How long can a vacuum pump survive these temps?

ariccio

Continuing with my co-ops almost textbook case of the "25 steps in the repair of a steam vacuum system", it seems they've jacked the pressure up again. Parts of my apartment are 80°F+ with the windows open even with the heat off because the walls (the ones with the steam pipes inside) are 95°F, other tenants have their air conditioners running on 35°F nights, and I can't even hear hammer in the returns anymore, just steam.


Now,  curious as I am, I went down to the garage and paid attention to the lowest return pipe throughout a cycle. It starts cool and empty as a gentle but all-encompassing whooshing sound fills the room when the boiler first kicks on and pushes steam through the supply pipes. After a few minutes, you can hear water rushing through the returns and the pipe warms up. 

After about 20 minutes, I can hear the boiler cycling on very short intervals... It's not a gentle and wide whoosh anymore, but I can hear what sounds like a gas very painfully screeching through one or two of the mains, and the returns getting hotter and hotter. I'm guessing that's it cycling on the high side of the pressure control.

I saw a new peak of 234°F on the return pipe! About as hot as the hottest supply pipe. And as hot as my radiators get upstairs. Now I know there's a million things that affect the accuracy of infrared measurements, but this pipe is painted and I've sampled many different places... I wouldn't be shocked if the actual temperature was in the 210°F-220°F range. I suspect it cools a bit further as it passes through some concrete on the way to the boiler a few walls away and below.

For reference, this condensate pipe is near the parking space for the family car, which is also really really annoying when I have to do some work on it and I'm sweating in an 80°f+ garage in the winter 🤣


So, question is, how long can a vacuum pump actually last like this? Mr. Holohan makes it sound like they last only a few hours when condensate gets *this* hot. *Perhaps* this is a higher end model of some kind? I dunno what that would mean, but I know engine builders have all kinds of options these days for pistons that withstand knocking and detonation a bit better. I don't think we'd spend that money.

If I put my ear up to the boiler room door, I can hear a different sound that I can associate with a struggling pump (see https://forum.heatinghelp.com/discussion/195776/what-does-a-vacuum-pump-sound-like-when-pumping-steam#latest). Notably it's a different sound than when the condensate pipes are a lot cooler.




I've been thinking of starting a betting pool on when it'll fail, but I have nobody in the building who will participate in it. So you do not need to worry - this is an academic exercise at this point. How long could a pump last like this? At the longest.

Spring is coming, so it may just make it until next winter at this rate.

Pumpguy

Sorry, but I can't answer this question. Much depends on the type of vacuum pump and what's going on inside it.

Many vacuum pumps will have temperature limit switches that will turn off the vacuum feature and only allow the unit to pump condensate. A typical setting for this switch would be 165*F. At the temperatures shown, just the energy the impeller imparts to the water will cause it to flash into steam, and the cavitation will damage or even destroy the the impellers.

What is the operating steam pressure? My tables for PROPERTIES OF SATURATED STEAM show for 227*F, thats steam at 5 PSI.

First recommendation here is so simple and easy; CUT BACK THE STEAM PRESSURE. Try setting the pressuretrol to off @ 1.5 PSI and on @ 0.5 PSI and see what happens.

ariccio

Yup, I've been telling the super to keep the pressure down. If not for wasted energy, but because it's causing half the fittings in the building to leak at a slow drip rate.

Of course, as a condo, nobody wants to listen, nobody wants to replace steam traps, and the person in the coldest apartment is still complaining! 

If I can guess to within a season or two when the pump cracks, I have a better chance of convincing people to listen when I eventually run for the board 


And then maybe I'll be able to enjoy a New York winter without needing to run two box fans, an air conditioner, and a 5 gallon per day humidifier

I don't actually *like* living in a wind tunnel 🤣

EBEBRATT-Ed

"Nobody wats to replace the steam traps" But they will easily write checks for all the wasted fuel and a vacuum pump replacement.

Pumpguy

EBEBRATT-Ed said:

"Nobody wats to replace the steam traps" But they will easily write checks for all the wasted fuel and a vacuum pump replacement.

Oh, this is such a common story.

EBEBRATT-Ed

@Pumpguy

Unfortunately, true. There are more messed up systems they ones running correctly.

jumper

At least since the sixties markets have gone toward packaged equipment as opposed to built up systems. There are methods to protect machinery but they occupy space.

ariccio

Pumpguy said:

EBEBRATT-Ed said:

"Nobody wats to replace the steam traps" But they will easily write checks for all the wasted fuel and a vacuum pump replacement.

Oh, this is such a common story.

It's amazing isn't it? The best part is when I speak to maintenance or management about this, and it's not only the first time they've heard of such a problem, but assume I'm a weird nut for suggesting such a thing.

I mean, I most definitely also am a weird nut, but I'm still right


I have adopted an assumption in my professional and my personal life that those who assume and do not measure are no more likely to be right than the flip of a coin. Sadly, assuming is the norm in many industries.


And as Mr. Holohan has said before, it's amazing what you can learn if you read a little bit. I'm suggesting it's also really amazing how few people have the single quantum of curiosity necessary to read about the systems they manage daily. *shrugs*

jumper

Original designs often incorporate what some salesman promotes. I think original heating vacuum pumps were Domestic single impeller machine for commercial & industrial buildings. Idea was that at lower steam temperatures unit heaters would cycle less. Then Jennings or Nash created multi-motor machines. Eventually salesmen convinced designers to incorporate machine in residential buildings. Once system is built who is going to take responsibility for changing anything?

Pumpguy

Nash's first vacuum condensate pumps (from around 1917) were combination vacuum condensate pumps with the liquid ring vacuum rotor and the centrifugal condensate impeller mounted on a single shaft and spun together, powered by a single motor. In one form or another Nash continued with this basic design until the mid 1960s.

With this design, if condensate needed pumping, the air rotor just went along for the ride. If an increase in vacuum was needed, the condensate impeller just went along for the ride. In either case, the rotor would pump air and the impeller would pump whatever condensate was available to the impeller.

The vacuum and float switches were wired in parallel so the pump and motor would run until both switches were satisfied.

Beginning in the late 1940s Nash started simplified things with separate pump and motor units for producing vacuum, and separate condensate pump and motor units.

This arrangement is still used today in the Type CLS vacuum units still being produced.

EBEBRATT-Ed

Vacuum pumps were not put in on someone's whim. They had advantages like lower stem pressure, the ability to return condensate to the boiler with little or no pitch which made steam work in long spread-out buildings and the ability to have a steam system and condensate system that uses smaller piping and, in some cases, lift condensate.

Those are the pros. The cons are the system has to be maintained especially the traps and vac pumps.