Summary

When axial deflections exist, and anchoring is not feasible or pressure loads are too high for sensitive equipment like pumps and turbines, the in-line pressure balanced expansion joint is a efficient method to solve a design problem. The principle of unit is that the axial pressure thrust is reacted by the pressure acting on a cross sectional area equal to the area of the working bellows.

Since this unit is entirely axial, the cross-sectional area needed to balance the pressure is placed around the outside of the unit. Because the pressure forces are generated by the pressure acting on the annular surface between the primary and outer or balancing bellows, the arrangement of the tie rods transfers and balances the pressure thrust. Now the forces needed to compress or extend the unit are only the result of the spring resistance of the bellows, thus main anchoring of the pipe or vessels is not required.

This expansion joint can be used to replace pipe loops or main anchor, and its cost advantage may be seen in reduced pumping energy by the elimination of pressure drop.

Features

· Stable at high pressures
· Eliminates change in pressure
· No main anchors required
· Conserves space

Types of Movement

· Axial compression or extension
· Lateral movements

Summary

Elbow pressure balanced expansion joints are designed to not only restrain the pressure thrust but in addition, balances the pressure thrust so as not to have anchoring of the adjacent piping or equipment. This pressure balanced elbow expansion joint can be designed as single or universal depending on how much lateral movement is required.

Elbow pressure balanced expansion joints are special joints which can consist of a single or double bellows in the flow section, and a balancing bellows of equal area on the back side of the elbow. Tie rods attach the outboard end of the balancing bellows to the outboard end of the flow bellows. Under pressure the tie rods are loaded with the pressure thrust force. If the flow bellows compresses in service, the balancing bellows extends the same amount without exposing the adjacent anchors to pressure thrust forces. However, the spring forces associated with bellows movements are imposed on the adjacent equipment. A pressure balanced elbow type expansion joint can accept axial compression, axial extension, lateral movements and very limited angular motion.

Features

· Absorbs axial and lateral movements
· Eliminates main anchors
· Pressure forces remain in balance
· No volume change
· Balance pressure thrust remains constant

Types of Movement

· Axial compression or extension
· Lateral movements
· Angular rotation