Entrained gas is one of the quietest causes of pump failure on a process plant. A centrifugal pump moving a liquid that carries even a few percent of gas can lose prime, run noisy, and stop delivering flow — a condition called gas-binding or vapor lock. A diaphragm metering pump dosing a fluid that off-gasses, such as sodium hypochlorite, collects gas in the pump head and keeps stroking while delivering nothing. These are not rare edge cases. They show up in disinfection dosing, reactor circulation, solvent transfer near boiling point, and any tank that is filling, draining, or venting. This page covers how Aulank pumps handle gas-entrained and off-gassing fluids, and which pump architecture fits which condition.
Why Entrained Gas Defeats Standard Pumps
Gas reaches the pump in several ways, and the source matters less than the effect. Common origins on a process plant:
● Off-gassing chemistry — sodium hypochlorite decomposes and releases gas; reactions evolve CO₂, hydrogen, or other gases during synthesis.
● Fluids near their boiling point — volatile solvents and hot condensate flash to vapour as pressure drops at the pump suction.
● Tank filling, draining, and venting — air is drawn in as levels change and lines empty.
● Suction-side air ingress — loose fittings, low liquid level, and vortex formation at the inlet pull gas into the stream.
The two failure modes that follow are well known. A centrifugal pump relies on the liquid’s density to generate head; when gas collects at the impeller eye, the pump cannot develop pressure and vapor-locks, losing flow entirely. A reciprocating diaphragm metering pump compresses and expands the trapped gas bubble through its whole stroke instead of moving liquid, so it keeps running but stops dosing — the gas-binding that plagues hypochlorite chlorination systems. Both leave the process starved of flow with the pump apparently still operating.
The Aulank Approach: Gas-Tolerant Regenerative Vortex Hydraulics
Aulank’s magnetic vortex pumps use regenerative-turbine (peripheral) hydraulics. A multi-vaned impeller circulates the fluid repeatedly through a peripheral channel, and the high-velocity vane action breaks entrained gas bubbles up and carries them through with the liquid instead of letting them collect. The practical result is a pump that keeps its prime and keeps delivering flow with gas in the stream — regenerative-turbine pumps handle a high fraction of entrained gas, on the order of 10–20%, where a standard centrifugal pump vapor-locks. The same design tolerates liquids at or near their boiling point, which is exactly the condition that causes cavitation and vapor lock in other pump types.
Combined with Aulank’s sealless magnetic-drive structure, this gives a pump that is both gas-tolerant and leak-free — the right combination for the volatile, corrosive, and toxic fluids that tend to off-gas in the first place. The regenerative-turbine principle is covered in detail in our industrial vortex pump selection guide, and the sealless containment logic in our industrial magnetic drive pump selection guide.
Pump Types and Working Principles
Magnetic Vortex Pump (Regenerative Turbine, Sealless)
A magnetic coupling drives a peripheral-vane impeller through a sealed containment shell. The regenerative-turbine action handles entrained gas, delivers high head at low-to-moderate flow, and the sealless structure removes the shaft-seal leak path. This is the primary architecture for gas-entrained corrosive and volatile fluids. Aulank’s MDH, MDS, and MDK stainless magnetic vortex pumps cover this duty in 316L; the AMC-F PTFE-lined magnetic drive pump covers it for aggressive and off-gassing chemistry like sodium hypochlorite.
Canned-Motor Vortex Pump
The rotor runs inside a sealed can integrated with the wetted end, removing even the magnet-gap space of a mag-drive unit. For continuous service on volatile or off-gassing fluids where the tightest containment is wanted, the PWH/PWD/PWM canned vortex pump series applies the same gas-tolerant regenerative hydraulics in a canned-motor structure. The three structural approaches are compared in our canned motor pump technology guide.
Stainless Magnetic Vortex Pump for Solvent Service
For volatile solvent transfer within stainless compatibility, the MDW stainless steel vortex magnetic pump handles near-boiling-point solvents with explosion-proof motor options for flammable-zone service.
Where Gas-Tolerant Pumping Solves a Real Problem
The conditions that produce entrained gas recur across many processes. The duties where a gas-tolerant sealless pump earns its place:
● Sodium hypochlorite disinfection dosing. Hypochlorite off-gasses and gas-binds conventional diaphragm metering pumps, stopping dosing while the pump still runs. A gas-tolerant vortex pump keeps delivering through the off-gassing, removing the most common chlorination-system failure.
● Reactor circulation with gas evolution. Synthesis reactions evolve CO₂, hydrogen, or other gases. A circulation pump that tolerates entrained gas keeps the loop moving without cavitating against the gas pockets.
● Volatile solvent and near-boiling-point transfer. Solvents close to their boiling point flash to vapour at the pump suction. Regenerative-turbine hydraulics handle this where centrifugal pumps cavitate.
● Tank emptying and drum drain-down. As a tank or drum empties, the pump draws in air. A gas-tolerant pump recovers prime instead of stalling, avoiding the manual bleed a non-self-priming pump needs.
● Condensate and flash-steam duties. Hot condensate flashes at the suction; gas-tolerant hydraulics keep the pump delivering.
Matching the Pump to the Gas Condition
The table maps common gas-entrained conditions to a recommended Aulank configuration. These are starting points; the actual fluid, gas fraction, temperature, and flow always need validating against the real process:
| Condition | Fluid example | Key requirement | Recommended pump |
| Off-gassing oxidizer dosing | Sodium hypochlorite | Gas tolerance + inert lining | AMC-F PTFE-lined magnetic vortex |
| Gas-evolving reactor circulation | Synthesis intermediates | Gas tolerance + corrosion resistance | AMC-F or MDH/MDS magnetic vortex |
| Near-boiling-point solvent | Volatile organic solvent | Vapor-lock resistance, flammable zone | MDW with explosion-proof motor |
| Continuous volatile transfer | Recovered solvent, condensate | Tightest containment | PWH/PWD/PWM canned vortex |
| Tank emptying / drum drain | General process fluid | Self-priming recovery | MDH/MDK magnetic vortex |
| Clean high-head, low-flow with gas | Process water, condensate | High head, gas tolerance | MDH/MDS magnetic vortex |
Key Selection Considerations
● Estimate the gas fraction. A few percent of entrained gas already troubles a centrifugal pump; regenerative-turbine vortex hydraulics handle far more, but the expected gas fraction should still be stated so the pump is sized with margin. Continuous high gas fractions may also call for suction-side design changes.
● Separate gas tolerance from dry-running. Handling entrained gas is not the same as running fully dry. Silicon-carbide bearings tolerate short dry-running during priming and drain-down, but sustained dry operation still needs protection. Define the worst-case dry-run time at selection.
● Match wetted material to the fluid. Off-gassing fluids are often corrosive — hypochlorite, acids, volatile solvents. The gas tolerance has to come with the right wetted material: 316L within compatibility, fluoropolymer lining for aggressive chemistry. The framework is on our corrosion-resistant pump solutions page.
● Confirm containment level. Volatile and toxic off-gassing fluids should be contained. Sealless magnetic-drive and canned-motor pumps remove the seal-leak path; the leak-control logic is on our leak-proof pump solutions page.
● Address the suction side. Gas tolerance at the pump does not excuse poor inlet design. Adequate liquid level, correct pipe sizing, and vortex-breaking at the inlet reduce the gas the pump has to handle in the first place.
Get a Gas-Tolerant Pump Configuration for Your Process
Whether you are dosing off-gassing hypochlorite, circulating a gas-evolving reactor, transferring volatile solvent near its boiling point, or emptying tanks and drums, our engineering team can match the right sealless magnetic vortex or canned-motor pump to your gas-entrained condition. Send us your fluid, estimated gas fraction, temperature, flow, and containment requirement and we will return a recommended configuration with material specifications and quotes within two business days.
Talk to our team: Contact Aulank | WhatsApp: +86 13773157367 | Email: info@aulankpump.com
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