Hydro Expansion Unit Principles of Operation

The TECO Hydro Expansion is the direct application of high internal hydraulic pressure within a lube in order to form a tight joint between the tube and tube sheet. This pressure or expansive force is accurately set, measured, repeated and controlled. The pressure level can be calculated or determined empirically.

Pressure from the control unit is intensified to the desired high pressure. It is transmifled through a 2.5 metre 18 feet), small bore, flexible high pressure tube to a lightweight hand held gun. The mandrel, which latches into the gun, directs the pressure to the inside diameter of the tube and is held within an accurately prescribed pressure zone. Pressure is contained within the expanding tube by a special elastic seal.

Pressure is applied over the full length of the joint in one step. Stress, crevice corrosion, and metallurgical changes are minimized.

A smooth transition from expanded to unexpanded areas, along with no change in tube material properties, reduces strain hardening, tube fatigue and stress induced corrosion cracking. Tube wall thickness and tube length change minimally.

Before contact is made with the tube sheet a small reduction in tube wall thickness and length occurs because a constant volume of tube material is expanded to a larger diameter. However, no change occurs during the high pressure expanding, eliminating the shear strain and loss of seal between tube and tube sheet that is a characteristic of roller expanding.

TECO Hydro Expansion cycle is automatic and initiated by the operator pedal on the footswitch. The tube is filled with clean water at a low pressure. It is then intensified to the higher pressure and held for the time required to allow the tube to expand into a stable condition. This dwell time is essential for the stability of exotic materials. Finally the pressure is released and the water drained back into the reservoir. All this takes is just a few seconds so the cycle time is fast.

Actual pressure of the water causing expansion is read on a digital indicator and can be printed out if required.

Hydro Expansion Mandrel Introduced

Water Introduced and de-aerated

Seals expanded

Tube is expanded to touch tube sheet hole

Further elastic deformation of the tube sheet hole

Pressure is released, elastic deformation will contract and uniform seal on the tube is established