Hi,

I am using a Expension bellow ( tied ) between a Anchor and Nozzle. [material is GRP]
the distance between anchor and nozzle is almost 1.8 m .


but with this tied bellow the axial forces on nozzle is quite high.
if i use untied bellow the results are almost same.

My question is what is the role of effective ID for this untied bellow in short span.
is it necesarry to give effective ID?
After removing effective ID for untied bellow , Nozzle easily meets the load.

Hi Adi,

Its not a good pracice to remove the effective ID or make it zero. I will advice you to check with the axial and lateral spring rate with standard bellow if any you have used or have a nice talk with vendor and ask them the required values.

If you can then reduce the axial and lateral spring rate (whatever causing problem) and check with vendor.

I guess that your pipe a straight run between anchor and nozzle. If you set the effective ID to zero, the pressure x area end force will also be zero, and you have laid out a clear route to disaster.

Equally a tied unit in a straight shot will not work, since any thermal expansion will defeat the effect of the tie rods. Modify your geometry.

Hi Adi
Are your nozzle & bellow are in a straight line ?

Effective Id of bellow is used to calculate pressure thrust force.

When tie rod is use , it will compensate pressure thrust load but at the same time take out axial flexibility of bellow hence you will get high axial load.

Since your nozzle will not experience full pressure thrust load ( effective area of bellow *pressure), it will only experience (effective area of bellow-internal area of pipe)*pressure load .

You can calculate nozzle load by deducting (internal area of pipe*pressure) from caesar output report for both sustain & operating case when you model untied bellow with effective ID.
Because rest of the pressure force will directly go to the pump cassine.
Before using bellow please go through EJMA.

Hi Shr,

How pratical is ur said approach.
In Which Edition and on which page this appraoch is mentioned in EJMA.
Will you please let me know ,
as i have to complete analysis in short time span.

Thanks

Hi Adi

EJMA explain about total pressure thrust, not partial as I mention.
Search this forum with "expansion bellow" you will find this concept.
I personally use this concept in our project.

I think you are working with cooling water suction line, there pressure itself will be very low so you can comfortable use untied bellow.

If pressure temperature of your line is quite high I suggest you go for another solution.

Practically speaking if your line is with cooling water service even if you use tied rubber there should not be any practical problem but you can not produce your stress report by Caesar.

In this kind of situation we check how much in piping bellow displacement without tie rod, if if it very low we draw conclusion that tied bellow in piping itself will take care of small thermal movement and finish report ignoring Caesar result on nozzle load. Because very small amount of axial movement in Caesar will create huge load.

Again yes it is very difficult to produce stress report.