that produced the fault. A rise across one component or operating state narrows the investigation.

PAPEC provides purpose-built air measurement instruments for this work. The QuickAir_OC and Squeezer support manual entrained-air testing. The Squeezer DualAir measures entrained and dissolved air, while the fully automated D_GR supports real-time dissolved-air monitoring. Select the instrument according to the type of air under investigation and the speed of process variation.

From patchwork fixes to root-cause correction

Once measurement confirms an air problem, trace its mechanism instead of applying the same response to every symptom. Increasing pump speed can worsen a suction-side pressure drop. Changing chemistry will not repair a leaking seal, and installing a larger pump leaves the gas source untouched.

Check the mechanical path

• Inspect suction piping for loose joints, damaged gaskets, seal leaks and packing-gland leakage where the line operates below atmospheric pressure.
• Check for clogged strainers, undersized suction piping, partially closed valves and abrupt fittings near the pump inlet.
• Confirm that the pump casing is vented correctly and inspect the impeller, wear components and direction of rotation.
• Examine tank returns for splashing, vortex formation and discharge directed toward the suction inlet. Compare performance at normal and minimum operating levels.

Do not diagnose every noisy, low-flow pump as an air problem. Empowering Pumps & Equipment recommends ruling out causes such as insufficient available suction head, worn clearances, clogged or eroded impellers, reverse rotation, throttled suction valves and excessive system head.

Match monitoring to the process

Manual measurements suit point checks, comparisons between locations and intermittent troubleshooting. Continuous monitoring is more useful when air content changes quickly with production rate, tank level, temperature or control actions. Put the measurement where it answers a specific question: whether air enters at the suction, forms across a restriction or remains after a removal device.

After corrective work, establish a stable baseline and compare it with pump delivery, actuator response and product quality. Repeat the measurement under the conditions that originally produced the fault to determine whether the intervention removed the air mechanism rather than temporarily hiding its symptom.

PAPEC brings more than 40 years of specialized experience to entrained-air and dissolved-air measurement and control. Our technical consulting covers pump performance, coolant and cutting-fluid systems, pulp processing, digesters, brownstock washing, screening and cleaning. Combining process knowledge with suitable instrumentation focuses corrective work on the locations creating or releasing air.

Discuss your fluid-line problem with PAPEC

If unexplained air may be limiting your process, use PAPEC’s contact page, call 253-335-3665 or email steve.dougherty@papec.com to discuss your operating symptoms and measurement needs with our Eagle, ID team.