Propane Gas Line

Users who are viewing this thread

Ryder

New Member
Messages
13
Reaction score
0
Points
1
Location
California
Hi Everyone!

I'm working on a small propane delivery pipe for an apparatus on a trailer... but that's not important...

I'm using the AGA Gas Code manuals (even though code doesn't apply in this case)... and the tables for 11.o" wc pressure (the pressure from my regulator) include a 0.5" wc pressure drop, for sizing pipe.

Now, I understand that the table has to use SOME pressure drop to be calculated, but I can handle a much larger pressure drop than the table is calculated for (3"). This suggests that I can use smaller pipe and be fine (saving weight and money), but the table doesn't exist for that...

How can I convert the table values for a larger pressure drop allowance?

Thanks for your kind help!
 

Ryder

New Member
Messages
13
Reaction score
0
Points
1
Location
California
OK, barring that, the low pressure formula would work to manually calculate it... but when I use it I'm not getting results that are all that close to the table values, so I don't really trust it that much.

Who here has used the low pressure formula to manually size pipe that might be willing to cross check for me?

Specific gravity 1.2463
Pipe lentgh = 20
pressure drop = 0.5 wc
Cubic feet per hour = 140

I'm getting a result of .76" pipe diameter, which is way worse performance than the tables claim. Tables tell me I can carry 418 in 3/4" pipe... so something ain't jiving.
 

DonL

Jack of all trades Master of one
Messages
5,205
Reaction score
72
Points
48
Location
Houston, TX
What kind of tank are you using ?

You need to calculate the temperature of the tank in your formula.

"I'm working on a small propane delivery pipe for an apparatus on a trailer... but that's not important... "

Really it is important if you want help.


Good Luck.
 

DonL

Jack of all trades Master of one
Messages
5,205
Reaction score
72
Points
48
Location
Houston, TX
So you will not give a clue for what you plan on connecting ?

With tanks that small I would hope not much.


Good Luck.
 

Ryder

New Member
Messages
13
Reaction score
0
Points
1
Location
California
Oh, I didn't know you had other questions.
It's instant hot water. (though why does that matter... pipes don't know what they are delivering to)
 

DonL

Jack of all trades Master of one
Messages
5,205
Reaction score
72
Points
48
Location
Houston, TX
Oh, I didn't know you had other questions.
It's instant hot water. (though why does that matter... pipes don't know what they are delivering to)


First off, LP gas is nothing to play with.

Normally you would look in the manual and install as manufactures suggest.

It will tell you the type of regulator, and tank size required. Yes these can be different than what you are trying to Afro engineer.

You seem to be knowledgeable, and you should know that you can not get out more than you put in.

No one on this forum wants to see you get blown up.


Good Luck on your project.
 
Last edited:

Ryder

New Member
Messages
13
Reaction score
0
Points
1
Location
California
First off, LP gas is nothing to play with.

Normally you would look in the manual and install as manufactures suggest.

It will tell you the type of regulator, and tank size required. Yes these can be different than what you are trying to Afro engineer.

You seem to be knowledgeable, and you should know that you can not get out more than you put in.

No one on this forum wants to see you get blown up.


Good Luck on your project.



I don't know who you think you're talking to... but you absolutely didn't answer any question I have... not even close.

I already know exactly what the manufacturer suggests, and it's useless... as my total consumption is way smaller, and my runs are shorter than their tables allow for. They expect the unit to be installed on a house... and I understand that... but that's not my situation.

I was specifically asking for conversion factors for the tables for larger pressure drops that the 0.5" standard... (because the unit can handle 3") and barring that, the use of the formulas directly for more precise calculations (as the drop can be added precisely). It's just that when I performed the calculation, the results seem wrong. Not passing the sniff test as it were. I'd like to chat with someone with *experience* manually calculating piping from the formula, and I'm discovering that pretty much nobody does. Engineers do.

If you don't know the math... fine, just say you don't know the math. That's why they invented tables. I have the tanks I want, the regulator I want... I have everything I want, except good numbers calculated from the low pressure formula for 3" of drop.

This is a math question, and nothing more.

Barring math help, I guess I'll pipe it, flow the gas and measure with the manometer.... get to it empirically.
 

Tom Sawyer

In the Trades
Messages
3,625
Reaction score
34
Points
48
Location
Maine
He issue here is at nobody understands just exactly what you are trying to accomplish. If the runs are short then your pressure drops are inconsequential unless you plan on using very small diameter pipe. If it's tanks then it's most likely propane which means your regulator will be in the 11-13 iwc range and the appliances should be matched for propane fuel. On trailers you typically want flexible tubing instead of hard pipe due to vibration so you're looking at either 1/2" or 3/8" tube.
 

Plumber69

In the Trades
Messages
2,380
Reaction score
214
Points
63
Location
Prince Rupert, British Columbia
propane tanks reg has a 250 psi and drops it to 8-12, then you would have a secondary reg that drops it to 11", this would be out side the trailor. From there on just think as it as a full 1" line, Some regs have the first and secondary built in for short distances
 

Ryder

New Member
Messages
13
Reaction score
0
Points
1
Location
California
Hi Tom,

Well, I started (first post) with the fact that this is propane, and also that it's 11" w.c from my regulator. This has been known from the very start.

I think people are skipping over the information presented.

Is there nobody here that can use the low pressure formula?
 

Reach4

Well-Known Member
Messages
38,798
Reaction score
4,412
Points
113
Location
IL
I am not, but I expect the velocity and turbulence is low. So I am thinking you could probably get almost twice the gas with double the drop in pressure.
 

Tom Sawyer

In the Trades
Messages
3,625
Reaction score
34
Points
48
Location
Maine
You're over complicating the whole thing. IOW, you don't need to bother with the low pressure formula.
 

DonL

Jack of all trades Master of one
Messages
5,205
Reaction score
72
Points
48
Location
Houston, TX
You're over complicating the whole thing. IOW, you don't need to bother with the low pressure formula.

I agree.

The unit has a regulator built into it. Or it should if it is approved.

I never seen mention of a Model number. Some units are not to be installed inside in close areas.

This is a Top Secret install, That may require a permit.
 
Last edited:

Ryder

New Member
Messages
13
Reaction score
0
Points
1
Location
California
You guys are all talking about non-issues. It's not that I *need* to bother with the formula, it is that I *want* to, because tables are not as accurate... many have built in increases in effective pipe length, etc. Different tables from different sources give different answers... but the physics behind the formula is far more "pure".

But I get it... nobody here knows how to use the formula... no worries.

Tom: How about this... two 40 lb propane tanks, auto-crossover, 11" w.c. reg... through 20' of 1/2 black pipe, to 4 feet of 1/2" O.D (3/8 nominal) type L flex copper to a 19,000- 140,000 BTU tankless water heater.

Regarding gas flow only:
What's the simple answer to that... Will the appliance run properly? Why/why not?
 
Last edited:

Ryder

New Member
Messages
13
Reaction score
0
Points
1
Location
California
I am not, but I expect the velocity and turbulence is low. So I am thinking you could probably get almost twice the gas with double the drop in pressure.

OK, so for any given table value with a half inch drop... you can expect to pull double the table value... with a 1" drop. Do I have that right?

Thanks,

R
 

Tom Sawyer

In the Trades
Messages
3,625
Reaction score
34
Points
48
Location
Maine
That will handle 201kbtu. Depending on outside air temperature though you may run into problems with there not being enough area in the propane tanks to properly vaporize propane fast enough.
 

Reach4

Well-Known Member
Messages
38,798
Reaction score
4,412
Points
113
Location
IL
OK, so for any given table value with a half inch drop... you can expect to pull double the table value... with a 1" drop. Do I have that right?
For slow flows, that is what I was trying to say.

I think that falls apart when significant turbulence appears. You may find discussions where the term Reynolds number is used in gas pressure drop discussions. It is a predictor of when turbulence will develop. It has been a long time since I tried such calculations.
 
Top
Hey, wait a minute.

This is awkward, but...

It looks like you're using an ad blocker. We get it, but (1) terrylove.com can't live without ads, and (2) ad blockers can cause issues with videos and comments. If you'd like to support the site, please allow ads.

If any particular ad is your REASON for blocking ads, please let us know. We might be able to do something about it. Thanks.
I've Disabled AdBlock    No Thanks