I have a high temp. system, 1200 deg F which is not a power plant. My Caesar run is showing most of the springs being sized as constant supports however I really need variable springs for this project. By inputting operating load and stiffness I'm able to change some of the constant springs to variables with less than 25% variability. However this is a trial an error method. Is there an easier way to convert constants to variables?

Change the criteria on the hanger dialogs that govern the decision to use constants instead of variables. There are a number of items here, so I can't be specific (check travel, extended range, etc).

At times, a system that is rather flexibile in the vertical direction shows very large vertical deflection. This large deflection will necessitate constant effort supports as spring hangers will have excessive load variation. But those constants may not be necessary.
Try this - if you have several spring selection points grouped together in your system, test what happens when you make the center spring support a rigid hanger. If the system is vertically flexible that hanger will not develop a large operating (thermal) load, and the vertical deflections nearby will be reduced allowing springs to be selected.
I'm not saying this is going to work for you but it may explain what's going on here.
Remember - CAESAR II can select springs from a catalog but you may be able to do a better job.

Hi mul211
This is general rule,
1)avoid any spring if possible,
2)use variable spring than constant spring

When variable spring is really required, it has to be, project specification can not dictate not to use variable spring.

However some trick can be use to avoid costly constant spring
1)Relocate spring support location (point where vertical movement little less)
2)Select spring manually by installed load & stiffness.
3)check vendor catalogue & try selecting less stiffness spring ( than Caesar selected) for same load.

If you wish for manual selection spring, Caesar will not cross check that, ensure load range, stiffness, load variation are within acceptable limit.

Regards

Habib

mul211,

Most of the times when a constant spring has been sized for the support point, I had failed to provide adequate vertical space for a Figure 98 double stack spring. The required travel fit the capability of the Figure 98, but the selection could not be made due to the 'specified' space available. Height of Figure 98 springs can be more than 40 inches. The default selection is then the Constant effort figure spring. A user could specify available space to be 50 or even 100 inches, to avoid unnecessary selection of the constant type spring.

Only if the required travel exceeds 4 inches should a constant spring need to be used for that extreme travel.

Your system with 1200 deg F might require some re-routing to take the vertical runs in smaller steps, instead of having large vertical risers with vertical expansion greater than 4 inches in each riser step.