Two centrifuges at the same RPM can pull wildly different G-force — because it is bowl radius, not just speed, that sets separation. If you compare or tune decanters on RPM alone you are reading the wrong number. RCF is the one that matters.
RPM is speed; RCF is force
RPM tells you how fast the bowl turns. Relative centrifugal force (RCF, in multiples of g) tells you how hard it throws solids to the bowl wall — and that is what governs the cut point and cake dryness. Because RCF depends on radius as well as speed, a large-bowl decanter at a given RPM develops far more g than a small-bowl unit at the same RPM.
Why G-force sets the duty
Barite recovery, high-speed dewatering and drill-solids removal are all G-force decisions. Low g (roughly 500–1,200 g) recovers barite and returns it to the mud; high g (2,000 g and up) chases fine drill solids and dewaters. Set the machine by the g it needs to make, then find the RPM that delivers it — not the other way round.
The equation
Relative centrifugal force from bowl speed and radius:
RCF (× g) = 1.118 × 10−5 × r × N²
r = bowl radius in cm (= bowl diameter ÷ 2); N = bowl speed in RPM. For radius in inches, use the constant 2.84 × 10−5 instead.
Never compare two decanters on RPM. A 14-inch bowl at 3,200 RPM and a 22-inch bowl at 3,200 RPM are different machines by nearly a factor of two in g. Set the target RCF for the duty (barite recovery vs dewatering), then solve for the RPM your bowl needs.
Common questions
Should I set my centrifuge by RPM or G-force?
By G-force. RCF is what determines the cut point, so decide the g the duty requires, then use the formula to find the RPM that delivers it on your specific bowl diameter.
Why does doubling the speed more than double the force?
Because RCF is proportional to the square of RPM. Doubling the bowl speed multiplies the G-force by four, which is why small speed changes have an outsized effect on separation and on bearing load.
