Make your own RV U Tube Manometer!
Okay, what the heck is a u tube manometer, anyway?
A manometer is a device used to check the pressure in your propane system. The
correct pressure is required to allow the various appliances to operate at their best level of performance. The
manometer measures pressure in units of water column inches and a simple, yet very accurate one can be constructed
for a dollar or two. These simple devices are so accurate that they are used to calibrate our more elaborate test
The propane appliances in your RV are designed to operate at 10.5 to 11 " of water
column. This is about .5 PSI (pounds per square inch) and is a very low pressure, indeed. The job of the regulator
is to reduce the tank pressure (250 + or - PSI) down to this operating pressure, regardless of the outside
What do I do with it?
The u tube manometer can be used to check and adjust the propane regulator to the
proper operating pressure. Also, it is an essential instrument for preforming a propane gas leak test. Both of
these tests are simple to do and are described further below.
All right, how do I build one?
You will need these materials:
- Piece of wood 6 " wide by 24 " long.
- 1/2 " vinyl tubing 60 " long.
4 or 6 clamps to hold the tubing to the wood.
- Measure 12 inches down from the top of the board and draw a line. Mark this as zero.
- Draw a line across the board at 1/2 inch intervals above the zero line and mark these as 1, 2, 3,
etc. up to 16.
- Clamp the vinyl tube onto the board so that it forms a large " U " shape with one end even with the
top of the board and the other end extending.
- Fill the " U " with colored water until the level reaches the zero mark.
- When measuring the propane pressure, the water in one side of the tube is raised while the water in
the other side is lowered. Therefore, each 1/2 inch on the scale (previously drawn on the board, (and
numbered zero to 16) represents one water column inch of pressure.
How do I do a leak test with the u tube manometer?
Note: this leak test checks the system up to the individual shut off or electrically operated valve at each
appliance. A leak on the other side of these valves will not show up with this test. See below for leak testing the
- 1. Remove the stove top cover and remove one of the burners assemblies.
- 2. Attach the long end of the manometer tube to the burner outlet and turn that valve to the on
- 3. Open the valve at the propane tank and then light one of the other burners on the stove top. Once the
flame is established and burning steadily turn it off and shut the valve at the propane tank.
- 4. Bleed off the pressure until the manometer reads 8 inches water column. You may want to light a burner
to burn off this gas. This is done to equalize the pressure across the regulator, to be sure that more gas is
not fed through the regulator to the low pressure side.
- 5. Let everything stand this way for 15 minutes - if the manometer drops any amount, you have a leak in the
If the manometer shows a leak, then what do I do?
- If a leak is shown by this test, then it means that gas is escaping somewhere
between the propane tanks and the appliance valves, or possibly, through one of the appliance valves. You will
need a soap solution in a spray bottle. You can use a few squirts of ammonia free dish detergent mixed with
water. (Ammonia will react with the various brass and copper components, turning them black) A better
alternative is to purchase an approved leak detector solution from your RV supply store.
- Turn on the main supply valve on the propane tank to re-pressurize the system. Shut it off.
- Spray the soap solution on every joint in the supply system, from the tank fittings to every appliance
including the piping underneath the coach.
- A leak will show itself as bubbles forming at the faulty connection.
- Tighten or repair the connection and repeat the first two steps.
- Repeat the manometer leak down test for 15 minutes to verify that no more leaks are present.
How do I check the regulator with my u tube manometer?
First of all, if you have a single stage regulator,
replace it before you proceed with these tests. Single stage regulators are OLD and not considered as safe.
New regulator design has a first stage that reduces the tank pressure to a few PSI, and the second stage
reduces that to the working pressure.
- You first need to tap into the system to provide a place to attach the manometer. If your stove does not
have it's own regulator then you can do this test by attaching the manometer hose to one of the stove top
burner nozzles. Most newer stoves have a small additional regulator built in and it is located under the stove
top cover on the left hand side.
- If your stove has a regulator you can disconnect the LPG line before the regulator at the flare fitting.
Next you'll need a flare union and a flare nut with a short piece of 3/8 inch copper tubing. The union is a
fitting with a male flare on either end and you should be able to buy this and a flare nut with the short piece
of tubing at any RV outlet or heating supply outlet. Screw the union into the flare that you removed from the
stove regulator and attach the flare nut and short piece of copper tubing to that. Tighten all fittings snugly.
You now have a place to attach the manometer tube.
The first test is the working pressure of the regulator.
- Turn on the gas supply valve.
- Fire up the rest of the appliances. (the refer, the water heater and the furnace.)
- With the appliances running, the manometer should read 11 inches of water column - if it above or
below this value, adjust the regulator.
Adjusting the regulator
- Remove the plastic cap on the front of the regulator. Beneath this is the adjusting screw (a large
plastic disk that screws in or out)
- If your pressure is lower than 11 w.c. turn the adjuster in (clockwise) until the manometer reads
11 w.c. with the appliances running.
- If your pressure is too high, turn the adjuster out (counterclockwise).
The next test for the regulator is the static pressure test.
- With all appliances off and the service valve opened, the reading on the manometer should register
below 14 inches of water column.
- Leave everything as is for 5 minutes, if the reading climbs above this value, replace the
Leak testing the appliances:
Instructions to follow, as time permits ...