Compliant joints have significant advantages compared to rigid-body hinges due to a monolithic design and the absence of friction, which prevents effects like wear, backlash and stick-slip behaviour. However, the loading capability is often limited and the support stiffness generally decreases during rotation, caused by the use of solid leaf flexures. Previously, a new design principle called closed form pressure balancing was introduced, which uses an incompressible fluid as the main compliant element in the joint. Although it showed great potential in terms of stiffness performance, theoretically not much is known about this design principle. This thesis analyses the fundamental working principle of closed form pressure balancing and introduces a design model to analyse the characteristic behaviour and to provide a practical design tool. This design model has been validated with a finite element method model, which shows a quantitative agreement. Additionally, a solution for the limited shear stiffness characteristic for pressure balanced joints is proposed. The potential of this solution is shown with the use of a case study on the design of compliant piston-slipper mechanisms, for which a prototype has been designed, built and tested.