We describe new experiments in which particle-laden turbulent fountains with source Froude numbers
$20>Fr_{0}>6$
are produced when particle-laden fresh water is injected upwards into a reservoir filled with fresh water. We find that the ratio
$U$
of the particle fall speed to the characteristic speed of the fountain determines whether the flow is analogous to a single-phase fountain (
$U\ll 1$
) or becomes a fully separated flow (
$U\geqslant 1$
). In the single-phase limit, a fountain with momentum flux
$M$
and buoyancy flux
$B$
oscillates about the mean height,
$h_{m}=(1.56\pm 0.04)M^{3/4}B^{-1/2}$
, as fluid periodically cascades from the maximum height,
$h_{t}=h_{m}+{\rm\Delta}h$
, to the base of the tank. Experimental measurements of the speed
$u$
and radius
$r$
of the fountain at the mean height
$h_{m}$
, combined with the conservation of buoyancy, suggest that
$Fr(h_{m})=u(g^{\prime }r)^{-1/2}\approx 1$
. Using these values, we find that the classical scaling for the frequency of the oscillations,
${\it\omega}\sim BM^{-1}$
, is equivalent to the scaling
$u(h_{m})/r(h_{m})$
for a fountain supplied at
$z=h_{m}$
with
$Fr=1$
(Burridge & Hunt, J. Fluid Mech., vol. 728, 2013, pp. 91–119). This suggests that the oscillations are controlled in the upper part of the fountain where
$Fr\leqslant 1$
, and that they may be understood in terms of a balance between the upward supply of a growing dense particle cloud, at the height where
$Fr=1$
, and the downward flow of this cloud. In contrast, in the separated flow regime, we find that particles do not reach the height at which
$Fr=1$
: instead, they are transported to the level at which the upward speed of the fountain fluid equals their fall speed. The particles then continuously sediment while the particle-free fountain fluid continues to rise slowly above the height of particle fallout, carried by its momentum.