Pressure Balanced Expansion Joints
By Joanna Robinson
We’ve just designed and built this unit for a customer in South America. It's not the first FlexEJ's made of this type but the engineering is a little more unusual than many metal expansion joints commonly in use.
This is a typical metal expansion joint design where the piping loads must be minimised - at connections to rotating equipment for example.
In this 32”NB example there are two bellows in the flow section – on the right in the picture - these allow both lateral and axial movement.
The balance bellows section (on the left side) is sized to produce an equal and opposite pressure force to that generated by the flow bellows, so under pressure the tie rods are in tension.
Eliminating pressure force using a balance bellows does however increase the spring rate of the system as all the bellows must move with the piping. If you take a close look at the picture you will see more convolutions in the balance bellows section as this single balance bellows must move the same amount as the two flow bellows.