When the variabilityof a variable springexceeds the MSS standard of 25%, the designer's first option would be to lowerthe spring rate so that the difference in load with the same amount of movementwould be smaller than that associated with the higher spring rate. The designerwould continue this exercise until a variability factor of less than 25% isachieved.
A spring support jacking bolt is a variable spring accessory that aids inremoving the upper limit travel stops. They are usually used in applicationswhere large installed loads are present. They are located directly above theupper travel stop. By tightening the jacking bolt, the installed load can bemore easily transferred to the spring load column.
F-Type Variable with Jacking Bolts
For variable springs there are 23 sizes with loads ranging from 50 lb. through 50,000 lb. For constant springs, there are 110 sizes with travel ranging from 1″ to 14″ and loads ranging from 0 lb. to 90,000 lb.
PTP-8 Type C Variable Spring Assemblies
Figure 100 C-Type Constant Springs
PTP 100-C Size 84 Constant
To check the load setting, examine the position of the bottom of the load indicator with respect to the scale on the spring's tag. Read from the bottom of the load indicator to determine position. Next, look at the size of the spring located on the tag. Then, refer to the appropriate load and travel table (Constant Load & Travel Table or Variable Load and Travel Table) to determine the respective spring rate and the “0” load (minimum working range load). Multiply the spring rate by the position value and add that to the “0” load value.