From the Technical Department: Thermosyphon Oil Coolers

Thermosyphon oil coolers for compressors have been designed in several ways. It has been a common design for the oil to be circulated through the “shell side” of a shell and tube heat exchanger, while ammonia is circulated through the tube side.

These oil coolers are typically ASME pressure vessels and bear an ASME stamp.

When shut off valves for the oil cooler are fitted, thus enabling isolation from the compressor package oil separator, they must also be fitted with pressure relief valves.

It might be presumed that a hydrostatic relief valve would serve as adequate protection.

However, the shell might be full of oil, or it might be full of ammonia vapor or it could be a combination of both. In some cases it could even contain some liquid ammonia.

But because it is an ASME vessel, the ASME Boiler and Pressure Vessel Code, IIAR 2 and ASHRAE 15 all require a vapor relief valve in the event of a fire.

So the issue of concern is how to handle both the compliance for vapor relief and the more likely scenario of hydrostatic relief of fluid. The following outlines a few ways to address this situation. 

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