Multi Ply Bellows

Features
Also know as : Monitored Bellows, Active Monitor Passive Monitor, Testable Bellows Redundant Ply, test port

DHF has ability to manufacture multi-ply bellows up to 6 plies. This is achieved by besting thin tubes inside each other before the initial punch stage of manufacture. Multi-ply bellows have the distinct advantage of containing the same pressure as an equivalently thick single ply design. But with much lighter spring rates and much higher cycle life.

For example a high pressure application might require a 1.5mm thick bellows to contain to hoop stress. A single ply 1.5mm thick or three plies of 0.5mm thick material will both handle the hoops stress in the bellows, but each ply in the multi-ply bellows will act individually where sidewall bending is concerned.
This drops the spring rate and significantly increases cycle life.

Sometimes referred to as a two plies testable bellows, redundant ply designs are used when it is necessary to monitor the integrity of the bellows inner or outer ply. Not to be confused with the multi-ply design, both bellows plies are designed for the full pressure and temperature cycles.

The first style referred to as " passive" only monitors the pressure and temperature cycles. If the inner ply is breached then the incident is detected as an increase in pressure on the measuring device, Pressure gauges and pressure transducers are the most common types of measuring devices. The second style referred to as "active" requires a vacuum between the piles.
Depending on the pressure reading an inner or outer ply failure can be detected.