You searched for: “hydrostats
hydrostat (s) (noun), hydrostats (pl)
1. An electrical device designed to indicate or regulate the height of fluid in a column, reservoir, or other container: The hydrostat Jim was using was a good protection against the destruction of his building from leakage or flooding.
2. An apparatus that is used to prevent damage to a steam boiler when the water gets below a specified level: The hydrostat that Susan had on her pressure cooker gave a signal as a warning when the amount of water got too low.