Northeast Controls Inc.
ResourcesMixing
Mixing8 min read

Tank Mixing Best Practices

Proper eductor placement, nozzle count, turnover rate, and motive pressure guidelines for effective full-tank mixing — with worked examples for common tank sizes.

Tank Turnover Rate

Tank turnover rate is the number of times the tank volume is circulated per hour. It's the primary design parameter for eductor mixing systems.

Mixing ObjectiveRecommended TurnoverNotes
Temperature equalization2–4 turnovers/hrGentle mixing sufficient
Blending miscible liquids4–8 turnovers/hrDepends on density difference
Preventing stratification2–3 turnovers/hrContinuous low-level mixing
Light solid suspension6–10 turnovers/hrParticles <100 micron, SG <1.5
Chemical dosing / dilution8–12 turnovers/hrRapid homogenization needed

Eductor Placement Guidelines

Aim toward the center of the tank

Eductors should be aimed toward the center of the tank floor at a downward angle of 10–15°. This creates a bottom-to-top circulation pattern that prevents dead zones.

Mount at 1/3 tank height from the bottom

Mounting eductors at approximately 1/3 of the liquid height from the tank bottom maximizes the circulation pattern and prevents the jet from impinging on the tank floor.

Space multiple eductors evenly

For tanks requiring multiple eductors, space them evenly around the tank circumference. For 2 eductors: 180° apart. For 3: 120° apart. For 4: 90° apart.

Avoid pointing at tank walls

Eductors aimed directly at tank walls create turbulence without useful circulation. Aim toward the center or at a slight angle past center.

Worked Example: 10,000-Gallon Tank

Given

Tank volume:10,000 gallons
Tank diameter:12 ft
Liquid height:15 ft
Fluid:Water (SG = 1.0, viscosity = 1 cP)
Mixing objective:Blending — 6 turnovers/hr
Motive pressure available:30 PSIG

Solution

  1. 1. Required circulation = 10,000 gal × 6 turnovers/hr = 60,000 GPH = 1,000 GPM total flow
  2. 2. Eductor entrainment ratio at 30 PSIG motive: approximately 4:1 (4 GPM entrained per 1 GPM motive)
  3. 3. Total flow per eductor (2″ nozzle at 30 PSIG): ~200 GPM (40 GPM motive + 160 GPM entrained)
  4. 4. Number of eductors = 1,000 GPM ÷ 200 GPM = 5 eductors
  5. 5. Pump requirement: 5 × 40 GPM = 200 GPM at 30 PSIG (≈ 5–7.5 HP pump)

Motive Pressure Guidelines

Higher motive pressure increases eductor capacity and entrainment ratio, but also increases pump energy consumption. The optimum motive pressure balances mixing performance against operating cost.

15–20 PSIG

Minimum

Adequate for gentle mixing in small tanks. Low energy cost.

25–35 PSIG

Recommended

Best balance of performance and efficiency for most applications.

40–60 PSIG

High Performance

For rapid mixing, large tanks, or viscous fluids. Higher pump cost.

Need a mixing system designed for your tank?

Provide your tank dimensions, fluid properties, and mixing objective — we'll size the eductor system and provide a complete layout recommendation.

View RTM Tank Eductors
Request PricingCall