Vacuum Pump delay after boiler cycle

SteamDrew

Hi all,

Wondering what everyone's thoughts are on a delay for a vacuum pump after the boiler shuts off. We see a lot of vacuum pumps running 24/7. Yesterday I set up a vacuum pump to be called by the boiler control and a delay that will run the boiler for about ~20 minutes after the boiler cycles off. These people seem to be changing their pump heads rather frequently, and although run time isn't the only cause of this issue, I figure running 24/7 cant help. Let me know your thoughts.

-Andrew Stoker

Pumpguy

If a vacuum pump needs to run 24/7 there's a problem.

Either the pump's undersized for the load, or system conditions, typically condensate that's too hot or too many air leaks, need to be corrected.

The typical and usual arrangement is for the vacuum pump(s) to run start - stop on demand of the vacuum switch(es). Typical and usual switch settings are off @ 8" Hg. and back on @ 3" Hg.

Operating the vacuum pumps start - stop can be a problem in mild weather when the heating plant operates part time. The vacuum pumps continue to operate when they're not needed.

Arrangements for vacuum pump operation that are tied to the building's call for heat are a better arrangement.

I like to see the vacuum pump start some time before the boiler. Maybe 10 minutes....... This will evacuate the entire system so when the boiler starts making steam, its making steam at a lower temperature. This will also help drain any condensate that may need a vacuum assist.

With both the steam headers and return lines at vacuum, the steam will flow quickly and evenly through the system giving a quicker and more even system warm up than just relying on steam pressure to push the air out.

As far as running the vacuum pump after the boiler shuts off, this may be helpful to drain the condensate from the system, but if designed and piped correctly, all the condensate should gravity drain to the pump and returned to the boiler or boiler feed tank.

Interesting side note:
I was called in to survey a large vacuum condensate pump in a commercial building, reporting on equipment condition and operation. Their SOP was to operate the vacuum pumps continuous.

The operating personnel were in the process of changing to smaller vacuum pumps since the existing were producing more vacuum (lower pressure) than their condensate pumps could discharge from. I recommended installing vacuum switches instead so the pumps could run start - stop between a preset range.

I never heard what they eventually did. They certainly didn't buy any vacuum switches from me. Oh well......., each their own I guess.

SteamDrew

@Pumpguy This system is full of leaks. 100+ year old 5-story courtyard building in good ole Chicago. We could spend weeks here fixing things but the owners don't want to spend the money. I've already fixed a few vacuum leaks crawling around in some old grungy heating tunnels and the system still never pulls a strong vacuum. Pumps are definitely pulling a vacuum though, once we valve it off it runs up to about 10" Hg and shuts off right away. Starting the pump before the boiler kicks on is a great idea though. Makes much more sense than running after the boiler cycles off. Thanks for the insight

Pumpguy

If you're interested in finding leaks in the return lines, you might want to consider doing a peppermint test.

The attached file goes into detail.

I'm not too far away from you, up in Spring Grove, Illinois. If you'd like my input on a specific job, feel free to call me. I will do all I can to help.