Steam with Vacuum Return Pump

Christian Egli_2

We're getting somewhere. I think it is already established well enough that this Nash pump sucks plenty hard enough. It's just that what it's sucking on is not moving.

Here's what's amazing with vacuum pumps for moving water around: thinking about them the way we do about ordinary hydronic circulators does not hold... water. With an ordinary circulator, obviously, if you want a bigger flow, you need a bigger pump - all in bigger energy proportions.

With vacuum lifts it's not so (but as usual, this is not alway necessarily true though). If a vacuum pump is good enough for one small lift, it is good enough for one enormous one too. Some sewer lift stations operate this way where the flow rate is determined more by the lift pipe diameter than by the pump size itself. A tiny pump could hypothetically raise the entire oceans as easily or as hard as it could just one vase full of water.

Anyways, this is no help to the Springfield building.

Option one,

It is entirely possible that the lift pipe itself (just the pipe, not the pump) is sized too small and so, it never stops continuously lifting water (like a sewer lift station would do) and thus never gets into impolite slurping mode where it's not just water being entrained but water and air. The air we want removed: slurping is called for. Factoring for slurping mode is first set by the lift pipe diameter.

We can do much thinking about these pipe sizes, (please tell more about it) but we can also assume that the system was properly installed in the first place and move on.

Option two, which I'd investigate first, I know... it should have been option one then...

Lift pipes look innocent enough, no moving parts, no seals, nothing to go wrong, except for one thing every house cleaner knows about the vacuum cleaner hose: it gets clogged. It gets clogged with the kids plastic toys. It gets clogged at the hose connections. It gets clogged at the kinks.

The vacuum lift station with kinks and reductions and vertical passages is the prime location for dirt clogs. Sadly, lift inlets of the past were not fitted with strainers. They really should be. Sadly also, many lifts that simply became clogged were jumped on as the opportunity for a whole lot of shady work.

Tearing apart the lift and shaking out the dirt will be a dramatic improvement. It may be as easy as opening dirt pockets. It may be a hacksaw job to remove the saxophone like pipe and go shake it outside, then reinsert it with no-hub connections for instance.

There.

I hope this sounds encouraging enough and I also hope it makes sense in your predicament. As you know - we're all putting our heads together here but we're still all speaking in a vacuum, you're the only one with hands.

Slurping is what gets air past the lift and the lift jammed with rust debris will never go into slurping mode. Practice on a milk shake - you'll see.

Option three, we can always keep on counting

If all fails and air still isn't slurped out of the lower set return line, we can very simply insert an air only bypass to the saxophone lift - but not unlike the alternate return trap, you need the insertion of a float device to open and close the bypass on lower inlet condensate levels. This is simple and works while providing the most entertainment.

But a cleaning everything out first sounds much easier.

BAB

Steam with Vacuum Return Pump

We have steam/vacuum return heating system in a commercial building (30,000 sq ft). The system has been neglected, misunderstood, cannibalized and abused for over 30 years. I recently got into it and am trying to make things right again. There is a 644,000 btu/hr, a 5 section Style 19 A. O. Smith boiler, 5 inch steam main, & a model 22 Nash-Jennings vacuum return pump. It is a well built two pipe system (steam supply line & separate condensate return line) & should work better than it does. There are about 80 radiators each with their own respective inlet valve & Barnes/J thermostatic steam traps (#122 & #134). I replace 10-15 of the steam trap inserts every year or so.

Recent investigations discovered no equalizer line between the steam main header and the vacuum air vent line. I placed a ½” swing check valve on the boiler main steam outlet area & noticed the dramatic improvement in the system heating cycle performance. I will now reinstall the swing check valve onto the steam main header upstairs (10-12 feet above boiler water line) with water seal P trap fashion then connect the other end to the vacuum pump chamber air vent line. On page 195 of “The Lost Art of Steam Heating”, mention is made of how motorized valves complicate systems due to the large vacuum build up during the steam condensation part of the heating cycle. I have five (5) heating zones and therefore have five (5) Honeywell motorized valves. Mention is made of installing “an inexpensive vacuum breaker” ahead of each motorized valve. Also mention is made that such a system “should also have a boiler feed pump”. My system has a Nash Pump which I think is referred to as a combination vacuum/condensate return pump. The general term of “boiler-feed pump” is confusing me. Also, should I run the “equalizer line” to all five steam sub mains? Or should I install the “vacuum breaker” before or after each motorized valve? Should I have five (5) swing check valve/water seal lines to each respective motorized valve steam zone or should I have only one (1) swing valve/water seal line to the main header and have five (5) vacuum breakers for each respective motorized valve steam zone? I hope there is someone out there that knows what I am asking.
Bromley

Ken_40

Brom,

You're gonna have to send us some pics lad.

Show the near boiler piping, the returns, the vacuum pump(s) and control panels.

I did a lot of Dunham-Bush Vari-Vac stuff with National vacuum pumps and just getting parts drove us insane. These jobs when finally fixed up can be extremely eficient, but if leaks exist to any significan extent, the price tag to restore is formidable, very formidable...

RonWHC

A single

properly sized equalizer from the above boiler piping should be sufficient.

If your existing vacuum pump is not flooding the boiler w/ return condensate, a boiler feed tank is not needed. If the boiler is flooded, at any time during or after the operating cycle, a boiler feed tank should be installed in series w/ tne vacuum pump & the boiler. The boiler feed tank will act as a reservoir for excess condensate. If you go that route a pump controller must be installed on the H. B. Smith 19A to activate the pump on the tank. Ask the Smith folks where to locate it. Their I&O Manual still needs work.

Vacuum pumps should have a switch to control minimum & maximum vacuum. Typically cut in is 3" w/ cut out 8".
We don't use vacuum breakers @ the valves. However, we do install one on boiler feed tanks & set to open above 8". If the piping leaving the valve(s) is trapped so that condensate can accumulate, a radiator trap should be installed to drain the condensate. 2-4 minute opening valves are best for vacuum, or steam, where pressure is maintained. Smooth, quiet, & easier on everything downstream.

BAB

response

Thanks for the response. There is no flooding of the boiler with condensate. Towards the end of a long heating cycle (early morning heat up) the boiler does start to fill up, ... but never excessively or of concern. The vacuum pump has no vacuum switch, or vacuum limit switches. It is turned on/off by level control only. The vacuum switch box is still there but the guts are gone & the pump wiring run thru it direct to the level contro switch. I have requested a vacuum switch quote & will install soon, I hope. The vacuum piping loop has a valve after the discharge check valves (one swing & one spring loaded). It also has a valve prior to the pump collection chamber, next to the strainer assembly. My manual tweeking & trial & error has resulted in the pump drawing 8-12 inches of Hg during the pumping cycle. This vacumm is slowly dissapated to 0 inches of Hg until the next cycle. I know the recommended vacuum is 3-8 inches of Hg but there is a small piping lift (18") in the condensate return piping about 10 feet before the pump which should require some more vacuum. Photos are a good thought & I will do some this week. Bromley

BAB

response

Thanks for the response. There is no flooding of the boiler with condensate. Towards the end of a long heating cycle (early morning heat up) the boiler does start to fill up, ... but never excessively or of concern. The vacuum pump has no vacuum switch, or vacuum limit switches. It is turned on/off by level control only. The vacuum switch box is still there but the guts are gone & the pump wiring run thru it direct ti the level contro switch. I have requested a vacuum switch quote & will install soon, I hope. The vacuum piping loop has a valve after the discharge check valves (one swing & one spring loaded). It also has a valve prior to the pump collection chamber, next to the strainer assembly. My manual tweeking & trial & error has resulted in the pump drawing 8-12 inches of Hg during the pumping cycle. This vacumm is slowly dissapated to 0 inches of Hg until the next cycle. I know the recommended vacuum is 3-8 inches of Hg but there is a small piping lift (18") in the condensate return piping about 10 feet before the pump which should require some more vacuum. Photos are a good thought & I will do some this week. Bromley

Christian Egli_2

We want no business with the atmosphere

It is disappointing to hear your system is not running as good as you'd want - can you explain a bit more of the deficiencies you have?

Plus, what kind of radiation do you have? Do you have any lift stations? And finally, though the system was well built, did the pipes get laid with sloppy slopes just because the vacuum pump would take car of everything... and as we all know, the vacuum pumps they just suck. How deep does the Nash-Jones pull and how quickly does the gauge drop on start up?

EDIT, I was busy typing away while you were answering the questions that seem stupid now... sorry. 8-12 inch Hg is plenty impressive.

To talk about the vacuum breakers

Completely unlike plain vanilla one pipe steam and the deluxe super low pressure vapor two pipe systems which both operate with much consideration to the A and B dimensions, the vacuumized system does not. If these designs were hinged on B stacking height, you'd be looking at the bottomless boiler pit, a whole 33 feet down. Deep indeed.

You can't worry about such a ridiculous dimension, thus all vaccumizers are de facto feed pumps. They all also incorporate some form of accumulation that matches the system size. If you find your originally planned accumulation volume to be too small, I'd first start looking into why the returns are getting slow... you know... sags... dirt... all the good clean fun.

Also, since the A dimension game is moot, the fuss about vacuum breakers and obstreperous one pipe zone valves is much of a non-issue on vacuumized steam. Problem sucked away.

The Hoffman pumps come with a big vacuum breaker right there at the vacuumizer - I strongly object to this: it breaks my heart to have to get out the whip while forcing the vacuum pump to work its hardest to achieve the best vacuum we can get to then watch the incredibly ignorant breaker lazily spoil everyone's hard work.

Since stuff goes from high pressure to low, within the system, we want the lowest system pressure to be present at the vacuum pump inlet, imperatively. Thus, this location is also the worst possible for a vacuum breaker that opens into the atmosphere - mine have long been replaced by more efficient plugs. (this is not a plain vaporic two pipe system where the open returns are at atmospheric pressures and where placing vacuum breakers is always beneficial)

The purpose of the vacuum breaker is only to ensure the steady pressure gradient within the system: high at the boiler, low at the return end. Keep everything in that order, and all remains peaceful. With that in mind, it's obvious there is no good place for any breaker that opens to the atmosphere nowhere on subatmospheric vacuumized systems. What you need instead is the anti-deeper-vacuum-in-the-boiler-than-in-the-return line. The special equalizer with the one way check valve from the return to the boiler. This one is very important. One anti topsy-turvy line from the boiler departure to the return ends is what's needed.

It is possible to need some beyond the zone valves too. Again, not a breaker that opens into the atmosphere but a breaker that opens into the subatmospheric returns. Normally, a plain F&T trap operates well enough as this breaker providing there is no quirk of piping and providing the zoned remnants of collapsing steam collapse no faster than the possible equalizing backflow can occur through the trap. So, slow zone is better. If needed, add a check valve leading into the zone to by-pass the trap; this check valve, on a line from the return (a return with unhindered air passage to the vacuum pump) and back to the steam cavity.

Does all this make sense so far?

Usually these days when tip toeing around vacuum, the most paralyzing fears are instilled in all of us. The fear being that on shut down, the atmosphere that should reenter the system in an orderly reverse fashion will just jump to where the vacuum is and mess things up. True enough in rapidly firing modern non vacuum systems. But in our deliciously vaccumized pipes, we've taken care that the orderly high to low pressure gradient is insured through piping schemes - here, maintaining the most vacuum we can during and between cycles seems ideal.

Note, that steam pipes are rarely tight to begin with, and realistically a vacuum won't last all that long anyways. Not as long as it takes to read this post at least.

*** More

I live in fear that live steam will make it through from the steam mains directly into the vacuum pump, a death warrant, death by cavitation. To protect my harmless pump from this horrible torture, and knowing that check valves are easy turncoats, I include a thermostatic trap in line with the check valve on my anti-topsy-turvy line. I put the trap on the return side of the check valve - it probably will never have any work to do, but if ever it does, it will be cheap insurance.

I also worry about end of main F&T traps. They're usually undersized for the huge amount of condensate that comes to them on start up, this is only a short lived moment, nonetheless, these slugs of stuff hammer harshly on the thermostatic element within the F&T trap. Once this item is shot, live steam gets to go a rampage in the returns without the benefit of radiator cooling time. Within the returns, what's the most fun to go bang on? the vacuum pump. Keep F&T traps in good shape, keep steam out of the returns, keep cavitation in reserve for your worst enemy.

A last insurance, is the aquastat on the vacuum pump. When things get dangerously hot, intervene and stop the pump. These vacuumizers are so selfless and so devoted to there task, they will hurt themselves for us - I think we can reciprocate some love.

Bromley, I think what you're doing is great, particularly compared to all those others who simply turn their back on the pump and never worry about maintenance and efficient operation. Good for you.

Where is this building located? Office or warehouse?

BAB

A ton of thanks!

The building is located in Springfield, MA. Used to be "The Springfield Shopping News" building, built in 1934, concrete, brick & wide flange steel beams. Concrete floors have ample 3/4" black stone aggregate then reinforced with 1/2" diameter steel rebar on 4" centers in a criss-cross fashion like window screening. It is a very solid building. I can not answer your comments this morning due to tight schedule. But do appreciate your general thrust which helps me a lot. I was confused & did not understand the big big push to achieve a 3-8 " vacuum in the condensate return line & then rush to place vacuum breakers here & there within the system. I do not have hot hot condensate return water near the pump or close to the boiler room. The piping is cool, not cold but definitely not hot. However, I do have five (5) heating zones that appear to require F/T traps. The zones have a thermostatic trap on the termination of a steam header usually after a short vertical drop. The F/T traps are not there now & have never been in the system. I had a trap sales guy in here last year & he did not understand my comments that I see most schematics showing F/T traps at the end of steam mains. He thought the thermostatic traps were adequate. I will be doing the equalizer swing check line this week & be back to you again on some of your comments. Thanks again. Bromley

Christian Egli_2

A ton of words

Have you done a heat loss analysis and have you added up each radiator's EDR?

Adding numbers on the back of an envelope, I see a 30,000 ft2 building pulling something on the order of 1,200,000 BTU/h. Just a ballpark estimate which says nothing about particulars. You said there was 644,000 BTU/h currently installed, which seems like a small amount. Perhaps this is something to check into and see if it is a source of problems.

I checked my files here, I have a nearly 30,000 ft2 building two floors, with about the same amount of windows as yours and it is home to two boilers of 1,000,000 BTU/h each (in Ohio) - and it has been running on just one for ever and is very economical. Another building, all sprawled, brand new junk from the seventies, about 20,000 ft2, this one in hot water, two boilers of 1,200,000 BTU/h each - until I got there and clipped things, this one had a voracious appetite for gas and a very low boiler efficiencies (not to say anything about even lower system efficiency).

So, at 644,000 BTU/h, you're doing something right. Plus, with a vacuumizer, undersizing the boiler output to the EDR demands is not the no-heat complaint problem it is in ordinary steam. So, you're doing something doubly right by maintaining the Nash and the system as a whole.

Anxious to hear more from you.

***

What F&T traps do that plain thermostatic ones don't

On main ends, the steam gets there with no cooling - you don't want it to cool. Nonetheless, some hot condensate always puddles there queuing up at the exit trap.

Traps open and close to lock steam in. Fair enough. Thermostatic traps do not close on steam per se, they close on thermic heat. Knowing steam is at 212F, closing on anything above, say, 180F locks the steam in - Fair, but what if there is a puddle of condensate that is at 180F? It gets locked in. How do you know it got locked in? It starts banging at the trap.

Radiator bottoms are suitably cooled to get thermostatic traps to open on cold condensate.

Main ends with thermostatic traps and no cooling leg are the death trap of condensate. That's why F&T traps are called for in places where there is no cooling puddle, like in end of mains and in air coils. Note how in standard two pipe home vapor heating, main ends are vented with a thermostatic crossover trap - BUT - there is also a drip down to the floor below the water line; this is the F part of a true F&T arrangement. Just implementing a T is never enough.

All this is all the more important on vacuumized systems where steam and heat appear with less dependence on one another than in natural steam.

***

Here is a thread to a picture of an anti-topsy-turvy line I replaced with the added thermostatic trap for added anti-cavitation safety. The check valve is beyond the picture, it is installed without the water stacking P trap arrangement - I have no opinion on that particular P trap idea, I can't figure if it makes life for the check valve easier or harder. I have no atmospheric vacuum breaker either.

http://forums.invision.net/Thread.cfm?CFApp=2&&Message_ID=209813&_#Message209813

The same link:

Topsy-turvy prevention


***

By now, I've sucked up all the words on this thread.

Mad Dog_2

You mentioned changing a dozen or so traps a year

All at once or don't bother. Mad Dog

To Learn More About This Professional, Click Here to Visit Their Ad in "Find A Professional"

BAB

trap changes

There are about 80 radiators & also about 20-30 drip legs so we have well over 110 traps. On a slow heating day we turn the boiler off & change 2-4 traps at a wack. When I say change a trap, actually I mean replace the guts. Pull the old trap innereds & replace with a trap insert (Tunstall). I did not follow (understand) your comment? Bromley

BAB

partial answers

We did summary of the active radiators EDR, came to about 588,000 btu/hr. We only use or rent about 60% of the building. Of the rented sections 1/3 is not heated, ... file storage. The colder part of the building we monitor to prevent freezeup of the fire sprinkler system. Of the five heating zones, one is capped off (steam & condesate)thus rendered dead. So you observations about the boiler being undersized is correct. Thanks for not saying it is undersized but we know it is. Since we only heat key parts of the building we can do ok. As we renovate areas for use we are been insulating. We plan to close off (exterior metal sheeting & insulation) a lot of the large single pane thermal leaking windows.

I miss typed the boiler size, ... the original quote was 644,000 btu/hr but Smith actually shipped it as 655,000 btu/hr with a Carlton gas burner setup nameplate rated at 725,000 btu/hr. Of the 5 heating zones one is dead & capped. Three of the zones are close to the boiler & heat in 15-20 min after the steam gets going. All three are happy after 15-20 minutes. The last heating zone is my problem. It is fed be a 3" sub main. The boiler has two 3" steam discharges that feed into a 5" steam main. Because the three zones close to the boiler heat quickly their respective motorized valves close and all the steam is sent to the last zone, the problem zone. The furthest radiator in this zone is about 200 feet from the boiler, the closest in that zone is about 150 from the boiler. 8 radiators (each about 18 feet long) are on the first floor & 4 radiators are on the second floor. The boiler is in the basement. In weather like this it takes 45 min to 1 hour for the boiler to satisfy the problem zone's heat requirement. The whole time the other zones are heated & their valves stay pretty much closed.

After reading your comments & the books I received I obtained two 3/4" F/T traps & will install in that zone. After the 150 foot run there is a large vertical drip leg for that zone. It has a thermostatic trap there now which I will replace with a F/T trap. There is also a 2" vertical drip leg at the very end of the zone steam supply header. It has a thermostatic trap there now which I will replace with a F/T trap. This will all take me a day or two but I will report any changes. Bromley

Bernie Riddle_2

Steam w Vacuum Return

F/T traps dump air into the consenate return line. Also at start up the boiler sends steam to the main header then to the radiators, ... this action pushes more air into the consenate return line. Anything & everything & everything else pushes compressed air into the condensate return line. I have pulled fittings & trap lids here & there to see what the **** is going on. The main condensate return line is loaded with a lot of compressed air. How does the air get out? I have a lift fitting at the end of my condensate return line just before the vacuum pump, ... same as the one shown on page 193 of "The Lost Art of Steam Heating". This lift design (14" vertical) may allow the water to be lifted up but not the air. The air appears to be trapped in that line forever. Is my system missing a blow off valve, or a swing check valve, or a air release valve or what ? I am not talking about the air vent mounted on top of the vauum pump collection chamber. I am asking about the air trapped in the main condensate return line before the hard piped verical inverted "U" lift. How is it vented ?

BAB

work'n on it

The cold weather does not make the piping changes to the boiler system ideal. We have a couple tenants that like consistant heat during the work day. Our piping changes have to be done quick then run down & turn the boiler on again, wait a heating cycle or so & do it again. Nevertheless we did install four F/T traps with strainers at the end of the main headers, ... and have one more to install tomorrow. Also installed two steam header/condensate return equalizers and located ideal locations for three more. I have often wondered about the condensate return lift with regards to its being clogged. After much reading on the subject & your recent comments I think we might attempt a good cleaning &/or update real soon. I remember replacing some condensate piping Swing check valves) in that area last summer & it was loaded with scale, growths & what not. Wondered how the stuff flowed, maybe should have redone more piping than we did. Shot some pics today but will not be emailing fo a day or so. Bromley

BAB

The Answer on Too Much Air

Thanks everyone for your imput, ... made us look at the system differently. Made us look in detail & found an open swing check valve in the main header. This valve was left from last week's investigation of the steam/condensate return equalizer line. During heatup or steaming the valve was closed, as it should be. After the heating cycle, as the steam cooled, the main header developed a vacuum and the swing valve opened. This open valve pulled in all that air I was complaining about. During heatup the system tried to burp all that air & then on the next heating cycle we picked up more air. The equalizer line is reattached correctly & things appear to have settled down. Thanks again.Bromley

EBEBRATT-Ed

I would suggest contacting: NES Co. tel: 1-800-297-3550 Fax1-866-476-6503. The handle Nash/Jennings pumps.

Get a copy of Bulletin # H-1031 "Some Basic Principles of Steam Heating Systems" (Mine is 1992) Maybe they have a newer version. It explains vacuum systems in detail.

I have been in that building. It's in the south end. It was years ago 20? Is this next to MacDonalds?? They didn't want to fix it right then so I got out of their.

ED

BAB

I have a lot of Barnes & Jones 122 & 134 thermostatic traps in my system (about 120 traps). I have been replacing the guts of defective traps with Tunstall trap inserts & recently installed 4 new Tunstall F/T traps. My boiler puts out 5-9 oz/sq in and when really cooking will get to 9-12 oz/sq in. The whole time the vacuum pump/condensate return line is at zero or sometimes up to 1-2 oz/sq in. I can not pull a vacuum on the condensate return line. I tested the vacuum pump independent of the system & it pulls a good vacuum. During a long heating cycle the vacuum pump kicks on & will run & keep the pressure/vacuum at zero, but never 3-5 in of Hg. At the same time the boiler pressure will react to the vacuum pumping action with the boiler pressure going from 9-12 down to 5-9 oz/sq in.

I have installed some test valves on the outlet side of the 4 new F/T traps. Only one new trap dumps condensate properly. All the others (3 new F/T traps) constantly pass steam, never interrupting the steam flow, wide open all the time. Also some of my drip legs constantly pass steam, regardless how many times I have replaced with new thermostatic trap inserts. So I have a lot of hot pipes constantly running steam into my condensate return line. The main condensate return line is not hot or warm but a lot of vertical drop lines are hot with live steam. I called & then went up to Tunstall main office in Chicopee, MA & they suggest installing replacement thermostatic inserts in their new F/T traps. I will be doing so this week. But is their brand of trap not sensitive enough to low temperature steam (< 212 deg F).
Bromley

BAB

lift station

Per your suggestion (C. Egli) I pulled the hard piped lift station apart. There was no sluge, just a couple small chunks of scale (rust). However, the bottom cap had a drain cock on it so everyone over the years, including myself, must have drained the sludge periodically, ... probably more for curiousity than routine maintenance. The 6" dimension on the vertical stem was correct. The inner pipe was 1-1/2 inch pipe size whereas the outer pipe was 2-1/2 inch pipe size, ... not the "twice the pipe size" in the design suggestions. I will rebuild using 3" pipe size for the outer sleeve in near future. Bromley

BAB

Good Progress so far

All of my postings on this site tend to cry for help, whine about my problems & in general project a negative picture. I wish to point out that my boiler used to run 15-20 hours a day in cold weather but now runs 8-10 hours per day, ... in general about half. On warm days it may run 1-2 hours, .... never before did we have this type of control. The heating zones also act totally different. All radiators funtion in each zone in a predictable & reasonable fashion. Before we had vacuum at the wrong time & air pressure or steam at the wrong time. Also each radiator seemed to have a mind of its own. I would spend days repairing an individual radiator, monitor it and usually end the week by scratching my head & drinking more Scotch than I did before.

Your suggestions & pontifications are apprectiated. I do read & reread them. I am pleased with the progress. But I realize that you can not correct 50-70 years of neglect in one or two heating seasons, ... nevertheless, cutting our heating bill in half or by two thirds appears to be a realistic goal. Bromley

A.J.

vacuum in my condensate supply

I'm sorry for crashing the thread but I have a simalar system with a newly installed vacuum pump that holds 2-6 inches of vacuum ( set a little lower becuase of the problem I'm having with it.
The system is working good but ever since I replaced the bearing assembly on the condesate side of the heat exchanger that feeds some radiant tube, I end up with a vacuum in the top of the condesate return.
I have a equalizer between supply and return with a check valve, no zone valves,about 1,000,000 input.
Any input would be appreciated.

Thanks Andy

A.J.

Vacuum in my condesate return line

Sorry to crash the thread but I have a simalar system(no zone valves,1,000,000 input,new vacuum pump).
Every thing was fine untill I changed out the bearing assembly on the condesate side of the heat exchanger that feeds a small radiant zone. About twice a week I need to get rid of the vacuum that is forming in the top of the return condesate pipe. The system is working fine even with the vacuum set down @ 2-8 inches, becuase of the promblem just mentioned.
I have some pics if someone cauld walk me thru the process.
Thanks for any thoughts Andy