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Gas flame oscillating

JackShelley
JackShelley Member Posts: 12
I am working on a propane fired Trane UH2c100 furnace converted to propane. The flame will occasionally start to oscillate at about 4 oscillations per second. The flame never goes out but kinda puff , puff, puffs quickly. I discovered that the low pressure gas line is a 3/8 inch line. This is undersized for the size of this furnace. Is it fair to assume the oscillation is due to the undersize or could it be a defective gas valve. All gas pressures are good, except they oscillate too!! New high and low regulators were replaced by the propane supplier as well as alcohol added to the tank. There is also a gas fire place and stove in the house, but the flame on the fire place is steady when this problem happens. Thanks for your help.



Jack Shelley

Comments

  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    What is the firing rate

    of the furnace (input)? How long a run of 3/8" tubing do you have?



    What did you have for gas pressure at the inlet of the gas valve when this was happening and what did you have at the outlet?



    Are you saying that the propane supplier replaced the first and second stage regulators already? If so why did they do that?
  • Empire_2
    Empire_2 Member Posts: 2,343
    Gas pressure.

    Yea, we need to know the pressure in and out of the existing GV on the furnace.  The pressure may be there, but volume could be the culprit.  Check the name plate on the furnace for min/max input settings and go from there.  Since the furnace draws or consumes the most propane, this in where it will be most noticeable. 

    You said the pressures were OK,......According to whom and how and where was it measured?  Just curious.



    Mike T.
  • JackShelley
    JackShelley Member Posts: 12
    Gas flame oscillating

    The input is 100,000 btu, my inlet was 11 inches, output was 10 inches, The 3/8 run is about 20 feet, and then it goes to several feet of 1/2 black iron pipe near the furnace.



    They replaced both regulators in an effort to solve this flame problem.
  • JackShelley
    JackShelley Member Posts: 12
    Gas flame oscillating

    The input is 100,000 btu, my inlet was 11 inches, output was 10 inches, The 3/8 run is about 20 feet, and then it goes to several feet of 1/2 black iron pipe near the furnace.



    They replaced both regulators in an effort to solve this flame problem.
  • JackShelley
    JackShelley Member Posts: 12
    Gas flame oscillating

    The input is 100,000 btu, my inlet was 11 inches, output was 10 inches, The 3/8 run is about 20 feet, and then it goes to several feet of 1/2 black iron pipe near the furnace.



    They replaced both regulators in an effort to solve this flame problem.
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    Your propane company

    should have figured this out but here goes:



    3/8" tubing at 20 feet can only handle 64,000 BTU's at a .5" W.C. pressure drop on LP at a specific gravity of 1.5. So you are undersized. 1/2" K or L tubing will handle 129,000 at 20 feet. 1/2" pipe will handle 200,000 BTU's at the same pressure drop and 20 foot length.

    You need to run 1/2" tubing direct from the second stage regulator to the furnace at a minimum size. Make sure however if there is other equipment off this line to figure all of it in. A gas cooking range can have a BTU draw of 65,000 BTU's or higher plus the fireplace insert.



    If I figure all of this in 100,000 furnace, 65,000 gas range and insert say 40,000 that is a total over 200,000 BTU's. If that is the case then you are looking at a minimum 5/8" tubing which will handle 20 feet and give you a capacity of 226.000 BTU's.
  • icesailor
    icesailor Member Posts: 7,265
    Oscillations

    Thanks Tim.

    In Massachusetts, we all went over that in the CEU classes required for our license renewals next year. All LP Installers, Licensed Gas Fitters and Plumbers.

    Does anyone ever consider a gauge where the gas comes out of the regulator and one at the gas control and check the pressure drop between the two? The gas company only wants to sell you gas. They don't want to train their service folks. Costs too much money. They have insurance in case something goes wrong and someone has a policy that says that something will. It's a win-win for all, except for the consumer.
  • JackShelley
    JackShelley Member Posts: 12
    Gas flame oscillating

    I went to the customer to double check my story.... I didn't notice the 1" line coming directly out of the back of the regulator! There were two 3/8 inch lines but one was a line for a remote vent. Could this be a defective gas valve???



    Thanks for your help.



    Jack
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    There is a step by step

    procedure for testing pressures on LP systems. Most LP companies are very good at this. I can no longer speak for natural gas companies who stopped giving the kind of training that I give back in the 1990's. There are special gauges for doing this pressure testing that come in a kit which I advertise at my center and can be purchased from Ray Murray Inc. that along with Presto-Tap fittings make taking pressures very quick and easy.
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    Jack what is the Make and number of the gas valve?

    You will need to put a manometer ahead of the valve and one after the valve and watch what happens when this oscillating occurs. If the pressure on the inlet during this oscillating fluctuates then your problem is the second stage regulator or the piping. If only the outlet oscillates then it is the gas valve. Make sure the sensing port on the outlet inside of the gas valve is not partially blocked. Watch out for pipe dope or Teflon tape partially blocking it.



    I didn't notice the 1" line coming directly out of the back of the regulator! WHAT IS THE 1" LINE GOING TO?





    There were two 3/8 inch lines but one was a line for a remote vent. WHAT KIND OF VENT AS THAT DOES NOT MAKE SENSE ON AN LP SYSTEM? WHAT DOES THE VENT DO?
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    I might add here that I have offered my

    services to all the gas companies in the northeast and they are not interested in the training I offer. They want to sell equipment and gas which the equipment burns is their final product. One very astute gent from one company said to me "We do not want to talk about troubleshooting as it may give the impression that these systems have problems" The utilities stopped giving same day service in the winter many years ago, Calls to the local company here can take as much as four days to get your call answered. An elderly neighbor of mine called me the other day as they had been waiting for three days for gas service. I went over found their problem got them running in about 15 minutes. They are still waiting for the gas company to show.
  • icesailor
    icesailor Member Posts: 7,265
    Vents:

    Isn't there a vent on the primary regulator that has to be moved or piped to a remote location if it is too close to a source of ignition? Like an electrical meter or an AC condenser? With no threads on the opening so someone can't cap it and defeat the purpose? Where I work, gas is all LP. I see these vents all the time when the regulator is too close to a prohibited device.Maybe they fed the first stage with 3/8" OD tube and the second regulator is copper. But the vent is usually 1/2" OD copper.

    Or it is an underground or remote location tank, piped underground with 3/4" or 1" IPS pipe into the first stage regulator and both lines (3/8") are a feed and a vent. I've seen a lot of things piped with 3/8" soft copper. Not what I learned in my CEU's but hey, they're smart, I'm not. I hook up what the code says. I pipe it to the outside. The LP supplier supplies the connections outside to the regulator and tanks..

    Maybe that's what he is seeing.

    I've seen that fluttering when the first stage regulator was screwed up and the vent wasn't working properly. Where I work, if this problem occurs, the LP provider is the one to fix it. Maybe it is different in other places.

    You're the man though, Tim. You've forgotten more than I will ever know about gas. And I mean that as a sincere compliment.
  • icesailor
    icesailor Member Posts: 7,265
    Gas Service:

    Tim, my man. This is the age or Corporate America where the bottom line rules. Stockholder have more rights than the consumer.

    All it will take is a serious mishap where a lot of people are killed and some good tort lawyers to put the blame where it belongs. He who owns the gas, has some liability. Just because they gave up service, doesn't absolve them of responsibility. If you call for a problem, and they take over 4 days to get there, the very fact they they are coming shows that they are accepting responsibility.

    They at one time, had the best technicians available to be trained. I know a guy who worked for a gas company for quite a few years doing installs and TS'ing. He is now a Master Plumber. He asks ME gas questions and questions about gas and heating situations. I'm not saying there is anything wrong with his knowledge. I just wonder about his training.

    Utilities all over the country are saving money by cutting back on their service departments and pushing it off on us. The responsibility and liability make my head hurt just thinking about it. There was a time that if you called the gas company about a problem, they sent someone out to check to see if it was their problem. Now, they tell you to call a plumber. To let them decide if it is their problem. If it is, they will be there in over 4 days or under. Unless you smell gas.
  • Tim McElwain
    Tim McElwain Member Posts: 4,506
    Without more information

    it is hard to figure out what Jack has on his hands a few pictures would help.
  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    Stockholder have more rights than the consumer.

    You are right as far as it goes. But as a stockholder of a small bunch of corporations, I can assure you that the stockholders, for the most part, have no influence over the corporations they technically own. Corporations are nominally governed by the board of directors, and the directors' fiduciary duty is to represent the interests of the stock holders. That is the theory. But that is like saying that the United states is governed by the house and senate, and the president is elected by the citizens. Actually, the board of directors represent themselves, they are appointed by the banks, pension funds, and mutual funds that own most of the stock. As in the case of the US government whose senators and representatives actually represent the interest of the money that owns and corrupts them, the corporations do what the people who pay the directors, and I do not mean the corporations. The boards of the various corporations are run on a single-party ticket, like the former government of the former Soviet Union. As a practical matter, thecorporation's duty is to pay off its top executives, not the stockholders.
  • icesailor
    icesailor Member Posts: 7,265
    Flames"

    Corporations are people and have special rights to screw people.
  • JackShelley
    JackShelley Member Posts: 12
    Gas flame oscillating

    This setup has a high pressure regulator on the tank which feeds 2 or 2 psi to the low pressure regulator . The low pressure regulator was located near the intake of the furnace so the vent on the regulator was piped a few feet away from that location to satisfy codes.

    The 1" line I spoke of is the outlet of the low pressure regulator, which is located on the underside of the regulator. This 1" line goes directly into the house and supplies the three appliances. I am going to double check the inlet gas pressure , but I recall it oscillating. I will take pictures next visit.
  • JackShelley
    JackShelley Member Posts: 12
    Gas flame oscillating

    This setup has a high pressure regulator on the tank which feeds 2 or 2 psi to the low pressure regulator . The low pressure regulator was located near the intake of the furnace so the vent on the regulator was piped a few feet away from that location to satisfy codes.

    The 1" line I spoke of is the outlet of the low pressure regulator, which is located on the underside of the regulator. This 1" line goes directly into the house and supplies the three appliances. I am going to double check the inlet gas pressure , but I recall it oscillating. I will take pictures next visit.
  • icesailor
    icesailor Member Posts: 7,265
    Oscillations:

    Years ago, I had a restaurant customer that had a whole tribe of tanks to increase the boiling area. They had 2 stage regulators. One regulator went bad and the flame would oscillate like you describe (to a point). Changing the regulator solved the problem.

    But I had another one that had a vent and spiders moved in and made a nice web that was thick enouth to affect the venting of the regulator.

    As I remember.
  • JackShelley
    JackShelley Member Posts: 12
    Gas flame oscillating (pulsating)

    I found out the source of the problem. After being assured by the propane supplier that the tank, lines and regulators were ok. I tried a new gas valve, to no avail. Still oscillated..

    But the remote vent line was still bugging me so I went outside and disconnected it while the problem was happening and as I unloosened the connection, The pulsating disappeared!! The line was not clogged, but apparently a 1/2 in. copper line is not enough to properly vent the regulator. It is about 10' long.
  • Empire_2
    Empire_2 Member Posts: 2,343
    A Thought on your Furnace.

    Pop off the screw cover to the gas valve adjustment regulator.  Fire and see if there is a difference... 



    My .02

    Mike T.
This discussion has been closed.