Summary

Pressure balanced expansion joint is used most frequently in applications similar to those shown for the single expansion joint, but where pressure loading up on piping or equipment is considered excessive or objectionable. The major advantage of the pressure balanced design is its ability to absorb externally imposed axial movement without imposing pressure loading on the system.

Where large amounts of lateral deflection are involved, a pressure balanced universal expansion joint must be used. Two bellows are used in the flow end of the expansion joint and a single bellows in the balancing end. Normally, the balancing bellows will be subjected only to axial movement if the tie rods are properly designed to rotate or pivot at their attachment points.

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

Summary

Knowing and minimizing the expansion joint stiffness is even more critical in advanced designs such as the pressure balance arrangement.

In this arrangement,the primary function is to balance or cancel out the internal working pressure in order to minimize the net end loads acting on adjacent piping or equipment.

Minimizing pressure forces makes the remaining force largely that of the expansion joint stiffness. Because there are two expansion joints in a pressure balance arrangement, the stiffness values are roughly double.

The two expansion joints perform together to accommodate external movements, e.g., thermal, vibration, settlement, etc.

Features

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

Types of Movement

· Axial compression or extension
· Lateral movements