How to Use a Selection Table for Variable Springs

READING A SELECTION TABLE FOR VARIABLE SPRINGS

  • To choose the correct size of a spring, identify the actual size of load to be supported (pipe weight, insulation or ancillary parts) and the direction of pipe displacement (from cold to hot position). Identify the working ranges (AG680, AG700, AG720 & AG740) and types (A, B, C, D, E, F, G, H & K) depending on the headroom allowance or direction of support.
  • Using the load table, find the actual load of the pipe (in this case, in Kilograms). Normally, this is the hot load. 
  • If the cold load value lies outside the working range of the variable spring hanger, move the actual load to the adjacent column and identify the cold load capacity of the hanger. If the hot and cold loads are within the working range of the hanger, then the hanger size is the one found at the top of the column.
  • If it is impossible to choose a hanger in a specific series such that the cold and hot loads lie within its working range, opt for a series with a wider working range.
    • Note that for cold loads, the spring scale is read up or down (depending on the direction of movement). The chart is read in the opposite direction to pipe movement. The final magnitude represents the spring’s cold load capacity.

    Practical Example

    A pipe has a hot load of 636 Kg with pipe movement limited to 20mm (from cold to hot load) and a maximum variability of 25%. Which hanger is appropriate for this piping system?6

    CLICK TO ENLARGE

    1.   The actual load 636Kg lies within the size 10 variable spring support on the table above.
    2.   The next step is to confirm the variability.
    3.   From the AG680 working range, the lowest spring rate is 9.2 Kg/mm
    4.   Variability (%) = Movement X Spring rate / Hot Load X 100
    20 * 9.2 / 636 * 100 = 29.3%
    Which means the variability is beyond the allowable limit of 25%
    5.   The next working range on the table is the AG700, and the spring rate is 4.6Kg/mm
    Variability = 14.5%, which lies within the acceptable limit. Therefore, the right variable spring support size is AG700, size 10.
    6.   The cold load for the system will be Cold Load = 636 – 20 * 4.6= 544
    7.   The actual (hot load) is 636Kg and the cold load is 544Kg

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