Hi DA72
if you are talking about devices to stop pump impellers rotating in reverse (backspinning) under reverse flow conditions, they have several uses.
First they eliminate the possibility of trying to start a backspinning pump if, for example, a check valve has failed.
Second, they can prevent backspin overspeeding and the impeller exploding. This could happen with staged pumps feeding a pressure vessel such as a boiler, if the next to final stage pump blew out.
Third, they can prevent damage to unidirectional mechanical seals.
In the majority of cases they are not necessary as very few pumps will hit overspeed under reverse flow, unless the specific speed is very high.
There are probably a few cases I have overlooked.
Cant think of any reasons not to fit an anti runback device other than cost, and something else to go wrong.
