Hi Fellow Sunliners
This might help some so I thought I would make a post of it. Just did ours last weekend for this year. A very good annual camper maintenance item is to do these 3 propane gas system checks.
1. A system pressure drop test
2. A main regulator pressure set point test
3. A main regulator lock up or max pressure test
If you do not do these yourself it is good to have a RV repair place do them for you once a year. Propane is similar to your camper electrical system, there is some know how involved and some safety things to learn and follow before attempting this kind of work on the system. So only do any of these checks if you feel you can handle this and have researched how to work on your system safely.
Here is how I do mine and what each test accomplishes. Even if you do not do yours, you can learn what to ask for and why to the RV repair dealer. Also, I do not do this for a living, but do work around it. So if we have a propane service man here on the site, please add and or correct anything that I have stated that my have changed in local codes. What we are doing here is more maintenance of the system, not creating a new one. First some links to other sites that help show this too. There are many more and if someone has some other good ones, post away.
The first is the system pressure drop test. This checks the system for leaks and I do this first. I’ll explain why later. It does not find the leak, but tells you if you have one or not to go looking for one. Since our campers bounce down the road things loosen up and things wear. And there is also the fact that we are talking about an RV that is made to RV standards, not like a home or industrial system. To keep cost down many components are throw away’s. They work right and then when they don’t, you replace them. Rebuilding them is normally not done. This applies to regulators and gas valves mainly.
The first thing is you need a manometer to measure pressure. You can buy one or make a water U tube manometer. I have made my own and it does not cost much and is very accurate. When we talk about propane pressure of 11 inches of water column, it is literally that. The pressure required to lift the weight of water 11 inches vertically.
See here for mine. Need clear tubing and a backer board of some type that can stand up vertically. Then you make a U tube and graduations in 1/2” marks. The hose end has a set of fittings that can slip over a stove burner orfice fitting. You may have to adapt a few sizes pending that size hose you start with. A web search under “U tube manometer” can turn up other home made ones as well. Or buy an industrial one here http://www.mcmaster.com/#manometers/=66fdw5
My home made one cost about $5 to 8 bucks I think about 4 years ago.
Here it it. Nothing fancy but it works well and very accurate.
Here are the 1/2” graduations. They go up above a 0 point and down below a 0 point. A pressure that is 1” of water column, (WC) drops 1/2" down on one side and rises 1/2" on the other. If you drew finer lines at 0.05” graduations you can get 0.1 accuracy. To make it easier for my me to read I wrote 0,1, 2 etc going up at 1/2" intervals as you see on the right hand side. Technically you add the amount below and above zero to get whole inches of water. I have just scaled it so I can read it easier.
Then very carefully you fill this with water. Tap water works. I use a turkey baster as a squeeze tube to add gently. Key is get the air out. May have to wiggle, blow air in and move the U tube to get the air out of the water and all attached water droplets in the hose down into the liquid and not stuck to the inside of the hose. If you over fill, roll up a paper towel, stick it in shorter tube on the right and slowly apply pressure on the long tube. The water will slowly rise and absorb into the towel, then let it fall and zero out. Keep fiddling until you get it right at zero. And use it in the next several hours as water evaporates too. I plug the ends when not using it to help stop the evaporation while using it. But when done using it, drain the water out or calilcum can milk up the tube.
1. System pressure drop test
Make sure the LP is off at the tank, turn off the battery OR pull the fuse on the stove DC circuit if you have electronic ignition on the stove top. Do that first and verify the stove igniter is dead.
Then take the stove top off and attach the one hose to a burner orifice. Move burner as needed. The Atwood stoves have a few types but key is to get the hose over the orifice and tight. A hose clamp here helps. Any leak in your hose and it will give a false reading.
Here is the sealed burner top in my T310
Here is the top off my prior T2499 that has different burners.
Attach the hose to the stove burner orifice and tighten the clamp snug but not over tight. The T310
The T2499. Same concept just different setup.
Make sure the U tube is at zero. You may have trapped a little pressure in the hose while pushing on the fitting. If so, take hose off, bleed and slowly put it back on. Need to be at 0 to start with. Also if the system is not yet charged with LP, open a 2nd stove burner to bleed the pressure from the tube.
Open the stove gas knob to the manamoter. Now turn on 1 tank valve and do it slow to not slug the system. Wait a minute or so the excess flow valve in the green tank nut fully opens. Go inside and read the pressure. It should be at 10” WC. Note: That is after the stove regulator. Most stoves have a 2nd regulator to be even more steady on pressure. If it is lower the 10” WC, that is an early heads up something can be wrong in the stove regulator, the main tank regulator or a leak.
Record what you have at the stove regulator and now go turn the tank off. Come back and slowly open one of the other stove burner valves to bleed the pressure down to 8.5 to 8” WC. Some web links say 9 +- 1/2 some say 8. There is a reason it needs to be at least at 8 and no not much more then 9. You are doing this to open up the main tank regulator so you can leak check all the way to the tank valve. If you over shot and are below 8 , well charge it up again and do it over. You want to test with as much pressure as you can but the main regulator needs to be open. Staying up in the 10 plus area, the regulator can be closed and pressure can leak by it even if the tank valve is off.
Look at the exact point the water is at. Use a piece of tape or ruler to know right where it is. 8.5, 8.2 etc. Now start a stop watch. Time for 3 minutes. You can find sites that stated 10 minutes but most time I have seen that is on a new installation. Once installed and past initial testing it must pass a minimum of a 3 minute drop test to be considered gas tight. You can go to 10 and that is good too, it will not hurt. If you put new pipes in, then it is a different proceedure. If the system is tight, it can do 10 just fine. There must be “no” drop during this test 3 minutes. No means none. If you have a fine leak it will drift down. A real slow leak may be 0.5” WC after 3 minutes. A bigger leak drops quick.
If you fail, you need to make sure the hose attached to the orifice has no leak and your hose adapters. Gas leak solution can help show this. And a test repeat to confirm is OK too. I bought leak solution at Lowes. It is encouraged to not use soap and water as it can in some cases pending water Ph and water make up be corrosive to the fittings.
Now I will assume you past the 3 minute pressure drop test. Turn off the propane tank valve, bleed down the pressure at a stove valve, read 0 on the manometer. If you had a leak you need to go leak hunting before proceeding.
2. Main regulator pressure set point test
Next you are going to check the main tank regulator and to do this you are going to open up the system. This is why I did the initial leak check first to make sure the whole system is sound, first. You need to get into the system upstream of the stove regulator but down stream of the main tank regulator. I used the gas line feeding the stove regulator. Next year I’m going to put a Tee fitting in here with a cap on one end to make it easier to test each year.
Once hooked up, then turn on the propane ad leave it on. Go read the manometer. It needs to be at least 11” WC. It may be a little over but must not be more then 14WC ever.
This now tells you the main system pressure. If you are at 11 but not more then 14” WC. (Ideally in the 11 to 12 area) turn on the furnace. This is going to create a draw in the system. The furnace may take 2 times to fire to bleed the air out of the lines. While the furnace its burning the pressure should not drop below 11” WC. Regulator droop is expected somewhat but not many inches of WC. If you look up the Atwood specs, they need 11” WC to work right. Less means they cannot work at full efficiency. If you dip much below 11”WC, shut off the furnace and tank valve and adjust the main tank regulator. On the back side of the regulator is a black hex on the Marshall 425 change over 2 stage system. Inside there is a hex for an allen key. Clock wise increases pressure.
Once tweaked, open tank valve, read pressure inside, fire up furnace and check under running control. If you have 2 people you can tweak while running. But if I'm by myself, I tweak, check then refire the furnace. If I over do it at 15 or so I have way too much.
I have had a main regulator go flakey and I would never of found it if I did not do this test. The pressure started out as 10.8 then once the furnace was on, it dropped to 9.5 and bobed around. The furnace was still running but this is not good as your below the 10” stove regulator also and the stove regulator it is not regulating anything. I had turned the adjusting screw 2 full turns ad had it up to almost 13 and it almost dropped to 10.8 while running. I declared for $36 to buy a new one. I have found these regulators work really good or not good at all. When they are working right, a slight drop is expected. So having a static pressure of 11.8 and dropping to 11 is OK. Dropping 2” plus WC for me is too much as this is the beggining of the end.
Once past the main pressure setpoint check, turn the furnace off but leave the tank valve on.
3. Main regulator lock up or max pressure test
Now start your stop watch again and watch the pressure for 5 minutes. The pressure must not rise above 14” WC. This is testing that the main working regulator locks up (shuts off) and will not let the gas pressure rise above 14” WC. If it does not lock up, replace the regulator. You cannot fix them.
Once past this lock up test, shut the tank valve off. You can fire the furnace to burn out the last slug of gas then shut it down. Take the hose fitting off and rehook back up the stove regulator feed line. Now you need to hook back up to the stove burner orifice and do another 3 minute leak check. Also now read the manometer before bleeding the system down. You know the main system is 11” WC, the stove regulator should be 10” WC. If it is off much, you need a new stove regulator. I had one of these have a pin hole in the diaphragm from almost brand new. It held 10"WC but I had a fine leak out the vent of the regulator and failed the pressure drop test.
Hope this helps. This is something some may have not know about but is a safety item as these components do go bad from time to time.