Anyone ever looked at installing a bellows system to protect liquid filled piping instead of a RV? I am thinking this might have use if the liquid must be relieved to a vent system (i.e. the vent piping system cost would be substantial).

How about daisy chaining RVs at higher set pressures into piping operated at lower pressures?

Any ideas?

Most of the places I work hate bellows because of the corrosion and resulting monitoring/inspection issues. They are usually a last option to address piping stress problems, doubt my clients would agree to use them for a thermal expansion issue though it's an interesting idea. Something akin to a pulsation damper on a plunger style PD pump might be more acceptable and would give similar protection.

By "bellows" I assume your talking about a canister with an internal diaphragm - same as a pulsation dampener. Yes, I've used those for protecting piping from liquid thermal expansion. They're just as effective as a vapor pocket withing the line. These are off-the-shelf devices. One name that comes to mind is Sentry. You can fine them on the internet.

A "daisy chain" of PSVs is another way to solve the problem. That usually requires using pilot operated valves, except for the final one, because the backpressure is too high for a balanced PSV.