The Constant Volume component models fluid compressibility and contains a mixture of liquid and a small amount of non-dissolved gas, which is used in an approximate model of cavitation.

The fluid bulk modulus, $K$, and atmospheric pressure, $p_{\mathrm{atm}}$ come from a Fluid Properties record at the same or higher level in the overall model.

$E\=\{\begin{array}{cc}K& \mathrm{\alpha }\=0\\ \frac{\frac{1}{\mathrm{\alpha }}\+\frac{1}{\mathrm{\gamma }}}{\frac{1}{\mathrm{\alpha }K}\+\frac{1}{k\mathrm{\gamma }\mathrm{\beta }{p}_{\mathrm{atm}}}}& \mathrm{otherwise}\end{array}$

$V_f\=V\left(1\+\frac{p}{E}\right)$

$\mathrm{\beta }\=1\+\frac{p}{p_{\mathrm{atm}}}$

$\mathrm{\gamma }\={\mathrm{\beta }}^{\frac{1}{k}}$

$p\=p_A$

$q\=q_A\=\frac{\mathrm{d}{V}_f}{\mathrm{d}t}$