Abstract: This invention relates to apparatus for minimizing the amount of fluid leaked from a component in a hydraulic power system when the component has failed.The apparatus comprises a tank for use as a reservoir for the hydraulic fluid, the tank having a first chamber for storing a main volume of the fluid and a second chamber communicating with the first chamber for storing a reference volume of the fluid. The second chamber is provided with a fluid level switch which deactivates the system power source when the quantity of fluid in the second chamber has fallen to or below a preset level as a result of its leakage from the system via a burst hose or the like. The chambers 2 and 3 are dimensioned so that for a given quantity of fluid entering or leaving the tank, fluid level fluctuation in the second chamber is greater than the corresponding fluid level fluctuation which would occur in the first chamber if the fluid were only entering or leaving the first chamber.