Eductor Nozzles

An eductor nozzle has no moving parts, no motor and no shaft seal. A fast-moving motive jet creates a low-pressure zone that sucks in surrounding liquid and discharges the combined flow, the cheapest reliable way to keep a tank mixed or a sump pumped when a mechanical agitator is overkill or impossible to fit. If you are asking what is an eductor in buying terms: it is the device that lets a small pump circulate a large tank, because every litre of motive flow drags several more litres of tank liquid along with it.

Why an Eductor Instead of an Agitator

Inside the eductor, the motive flow accelerates through a converging nozzle, drops in pressure at the throat (Bernoulli at work), entrains the surrounding liquid, and slows through the diffuser where pressure recovers. The result is circulation: for every litre of motive flow the eductor moves two to five litres of tank contents, at the top of the band the amplification runs to 4:1 or 5:1, the ratio the industry uses for sizing.

That matters on tanks where an agitator cannot reach, tall slender vessels, tanks with manways too small for a mechanical drive, or process vessels where a shaft seal is a leak risk you do not want. Eductors are also the standard answer where a fixed pump already exists: it becomes the motive source and the agitator disappears entirely. The only penetration through the vessel wall is the motive line, which is why eductors are the default on sealed, flammable or toxic services.

Range Walkthrough

The range is graded by the motive flow the pump can deliver, because that fixes the body size and the tank volume one eductor can circulate. Three classes cover nearly every duty.

Mini eductors (motive flow up to about 12 L/min): the compact end of the range, built for plating baths, rinsing lines and small process tanks where the vessel is small but the solution must stay uniform. Mini bodies hold the same 3:1 to 5:1 induction band as their larger siblings at a fraction of the flow, and they sustain the 10–25 tank volumes per hour that surface-treatment baths need. Threaded connections at this end let them drop straight into a recirculation line or a tank wall.

Standard tank-mixing bodies: the workhorse class, and the one sized by the turnover method. A 20 m³ tank mixed at four turnovers per hour needs 80 m³/h of circulation; divide by the nominal 5:1 ratio and the motive flow comes to 16 m³/h, a modest pump duty. Bodies in this class suit tanks from a few cubic metres to tens of cubic metres, pass light solids through the flow-through chamber, and are the default for blending, pH equalization, dilution and additive dosing.

High-flow bodies and header systems: for large storage tanks, tank farms and process vessels where one body cannot move enough liquid. Multiple bodies on a single header multiply the pump’s output: one per 2–3 m of tank length, all discharge streams pointing the same way so the plumes reinforce. A 2,000 L/h motive stream through a well-fed body already circulates about 8,000 L/h, and three bodies on the same header turn a 10 m³ tank over every 25 minutes. Flanged connections at this end suit the larger pipework.

Application Matrix

Duty	Typical installation	Recommended class	Why
Tank mixing and blending	Slurries, emulsions and additive doses kept homogeneous	Standard body	Discharge plume carries concentrate across the whole volume
Plating and surface treatment	Plating and rinsing baths at 10–25 turnovers/h	Mini body (≤ 12 L/min)	Uniform solution with no rack interference
pH and chemistry equalization	Reagent pulled into circulation, no acid or alkali pockets	Standard body, aimed along the floor	Erases the dead zones where pH probes read lies
Dilution and dissolution	Solids kept in suspension while they dissolve	Standard body	Aimed discharge keeps the floor swept
Heat equalization	Hot zone pulled through the tank, no stratification	Standard body or header	Uniform temperature means honest sampling
Jet pumping and sump duty	Lifting liquid 3–6 m from a pit or sump	Body sized for the lift height	Nothing submerged but the body; no pump in the pit
Vacuum generation	Filtration, degassing and priming at 3–6 kPa abs	Liquid-driven body	No vane or oil touches the process fluid
Liquid transfer and dilution	Entraining one liquid into another inline	Standard body	Doses a concentrate without a second pump
Aeration and oxidation	Air drawn in with the liquid stream	Body with air-induction design	Aerobic treatment without a separate blower
Tank washing and cleaning circulation	Cleaning solution circulated through a vessel or sump being flushed	Standard body or header	High-velocity discharge sweeps debris and sludge toward the drain

Three-Step Selection

If the full duty sheet feels heavy, the decision collapses to three questions, in this order:

1. Pump flow at the eductor, measure the motive flow the pump actually delivers at the body, not at the discharge flange. Line losses cost head over long runs: a pump making 5 bar at the flange may present only 3 bar at an eductor 20 m of pipe away, and the induction ratio falls. The available flow picks the class, mini, standard or high-flow.

2. Amplification ratio from the pressure, with the pressure at the eductor known, read the induction ratio off the operating band: 1–2 bar gives roughly 2:1 to 3:1, 2–3 bar gives 3:1 to 4:1, and 3–4 bar gives 4:1 to 5:1. Divide the required circulation, tank volume times turnovers per hour, by that ratio to get the motive flow, then split it across bodies on a header.

3. Material, an eductor is just carefully shaped holes, so it can be made from almost any machinable material. 316L stainless is the standard for process and hygienic duty; PP and PVDF suit plating and aggressive chemicals; PTFE options cover the most corrosive services. Match the body to the liquid, its temperature and its solids content, not the other way round.

Reference Specifications

The figures below reflect the operating envelopes published across the industry for this nozzle class. They are compiled as a sizing starting point, not as a datasheet.

Parameter	Published band
Motive pressure at the eductor	0.5–4 bar (7–60 psi) typical for tank-mixing bodies
Induction ratio	2:1–3:1 at 1–2 bar; 3:1–4:1 at 2–3 bar; 4:1–5:1 at 3–4 bar
Circulation per litre pumped	3–6 L across the band; sizing default 5:1
Nozzle-to-throat area ratio	2–4: fixes the operating point on the entrainment curve
Diffuser half-angle	5–7°: too steep and flow separates, too shallow and the body gets long
Jet-pump lift	3–6 m depending on motive pressure
Vacuum generation	3–6 kPa absolute
Plume reach	Roughly 4 m per 1 bar of pressure drop across the body
Mini body inlet flow	Up to about 12 L/min

The sizing arithmetic always starts from the duty: a 20 m³ tank mixed at four turnovers per hour needs 80 m³/h of circulated flow, which the nominal 5:1 ratio converts back to 16 m³/h of motive flow. A pump delivering that at 3–4 bar at the eductor holds the 4:1 to 5:1 band and circulates the tank four times per hour.

Frequently Asked Questions

How much flow does an eductor amplify? Published figures: entrained flow is three to five times the pumped flow, and total circulation four to six times. The standard sizing default is a 5:1 ratio, divide the required circulation by five to get the motive flow.

What pressure do I need at the eductor? Most tank-mixing bodies run in the 0.5–4 bar band (about 7–60 psi). The induction ratio climbs with pressure, with diminishing returns, doubling pressure does not double entrainment. Always size from the pressure measured at the eductor after line losses, not the pump nameplate.

Can an eductor mix my tank with the pump I already have? Usually yes, if the pump delivers enough pressure at the body, most tank-mixing eductors need roughly 1–4 bar at the eductor. Send the vessel volume, the pump curve and the duty, and the motive flow falls out of the turnover calculation.

Does an eductor shear or damage the product? Much less than an agitator. The jet is intense only in a small zone near the body; the rest of the circulation is gentle drag. For shear-sensitive products an eductor loop is usually the safer choice.

Do I need an agitator instead of an eductor? Only if the duty is genuinely high shear, milling, emulsifying to a fixed droplet size, or disintegrating lumps. For blending and equalization, the eductor is cheaper to install, has no shaft seal to leak and needs maintenance measured in years.

Why is my eductor not pulling suction? Motive pressure below the minimum at the body, under-submergence pulling air instead of tank liquid, or a clogged throat. Measure the pressure at the eductor, check the liquid level above the suction ports, and clean the strainer.

How many eductors do I need? Set the target turnovers per hour, divide the required circulation by the induction ratio to get total motive flow, then split it across bodies. A common starting layout is one eductor per 2–3 m of tank length on a header, with all discharge streams pointing the same way.

What should I send with an enquiry? Vessel geometry (diameter, height and liquid depth), the pump flow and pressure available at the connection, the liquid and its temperature, whether it carries solids, and the duty, blend, dilute, equalize, pump or clean. That is enough to size the body, the ratio and the material.

Related Guidance

Our what is an eductor guide walks through the Venturi principle, the published flow-amplification figures and a worked sizing example in detail. For mixing on small tanks with a limited pump, see the eductor tank mixing guide.

Need an eductor sized for your tank? Send the vessel geometry and the pump you have available to the application team and we will spec the motive flow, the nozzle size and the material from your numbers.