The invention relates to a pump arrangement, in particular a centrifugal pump, in particular a main coolant pump for power stations, comprising a pump housing (2), which defines an interior (3) with an inlet opening (4) for aspirating a conveying medium and with an outlet opening (5) for expelling the conveying medium and which also defines a chamber (7) that is connected to the interior (3), a seal water system (22), which has a first conduit system (29) in order to supply seal water into the chamber (7) defined by the pump housing (2), a second conduit system (32) for evacuating a controlled leakage flow from the chamber (7) defined by the pump housing (2), and a protective valve (35), which is arranged in the second conduit system (32) in order to block the leakage flow that is evacuated from the chamber (7). The invention further relates to a protective valve (35) and to the use of a protective valve (35) in a pump arrangement (1).