The Wall
Forum / Gas Heating / Bouncing Gas Pressure
  • Post a Reply to this Thread

    Bouncing Gas Pressure (33 Posts)

  • NYplumber NYplumber @ 9:23 PM
    Contact this user

    Bouncing Gas Pressure

    Good evening wallies,

    Writing up a small paragraph and posting two videos in hopes someone has come across this issue before and can lead me in the correct direction.
    Have a small building with two 600mbh condensing boilers. Two inch gas line from the street to the boilers. Low pressure in the street so there are no regulators. Gas main has a wye strainer which is clean and removed the basket for testing with no relief, so it was re-installed. Meter is a rotary style meter that is brand new due to me thinking it was the cause of the nuance spikes.

    The first video is when only the commercial 160mbh dryer is running. Second video is when only a single boiler starts up and runs. The only thought I have is that there is water in the line however the drip legs were dry other then a few drops of oil. When one boiler is on, the second will lock out intermittently due to an unstable gas pressure. No regulators on the line. Gas company says they did their job as there is six inches of water column at the meter.
    Hopefully your internet connection is fast enough to see the needle vibrating.



    While I have you guys here, can anyone assist in sharing a source or pdf that illustrates and instructs how one can oversize a NG line to compensate for not enough pressure on start up? General gas sizing information would also be helpful as I can use a good brushing up on pressure drops, fittings and line length.

    The boiler company said we need a pressure booster since the street cant deliver over seven in-wc. Never heard of such an apparatus.
    Comments & suggestions welcome.
    This post was edited by an admin on July 1, 2014 9:36 PM.
  • Techman Techman @ 2:49 AM
    Contact this user

    Gas press

    What is the closest you can get to the street press to get a reading there when boilers startup? Is there any gas cocks in line that might be too restrictive?
  • NYplumber NYplumber @ 9:33 AM
    Contact this user

    before the meter

    There is a test port before the meter, however the guage reads identical.

    All gas cocks are full port commercial style full port with a hole for a lock.

    Thank you for your reply.
  • Rich Rich @ 7:42 AM
    Contact this user

    Gas pressure

    and sizing are amazing in that they can go awry if close attention is not paid .  Please inform of what boilers these are and what method was used to size the piping for this system.  Where are you located  How far are these units from the meter and what is there position in the order ?  Forget about where you are I did not look at whom was posting
    You didn't get what you didn't pay for and it will never be what you thought it would
    This post was edited by an admin on July 2, 2014 7:43 AM.
  • NYplumber NYplumber @ 9:35 AM
    Contact this user


    Knight boilers. Located 35 feet away from the meter. Pipe sizing looks to have been longest branch method.

    Thanks for your reply.
  • Snowmelt Snowmelt @ 12:56 PM
    Contact this user

    I came across

    A job where the unit kept fluctuating when in high fire.

    The tee in the street was rotted, the gas company came, it was a 2 day event. They Dug the street up and one of the PSE&G guys told me that the particular fitting that rotted they don't use. Also then he told me that it might of been the end of the day when installing that particular fitting but it should of never been installed because it rots out.
  • NYplumber NYplumber @ 1:03 PM
    Contact this user


    Thanks for the reply. Would you have any photos of the fitting, or any other info how you got the gas company to commit and join forces to fix the issue?
  • Snowmelt Snowmelt @ 5:46 PM
    Contact this user


    They used common sense, I told them on the phone that the water heater was dropping way to much and I think it's before the meter, they came out and said yep there's a break somewhere. And then did what they had to do to fine the leak.
  • Tim McElwain Tim McElwain @ 6:33 PM
    Contact this user

    A 2 inch gas

    line with an allowable .3" W.C. pressure drop 30' long will handle 1,680,000 BTU's
    a 40' long will handle 1,440,000 BTU's. That information is taken from Table 6.2
    (a) Schedule 40 Metallic Pipe  from ANSI z223.1/NFPA 54 National Fuel Gas
    As I told you on the phone you need to get a supervisor from the engineering
    department at the gas company to look at this problem. The original installer
     should also be involved. I would not be surprised to find that when the main
    was taped the wafer was left in the main as the fluctuation shows on the gauge
    it is vibrating causing  your problem. The sensitivity of negative pressure gas
    valves will often cause nuisance lockout when gas pressure is not stable.

    As Ray mentioned in his posting and as I told you on the phone about the boiler job I commissioned for a church we had to run a 3" welded line 50 feet to insure stable gas availability when the boiler fired. The gas company would only guarantee us 5" W.C. gas pressure coming out of the Rotary meter. This should have been handled by the local utility and the original installer of the boilers.
    This post was edited by an admin on July 2, 2014 6:39 PM.
  • RayWohlfarth RayWohlfarth @ 6:27 PM
    Contact this user

    Couple ideas

    Hello Moe,

    Let me tell you that I have been in your position and it

    I have a couple thoughts:

    I did a consulting job in NY and they had a gas
    compressor that would boost the gas pressure and they had some issues getting
    it resolved. They are very expensive and tempermental.

    I would try a couple options before having the client
    install one of those. You mention that there is no regulator I would try adding
    a surge pipe in the gas train This allows the gas pressure to be steady when
    starting. Make sure that you stagger the inlet and outlet so that the pulsation
    does not carry through. I have enclosed a crude drawing that may better show
    you The other thing is to oversize the gas piping This may take the swings from
    the gas pressure Good luck and let me know how it goes.

    Ray Wohlfarth
    Ray Wohlfarth
  • NYplumber NYplumber @ 7:14 PM
    Contact this user

    Surge sizing

    Good evening Ray,

    Any formulas or rules of thumb to calculate surge pipe sizing?

    Thanks in advance.
  • NYplumber NYplumber @ 12:54 AM
    Contact this user


    A SPECIAL thanks Tim and Ray for stepping in and replying! It seems that the line was sized for a specific inlet pressure that is actually not present every day, hence the intermittent lockouts.

    We used a chart with a multiplication factor to work back what we are getting based off of our pressure drop from the meter to the boiler and the approximate length (including fittings). Slurping a slurpee through a coffee straw is whats going on. Had my head too wound up in the charts to realize the chart is based off of .3inwc and we had a deeper draw.

    We spoke about adding a buffer pipe like Ray mentioned, however was told if any money was to be spent on gas, just run a new line rather then waste time at this point.

    These boilers are EXTREMELY picky. You could sit there all day and baby sit them and they will lock out ten minutes after you leave. As a heads up for anyone buying, installing or servicing condensing equipment, be ready to be on your own and not get real help from the manufacture. They have been less then helpful here and in the past.

    Ray, would you be able to lead me to a formula to use when up sizing piping diameter and length to aid in ignition?

    Thanks again guys!
  • SWEI SWEI @ 1:19 PM
    Contact this user

    Series Summation Method

    Anyone know of software that supports this?
  • Rich Rich @ 8:47 PM
    Contact this user

    Gastite manual

    Pages 39-43 .  I believe they have a program online to size in this manner Swei .  When this stuff first came out long ago I began to wonder how it was that you could run smaller diameter pipe when that type of pipe had a higher pressure drop per foot .  The answer was right in the International Fuel gas code .  3 acceptable methods for sizing , #3 other approved engineering methods .  This is CSA approved and is shown plainly in the manual .  The charts will plain and simple rob the money right out of your bank account with the price of metal now . Charge same price and offer some piece of mind .  This method pretty much relies on 402.5 Allowable pressure drop . Written right in the code for those whose money and perhaps meeting the intent and spirit of the code mean something . You should check it out , it is really economical and will leave you with more of your profit .
    You didn't get what you didn't pay for and it will never be what you thought it would
  • Tim McElwain Tim McElwain @ 7:28 PM
    Contact this user

    Rich, which version of the Gastite manual

    my manual I have does not cover this.
  • Rich Rich @ 7:11 AM
    Contact this user

    Just Seeing this

    Tim , sorry for the delay .    The series summation method is CSA approved engineering method .  The book on my desk is dated November 2006 but the method has not been changed . It appears on page 36 of that text and the iron pipe pressure drop tables appear on pages 88-91 and cover load and sizing from 10,000 through15,000,000 BTU ..  Gastite also has a downloadable size it program that supports every method . 
     We had a hell of a time explaining this method to inspectors . Had lots of resistance and finally DCA assisted with a communicator to all inspection departments validating the engineering method and it's acceptability . We still have guys that need it explained to them .Gee , imagine that !
    You didn't get what you didn't pay for and it will never be what you thought it would
  • Rich Rich @ 7:03 AM
    Contact this user


    We have been sizing using series summation (allowable pressure drop) for years now without a hitch .  We have also been called in several times where people installed tankless 199,000 water heaters and found that the meter was sized tight when there was a typical storage water heater (40,000) but when the tankless was installed the pressure drop through the meter would increase from 1/2" to 2" leaving the equipment woefully short of required minimum inlet pressure . 
    The series summation method is segmented , main to tee , tee to appliance and makes for easy math while sizing and determining what size pipe is needed and it's maximum length .  Over the years we have saved loads of material and labor money and been able to locate and point to any possible problem or condition easily .  It works on all pipe where pressure drop is known for a given load for that pipe , a good example of the method is shown in Gastite manual , there are iron pipe pressure drop tables in rear of manual . Just size the system as they would have you do it using their product , ignore the wording CSST and substitute with iron pipe .  Using this method is accurate , labor saving , economical and will minimize the hazards associated with the distribution and storage of --------- within the structure , in other words , the INTENT of the CODE .  It is an approved engineering method and will save you time and money .  Just remember to ream, every piece of pipe , you probably already do that but many don't .  Tim or Ray may be able to verify the validity of this method , I am sure .
    You didn't get what you didn't pay for and it will never be what you thought it would
  • icesailor icesailor @ 11:09 AM
    Contact this user

    If I can ask:

    I've never seen this actually, and I never will. But, what is basically a "Accumulator" to increase stored gas and pressure with a short, larger section of pipe between the meter and the appliance is supposed to help with fluctuating pressures?.

    It was stated that the gas piping is run some distance (30'?) from the meter to the appliance. Replacing the 2" with 3" would seem to be a giant PITA. Welded? But, if a second 2" gas line was run parallel to the original line from as close to the meter as possible to as close as you can get to the appliance, would that aid in the short term pressure drops? Its almost equal to a 3" pipe.

    In water systems that are piped too small or water systems with wells, they act similarly and adding pressure storage seems to smooth out fluctuations. Of course, if the incoming flow drops well below the static pressure, all bets are off.

    This must be an ongoing problem where you live because when I went to a 2 day Viessmann class, someone (perhaps you) brought up this issue about the area in NYC with the low pressure unregulated gas and the pressure dropping during peak loads. The onboard computer of the appliance was supposed to adjust to this problem. Or so they said.

    Sounds like the Wall Street Crime Syndicate needs to get off their wallets, cut back on the dividends to their gangster investors, and put some REAL investors to work. The people who actually exert themselves to do anything other than opening their monthly statements of going to the bank and clipping coupons.  Replacing those old, rotten low pressure gas mains with something with higher pressures and regulators. If they want to promote gas the way they have and get everyone else to dump oil, they need to use some of that new profit on improvements.

    Don't hold our collective breaths.
    This post was edited by an admin on July 3, 2014 11:12 AM.
  • RayWohlfarth RayWohlfarth @ 3:54 PM
    Contact this user

    Gas line sizing

    I use the tables in the International Fuel Gas Code for sizing a gas line.
    Good luck
    Ray Wohlfarth
  • icesailor icesailor @ 5:57 PM
    Contact this user


    I guess what I was asking is that sometimes, if you feed something from both ends, things smooth out. The greater the overall volume of  a pipe, the less it is subject to changes in pressure from one end.
  • Techman Techman @ 12:46 AM
    Contact this user

    Pipe sizing

    Gas size piping charts. Are they sized for systems where there is a regulator which restricts the flow of gas based on the gas main having a greater press than the gas appliance gas press. Now this is where my mind gets fuzzy. On this system there is no regulator, just 5" wc. So to supply the gas appliance ,with/from a lower supply side press, wouldn't the gas pipe in the bldg. have to be bigger due to the lesser "make up ability" of the gas main? KindaSorta like the gas main being 4''wc.
    This post was edited by an admin on July 4, 2014 1:20 AM.
  • j a j a @ 9:35 AM
    Contact this user


    Just some of my input hope it helps, maybe some of the questions are already answered.

    1 What is minimum gas pressure the manuf. requires for proper operation
    2 what is static and dynamic pressures with each appliance running separately and combined.
    3 Did you or anyone check for moisture in the gas, suggest pull off supply nipple at gas valves and check inlet screen if applicable…Recently I had moisture in customers gas line
    had to have inline filter installed…Showed as a rusty red color.
    4 What is the min.gas pressure your gas provider guarantees

    Its not uncommon to see oversized gas lines on the inside fit for low press. areas Kind of like a reservoir in some peoples minds…The current code book in your area gives min. sizing…
    My opinion.either wet gas,or pressure to low on street side….

    hope you get it fixed
  • Tim McElwain Tim McElwain @ 1:38 PM
    Contact this user

    This is not rocket science

    just pipe sizing and pressure as they relate to each other. Keep it simple I do not care what system you use bottom line the equipment has to operate with NO PRESSURE DROP PERIOD WITH ALL THE EQUIPMENT RUNNING.
  • NYplumber NYplumber @ 7:17 PM
    Contact this user


    1. 4inwc
    2. Cant recall
    3. no moisture
    4. 4inwc
  • j a j a @ 2:54 PM
    Contact this user

    gas pressure

    measure the pressure static and dynamic …If gas sizing and pressure is good look elsewhere Very recently my area has had moisture issues…Filters have been installed by the gas company…..low pressure areas are a bit touchy….
  • Bob Harper Bob Harper @ 7:49 PM
    Contact this user

    voice of experience

    Yes, you must do your calculations and as Timmie says, the proof is in the pudding regarding performance at the appliance under full load.

    Now, I wanted to share a case where I had a similar problem. My first thought was a regulator upstream but it turned out to be a low point in the piping forming a bit of a trap. I could feel and hear the vibration from the turbulence. Re-piped it and got some water/ emulsion out and it worked fine. No evidence in the sediment traps. In the old days of wet gas, "drips" were installed right inside the building and the pipes were pitched for drainage.

    I investigated a case in the mountains with LPG delayed ignition. Turned out it was gravel (rocks) in the copper tubing. The LP supplier carried copper tubing uncapped in the rear of the truck they use to deliver and set up service. Gravel from driveways must have gotten into the tubing. Before changing a valve, I cracked the gas cock and gravel bounced off my hand! Got it on camera.
    Just a thought.
  • NYplumber NYplumber @ 10:41 PM
    Contact this user


    The system is being run temporarily in limp mode while we ensure equipment is working.
    One day we will disconnect the appliances and blow compressed air through the system to see if any moisture comes out. I have heard stories first hand that when a large gas line has leaks they fill it with water, leave it open to rust and blow out the water. If that happened here, maybe they didnt blow it all out?! Time will tell.
  • icesailor icesailor @ 11:49 PM
    Contact this user

    Blown Air:

    You would be surprised at what you can do with a small air compressor. You can use as much or as little air and pressure as you want. The air doesn't burn or smell.
  • Tim McElwain Tim McElwain @ 1:35 AM
    Contact this user

    I can't believe

    some of the things I hear on Heatinghelp.

    I have heard stories first hand that when a large gas line has leaks they fill it with water, leave it open to rust and blow out the water. If that happened here, maybe they didnt blow it all out?! Time will tell.

    This is a new one on me I would love to know who it is that does this stuff they must be nuts!
  • Bob Harper Bob Harper @ 9:43 PM
    Contact this user

    blowing air into gas lines?

    First of all, if you plan on blowing any gas under pressure above 1/2 psi, you'll have to disconnect every appliance. Next, you'll have to replace the gas cocks if the pressure exceeds 5 psi. If you blow compressed air, you will probably just add a lot of water into the piping where it will find a low point and puddle and, it will not blow out standing water. If you had a short section and wanted to blow it out, rather than going to all the trouble of rigging up dry N2, just replace the offending section. I know of no method that has been proven reliable at clearing gas piping once contaminated. Moreover, should there be an Ooops! down the road, they would do everything they could to pin it on you and your blow down procedure. Deliberately causing rust inside a gas pipe is insane, grossly negligent and probably criminally negligent.
  • icesailor icesailor @ 11:24 PM
    Contact this user

    Asking for help:

    If you are pointing at me, sometimes in the REAL world, you get in situations where you've exhausted all hope of help, and they have basically left you to your own devices. Someone once said that the best bilge pump for a sinking boat is a guy, up to his knees in water with a 5 gallon bucket. When you are given a situation to resolve, and nothing resolves it, and everyone you ask has no solutions, where do you turn? You turn to yourself. By that time, it is hoped that you have enough experience to know that you have to turn off pressure to any and all appliances.
    You do what you have to do. Or you tell them to call someone else. "Someone else" may know less than you. But they will never call "someone else" being you ever again. In this case, you or I aren't there. We can't use that intuition we develop with experience. If you have a supply issue, the supplier will deny with their dying breath that there is anything wrong with their supply. Until you overwhelmingly prove they are wrong.
    "Water in the air that I could put into the gas line and cause rust?" I have an air dryer that I can quick connect to my compressor. You can't have water vapor in the air when you use a paint spray gun. Water specks in the finish paint. If there is a water trap pocket, where did it come from?
    Some times in life, all the fancy tools don't solve it and you have to do like the old dead guys did. However they could.
    As a plumber, someone once said that no matter how old you got, you still need a shovel in the truck. Because you will need it. Even "Old Man Bartlett" in his 80's needs  one and uses it.
    Or like my old dead boss said, when you get to this level, you're supposed to know what you are doing.
  • 4Johnpipe 4Johnpipe @ 7:24 PM
    Contact this user

    The Bounce

    Wow I saw the bounce!!! Did you resolve this issue? If not I would suggest checking the regulator out at the gas meter. If it has a threaded relief port...try plugging it off and perform the test gain. It looks like a delivery issue...If you can not plug off the relief port (temporarily) have someone stand ready with a gas sniffer and test for gas discharge at the regulator.
    Considerate People, Considerate Service, Consider It Done!
    This post was edited by an admin on August 8, 2014 7:26 PM.
  • Tim McElwain Tim McElwain @ 3:59 PM
    Contact this user

    This system is

    connected to a low pressure gas system less than 14" W.C. pressure available. There is no regulator involved.
Post a Reply to this Thread