The Model VS-SP is a vane type waterfl ow switch for use on wet sprinkler systems. These devices may be used as sectional fl ow indicators on large sprinkler systems and on smaller sprinkler systems such as mobile homes and residential dwellings. The VS-SP does not have a retard to prevent false alarms due to water surges. Therefore it should NOT be used on systems with variable water pressure supplies except in the case of elevator recall.