Good demo of steam expansion, condensation and air pressure

CarlM

I always recalled my HS physics class where the teacher boiled water in a gallon gas can, capped and cooled it.  Steam expands 1700 in volume to liquid water.  This old Julius Sumner film demos this and the power of normal air pressure and condensation of steam.  

📸 Watch this video on Facebook https://www.facebook.com/share/v/RWJUX1KsRyLkHgLJ/?mibextid=0csxmW

EBEBRATT-Ed

Anyone who does not under the power of steam and the power it has should watch this video. Why every steam boiler need a vacuum breaker or sufficient air vents to let air back in the system when the boiler shuts down. steam to water or water to steam changes in volume 1700 times.

This is what also causes water hammer and knocking in a steam system when you have sagging pipes and water pockets.

Vacuum can cause condensate to hang up in the system,

jesmed1

This is a fun one too. Collapse induced by pulling a vacuum, not steam condensation, but the result is the same.

https://www.youtube.com/watch?v=Zz95_VvTxZM

PMJ

EBEBRATT-Ed said:

Anyone who does not under the power of steam and the power it has should watch this video. Why every steam boiler need a vacuum breaker or sufficient air vents to let air back in the system when the boiler shuts down. steam to water or water to steam changes in volume 1700 times.

This is wat also causes water hammer and knocking in a steam system when you have sagging pipes and water pockets.

Vacuum can cause condensate to hang up in the system,

I have to point out that the 1700 times factor speaks to how small a volume of water is required to fill the system as steam. It does not speak to the maximum pressure that would be exerted on the system components from the outside if there was no air left inside the system at all after the steam condensed(which there always is). That number is 14.7 psi and is obviously not physically threatening to any components of a steam system. That same 14.7psi(or even much less) placed on the outside of every square inch of a very large vessel not designed as a pressure vessel at all will of course collapse it.

Also, my 2 pipe system goes into about 4-5 in hg vacuum after every burn. I have never experienced a change in the return of the condensate one time. The whole system is one open pipe and the whole system pressure changes but no relative pressures inside do. Gravity is the only force running the condensate, and frankly it doesn't care what the absolute pressure inside the system is.

EBEBRATT-Ed

@PMJ in a closed system as you say the pressure in the entire system can be in a vacuum and not affect the condensate.

Take a two pipe system with traps and the condensate returns to a vented condensate or boiler feed tank and that all changes. Not all jobs are residential. Take an air handler with a steam heating coil or a shell & tube heat exchanger with motorized valves controlling the steam. When the valves shut the coil or HX goes into a vacuum which can result in vacuum damage or freezing coils because they can't drain unless they have a vacuum breaker or an air vent to let air in

PMJ

@EBEBRATT-Ed,

My comment was clearly about my residential system. And I am well aware that all jobs are not residential. I own and have operated a process steam system with a 200 HP boiler for 30 years as well. I do have vacuum breakers on that one as vacuum in coils heating highly corrosive liquids quickly pulls those liquids into the boiler water in the event of a pin hole...obviously not a reasonable risk to take. Large process systems with many varied requirements of the steam are a whole different animal I agree.

Your comment did say "every steam boiler" and I was reacting to that. These pages are quite full of warnings of the woes that supposedly will befall owners who allow vacuum in their residential systems and I find that unfortunate. Vacuum has provided a very large improvement to the performance of my home system. Having actual significant experience with steam in both worlds I have found that in the case of residential, vacuum is my friend and air the clear enemy. Horsing a ton of air in and out of the piping every time the boiler fires in simple 2 pipe gravity return vapor systems really is wasted effort and provides no benefit.

EBEBRATT-Ed

@PMJ

Your right. Every job is different with steam. Vacuum can cause a lot of issues, or it can be your friend.