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Monday, January 1, 2001

What the Pro's Do - Propane System

What the Pro’s Do (or should be doing!)

By Gary Bunzer

Throughout many of my RV owner articles, seminars and RV Doctor Columns, I make frequent reference to this declaration; “Do not attempt this yourself. Only allow certified or master certified RV service technicians to work on your ____________ (fill in the blank).” Whereby I’m simply implying that certain tasks should be left to the professionals. There are some procedures, processes and practices that even the most experienced RV owners should not attempt. In most cases, it is in regard to the need of specialty equipment or high-dollar diagnostic test devices or support literature, (schematic wiring diagrams and product service bulletins for instance), which I’m sure most RV owners would not possess. In other instances, it is because specific training is required since some tasks are a challenge even for veteran service techs until hands-on practice or repetition breeds continued success. 
Am I stating that certified or master certified RV service technicians are perfect because they are certified? That they will be able to diagnose and repair your RV and get you back on the road in the fastest amount of time, job complete, without fail, every time? Absolutely not! But I can tell you this…. You stand a much better chance knowing that a given technician has completed some form of training and has passed a rigorous exam, or worked his/her way through five specialty areas (successfully passing six different exams) to obtain RV Industry certification, and has continually earned forty recertification points every five years. More so, at least, than the guy over at Joe Blow’s RV Service Shop, who hung out his shingle because he once owned a folding camping trailer! (My apologies to anyone owning a real business called Joe Blow’s RV Service Shop!). But I sincerely hope you get my point. The first question I encourage RVers to ask when forced to stop at unfamiliar repair shops or dealerships during their travels is, “Do you have any master certified technicians working here?” The odds are in your favor, always, by taking your recreational investment to a certified technician for professional troubleshooting and repair!

RV Industry technician certification is a joint effort developed, supported and endorsed by RVIA, the RV Industry Association (a trade group representing over 90% of all RV manufacturers) and RVDA, the RV Dealers Association (representing a nationwide network of selling dealerships). Both associations have committed to developing ongoing service technician training programs and are the only agencies authorized to “certify” technicians. Independent RV training schools may also do their own “certifying,” but it’s the above patch that really matters.

The RV Propane Gas System
One area where my aforementioned admonition is paramount is with the RV propane system, the system in general, as well as the internal happenings inside the propane appliances. That said, there are many RV-owner-type propane preventive maintenance tasks you can perform with a little knowledge and common sense. I’ve written extensively regarding the RV furnace, water heater and refrigerator. Frankly, there is not much preventive maintenance involved with the cooktop or range other than to simply keep the burners clean.

But the one common denominator regarding all four of the propane-burning appliances, common to the vast majority of recreation vehicles, is the main propane pressure regulator.

In the RV Doctor Newsletter I touched on the importance of the pressure regulator and that only certified technicians be allowed to make adjustments to the operating line pressure. I also mentioned a couple other tests associated with the regulator that should be performed annually, as well as the requirement of obtaining specialty devices to have those tests performed. The reason? It is impossible to adjust the regulator by simply looking at a burner flame. Small incremental adjustments in the operating pressure will manifest no visible flame differentiation at any given burner. It cannot be detected by eye; it must be measured.

All that said, I do believe it’s important for RV owners to understand why the three pressure regulator tests and measurements are mandated. Such as, why is the delivery pressure set to 11.0 inches of water column? What is regulator lock-up? And, how can it be determined, with 100% certainty, that a given RV propane system is leak-free? Or conversely; how to know, with 100% certainty, leaks are indeed present somewhere in the system. And what to do to locate and rectify them!

Therefore, what follows are the specific tests your professional, certified RV service technician should be doing to guarantee your propane system remains in top-notch condition and you can be assured no leaks are present as you use your RV.

Lock-up Pressure
In previous articles, I’ve stated that all propane appliances manufactured for RV use are set to operate at an operating line pressure between 10 and 14 inches of water column. All appliance makers and RV industry educators proclaim the propane system operating pressure should be adjusted annually to 11.0 inches of water column. Why 11.0 inches? It’s due to something called regulator lock-up pressure. That pressure contained in an RV gas system that has an open service valve on the propane container, and all the appliances turned off. In other words, there is pressure, but no flow of propane. In a properly adjusted system, the lock-up pressure, that pressure required in a gas system to close the seats inside a two-stage regulator and stop the flow of gas, is typically 1.0 water column inch above the set pressure.

If the regulator is set at 11.0 inches of water column and the lock-up pressure raises it to 12.0 inches of water column, as it should; that falls right in the proverbial center of the 10-14 inches the appliances were designed for. In other words… its optimum setting.

Therefore, in addition to a visual inspection, the pro tech will adjust the operating pressure to 11.0 inches of water column and measure the additional lock-up pressure to verify the condition of the regulator. As it states in the RVIA textbooks used to train professional service technicians,

“Lock-up pressure is a direct result of the regulator operating pressure adjustment and the condition of the regulator. It cannot be adjusted to fit within the operating parameters of the regulator lock-up requirements. The only adjustment that can be made to the regulator is operating pressure.”

The maximum allowable lock-up pressure, by the way, is 14.0 water column inches; the upper end of that 10-14 spectrum. Typically, the pressure will only rise one-inch under a regulator lock-up condition. It should certainly stop at no higher than 14.0 water column inches. If it continues to creep upward after about three minutes, the regulator is faulty and should immediately be replaced. Therefore, measuring the regulator lock-up pressure is one test that will confirm or condemn the integrity of the main pressure regulator.

Pressure Measuring Equipment
So how does the professional RV service technician go about measuring, setting and adjusting the operating line pressure and checking the lock-up pressure? By using a measuring device called a manometer and another assembled test device. A manometer and the test device are two must-haves for every pro technician. If your technician asks, “What’s a manometer?” quickly and carefully back your RV out of the service entrance and find another shop!

There are three types of manometers used in the RV industry, a gauge type, an electronic type and a true water column manometer, (also called a U-tube or slack-tube manometer). I always teach my technicians to use a true column of water when measuring and adjusting the pressure regulator. Why? When set up correctly, the true water column manometer is 100% accurate and I like that number! The other types of manometers must be calibrated periodically to validate their accuracy and integrity. And guess what is used to calibrate a gauge-type or electronic manometer? Yep, a true water column manometer!

A water column manometer is simply a U-shaped column of water and a ruler of sorts, marked off in incremental inches. A short piece of clear tubing, attached to the top of the manometer, is for connecting to the pressure tap in the RV propane system. Really a simple device, a true water column manometer can even be constructed using vinyl tubing and a couple of common rulers. Fancier, professional-grade manometers will be equipped with shut-off valves, check valves and have a sliding scale so the “zero” mark can be set correctly at the level of the water in both sides of the U- tube.

When measuring the gas pressure, the incoming fuel forces the water down one side of the manometer and up the other side. The pressure measurement is obtained by adding the two sides together. As an example, in the diagram here, the operating line pressure is 6.0 inches of water column.

Making sure the water levels start out at 0.0 inches before pressure is induced into the manometer determines the accuracy and is so deemed, a crucial step.

So where does a professional technician tap into the propane system to measure the pressure? It usually depends on the task at hand. Theoretically, the manometer can be connected anywhere into the propane system after regulation; in other words, downstream of the regulator.

If the assignment is to troubleshoot a specific, operational issue with one of the appliances, the tech should attach the manometer directly at that appliance. All RV propane appliances will be equipped with a pressure tap somewhere.

For instance, on a pilot model water heater, the pressure tap is located on the bottom side of the gas control valve as pictured here. The pros apply their product knowledge and previous training to know where the pressure tap is located on any given appliance. 

Propane Test Device
But if the assigned task is to purposely measure and set the operating pressure, verify the lock-up pressure and check the coach for leaks (a typical service request), the pro technician will use an assembled propane test device, brilliantly called a “propane test device.” The propane test device is simply constructed using an assortment of gas valves and fittings. All RV service shops should be equipped with at least one propane test device though most pro techs will have their own. Just as previously mentioned about the manometer, if a shop questions what a propane test device is, I’d search for another repair facility.

My propane test device includes two gas valves, one to control the flow of propane to my connected manometer and another to control the flow required to “load” the regulator during the adjustment phase (more on this later). But the main advantage of using a dedicated propane test device is that connections, measurements and adjustments are all executed right at the main pressure regulator at or near the propane container(s).

Additional Pressure Regulators
In years past, it was quite convenient for RV service technicians to tap into the propane system at the cooktop. Stove burners used to be easiest place to connect the manometer. Simply remove a burner (usually one screw, if that), and the rubber hose from the manometer would slip right over an individual burner orifice hood fitting.

However, many of today’s newer, more efficient propane appliances actually require less pressure and fuel to operate at their optimum. In these appliances, an additional regulator is often at work internally to the appliance (here’s one on the fuel inlet fitting to an RV range/oven). These individual appliance regulators further reduce the incoming 11.0 inches of water column pressure in the system to even less pressure, typically less than 10.0 water column inches. These so-called, “third-stage” regulators are all non-adjustable.

If the technician were to unknowingly tap into the system at an appliance outfitted with an internal regulator, it would be impossible to obtain the correct setting of 11.0 water column inches as measured on the manometer because the appliance regulator would limit the pressure measurement to its maximum allowable setting, somewhere below 10-inches. Therefore, the easiest, most efficient place for the technician to tap into the system is right at the outlet of the main pressure regulator, using the propane test device.

Loading the Regulator
The correct procedures for setting the operating line pressure include making pressure adjustments on the regulator, but only while it is under a load. In other words, there must be propane flowing in order to accurately adjust the propane pressure correctly. It is possible to have pressure without flow (remember lock-up pressure?), so there must be gas flowing at a rate equal to about one-half the total rated capacity of the appliances (approximately 75,000 Btu/hr). The propane test device accomplishes this.

To replicate a flow of approximately 75,000 Btu/hr., an orifice hole is drilled into a brass fitting on the test device. A #41 drill opening provides a flow rate of approximately 30 cubic feet per hour and represents about 50% or more of the Btu/hr flow rate of the RV’s appliances. A propane regulator must therefore have a rated capacity equal to or greater than the total Btu/hr input of all the appliances combined. Without gas flow taking place while the regulator is being manipulated, it simply cannot be adjusted accurately. 

Attaching the propane test device to the RV’s gas system is accomplished by first making sure the propane container(s) are turned completely off. The existing low-pressure flexible hose at the outlet fitting on the regulator is removed (usually a flare-swivel connection), and the test device is connected directly to the output fitting on the regulator. I either use a short, flare-to-flare fitting (the separate fitting in the photo to the right), or a longer flexible rubber hose also equipped with flare-swivel connections on both ends, depending on how tight the working space.

The previously removed hose leading to the main propane manifold and the appliances is then connected to the opposite flare fitting on the test device. The hose for the manometer is connected to the barbed fitting on the test device. Individual shut-off valves on the test device control gas flow to the manometer and through the #41 orifice. The propane test device is effectively connected in series between the outlet of the regulator and the remainder of the gas system downstream of the regulator.

Operating Pressure Test
In addition to completing proper documentation, professional RV service technicians perform (or should perform) the operating pressure test in the following manner.

1.   Verify the propane container(s) and all appliances are turned completely off.
2.   Disconnect the factory-installed low-pressure hose at the main regulator outlet fitting.
3.   Connect the propane test device into the system at the outlet of the regulator and reattach the low-pressure hose to the test device.
4.   Connect the manometer to the barbed fitting on the test device.
5.   Open the service valve on the propane container fully and bubble test all the connections at the regulator, the test device, the manometer, and the low-pressure hose leading to the coach manifold system downstream.
6.   Slowly open the valve for the #41 orifice fitting on the test device.
7.   Slowly open the valve for the manometer connection on the test device and note the pressure measurement.
8.   Access the pressure adjustment screw on the regulator and slowly adjust the pressure to obtain exactly 11.0 water column inches on the manometer.
9.   Once the pressure stabilizes at 11.0 inches of water column, close the orifice valve on the test device, simulating turning the appliances off and immediately note the rise in pressure at the manometer due to regulator lock-up.
10. If the lock-up pressure does not exceed 14.0 water column inches within three or four minutes, the regulator is deemed good and new adjusted properly.
11. Turn off the service valve on the propane container fully.
12. Remove the propane test device and reconnect all fittings back to the norm.
13. Open the service valve on the container, once again pressurizing the system.
14. Bubble test all fittings that were “opened” and reconnected, verifying no leaks were created by using the test device. The system is now ready for appliance operation.

Temperature differences in a propane piping system can cause lock-up measurements to vary. The pressure will rise when the temperature rises and decrease as the piping system cools. The temperature of both the ambient air and the distribution piping need to be approximately the same and a uniform temperature must be maintained throughout the test period. If an RV is driven into an enclosed and heated service bay after spending time in a very cold climate, the technician must allow for the temperature difference to equalize before conducting the above operating pressure test.

Timed Pressure Drop Test
A third test the pro technicians perform is the timed pressure drop test. Conducting a timed pressure drop test will verify, with 100% certainty, if a leak exists anywhere in the propane system. This test should be performed annually, if the propane odorant is ever detected, or if any doubt exists.

Theoretically, the timed pressure drop test can be conducted at any point downstream of the pressure regulator, but ahead of the propane appliances. For me personally, I conduct this test right after the operating pressure test and the regulator lock-up test, while the propane test device is still connected into the system.

For our purposes here, I’ll use a cooktop burner to explain the process for an independently-conducted, timed pressure drop test since it can be performed safely, without the need to open the system (disconnect any fitting). Wait a minute Doc! Didn’t you earlier state that some appliances might have an internal regulator that further reduces the 11.0 inches of water column pressure once it enters the appliance? True, I did state that, but the timed pressure drop test is used only to determine IF a leak is present. It is actually conducted at a pressure below the previously set 11.0 inches anyway. Here’s how the pros do it; or should be doing it!

1.   Verify the propane container(s) and all appliances are turned completely off.
2.   Gain access to the cooktop and remove one of the burners.
3.   Connect the manometer directly to the burner orifice hood at the closed burner valve.
4.   Fully open the service valve on the propane container.
5.   Slowly open the burner valve that the manometer is attached to, thereby pressurizing the manometer. Leave this burner valve open.
6.   Turn off the service valve on the propane container fully, once again.
7.   Slowly open a second burner on the cooktop and reduce the measurement on the manometer to about 8.0 inches of water column.

Note: Reducing the pressure to 8.0 inches of water column removes the lockout condition of the propane regulator. Be ready to close this second burner valve; once the system pressure is reduced, the manometer measurement will drop relatively quickly, though it may take some time to reach that point.

8.   Once reduced pressure is reached on the manometer (nominally 8.0 inches of water column), make note of the exact measurement and wait three minutes. No pressure drop should be indicated during the three-minute test.
9.   If no drop in pressure is measured, the system is 100% leak-free. If the pressure rises substantially, the service valve on the propane container may be faulty and further troubleshooting is in order. If the pressure rises only slightly, it could be the effects of thermal expansion in the system and the timed pressure drop test should be conducted again.
10. If the pressure drops any at all, there is a leak somewhere in the system and further troubleshooting is in order.
11. Once the leak(s) are located and rectified, the timed pressure drop test is performed again to verify no leaks remain.
12. Once verified no leaks exist, close the manometer burner valve, remove the manometer and reinstall the cooktop burner, returning the system to full operation. 

Locating Propane Leaks
If the timed pressure drop test detected a drop in pressure, however slight, during the three-minute test, there is a leak somewhere in the system. The pro tech should now troubleshoot further and pinpoint exactly which component is leaking. It could be a loose flare nut, a faulty tubing flare, deteriorated thread sealant, a hole in a flexible hose, or a faulty component in an appliance.

The first thing the tech will do is eliminate the appliances as the leak source. It is possible, in some instances, to have propane leak through an internal appliance valve even though that appliance was turned off. Disconnect the flare nut at each appliance, one at a time and plug the tubing with a flare plug. It will be necessary to conduct a timed pressure drop test after plugging off each appliance, one at a time. All technicians will have the various sizes of flare plugs and caps to use when isolating propane leaks.

If the leak is eliminated after disconnecting the furnace, for instance, the problem lies somewhere inside the furnace. If the leak persists after disconnecting every appliance and plugging the incoming copper lines with flare plugs, the technician must troubleshoot further.

Professional RV service technicians conduct a timed pressure drop test to determine IF a leak exists and use either an electronic leak detector or leak detection fluid to determine WHERE the leak(s) are located. Opening the service valve on the container once again pressurizes the system and the tech will literally have to test each connection in the system to determine the culprit(s).

RV owners can also check each fitting and connection by using a bubble test. Start at the service valve on the propane container and test each fitting and connection throughout the propane system. It is not necessary to purchase a special leak detection solution as in this photo. Simple dish washing soap mixed and diluted with water, or better yet, a bottle of children’s blowing bubbles works extremely well. Avoid using dish soap that contains ammonia or chlorine products.

If bubbles appear around any fitting after a few seconds, try tightening that fitting. Always use a backup wrench when tightening any propane fitting. Daub a little more solution to verify the leak has been eliminated. Also, while going through the system, fitting by fitting, keep a sharp nose for the unmistakable presence of the mercaptan odorant. Many times your nose will determine the culprit fitting before even applying the soap bubbles. Once you think all leaks have been rectified, have a certified technician perform one final timed pressure drop test to verify.

Remember, to be 100% leak-free, there should be no drop in pressure during the three-minute test. Remember also, RVing is more than a hobby, it’s a lifestyle!


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If you are in doubt or do not feel comfortable about a procedure, do not continue. Simply call your local RV service facility and make an appointment with them. The advice, recommendations and procedures offered by the RV Doctor are solely those of Gary. They do not necessarily reflect the opinions, procedures and recommendations of our sponsors or advertisers.