  We present high-pressure electrical transport measurements on the newly
discovered V-based superconductors $A$V$_3$Sb$_5$ ($A$ = Rb and K), which have
an ideal Kagome lattice of vanadium. Two superconducting domes under pressure
are observed in both compounds, as previously observed in their sister compound
CsV$_3$Sb$_5$. For RbV$_3$Sb$_5$, the $T_c$ increases from 0.93 K at ambient
pressure to the maximum of 4.15 K at 0.38 GPa in the first dome. The second
superconducting dome has the highest $T_c$ of 1.57 K at 28.8 GPa. KV$_3$Sb$_5$
displays a similar double-dome phase diagram, however, its two maximum $T_c$s
are lower, and the $T_c$ drops faster in the second dome than RbV$_3$Sb$_5$. An
integrated temperature-pressure phase diagram of $A$V$_3$Sb$_5$ ($A$ = Cs, Rb
and K) is constructed, showing that the ionic radius of the intercalated
alkali-metal atoms has a significant effect. Our work demonstrates that
double-dome superconductivity under pressure is a common feature of these
V-based Kagome metals.
