Pressure change in a fixed volume as steam condenses 2

[BronYrAur]

In a fixed volume, such as a steam coil with a now closed steam valve on one end and a closed trap on the other end, and no vacuum breaker, how do I quantify the the pressure change in the coil as the steam condenses? Let's say I have 10 psig steam. I want to calculate the pressure after it condenses. I know that it goes into a vacuum, but how do I quantify it?

Same question if the steam is already in a vacuum, say 15" Hg. When it condenses, it will no doubt go into a deeper vacuum. I'm troubleshooting a vacuum steam system and think I may need a "vacuum breaker" between the steam side and the condensate side. They are both already in vacuum, but I an suspecting the steam side falls into a deeper vacuum when the steam condenses, thus preventing gravity drainage from the coil.

 

[ehbadger]

Silly question time- why do you want to get the condensate out if the steam supply is switched off? Why do you care if the heating coil stays full of condy?

Maybe to prevent it from freezing and breaking the coil? Or to prevent CIWH when steam is reintroduced?

 

[itdepends]

Agree RE CIWH- always a risk when reheating a line- but this is only a small heating coil.

Freezing- good point. Not an issue in my location so it didn't spring to mind (if it gets realllly cold- we might hit -2Celsius, for a couple of hours before dawn in winter).

As a chem eng/metallurgist the first part of any answer I give starts with "It Depends"