steam boiler w/vac pump, Input please?

Steamhead (in transit)

Most vacuum pump systems only maintained vacuum in the return lines. But a few, notably the Dunham "Differential Vacuum" or "Vari-Vac" systems did maintain vacuum on the steam side as well. Look at the control system, especially older controls that may no longer be connected. These might give you a clue as to what the system was actually designed to do.

Maintaining vacuum on the steam side allows you to vary the steam temperatures, resulting in greater operating economy. If you have a lot of big buildings, you might want to check this out further. MEPCO is the successor to Dunham and they still make the Vari-Vac. Go here for more:

http://www.mepcollc.com/VV.htm

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tim smith

steam boiler w/ vac pump, Input please. Steamhead?

Have a 60 unit apt bldg with 2 yr old steam boiler replaced by others, also have vac pump. When boiler off but vac pump on, the vacuum is 10". Boiler fires and build up steam, pressure still never gets above 1" of vacuum on boiler gauge when boiler at full firing. ?? is, I am trying to figure why pressure never builds above 0. My suspicion is one of two things. The boiler is marginally sized so can't overcome vacuum on system, or many steam traps are bad and never close allowing vacuum to always be pulled to boiler. System does heat ok but lo high firing rate on burner is never in use as it never gets up to positive pressure. Just a quirk but would like to figure the reason as with old firetube boiler it would always get up to 5psi steam. Feed back much appreciated, Thanks in advance, Tim.

RonWHC

Not Steamhead, but

if the vaccum system is heating; why would you want 5# of steam pressure? Vacuum systems start heating w/ water temps @ about 160*. We set most vacuum pumps to cut on @3" & off @ 8". Have a well heated 208 unit vacuum bldg that seldom gets a cycle pressure above 1#.

If you are concerned about the high vacuum, reduce the cut out. You might also want to check for an equalizing line between the vacuum tank & the boiler header. Sometimes that is left out w/ boiler replacements. If you have bad traps, you will know it, vacuum pumps don't work well w/ high return temps, & the hurling tank overflow would be throwing steam.

tim smith

rons reply

Ron, it is not that I want it to run a 5psi but I was just interested in the change that has occurred, also trying to figure out the best way to control this boiler along with the vacuum. Would like to see the burner be able to use it's low high firing also. ps. another note, I guess honeywell has stopped making vacuum stats, now that also poses a dilemma.

RonWHC

The mercury switched

vaporstats are to be produced until 31 March, this year. Some wholesalers are stocking up on them. The replacements are available now. Not much acceptance from those of us who like to see visual proof of what is happening.

Sounds like the equalizer between the tank & header is not there or the check valve is stuck. As suggested, you might also reduce the vacuum cut out. That may allow you to produce pressure. If you are firing w/ a power burner & a 135 ohm firing rate motor, the L91B pot should allow modulation @ about 1#.

If there is no requirement for continuous steam, you might consider a cycling controller. A Tekmar 269 or the appropriate Heat-Timer should do it.

tim smith

Reply to steamhead

I have known this system for years, It never had a vari vac system on it in the last 15 yrs, what do you think about the possibility of switching it to vari vac? would it be a problem? Would there be a benefit?, or cost or system prohibitive. PS i am going to look at for a equalizer line between header and vac pump. Any further input?? or questions.

tim smith

Response to Ron

Ron, this is a 2 position gas valve, not mod. I will be checking for the equalizing line here early next week as I forgot to when I was doing intitial inspect. Thanks again for reply.

Steamhead (in transit)

I know it's been done

I have a Dunham-Bush catalog from the 1950s that talks about fuel savings possible from this type of conversion. Unfortunately it's now at the shop and I'm not. My other Dunham books don't have any case histories in them, but I seem to remember savings on the order of 40% over vacuum-return systems. One reason for this was that all the steam piping was kept at reduced temperatures along with the radiation, which cut losses from this source (in spite of pipe insulation).

I'll see what I can find when I get back to the shop.

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tim smith

Thanks Steamhead, I guess also right now the system is always running in a vacuum so kinda sorta vac steam system and it is heating the building. I just wonder if there is any problem with how it is running currently. Tim

Long Beach Ed

Tim,

As Steamhead says, they readily advertised 30% - 40% savings with the vacuum system fro the reasons he mentions. I have worked on these systems. The NYC Housing Authority has used them in many of ther 1940 - 1950's buildings.

I have no comparisons to speak of, but producting steam at 160 degrees has to save you money, especially in areas where mild weather is the rule, as it is in New York.

My biggest challenge was dealing with vacuum leaks. You'd have to figure out if you can hold a deep vacuum on your pipes.

I don't believe installation would be too big a deal, though we'd have to see more about your system to tell for sure. Generally there is a Steam Control Valve on the steam supply and a "Differential Controller" that measures the pressure difference between steam lines and return lines. There's a vacuum pump, a "control radiator" and the controls.

If you intend to keep this building for a few years and the system is tight you really should consider this...

Lets see what info Steamhead comes up with.

Long Beach Ed