You have a 10,000-liter tank that needs to be uniform — same pH top to bottom, same additive concentration, no stratified layer of settled product. The pump you have moves 2,000 L/h. On paper that pump would take five hours just to pass the whole volume once, and in practice it would never catch the corners. The instinct is to buy a bigger pump or a mechanical agitator. Before you do, understand the device that already solves this: the eductor. This guide answers what is an eductor in operating terms, and shows why a small pump plus an eductor often outperforms a large pump alone.
So What Is an Eductor, Exactly?
An eductor (also called an ejector or jet mixer) is a static mixing device with no moving parts. Liquid — called the motive flow — enters through a converging nozzle at pressure and high velocity. That fast jet passes through a narrow throat and into a diverging section. Because the jet is moving quickly and the cross-section opens up, it creates a local low-pressure zone, the same Venturi effect a carburetor uses. That low pressure draws surrounding tank liquid in through side ports. The two streams then leave the eductor together and discharge into the tank.
Nothing rotates. There is no impeller to shear product, no seal to leak, no motor on the tank. The eductor is, in effect, a specially shaped nozzle that turns pressure energy from a small motive stream into bulk movement of a much larger volume of liquid.
The Momentum Trick That Does the Real Work
The reason an eductor punches above its pump size is momentum, not magic. A jet of liquid carries momentum. As it shoots through the tank it drags the surrounding fluid along with it by sheer entrainment — the fast core pulls slower liquid into its wake. An eductor is engineered so this entrainment is concentrated and directed: the side ports feed the surrounding liquid right into the jet, and the diverging section converts the jet’s velocity back into pressure so the mixed stream pushes deep into the tank instead of stalling at the nozzle.
The standard rule of thumb is that a submerged eductor installation circulates several times its own pumped volume. A pump moving 2,000 L/h through a well-placed eductor can turn over a 10,000-liter tank in well under an hour, because the eductor is moving 2,000 L/h of motive flow plus the tank liquid it entrains. The pump only has to supply the motive stream; the eductor supplies the muscle.
Why a Small Pump Is Suddenly Enough
In a conventional loop, the pump has to physically move every liter you want mixed, and it has to overcome the friction of pushing that volume through pipe and back. In an eductor loop, the pump’s job shrinks to two things: deliver the motive flow at adequate pressure, and feed the eductor. The bulk circulation is done by entrainment.
That changes the economics. A modest transfer pump you already own becomes the motive source. You add one or a few eductors on drops or on a recirculation line, and you get tank-wide mixing without upsizing the pump or hanging a gearbox over the tank. For blending additives, equalizing temperature, or pulling a stratified layer into solution, the eductor loop is usually cheaper to install and far cheaper to maintain than a mechanical agitator.
Where Eductors Earn Their Place
- Tank blending and additive dosing — inject a concentrate and let the eductor distribute it through the whole volume instead of pooling at the inlet.
- pH and chemistry equalization — pull reagent into circulation so the tank does not develop acid or alkali pockets.
- Dilution and dissolution — keep solids in suspension while they go into solution rather than settling under the inlet.
- Heat equalization — if one zone runs hot, an eductor loop pulls that heat through the tank instead of letting it stratify.
- Hazardous or sealed tanks — no shaft penetration, no seal to fail, which matters for flammable or toxic services.
The eductor is a circulation tool. It is not a replacement for a high-shear mixer when you need to actually break a material apart — it will not mill, emulsify to a fixed droplet size, or disintegrate a lump. It moves and blends what is already fluid.
Placing the Eductor Beats Specifying It
The single biggest performance factor is submergence and position. An eductor has to run submerged, with enough liquid above it that the suction ports draw tank liquid rather than air. Mount it too high and it pulls a vortex and loses entrainment. Aim the discharge along the tank floor or across the long axis so the induced flow sweeps the whole volume; a loop of two or three eductors on a header will clear corners a single unit cannot reach.
Pressure matters too. The motive flow needs enough pressure at the eductor to form a coherent jet — most eductors are sized for a specific motive pressure window, and dropping below it collapses the suction. Size from the pump curve at the eductor, not at the pump, because the run to the tank costs head.
Sizing the Motive Flow You Actually Need
The number to start from is not the tank volume but the turnover you need per hour. Decide how many tank volumes you want to move each hour through entrainment, then back out the motive flow the eductor needs to deliver that. Because a submerged eductor typically circulates several times its motive volume, a modest motive flow already turns the tank several times over — but only if the eductor is the right size for the pressure your pump actually delivers at the tank.
Two errors dominate bad eductor specs. The first is sizing from pump nameplate pressure instead of the pressure at the eductor after line losses; the suction collapses and entrainment falls. The second is under-submerging the body so it pulls air instead of tank liquid. Confirm both before you buy, and the small pump you own will do the work of a far larger one.
Eductors and Nozzles Are Different Jobs
It is easy to conflate an eductor with a spray nozzle because both are nozzle-shaped and both use a jet. They are not the same duty. An eductor is for moving and blending liquid inside a tank. A spray nozzle is for putting liquid onto a surface or into a gas — quenching, scrubbing, cooling, coating. Spiral nozzles and spiral spray nozzles are the open-path spray types that keep flowing in dirty recirculated water, and they belong on the spray side of the system, not in the mixing loop. If your project needs both — circulate the tank and then spray it — the spiral nozzle range covers the spray duty while the eductors handle circulation, and the two are specified independently.
The Trade-Off to Accept
An eductor is not free energy. Entraining tank liquid costs pressure — the diverging section that recovers velocity into pressure is not perfectly efficient, and you lose some motive head to the suction and mixing. That is the price of moving several times the pumped volume. For most blending and equalization duties the trade is wildly favorable, but if your pump is already marginal on head, size the eductor for the pressure you actually have, not the pressure on the nameplate.
If you are weighing an eductor loop against a bigger pump or an agitator, send us the tank volume, the pump you have, and the duty — blend, dilute, equalize or suspend. The engineering desk will size motive flow and submergence so the small pump you own does the job of a large one.