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LP or Propane Gas Pressures & Natural Gas fuel supply problems & solutions.
Here we describe the common causes of inadequate LP or natural gas flow or pressure to appliances and generators. Inadequate gas flow can cause appliance malfunction such as backup generator surging and may be unsafe as well.
This article series gives the standard pressure ranges and pressure settings for LP gas, propane gas, and natural gas fuels, including pressures found in the distribution service piping, in the in-building gas piping, and at gas fired appliances such as gas stoves, clothes dryers, furnaces, boilers, and LP gas or natural gas fired water heaters.
On 2018-10-09 by Travis
As more and more propane powered generators, or dual fuel as they're called, become available, there should be an explanation of how much pressure is required to power one.
For instance, would it be possible to run a portable one off a household propane or natural gas line? I have found very little explanation of this.
If a manufacturer produces a generator that can run off of household pressure, they'd have a big seller. In a hurricane it would last a long time powering necessary home appliances, such as refrigerators.
Thank you for asking interesting and important question. We have fielded questions about this from a number of readers.
I'm what I have learned so far, pressure isn't the issue because the pressures are pretty standard and are the same as for other typical Propane fuel appliances.
The problem arises when people run fuel lines over a greater distance. All of these generators come with a table that will show that for a given piping distance you may need to increase the diameter of the fuel piping.
The most Troublesome example of this came up in discussion with a reader who couldn't get his generator to work properly because it never had enough fuel flow.
The static pressure was correct but as soon as the generator started using fuel the pressure in the system dropped because his piping was considerably under sized for the length or which it had been run.
That said, I'll see what else I can find and we'll add it here. Thanks again
Also see BACKUP ELECTRICAL GENERATORS
There is a regulator exiting the propane tank and a regulator at the split that supplies the stove and the generator.
Frequently, when the generator is running in case of a power outage, the generator will "surge", causing the lights to flicker and this is not good for motors or electronics.
I have on several occasions noticed the two regulators "fighting each other" and I learned in school that you can't put two pressure controllers back-to-back and expect either of them to work.
Is there some method using orifice plates to regulate the pressure between the tank and the second (house) regulator to maintain the requisite pressure at the upstream side of the house regulator with a "control action"?
These questions were posted at at GAS PRESSURES LP vs NATURAL GAS or as comments and replies at the bottom of this page.
On 2018-07-24 by (mod) - How to Fix Inadequate LP Gas Supply to an Electrical Generator
Fixing Inadequate LP Gas Supply to an Electrical Generator
An authoritative answer should come from your gas supplier as I'm uncertain myself of the right solution. But I suspect that the regulators are not properly placed, pressures are set wrong, or the gas piping is too small.
Less common is an under-sized LPG tank itself. (250 gallon is a common minimum size).
The photo, adapted from Generac cited below, shows a typical LPG regulator on a Generac LP gas fueled generator
Details of how to fix this problem are at GAS SUPPLY for ELECTRIC GENERATORS where we give a list of things to check and fix.
Also see BACKUP ELECTRICAL GENERATORS
More information: LPG PROPANE TANK PRESSURES is a separate article on propane pressures at the tank and meter.
On 2018-07-26 by David Morris
After some more research on the regulators in my system, they appear to be sized properly. The "primary" or "first stage" regulator at the tank is rated for 2.5MM Btu/hr and is adjustable from 5 - 10" psig.
The "secondary" or "house" regulator is sized rated for 935,000 Btu/hr and will deliver up to 11" wc with a 10 psig inlet pressure.
My maximum, "full load" use is 372,000 Btu/hr or about 149 cfh @ 2500 Btu/scf for propane which is between the "gross" and "net" heating values and closer to the "gross".
The generator at full load consumes 136 cfh and my small space heater uses 13 cfh. So now my focus shifts, first to the supply tubing size.
From the tank regulator to the house regulator is right at 50 feet and it's 1/2" Type-L copper. However, the installer used 3/8" tubing from the house regulator to the generator inlet and that distance is about 3 feet. So my real question is this:
Are the minimum line size requirements for the distance from the tank to the generator or from the house regulator to the generator?
In any event, I realize that the 3/8" is likely too small even given the short length of run. With my pressure gage (a good Dwyer gage calibrated from 0 - 15" wc) attached at the debris leg right at the generator inlet, I tested the system. The static pressure with the generator down was 11" wc.
I started the generator manually (no load, just in "exercise" mode) and the pressure dropped to 9". That's an 18% pressure loss at no load. I've got a Kohler technician coming out next week to take a look at it and when he gets here I'll shut the utility power off and let the generator load and do some more fuel system hydraulics investigation.
Comments, especially on the "minimum piping size" portion of my issue?
On 2018-07-26 by (mod) - under-sized gas piping causes inadequate supply to larger generators
While I am reluctant to rule out a problem with the regulator first stage, nevertheless at sounds from your notes as if from my reading of the table your pipe diameters are all too small. You need 1 inch.
see if I'm right, check the tables in the reference that I gave you
EXAMPLE: 20kW Generac LPG-fueled generator using a 3/4” diameter gas line can run just 15 feet of pipe. To go to longer distances (up to 115 ft or 35meters) you’d need to use a 1” diameter gas line.
Also see BACKUP ELECTRICAL GENERATORS
On 2017-08-12 by (mod) - normal pressure for natural gas within a household piping system
Thank you Jack for the question, as I am always really grateful when a reader helps us make our information more clear or helps correct a mistake.
I think both statements are correct and reasonable.
Natural gas pressures arriving at a building's gas meter from the gas company's piping vary considerably depending on the location and supplier.
And in fact the service gas pressure may also vary during the day or from season to season, but it must always be at or above the required minimum pressure for gas appliances in the building to work properly.
You'll see a gas pressure regulator at the gas meter, providing a regular supply in the pressure range we cited in this article:
A typical gas pressure on the house side of the gas meter and its incoming gas pressure regulator will be 0.27-0.29 psi and in any case should not be less than 0.25 psi - that's in order to deliver a standardized gas pressure to building gas burning heaters or other appliances.
Virtually every gas appliance or heater ALSO has its own local gas pressure regulator feeding gas smoothly into the appliance, recognizing that the line pressure might be a bit higher than the specific appliance wants.
Furthermore **IF** a specific gas appliance actually requires a lower gas pressure than 0.25, the regulator will handle that pressure step-down.
Notice that the AGA's text that you quoted says ... to under 1/4 psi IF THIS IS NECESSARY.
Examples of local appliance gas regulators are at GAS REGULATORS for APPLIANCES - https://inspectapedia.com/plumbing/Gas_Regulators.php
There we point out that the reason for local gas pressure regulators at the appliance is to assure not just appropriate static gas pressure, but to be sure that the gas FLOW is adequate - and is maintained at the necessary pressure.
For example the total incoming gas flow rate on a gas cooktop will be much greater when all four or five burners are on than when just one burner is on. It's the appliance regulator that handles that.
If things still look wrong to you, help me out by pointing out what specifically seems odd to you and I'll be glad to work on this topic further.
On 2018-08-01 by purushottam - do I need 3 regulators in parallel?
do we have to go in for 3 regulators of 230kg/hr or increase the set pressure to about 2bar to get required capacity of 630kg/hr using only two regualtors in parallel?
On 2018-08-01 v by (mod) - how do I get the right pressure? 3 gas regulators?
I think you'll need a larger LP gas regulator - running 3 in parallel seems a bit of a kludge.
I'd be reluctant to go too high on outlet pressure as you may overpower the second-stage at-appliance regulator that's using the gas.
Usually high capacity high-demand systems use a two-stage regulator design.
That would be perhaps the best alternative. Check with your gas supplier to be sure they agree as if they don't they will probably stop gas delivery (and your system could be unsafe)
On 2017-08-12 by Jack From Michigan
Under Typical Natural Gas Pressures at GAS PRESSURES LP vs NATURAL GAS
"Natural gas pressures in the building gas piping between the gas meter and the appliance regulator is typically about 7.5 to 8" wc (about 0.27-0.29 psi) and needs to be at least 0.25 psi to meet the appliance regulator's output requirements."
Under The American Gas Association offers this explanation...
"At the customer's gas meter the incoming natural gas passes through another regulator to reduce its pressure to under ¼ pound (0.25 psi) if this is necessary.
(Some services lines carry gas that is already at very low pressure.)
This is the normal pressure for natural gas within a household piping system."
They cannot both be true, so which is it?
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