Spring washers can be used as a type of lock washer to eliminate rattle or vibration that might unscrew a bolt. These are common in instances where a coil spring would be impractical or too large. Disc springs are common on pipe flanges to combat flange leakage from high temperatures and varying pressure. These small devices are also found in many types of valves and pumps, braking systems, types of couplings, machine presses, aerial cable cars, boiler suspension systems, and overload protection components in electrical transformers. Not until the 1930s did the disc spring become prominent, when formulas to calculate disc springs were developed pre-World War II in the United States. As such, the spring washer was used in anti-tank mines and artillery guns.
Piezoelectric pump; M4 AT mine. Image credit:Math Works