Tap Density Tester
Taps a graduated cylinder of powder a set number of times from a fixed height so the bed packs down. The starting and final volumes give bulk density, tapped density, Carr's index and Hausner ratio.
- Pharmaceutical
- Nutraceutical
- Chemicals
- Food & beverage
- Powder metallurgy
How Tap density tester works
Repeated mechanical tapping rearranges particles and removes air spaces, so the bed volume falls to a near-constant tapped volume. Density is mass divided by volume, and the change between bulk and tapped volume reflects inter-particle friction and cohesion.
The path of a sample
- 01
Sieve and weigh
The powder is passed through a sieve to break up lumps and an accurately weighed amount is taken.
- 02
Fill
The powder is poured gently into a dry graduated cylinder without compacting it.
- 03
Read V0
The unsettled (bulk) volume is read to the nearest graduation.
- 04
Tap
The tester drops the cylinder a fixed height a set number of times.
- 05
Read Vf
Volumes are read after set tap counts until the change is within the limit; the final reading is the tapped volume.
- 06
Calculate
Bulk density, tapped density, Carr's index and Hausner ratio are calculated.
Main parts and what they do
Graduated cylinder
Typically 250 mL, readable to 2 mL, of stated mass; 100 mL cylinders are used for small samples.
Cylinder holder and anvil
Holds the cylinder and lets it fall onto a fixed base.
Cam drive
Lifts and releases the cylinder to give a fixed drop height at a set rate.
Tap counter / controller
Sets and counts the number of taps and stops automatically.
Sieve
Breaks up agglomerates before filling (often about 1 mm aperture).
Terms every analyst should know
Bulk density
Mass ÷ untapped volume (g/mL). Includes the air spaces between particles.
Tapped density
Mass ÷ final tapped volume (g/mL). Always equal to or higher than bulk density.
Carr's index (compressibility index)
100 × (V0 − Vf) ÷ V0. Higher values mean poorer flow.
Hausner ratio
V0 ÷ Vf. Values close to 1 mean good flow.
Drop height and tap rate
Fixed by the pharmacopoeial method; changing them changes how fast and how far the powder settles.
Keep every Tap density tester in control: usage logs, calibration and maintenance schedules, and automatic blocking of overdue instruments.