Variable supports are used for piping subject to vertical movement where some change in the supporting effort with change of pipe position is acceptable.
Characteristically, a variable support gives a supporting force which varies with the deflection of the support spring.
Variable supports are recommended for general use on non-critical piping systems or in critical systems where vertical movement is of small magnitude, typically up to 50mm. Accepted practice is to limit the amount of supporting force variation to 25% of the hot load for critical system applications.