LP regulator at altitude

Old-Biscuit wrote:

joshuajim wrote:
OK, I got my thinking backwards. The spring is augmented by air pressure on the diaphragm as indicated on the attached pic. This would result in decrease in output pressure as you gain altitude, which would be a good thing.

Regulator

Yes there are vents (2 of them) on a 2-stage regulator.
One small on high pressure side and one large on low pressure side.
They do allow for air movement in/out as diaphragm moves.
Spring tension is spring tension regardless of atmospheric pressure.
Spring tension is pre-set based on desired out put.

The vents provide a means for exhausting gas if internal relief valves open OR as 'leak' detector should diaphragms crack

It's exactly the diaphragm vent that allow atmospheric pressure to be exerted on the diaphragm whether it be 14.7 PSI or some lesser amount. On a 2.5" diaphragm that could ne 72# (if the opposing pressure was nil :) .The pressure in the tank has little bearing on the regulatory function until it gets very low.

joshuajim wrote:
OK, I got my thinking backwards. The spring is augmented by air pressure on the diaphragm as indicated on the attached pic. This would result in decrease in output pressure as you gain altitude, which would be a good thing.

Regulator

Yes there are vents (2 of them) on a 2-stage regulator.
One small on high pressure side and one large on low pressure side.
They do allow for air movement in/out as diaphragm moves.
Spring tension is spring tension regardless of atmospheric pressure.
Spring tension is pre-set based on desired out put.

The vents provide a means for exhausting gas if internal relief valves open OR as 'leak' detector should diaphragms crack

joshuajim wrote:
OK, I got my thinking backwards. The spring is augmented by air pressure on the diaphragm as indicated on the attached pic. This would result in decrease in output pressure as you gain altitude, which would be a good thing.

Regulator

A propane tank being a closed system, I'm pretty sure internal pressure won't be affected by altitude changes. Extreme temperature fluctuations will affect pressure, though.

OK, I got my thinking backwards. The spring is augmented by air pressure on the diaphragm as indicated on the attached pic. This would result in decrease in output pressure as you gain altitude, which would be a good thing.

Regulator

joshuajim wrote:
I'm still having a problem with this. At sea level the air pressure is 14.7 psi on a diaphram which is opposed by a spring in the regulator to produce 11" WC. As you increase elevation say to 6,000 MSL the air pressure drops to 11.8 psi, but the spring is still exerting the same pressure.

This tell me that the output pressure would have to increase. It would be the same as increasing the spring pressure at sea level while maintaining the same atmospheric pressure which increases the output pressure.

I know that my appliances still work at high altitude, but that is not the question.

Please read my post right above yours. Doug

The LP regulator is not dependent on atmospheric pressure to operate.
It operates off spring pressure on a diaphragm and inlet pressure on other side of diaphragm.

The functionality of the appliances is dependent on air/fuel ratio which can be affected by altitude.

Fridge & furnaces seem to be less affected due to fixed metering of gas (small flame on fridge) and blower supplying combustion air on furnace.
Water heaters tend to be more affected due to distance from orifice and where flame occurs but they have adjustable air shutters that can be used to correct mixture

I have yet had to do anything to any of them when at high altitudes.....CO/UT/WY/MT/ID etc.

I'm still having a problem with this. At sea level the air pressure is 14.7 psi on a diaphram which is opposed by a spring in the regulator to produce 11" WC. As you increase elevation say to 6,000 MSL the air pressure drops to 11.8 psi, but the spring is still exerting the same pressure.

This tell me that the output pressure would have to increase. It would be the same as increasing the spring pressure at sea level while maintaining the same atmospheric pressure which increases the output pressure.

I know that my appliances still work at high altitude, but that is not the question.

The regulator is NOT affected by altitude. The LP regulator takes the VERY HIGH pressure from the LP tank and drops it to 11.5 inches water column. Most RV's have a 2 stage LP regulator. That means it takes the very high tank pressure and drops it and then takes that dropped pressure and then puts out the 11.5 inches pressure. This 2 stage regulator makes for a very good even 11.5 inches unlike a 1 stage LP regulator. What IS affected by Altitude is the LP/Air mixture at the appliance. The LP is usually OK, but lack of air (hi altitude) causes clean burning issues. The output pressure of a LP DOT or ASME will be about 240 psi that the LP regulator drops down to 11.5(or .5 psi) inches water colume. Doug

I will modify my post. The FIRST stage drops the 200 psi LP pressure to about 10 to 15 psi. the 2nd stage drops it to the .5 PSI which is the 11.5 inches Water column that RV appliances run at. The 10 to 15 psi is still 20 times higher than the 11.5 inches W/C the LP appliances run at. Hope this clears it up for the Poster below.

While tanks/regulators aren't much affected by high altitude, propane appliances are. All rely on a fairly specific fuel-air blend to run clean, and some will refuse to function at all above 6,000 feet or so.

There's an interesting article explaining this phenom at least as it affects water heaters at this link.

It's worth mentioning, too, that indoor-approved portable propane heaters like the Buddy have low-oxygen shutoffs that often render them unusable at high altitudes.

A propane bottle and regulator worked great for me (stove, lantern) at Goethe Lake elevation 12,600 feet, Sierra Nevadas California