  We report thermal expansion and magnetostriction of the cubic non-Kramers
system PrIr$_2$Zn$_{20}$ with a non-magnetic $\varGamma_{3}$ ground state
doublet. In previous experiments, antiferroquadrupolar order at
\hbox{$T_{\mathrm{Q}}=0.11$\,K} and a Fermi liquid state around
$B_{\mathrm{c}}\approx5$\,T for \hbox{$\boldsymbol{B}\parallel[001]$},
indicative of possible ferrohastatic order, were discovered. For magnetic
fields \hbox{$\boldsymbol{B}\parallel[001]$}, the low temperature longitudinal
and transverse thermal expansion and magnetostriction are highly anisotropic.
The resulting volume strain is very small, indicating that the Pr valence
remains nearly constant as a function of magnetic field. We conclude that the
Fermi liquid state around $B_{\mathrm{c}}$ forms through a very little change
in c-f hybridization. This result is in sharp contrast to Ce- and Yb-based
Kramers Kondo lattices which show significantly larger volume strains due to
the high sensitivity of the Kondo temperature to hydrostatic pressure.
