RV Doctor: What is loud thumping noise from RV propane regulator?


Dear Gary,
Our goal in buying a new travel trailer was/is to enjoy the outdoors, but we are experiencing a thumping sound anytime an appliance is utilized which runs solely off propane. I can adjust the tank selection valve slightly and it goes away, only to have it come back on when I adjust it back.

Our bed is located just behind the tanks/regulator, which makes sleeping a thing of the past. This trip out, I shut off the propane valves altogether at the tanks, but we would still get the noise, one pop at a time in 15-minute increments.

That said, if you could point me in the right direction I will relay it to the tech if I can’t fix it myself. During my first conversation with the tech, he advised spraying WD-40 into the regulator – which doesn’t make sense as it’s completely sealed and any liquid sprayed into the coupling would then be sent to my appliances via the propane hose.

I’m sure there is a fix – I just have to find it. We have taken it out only twice and the tanks (propane) were full upon delivery of the trailer. Also this noise comes on regardless which is selected as the primary, and with both tanks open or just one. We thank you! —Shawn and Angie

Dear Shawn and Angie,
Propane regulators can and do create an audible whistling or humming noise while operating. Some humming, caused by the vibration of the diaphragm inside the regulator, is normal, but not a banging or clanging noise such as you are experiencing.

But the recommendation regarding WD-40 is 100% incorrect! Never spray anything into the gas regulator! Typically the noise you are hearing is not created by the regulator or the changeover valve, but rather from the pigtails that run from each cylinder to the changeover mechanism atop the secondary pressure regulator. I’m personally appalled at the quality of the propane equipment used today. Most of the components are cheaply produced, usually acquired off-shore and quite deficient when compared to the quality of products from yesteryear.

Each propane pigtail contains a redundant safety mechanism called an excess-flow check valve inside the ACME nut that attaches to the manual service valve at each cylinder. This excess-flow check valve consists of a spring, an orifice, a brass seat and a ball bearing along with other safety components forming, effectively, a flow-limiting device at each DOT cylinder. Here’s what it looks like inside the ACME nut:

The purpose of the flow-limiting portion of the ACME connector nut is to restrict the flow of propane gas should an excessive leak exist anywhere in the propane system; it’s a safety device. Just about every time the DOT cylinder service valve is opened, this small ball bearing in the nut assembly is moved towards the piping system and into a brass seat, restricting the flow of gas. It does not, however, fully shut off the entire gas flow; the ball bearing only restricts it.

By design, a small amount of gas is allowed to bypass the ball and continues to flow into the changeover valve, into the second stage regulator and then into the rest of the distribution piping system. As long as all the appliances are turned off and there are no propane leaks anywhere in the system, this small amount of bypass flow quickly builds up enough back-pressure that it eventually equals the incoming bypass flow pressure coming through the device. When that happens, the small spring pushes the ball bearing back and off the seat and permits unrestricted flow of gas into the system.

This whole process takes about five seconds and is designed to work in this fashion. What you are hearing is the back and forth movement of the ball bearing slamming into the brass seat inside the ACME nut of a cheaply constructed, high pressure pigtail hose. Replace the pigtails with a quality replacement hose. Avoid those cheap (by construction standards) imported hoses that most RV accessory stores stock these days.

There’s an outside chance the second stage regulator is faulty too, but I’m guessing your thumping noise will go away with a pair of quality pigtails installed. To be sure the propane regulator is working properly, have a Certified or Master Certified RV service technician (not that other guy!), run a propane regulator test, including a flow test, lock-up test and timed pressure drop leak test. Also be sure the DOT cylinders are never overfilled. But I’d wager that 90% of the time that banging noise is caused by vastly deficient pigtails.

gary-736Read more from Gary Bunzer at the RVdoctor.com. See Gary’s videos about RV repair and maintenance.


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4 months ago

Any recommendations for a “quality” brand name?

Will B.
5 months ago

So, the “tl;dr” is “replace the pigtails”?

Tommy Molnar
5 months ago
Reply to  RV Staff

“tl;dr” I don’t understand the need for abbreviations like this. Just say what you mean or want to say. How tough is that?

5 months ago
Reply to  RV Staff

Dianne, if “tl;dr” means “Too long; didn’t read” in that sentence, the sentence then does not make any form of a syntactic unit.
So, the “too long; didn’t read” is “replace the pigtails”? What piglish is that?

Larry H Lee
5 months ago
Reply to  Will B.

No. It is “Replace the pigtails first as the easiest, cheapest and ‘most likely to solve the problem’ fix. If that did not work then here is a list of other possibilities to run down. Also a neat lesson in how the flow restrictor works including a cut-away picture.”
Really, Will, if you just want the answer without any explanation you are looking in the wrong place. Typical (stereotypical? ) RVers want to know how things work so they can figure it out for themselves or perhaps help a neighbor RVer in the future.
Long enough comment for you or would you like more?

5 months ago
Reply to  Will B.

Will, you need to learn how to skim. Then nothing is too long to read.

I find most YouTube videos too long to watch (tl;tw), so I keep my finger near the right-arrow key on my computer. A quick press skips forward 5 seconds, a long press fast forwards. Same with the back arrow key.

4 months ago
Reply to  Irv

I watch them at 1.5 or even double speed most of the time. Then slow down the parts that are useful.

5 months ago
Reply to  Will B.

From UrbanDictionary:
1. When responding as a first post, and only as a first post, on a thread, it means the OP’s post was so long and unimportant or uninteresting that the user deemed it unworthy of his/her time. If the topic really is unimportant and uninteresting, and long enough to need more than a minute to be read and understood, the user ends up looking clever, though on some communities the user may end up looking like a troll or a lazy bum.
I vote for looking like a troll.

4 months ago
Reply to  Will B.

I found the detailed description insightful, but then I like to know how things work it goes a long way when troubleshooting a problem.

Thanks for the well written explanation Doc.