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Vaporstat sticking / biasing after vacuum

Binnacle Member Posts: 126
Have a L608A 1046 2 Vaporstat picked up used.

Generally works well, though I can gripe that the faceplates are only approximate indicators, requiring one to rely mostly on the low-pressure gauge, and that this particular Vaporstat cannot diff less than 3 ounces.

But today I nailed down a problem that has been most vexing. Due to a lack of pipe insulation (coming this summer) the furthest radiator hammers when the system exceeds 8 ounces. I've set the Vaporstat to 4.5 cut-in 7.5 cut-out and most of the time it works fine.

Yet every now and then that radiator starts hammering away. I run down to the boiler and, there it is 9 ounces on the gauge!

Was observing the system just now and finally saw that what's happening. After long cycles all the vents close and the system pulls a decent one-inch vacuum as it cools. I was watching the needle on the expensive low pressure gauge reversing half way around the dial worried it would wreck the gauge when the Vaporstats makes a loud WHACK sound and gives me a start.

Seems when the vacuum pulls hard the mechanism jumps from a neutral balanced state to a negative stop of some kind, overcoming a good deal of friction.

Then on the next cycle the Vaporstat biases a full ounce-and-a-half, possibly two ounces higher than the nominal setting of 7.5 ounces and then WHACK again and it's back to normal.

After detaching the Vaporstat at the union, I was able to reproduce this behavior by simply sucking and blowing on pressure inlet.

Has anyone see and/or dealt with this sort of glitch? I'm quite pleased the system is tight enough after 90 years that it may be possible to experiment with vapor-vacuum, but for the moment I'd just like to get that Vaporstat behaving properly after cycles ending with vacuum.


  • nicholas bonham-carter
    nicholas bonham-carter Member Posts: 8,575
    Caveat emptor

    Why not extend the tee on your gauge tree so a check valve could be installed to relieve the vacuum.

    I don't think anyone else in the vacuum fraternity has had a problem with a vaporstat or a gauge suffering damage from a vacuum, you you must just need a new vaporstat.

    Have you identified the cause of the noisy rad?--NBC
  • Binnacle
    Binnacle Member Posts: 126
    tried WD-40

    But no joy.

    Sprayed it mostly at the push-rod that ascends from the diaphragm assembly; plenty of lubricant followed the rod down in there.  Then exercised it with lung power.  Sounds like the diaphragm retracts about 1/2 inch with negative pressure, more a CLUNK than a WHACK.

    Ran a test by sucking the diaphragm down to the retracted position, putting the Vaporstat back and cycling the system.  Hit about 15.5 ounces of pressure before the diaphragm popped up.  No wonder that radiator hammers!

    I may try taking apart the diaphragm assembly to see if whatever is causing the friction can be made less sticky, or if perhaps some sort of adjustable stop exists that can be tweaked to prevent retraction.

    Have an older bellows-style L408A 1074 2 with the large bottom (ostensibly never used) coming in soon.  Hopefully this unit doesn't have the problem, which seems a design flaw.
  • Fred
    Fred Member Posts: 8,541
    edited March 2014
    Push Rod

    I think when you take the unit apart you will find that that "push rod" just sits on top of a free floating thimble that sits on top of the diaphragm. Lubricating that really doesn't lubricate anything. I doubt that15.5 oz. of pressure (at cut-out) would cause any water hammer at the radiator.Sounds like a separate issue, the radiator or supply pipe may not be sloped properly.
  • Binnacle
    Binnacle Member Posts: 126
    15.5 ounces is WRONG, regardless

    I was perfectly, crystalline clear as to WHY the radiator hammers.  This is NOT A MYSTERY.

    Above 8 ounces this happens and I'm NOT planning to fix the root cause (lack of insulation) till some time in the future.  The POINT is that by setting the maximum pressure to 7.5 ounces the problem is 100% mitigated.  END OF DISCUSSION.

    The Vaporstat is SUPPOSED to control the pressure in the range set on the front-panel adjustments.  This unit is allowing the pressure to rise to DOUBLE the setting on the front.  I.E. it is not working as it is supposed to.  Vaporstats are supposed to provide fine, accurate control over pressure in a system.

    I'm interested in constructive information regarding just the one single topic, which is that the Vaporstat is doing something that it is not supposed to do and how this might be repaired or corrected.  It seems to me that this glitch has the aspect of a problem that might be fairly common and that others may have encountered it in the past.  Hence the post.
  • Fred
    Fred Member Posts: 8,541
    Wow, What's your problem?

    Most people post here to try to get opinions and some insight into what might cause a problem. You are the one that raised the water hammer issue and tied it to the Vaporstat. Little did I know that any discussion that that might be an unrelated issue, which it is, was off limits.  You have a Vaporstat issue, in addition to the water hammer and I can assure you that people aren't going to be very receptive to trying to help you if you come back and bite their heads off because you don't like what they have to say.
  • Binnacle
    Binnacle Member Posts: 126
    thread topic is NOT hammer

    I am annoyed because *nowhere* do I solicit help regarding the water hammer problem and so far the only comments focus on it.  The water hammer is entirely under control and nothing written here by me in any way indicates otherwise.  That the radiator hammers over 8 ounces is simply background information and I now wish I had left it out as it is incidental to the issue and people seem to obsess about it.

    I do NOT want advice or help  regarding water hammer.  It is a simple problem with a labor-intensive solution, but a trivial work-around and that is therefore being deferred to a time in the future.  This should be easy to grasp.

    So PLEASE, do not comment on the water hammer because the information is of no value and is off the topic.

    The topic is a malfunctioning Vaporstat.
  • Fred
    Fred Member Posts: 8,541

    OK, I'll stick to the vaporstat! So Stop buying used control devices in unknown condition. Put a new one on there.
  • Binnacle
    Binnacle Member Posts: 126
    edited March 2014
    older Vaporstats are superior

    Per this thread


    new revision Vaporstats that employ relay contacts are inferior to older generations that have a mercury switch.  New Vaporstats are notorious for having way-off calibration and for non-linear pressure sensitivity.  Situation is bad enough that Steve Pajek of Gill Plumbing designed a water-column pressure controller that Gerry and Steve now install in applications where good pressure control is important.


    In addition, the system here has an excellent millivolt (aka Thermopile) control system that runs off electricity generated from the pilot-light.  These controls run at around 0.50 to 0.75 volts, but draw very high amperage when opening and closing the gas valve as a consequence.  Millivolt systems will tend to cause air-exposed contacts to arc and corrode, and the very-low voltage then has trouble overcoming the resistive effect of the contact damage.  Mercury bulb switches (in both the thermostat and Vaporstat) are immune to this problem.  The LWCO has relay-style contacts, but since the duty cycle for the LWCO is just a few times each year during testing, this is not an issue.

    So the old mercury-bulb Vaporstats are the way to go for anyone who is not constrained by regulations against installing equipment containing mercury, i.e. private homeowners.
  • Fred
    Fred Member Posts: 8,541

    That, my friend, assumes they are working. A used unit, with an unknown history is not as good as the current version Vaporstat. Safety and Control are at issue.
  • Binnacle
    Binnacle Member Posts: 126
    off topic

    The topic is how to resolve a problem with an old model Vaporstat.
  • vaporvac
    vaporvac Member Posts: 1,520
    edited March 2014
    Edit post

    The easiest way to stop people from commenting on the water hammer is to delete the reference in your first post.

    My original Vsat is a mercury one...very accurate., but delicate as are the new ones. There are posts here that deal with fixing them if you search. I'll do that if I have time later. I bought a "new" one from a fellow Wallie who kindly calibrated it for me as I found that to be the easiest route for my second Vstat. I now have an old and new one on my new twinned system with the old vacuum gauge that are hard to come by. I would love to have installed the water column, but my system took enough time to get running as it was and I really just needed mine for control. Time will tell if the "new" one works well enough.

    I think the best rule on this Wall is to be nice. People really try to give the best advice and sometimes it's difficult to convey what one really means so that everyone understands. My posts go off topic all the time and I gently try to bring it back to the original question. I'm just happy that anyone is taking their time to help at all and that it generates interest and discussion.
    Two-pipe Trane vaporvacuum system; 1466 edr
    Twinned, staged Slantfin TR50s piped into 4" header with Riello G400 burners; 240K lead, 200K lag Btus. Controlled by Taco Relay and Honeywell RTH6580WF
  • BobC
    BobC Member Posts: 5,407
    Mine works fine but at lower vac levels

    I have a 0-4 mercury bulb based vaporstat that I have run as low as 12oz high and 4oz low limit and it never faulted. It' also reads very accurately which is probably just the luck of the draw. However my system never went over 1/8 revolution of vacuum on my 0-3 gauge so I don't see the depth of vacuum you are seeing.

    I run the low end higher now because I have a cycleguard on the new boiler and want the boiler to come back on as quickly as i can if it does trip the high limit - which it only does on long burns in cold weather or when it comes back from a 3 degree setback in the morning.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • ChrisJ
    ChrisJ Member Posts: 14,920

    Would it be possible to take pictures of what the linkage in the vaporstat looks like?  I've never seen one and am curious how it compares to my mercury type pressurtrol.

    Bobc, if my boiler came with a Cycleguard it would be right by my autofill on the shelf.  There is absolutely no way I would tolerate what that thing does.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Binnacle
    Binnacle Member Posts: 126
    existing pic

    If one right-clicks on the existing picture and does a "open link in new window" the picture should show up all by itself in a new browser window.

    Then type CTRL+ a few times to zoom it up.

    The mechanism is reasonably visible.  Consists of a push-rod ascending from the diaphragm assembly below a lever plate with a triangular balancing hinge.  Plate extends over to the spring tensioner.

    I can take a picture with a digital camera (instead of the phone) and from a better angle if you want a higher quality image, but it will require some fussing.  Will do if you definitely want more detail.
  • ChrisJ
    ChrisJ Member Posts: 14,920

    A better picture would definitely help. I can't see what's behind the scales and zooming in on a low res picture doesn't do much for me.

    I can't guarantee I'll have a solution for you but I can try and am curious how it functions.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Binnacle
    Binnacle Member Posts: 126
    post WD-40

    Since I WD-40'ed it is has not glitched to high-pressure.

    So possibly this did help.  I sucked rather hard on the inlet when retracting the diaphragm and it made a hard, loud clunk, so that test may have been a bit extreme compared with the way the system actually transitions to vacuum.

    On the other hand, it's been warm and I'm not sure the system has done the "harder vacuum" version of it's cycle-end.  The soft vacuum end goes to one-half inch negative mercury on the 30psi gauge.  The harder version that has caused the problem happens after a long-running cycle and is a full inch of vacuum and the low-pressure gauge winds back halfway around (a bit unsettling, but the Wika seems pretty tough and hasn't required re-zeroing).

    If that spring snowstorm shows on Tuesday I'll set the thermostat back when it's cold and the turn it up later to provoke the harder vacuum event and see what happens.


    I though a bit about the suggestion to put a vacuum check on the boiler (McMaster as them), but I'm quite interested in experimenting with vapor-vacuum at some point (how cool would it be to have a totally silent system?).  So I'd rather try to get the Vaporstat to behave well with vacuum cycles.

    None of the Honeywell  Vaporstat documents (old and new) I've found make any mention of vacuum and always specify pressure ranges as zero-based.  On the other hand steam boilers going into a vacuum state is hardly a new or unusual condition, so one would think they would / should have allowed for it in the design.
  • ChrisJ
    ChrisJ Member Posts: 14,920

    If lubricant is necessary I would use something designed for it which WD40 is not. Perhaps 3 in one or a light grease?

    Graphite might be best as it won't attract dust and lint.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Binnacle
    Binnacle Member Posts: 126
    good thought

    If I end up taking it apart I'll remove the WD-40 lubricant with acetone (WD-40 contains both a volatile cleaner and a lubricant) and apply graphite.
  • ChrisJ
    ChrisJ Member Posts: 14,920

    If you do take it apart, I would also check for any worn ridges or anything that could cause binding.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Binnacle
    Binnacle Member Posts: 126
    Neat !

    That's impressive.

    Now I want one but I'll bet these are hard to come by.
  • Clank Clank
    Clank Clank Member Posts: 30
    ... Going back to his favorite topic..

    Not bringing the topic up again just to get another tantrum, but I have a situation where the steam gets to and fills all the radiators just fine, and right at the top of the current pressure max, around 12 ounces, knocking starts. Feels random. The thread mentions lack of insulation being the cause for a situation that sounds similar. Question is how does that play a role in relation to the pressure? My pipes are insulated but only in the boiler room.
  • Binnacle
    Binnacle Member Posts: 126
    edited March 2014
    surge at the end

    Sometimes even with proper insulation, proper tilt, apparently reasonable pressure, etc. pipes and radiators have been known to hammer.  Generally it's because steam is condensing too rapidly and the accumulation of water to large to fast.  Water might be in the bottom of a sagging radiator, or might be flowing back down a pipe in too great a volume.

    You mention the risers are not insulated.  That is important.  Bare riser pipes condense steam and retard it's progress.  Makes it difficult or impossible to completely balance a system.

    Lowering the pressure an ounce or so might fix it since this slows things down at the far end of the system.  Yes I know steam flows faster at lower pressure, but at the end of long pipe runs with a lot of branches, it takes awhile for everything to heat up and when suddenly all the closer-to-the boiler vents close it can cause a  sudden surge out to the end of the line.  With incomplete insulation this is more likely.

    This "sudden surge into the last radiator" is precisely what causes the hammer here.  By cranking down the pressure I've slowed the arrival of that surge to the last radiator, and have given it time to heat up without a lot of condensate rushing back down the pipe and doing battle with incoming steam.

    Once the pipes are insulated I may go very low on pressure, perhaps 2 oz cut-in 4 oz cut-out since the pipes will remain hot between cycles.  If the boiler cycles once an hour, but runs for only ten minutes, then the total energy consumption will be the same and the temperature more stable and comfortable.  Without insulation the boiler spends too much time reheating the pipes relative to time delivering steam into radiators for the shorter cycle to be efficient.

    One might fiddle with vent settings in an attempt to balance things better.  Perhaps a radiator cut-off valve is mismatched in size and kludged on with bushings, perhaps it's half open.  Lots of little things should be examined when trying to figure it out.  BUT not on this thread!  Start a new one!

    With enough fiddling and patience most problems can be resolved.

    I haven't reached this point yet as insulation will change the behavior of the system dramatically and I don't want to spend a lot of time fine-tuning before all the major changes are complete.


    The one problem I ran into with lowering the pressure is that when it's set too low, that last radiator heats so gradually that the temperature swings about one degree before the thermostat cuts out (that last radiator and the thermostat are in the same room, but I'm definitely not moving the thermostat).  Yes of course this is much more comfortable, but due to the lack of insulation, it takes almost 15 minutes from the time the boiler starts firing until heat is really getting out to the radiators.  With the shorter one-hour cycles the system uses a lot more natural gas, spends too much time bringing the pipes up to temperature.   So I set it to the highest pressure that does not cause water hammer. This results in an additional five or six minutes of active burner time thus sending enough energy out to the radiators to get them loaded with extra heat.  More temperature overshoot, but a two hour cycle instead of a one hour cycle and probably 30% less fuel consumption.

    With lower pressure, the amount of wall-clock time the thermostat is calling for heat is roughly the same, but the pressure control turns the burners off for a larger percentage of that time.  Once the risers are insulated the duration of the thermostat call-for-heat should be much shorter due to a greatly reduced pipe-warming interval.
  • Binnacle
    Binnacle Member Posts: 126
    same pic at full resolution

    It seems that the forum software aggressively down-samples images.

    I've posted the original here.  Much clearer.


    Will look at taking a better-still photo next time I'm fiddling.
  • Techman
    Techman Member Posts: 2,144

  • Binnacle
    Binnacle Member Posts: 126

    No improvement on next big-vacuum cycle.

    Removed four screws and the diaphragm assembly came away easily. Wiped away the residual WD-40 oil and a dollop of hardened grease that was perched on the tip of the push-rod.

    Fiddled with it, exercised the diaphragm and put it back together, but with the assembly reversed 180 degrees.

    Now it's working perfectly. The diaphragm has a point where it reverses with a THWACK (WHACK was closer than CLUNK I suppose), but now this happens only with a good deal of positive pressure and it pops right back with the easing of pressure. With negative pressure it no longer pops downward; doesn't budge.

    My guess is that either shipping, an earlier dismantling, or possibly even the factory assembly resulted in something out-of-alignment such that the point where the diaphragm reverses was somehow incorrect. It did feel like it was better assembled reversed relative to the way it started, even though the bottom appears symmetrical to the casual eye.
  • Binnacle
    Binnacle Member Posts: 126

    The Vaporstat wasn't diff'ing correctly, so I dismantled it again.

    Finally got to the bottom of this problem.

    The diaphragm was damaged during original manufacturing. The person responsible for punching mounting holes accidently dinged it and decided not to reject the part. Happened in 1984 when the unit was manufactured.

    So the WHACK/THWACK sound I've been hearing is the diaphragm flexing past the dent and popping. Definitely not normal. The point where this happens is just before the critical range traveled during operation. Pull a vacuum and it pops down past the dent's resistance. On the way back, extra pressure is required to push it past this resistance point.

    Since I have another unit if felt safe attempting a hack repair. The diaphragm is a single welded and sealed unit and all I could do was bend the outer edge in an effort to diminish the resistance of the pop. Seem to have improved it some. Also fiddled with the push-rod tip which is screwed on and adjustable.

    Hopefully this will work better till I have time to install the new-old Vaporstat.

    Photo of the hole-punch ding and another attempt at the internal mechanism below. Really can't get a much better view without disassembling the upper unit.


  • Binnacle
    Binnacle Member Posts: 126
    edited March 2014

    Bending the diaphragm rim slightly outward with a vice-grip improved it sufficiently to resolve the issue.

    Now it pops past the ding's resistance at 3 ounces on the way up and thwacks past it every time going the other way, with even slight vacuum.  Diff is back to where it was.  Had to set the cut-out to 3 ounces to obtain 7.5, but it's good enough for the present.

    Weird one.

    My original thought that perhaps others had run into this couldn't have been further off.  Likely a hole-punch ding that doesn't completely wreck the diaphragm is rare, or even unique to the one unit.
  • Binnacle
    Binnacle Member Posts: 126
    edited March 2014
    no visible arc

    I picked up the idea that millivolt may arc second-hand, but I'm not certain about it now.

    While fiddling with the diaphragm I ended up attaching a control wire while the thermostat was closed and saw no sparks, though I suppose it could arc microscopically.

    But I still find the argument that minor contact corrosion could interfere with millivolt control circuit continuity persuasive.  Seems the sort of problem that could lead to madding and elusive glitches (akin to the diaphragm dent issue).  In regard to avoiding such problems mercury-bulb switches are surely superior.  I believe they usually are filled with nitrogen rather than air, and either way no moisture ever enters the bulb.

    See the "advantages" section of the Wikipedia article for more detail:

  • Dave in QCA
    Dave in QCA Member Posts: 1,777
    My Experience

    I have two vaporstats on my system. One is an old style and the other is a new type. The vaporstats are subjected to pressure occasionally as high as 14 oz and vacuum as high as 9" Hg. It has not had any effect on either device.
    Dave in Quad Cities, America
    Weil-McLain 680 with Riello 2-stage burner, December 2012. Firing rate=375MBH Low, 690MBH Hi.
    System = Early Dunham 2-pipe Vacuo-Vapor (inlet and outlet both at bottom of radiators) Traps are Dunham #2 rebuilt w. Barnes-Jones Cage Units, Dunham-Bush 1E, Mepco 1E, and Armstrong TS-2. All valves haveTunstall orifices sized at 8 oz.
    Current connected load EDR= 1,259 sq ft, Original system EDR = 2,100 sq ft Vaporstat, 13 oz cutout, 4 oz cutin - Temp. control Tekmar 279.
  • Binnacle
    Binnacle Member Posts: 126

    For sure I would expect yours is the normal experience.  Thank you for the comment.

    I should have taken a better picture, but it was really clear on close examination that the hole-punch used to create the four mounting holes was pressed into the diaphragm surface near edge.  This warped the disc in such a way that it pops / twangs about 2/3rds through the normal range of motion.  In 1984 people made things, rather than robots, so perhaps someone was chatting with a co-worker and dinged it while looking away from their station.

    Overall the design and construction of Vaporstats is impressively sturdy and precise.  Is sort of amusing and that a bit of hand-craft error from 30 years ago traveled through time to visit me in the form of this maddening glitch.

    Probably the system where this unit spent those years never went into vacuum and so no-one ever noticed.