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System pressure does not seem to be controled by Pressuretrol

On a one pipe peerless steam boiler with a Pressuretrol PA404A 1009 pressure control with cut in set between the 0.5 and 2 psi lines and the differential is set with 1.5psi pointing directly forward(there is a line labelled OFF at this location) the system from an initial pressure of 0 and rises to and operates at 5.5psi.  The pressure fluctuates at most +/-0.25psi once 5.5psi is reached. I can not detect this Pressuretrol doing anything, i.e. no movement, noise, etc.  (assuming that electrically this is a simple open close switch I will check the resistance during burner on and off states.)  The burners come on for about 3-5 minutes and then off for 1-2 minute from initial starting throughout, for at least 45minutes.  There were no low water shut downs.  There is no return pipe temperature sensors.  The thermostat indicates the current room temperature is below the desired temperature all during this time.  Does this seem like the Pressuretrol is not functioning at all during this time and something else is truning on and off the burner which is causing the system to just happen to operate at 5.5psi and if so what would that be?  Or is the pressuretrol operating but severely miss calibrated?



There is a second pressuretrol, with a mercury switch, that seems to be set at 7ps, but does not seem to engage at all during this time.  I assume this is a safty shut off control and should not normally engage.  The scale seems to have slipped down.  Should the scale be placed such that it is snug under the mounting/set screw? 



The two pressuretrols are mounted in a "U"  shaped configuration, i.e. the pipe exiting the boiler is tee'ed down, split with a cross, extended and brass nipple risers into the pressuretrols.  This would seem to me to collect water, and crud, and not be optimal for sensing steam(gas) pressure.  Should this be changed so that these connecting pipes always drain?



Any insight or suggestions would be greatly appreciated,



Fred

Comments

  • Brad White
    Brad White Member Posts: 2,393
    edited February 2011
    Firstly

    That "u-shaped" configuration is your water seal, same thing in function as a pigtail, to protect your instrumentation from direct steam contact. It needs to be filled with water.



    But it also needs to be clear of gunk. Check that to make sure it is clear. 



    Your pressuretrol seems to be doing its job but at a higher range than you intend, obviously. (Your mercury pressuretrol I suspect as you do, is your safety high limit).



    I would also check to see that your settings are correct, your cut-out pressure being 2 and your differential being 0.5 is fine if it is subtractive. If additive as on some models, that still will not get you to the 5 psi range, so I suspect  that the tubing may be obstructed. How confident are you in your gauges?



    How is your venting? If sub-par and no main vents, you of course artificially raise your piping pressure by not releasing that air. Still, too high though. But any venting you have now, with that pressure, should be hissing like the audience at a Joan Rivers performance.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • crash2009
    crash2009 Member Posts: 1,484
    Could be three reasons that I can think of

      Here are some solutions.

    The switch is no good  http://www.heatinghelp.com/forum-thread/132867/How-do-you-test-Pressuretrol

    The pipe going to it is plugged

    The calibration is off  http://www.heatinghelp.com/forum-thread/128249/why-do-Honeywell-vaporstats-suck-so-badly



    Could you show us a picture of the U arrangement?
  • Frederick
    Frederick Member Posts: 19
    Hmm

    As to the "U": shape, I have another system that has the pipe coming out of the boiler tee'ed level and the two pressuretrols(mercury) coming up from there, i.e. the connecting pipes always drain.  Are you suggesting that I should convert that system to a "U" shaped (pigtailed) setup.  This other system has been in service like this for over 13years, without problems.



    I will clean the brass(?) riser to the pressuretrol.  It seems logical if that is clogged that it would require higher pressure to trip the sensor,  but I would have figured that the hysteresis would have increased also, i.e. the pressure would have to fall significantly more than the differential before the burners would cut-in again.  I have nothing to gaugage my trust of the 0-30psi gague.  It looks new, connected to the pipe directly out of the boiler, i.e. direct contact to steam.  I will add a freshly bought 0-15psi gague when I clean the pipe.



    I believe the pressuretrol to be additive.  The PA404A 1033, which seems to be the replacement to the model I have, states the differential to be additive, and the sticker inside my device states that the cut-out to be the cut-in plus the differential.  The max differential is stated to be 5psi.  Is my described behaviour what should be expected when the maximum pressure  is reached?



    The vents on the returns are old, rusty, and I do not hear an abundance of hissing.  They are next on my list, but I figured I would make sure the sensor and controls worked as expected, it makes debugging much easier when I screw thing up!.  So with the settings on the pressurtrol I would expect a poorly heated building given the lack of hissing of the vents, but the building heats fine, but the gas company is way to happy supplying me with fuel.  So I suspect the high pressure reading on the guage is probably correct.  Also I suspect the person who installed the boiler did not optimize the system, i.e. he turned it on, got steam and left.
  • Brad White
    Brad White Member Posts: 2,393
    Whatsamatta U

    What you describe is not a u-trap seal because the pipe always drains. Thus, your controls have been seeing direct steam pressure and this is not a good long-term strategy. In fact, we allow a plug for pre-firing filling so the instruments always have a water seal.



    The ideal way is to have brass pigtails below each device, but otherwise the pipe exiting the boiler would turn down, then over and up to a tee, into the branch. The run of the tee on each side would be a series of nipples and tees to install your instrumentation.



    The fact that the building heats well is encouraging though. Fine tuning when you are not chasing the basics (such as no heat at all or an ungodly racket), can be fun.
    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"



    -Ernie White, my Dad
  • Frederick
    Frederick Member Posts: 19
    It was gunk, but ???

    The "U" shaped pigtails were full of brownish pasty gunk.  After cleaning, refilling with water and turning the boiler back on the pressure cut off is much closer than it was before.  The pressuretrol, which is set at (cut in 0.5psi, differential 1psi, additive), cuts out when the 30psi gauge, which is above the water level in the pigtail,  reads about 2.5psi.  Is this difference normal, i.e. pressure difference between steam and water buffer?  Should I add a pressure gauge within the water buffer?



    One thing that I noticed is it takes much longer than 5 minutes to for the boiler to rise from dead cold to 2.5psi, but less than 2 minutes to fall below cut in pressure(0.5psi?).  Is this normal?  Should I be looking for steam/air leaks?
  • BobC
    BobC Member Posts: 5,317
    Don't trust 0-30PSI gauge

    Keep in mind that a 30PSI gauge really isn't very good at the low end of the scale so a reading of 2.5PSi does not mean it's cutting off at 2.5PSI. You might want to ad an auxilliary 3PSI gauge so you can see whet the pressure really is - http://www.gaugestore.com/prodinfo.asp?number=33020



    A pigtail acts like a trap that prevents the steam from reaching the pressuretrol or a non syphon pressure gauge. the steam pressure pushes on the water trap and that presses on the air colomn between the trap and the control and gauge. If you use a trap instead of a pigtail you might want to fill the trap with a little water because the larger pipes size might mean it takes a long time for water to accumulate in that trap. Make sure that trap really does retain water or you will damage the pressure control and any low pressure gauge.



    I've attached a picture to show what my setup looks like using a pigtail as the "trap".



    Bob
    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • Jamie Hall
    Jamie Hall Member Posts: 19,456
    That time relationship...

    between pressure rise and fall is quite normal.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
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