When thermal movements are substantial, the pipe may lift off the support if the thermal movement is upwards or the pipe may be subject to large expansion stresses if the thermal movement is downwards and the support does not allow vertical downward movement of pipe. Flexible or resilient supports allow movement of piping while still providing support to the pipe. Thus flexible supports can be defined as pipe supports that provide supporting force throughout the expansion and contraction cycle of the piping system. Spring supports are examples of flexible or resilient supports. Flexible supports are necessary when the pipe needs to be supported and at the same time permitted to move in the vertical direction. In general, when the permitted vertical movement is low to medium and the variation between hot load and cold load is less than 25%, variable spring supports are recommended to be used. When the permitted vertical movement is large, constant spring supports are recommended to be used. There are other factors which will determine the type of spring supports to be used which are beyond the scope of this article.
In a variable spring support, the load imposed by the spring on the pipe varies with the pipe deflection and the magnitude of the load variation depends on the spring rate (or spring constant) of the support. The load variation is the product of spring constant and pipe thermal movement. If a low variation in load is required such as on pump piping supports, it is desirable to choose a spring support with a low spring constant. In a constant type spring support, the load imposed by the spring on the pipe remains constant throughout the range of thermal movement of the pipe. Constant spring supports are used when the pipe deflection is large (above 50-75mm) and may be used near strain sensitive equipments such as pumps and turbines. The choice of using a variable or constant spring support will be based on the results of piping stress analysis.