Where is the story of "Install Vacumn Breaker Here", as written by Dan Holohan some years ago.

JUGHNE

Have a steam system being revised.
Has a heat exchanger with steam in shell and glycol in tubes.
Previously pressure maintained in boiler 24/7/365. Will be idle during summer time now.

What was the story and conditions that collapsed the shell?

EBEBRATT-Ed

Can't say I herd of a shell collapsing but I could be wrong. 1700 time is volume is pretty powerful

I usually put a Y pattern check valve on a tapping on the shell. If there is no tapping I have seen them on the steam line downstream of the control valve or on a tee up stream of the steam trap. Like to mount the valve horizontally and raise it up on a long nipple to keep the water out. I have also seen the other side of the check valve piped downstream of the trap to use return line to break the vacuum. Don't really like that idea but some are wary of an open check valve. 3/4" is usually large enough

I know Tunstall sells steam vacuum breakers probably others do as well

The story was on e of Dan's but can't remember where I read it.

JUGHNE

Yes, it was a Dan story from when he was a rep. The details were included as to how this happened. There was a plug in the shell and a warning "Install vacuum breaker here"

Pumpguy

As @EBEBRATT-Ed says, it's the vacuum of condensation that collapsed the shell. You could install a vacuum breaker on the downstream side of the steam valve feeding this exchanger, or at the location described above. A simple 3/4" Hoffman # 62 would work.

If this is a vacuum system, you don't want to use a vacuum relief valve. Instead, use an equalizer line with dropped check valve or thermostatic radiator trap, with outlet piped back to the return line. See attached illustrations.

JUGHNE

Thanks for the responses. As stated, one of the two boilers (each 2730MBTUH) have maintained 10 PSI 24/7/365 for 40 years. We are now going to HTP water heaters and have removed the water tank and abandoning the steam insert coil. So steam system will be off most of summer.
There are two pneumatic zone valves (1/3-2/3 capacity) that feed the shell when there is a call for heat. I suspect some steam may have leaked into the shell as the boiler ran to maintain the hot water indirect tank. The dual F&T's are below the shell but have to lift condensate 2-3' to drain to the feed pump pit.
Now the boilers will be switched off giving a cold system.
My concern is that although this has worked for 40 years will the cold start up have consequences??

Erin Holohan Haskell

@JUGHNE - This may be the article you're looking for: https://heatinghelp.com/blog/solving-a-steam-to-water-heat-exchanger-problem/

JUGHNE

Thank you Erin, that is not the vacuum breaker story I was thinking of. However the air venting may apply to this job as the boiler is shut off for the summer for the first time in 40 years.
The vac bkr story concerned a heat exchanger shell either collapsing or the tube bundle inside being crushed.

I don't know if this is a concern for my situation but when something changes, (no constant steaming) then something else will invariably change also. IMO

Erin Holohan Haskell

Thanks for letting me know, @JUGHNE. I'll let you know if I come across another one.

hvacfreak2

https://heatinghelp.com/blog/a-heated-exchange/

JUGHNE

hvacfreak2, that is the one I was thinking of, thank you both for your help.
Both may apply to my job.

So do we assume any steam shell HX needs a vac breaker?

JUGHNE

So I printed out both stories and gave them to the maint man.
He called the company concerning the tube and shell. That company now only handles the tube bundle. The factory man said you must have a vac breaker or your bundle would have been smashed to bits after 40 years.
Maint man and I searched the shell and found only a 3/4" tapping with a nipple and valve that was shut off. That is close to a plug.
So maint man will not run the boilers until we come up with a vac bkr.
I am wondering about an air vent for the shell also.

How about vac bkr or air vents for the boilers.
They are brought up to pressure before opening the valve feeding the common header.

Maint man says they just about never have not had a boiler on line. (DHW needs which we are eliminating with HTP water heaters.)
When they would bring on a boiler cold there would be water hammer in the coil.

Erin Holohan Haskell

hvacfreak2 said:

https://heatinghelp.com/blog/a-heated-exchange/

Thanks!

steamfitter

I have seen many a check valve (intentionally installed backwards to act as a vacuum breaker) leak during start up. I have had good results in the past with this vacuum breaker:
GROEN Z090787
As stated in one of Holohan's books, the main problem with HEXs and Steam Coils is that a natural vacuum forms when the steam control valve feeding it closes. When it re-opens the steam wips into the shell which is in a vacuum at great velocity and picks up any leftover condensate and slams it into the nearest object.
In the case of the HEX, it bounces off the inside of the cap on the shell and into the HW tube bundle.
The vacuum breaker will prevent this and can be installed anywhere between the outlet of the steam control valve and the inlet of the steam trap (F &T Trap). However, most engineers prefer it to be mounted directly into an outlet on the shell of the HEX.
They also generally recommend it to be installed in a heel tee right after a union on the return of any steam coil. The other outlet of the tee is where you drop down approximately 6"-12" and install a 2nd tee for a dirt leg (on the run of the tee) and a shut off valve and strainer (on the bull of the tee) for the steam trap.This drop down is essential as it allows the necessary static head pressure of the condensate to help in entering the trap and leaving the coil which prevents condensate backup (waterlogging).
For additional venting, I suggest you add a tee above the coil return heel tee. Install the vacuum breaker in the run (top of tee) and pipe out the bull of the tee into a thermostatic trap (1/2") and then pipe it into a tee connecting to the outlet side of the F & T Trap, always pitching the piping towards the F&T Trap.
The thermostatic trap will act initially as a vent during start-up and then close when the steam hits it. This increases venting and speeds up the heating of the coil, saving energy.
Sorry about the lengthy post. Hope it helps!

JUGHNE

Steamfitter, thank you, and you could go on at more length if you wished.
This shell/tube HEX ("convertor" from print) is fed by 2 pneumatic auto controls with total cap of 2400 #/HR. The two F&T's are 2 1/2" rated at 5000#/HR each. 2 1/2" drip out of the shell drops about 30" into the parallel F&T set up. They are not gravity drain but must lift condensate nearly 60" to horizontal drain to feed pump pit.
I assume that both sides of trap piping are full of condensate when steam is off.

There is a 3/4" tap (with valve that is presently shut off) on the top of the shell above and opposite of the cond outlet.
This seems to be a place to add vac breaker and air vent. IMO

Any other advice appreciated, thanks very much.