LP regulator at altitude

C Schomer wrote:
Doug, I didn't say it wasn't! This is what YOU wrote on the first page... "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". 13.8 isn't even ABOUT the same as 11.5. Craig

Yes, I was off a fraction. I rounded up. But, this is what YOU stated which is COMPLETELY WRONG.
"1 psi = 2.307' of water column = 27.68" wc so 11.5" wc is NOT .5 psi. Craig"
You will notice I clarified the .5 down to about .45. 13.8 is not an outrageous difference in W/C pressure. I was just keeping it simple. YOU, were completely wrong. Doug

Doug, I didn't say it wasn't! This is what YOU wrote on the first page... "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". 13.8 isn't even ABOUT the same as 11.5. Craig

C Schomer wrote:
I got certified in Denver in 78 so all this altitude stuff was covered but it's making my brain hurt trying to remember how to splain it. The reg delivers a set psig, not a constant psia, so because of this, the gas automatically derates itself with altitude. Nat'l gas in Denver is 829 btu/cf whereas NG at SL is ~1000 btu/cf. The same thing happens to LP. I don't remember if that's Boyles law or Charles law. This natural deration still isn't enough to satisfy the deration required by the AGA. An appliance built at SL is good to 2000' before additional deration is required but above 2000', the orifice must be derated for the full altitude, which is 4%/1000'. Any appliances bought in Denver are mfgr derated for Denver. The natural deration might be sufficient in most cases but I've seen furnaces in Denver that were brought from SL and not derated properly... terrible 'spilling' from the draft diverter. The mfgrs of RV gas appliances must have them derated enough to go to hi altitude w/o problems. There are some exceptions... it also make a big difference if the appliance has an exchanger or not. No exchanger isn't as critical as an appliance with an exchanger. There are a lot of factors involved! BTW, 1 psi = 2.307' of water column = 27.68" wc so 11.5" wc is NOT .5 psi. Craig

.5 psi is INDEED actually 13.8 inches water column. So 11.5 is about .45 psi. Doug

The answer to the ? is... psig doesn't change but psia does. And the bonus is... the btu content of the gas is naturally derated due to Charles Law. Craig

Perhaps a review of the concept of absolute versus relative pressure is in order. I would expect your LP regulator to maintain a (nearly) constant relative pressure measured in psig (pounds per square inch-gage).

I got certified in Denver in 78 so all this altitude stuff was covered but it's making my brain hurt trying to remember how to splain it. The reg delivers a set psig, not a constant psia, so because of this, the gas automatically derates itself with altitude. Nat'l gas in Denver is 829 btu/cf whereas NG at SL is ~1000 btu/cf. The same thing happens to LP. I don't remember if that's Boyles law or Charles law. This natural deration still isn't enough to satisfy the deration required by the AGA. An appliance built at SL is good to 2000' before additional deration is required but above 2000', the orifice must be derated for the full altitude, which is 4%/1000'. Any appliances bought in Denver are mfgr derated for Denver. The natural deration might be sufficient in most cases but I've seen furnaces in Denver that were brought from SL and not derated properly... terrible 'spilling' from the draft diverter. The mfgrs of RV gas appliances must have them derated enough to go to hi altitude w/o problems. There are some exceptions... it also make a big difference if the appliance has an exchanger or not. No exchanger isn't as critical as an appliance with an exchanger. There are a lot of factors involved! BTW, 1 psi = 2.307' of water column = 27.68" wc so 11.5" wc is NOT .5 psi. Craig

red31 wrote:
Minimally, adjustments can be made for less than ideal amounts of oxygen.

Ya recon a regulator like this is subjected to outside pressure?

Assuming that the black "knob" is an adjustable one, I'm going to answer this one with both a yes and no.

First the "no". The "first stage" regulation is via a small orifice which limits the amount of flow, the "second stage" regulation is via tapered needle which further limits flow. Basically, it works by limiting flow not pressure, but the end result is the same.

Now the yes answer. Physics dictates that the pressures must net out thereby the atmospheric pressure will diminish or increase the flow (to a very small degree).

Minimally, adjustments can be made for less than ideal amounts of oxygen.

Ya recon a regulator like this is subjected to outside pressure?

Red, if I understand what you have posted, atmospheric pressure does have some effect on output presure?

Vapor pressure or container pressure will not exceed 200 psia unless the temperature is above 100F, this happens in some places but not all. ie, container pressure is likely to be way less than 200 psi, especially if there is a need for heat and then the vapor pressure will be less than 100 psia (60F).

The main reason for the vent is to allow the diaphragm to move.

Let's say the the spring tension and atmos pressure is such that the regulator can operate between 9 and 14" wc. At 9" the linkage has the input OPEN and at 14" the linkage is so that the input is CLOSED. Ever heard em hum as the linkage moves open and shut rapidly?

Now lower the atmos pressure, the diaphragm now is slightly further away which causes the linkage to be closer to CLOSED. At the same flow rate this may be lower pressure ie it operates at 9-13" wc.

Pressure drop test done at 8" insures the inlet of the regulator is OPEN.