Process tool
Coating dispersion vessel and impeller sizing calculator
Vessel volume, diameter and impeller size for the dispersion quantity you are making.
- Runs in the browserNothing is submitted anywhere
- Working shownCheck every line by hand
- Plant figuresThe bands our grades run in
- Free, no sign-inNo account, no email
Written by the Rglax Pharma technical team, who formulate and manufacture every grade named on this calculator at our WHO-GMP works in Tahliwal, Una (drug manufacturing licence NNZ/23/238). Reviewed 3 September 2026. Licences and certificates.
Result
Minimum vessel
12.3 L
Includes 25% freeboard
- Liquid volume
- 9.8 L
- Vessel diameter
- 250 mmAt a height to diameter ratio of 1
- Liquid height
- 200 mm
- Impeller diameter
- 83 mmOne third of vessel diameter
- Impeller clearance
- 67 mmOff the base, one third of liquid height
How this was worked out
- liquid volume = 10.3 kg ÷ 1.05 = 9.8 L
- vessel = 9.8 L × (1 + 25 ÷ 100) = 12.3 L
- diameter = ∛(4 × 0.0123 m³ ÷ π) = 250 mm
Formula
vessel volume = liquid volume × (1 + freeboard ÷ 100) D = ∛(4V ÷ π) at H/D = 1 impeller ≈ D ÷ 3, clearance ≈ liquid height ÷ 3
Why this number matters
A dispersion mixed in the wrong vessel never disperses properly. Too wide and the impeller cannot move the whole volume, so pigment settles at the wall. Too narrow and you draw a vortex that pulls air in, which reads as spitting at the gun and spray marks on the tablet. The one third rules for impeller size and clearance are the standard starting geometry.
Where it goes wrong
Freeboard is not optional. A ready-mix powder entrains air as it wets out and the level rises before it falls, so a vessel filled to the brim will foam over on the first minute of mixing.
Worked example
With dispersion weight of 10.3 kg, dispersion density of 1.05 kg/L and freeboard of 25 %, the calculation gives:
- Liquid volume
- 9.8 L
- Minimum vesselIncludes 25% freeboard
- 12.3 L
- Vessel diameterAt a height to diameter ratio of 1
- 250 mm
- Liquid height
- 200 mm
- Impeller diameterOne third of vessel diameter
- 83 mm
- Impeller clearanceOff the base, one third of liquid height
- 67 mm
The arithmetic is 3 lines, shown beside the result above so it can be checked by hand: vessel volume = liquid volume × (1 + freeboard ÷ 100); D = ∛(4V ÷ π) at H/D = 1; impeller ≈ D ÷ 3, clearance ≈ liquid height ÷ 3.
Typical ranges
- Dispersion weight(kg)From the dispersion calculator
- Dispersion density(kg/L)About 1.05 for a 15% aqueous dispersion
- Freeboard(%)Headroom above the liquid, 20 to 30%
These are the bands our grades were developed in at Tahliwal. A run outside them is not wrong, but it is a run the published parameters no longer describe.
Other calculators
- Coating weight gainHow much dry coating material a batch needs at a target percentage weight gain, including process loss.
- Coating dispersionWater or solvent needed to disperse a ready-mix powder at a given solids concentration.
- Spray rateSpray rate per gun and total run time from your dispersion quantity and available process window.
- Pan speedTangential bed velocity from pan diameter and RPM, with the range most film coating runs sit in.
- Drying capacityHow much water your inlet air can actually carry away, and the spray rate that supports.
- Surface area and build-upSurface area per tablet and coating build-up in mg per square centimetre, which is how enteric coats are specified.
Every grade page carries the process parameters it was developed on, so you can start from a known point rather than a calculated one. Browse the grades.
Read next
- Film coating systemVessel geometry decides whether a dispersion is uniform when it reaches the gun.
- Aqueous gradesWater dispersed grades are the ones this vessel sizing is for.
- Tablet coating weight gain calculatorHow much dry coating material a batch needs at a target percentage weight gain, including process loss.
- Coating dispersion and solids calculatorWater or solvent needed to disperse a ready-mix powder at a given solids concentration.
- Coating spray rate calculatorSpray rate per gun and total run time from your dispersion quantity and available process window.
- Coating defects, and what causes themWhat the bed looks like when this number is wrong, and which parameter to move.
Need a second opinion
Talk to our technical team.
Send the core, the coater and the target and we will tell you what we would run, and which grade we would run it with.
From the calculation to the pan.