Constant-flow valves have been presented in industrial applications or academic studies, which compensate pressures of bearing recesses as load fluctuates. The flow rate of constant-flow valves can be constant in spite of the pressure changes in recesses. However, specific condition of design parameters must be satisfied. This paper utilizes analytical method to study the static and dynamic characteristics of constant-flow valves, three types of constant-flow valve are DDE-type, DSI-type, and spool-type. The static analysis gives the specific relationships among design parameters for constant flow. The dynamic analysis gives the variations around the constant flow rate as the working pressure fluctuates.