def METHOD_NAME(self):
    r"""
    Calculate the residual values of pressure equality equations.
    Returns
    -------
    residual : list
        Vector with residual value for pressure equality equations.
        .. math::
            0 = p_{in,1} - p_{in,i}\forall i \in \text{inlets > 1}\\
            0 = p_{in,1} - p_{out,j}\forall j \in \text{outlets}
    """
    residual = []
    inl = []
    if self.num_i > 1:
        inl = self.inl[1:]
    for c in inl + self.outl:
        residual += [self.inl[0].p.val_SI - c.p.val_SI]
    return residual