Nat gas pressure drop vs. pipe length

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OK, took delivery of a 15,000 W tri-fuel generator, with a Honda GX690 motor, 690 cc, about 22 hp. Couldn't get it to run off propane, cuz their regulator (that attaches to the tank itself) seems to be faulty. Haven't tried gasoline yet.
So I was able to kluge together a nat gas connection, some distance away, via a 50 ft coil of 3/8 id air hose.... yeah, I know, I know, chill, it was just a test.....
Generator ran fine, and I was a little surprised, given the narrow id and rel. long hose length. Under no-load conditions.
So here's the Q: With typical natural gas pressure (I'm sposing 5-7" water), how much actual load (hp) can be powered with 1/2" black pipe, of negligible length? Or, per actual sq in of pipe cross section. And then, how would that power capacity drop off with pipe length?
This will affect the size of the piping, and poss. the location of the unit. Tomorrow, I will wire up some temp. elec connections, and load as many heaters etc as I can, to see if I can detect some fuel-bottleneck under heavy load, thru 50 ft of 3/8" hose. If there is no perceptible bottleneck, then long-ish lengths of 1/2" pipe should be fine, 50 ft max.
Just wondering what I should expect.
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Seek and ye shall find.... I think.... http://www.propane-generators.com/natural-gas-chart.htm toward the bottom, has a chart of gas supply in cfh, for diam and length. Further up was made parenthetical mention that a 10 hp engine requires 100 cfh of nat gas, so 20 hp would be 200 cfh.
The relevant part of this chart indicates that 3/4" pipe would deliver 363, 249, and 200 cfh at lengths of 10', 20', and 30'..... wow, quite drop wrt. pipe length.
So in all practicality, I'm limited to a 30 ft run, according to this chart. Hmmmm, so much for 3/8 hose, or 1/2 pipe. 1/2" pipe, btw, will supply 174 cfh, at 10 ft, not quite the req'd 200.
So sez this site/chart. Any opinions, experiences?
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http://www.generac.com/Brochures/0172610SBY.pdf
Table 4, says 3/4" will be good for only 10' for 20 hp/15 kW, and not even for the full 15 kW -- they want 1". We'll see what happens.
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What is the end goal here? Is this generator going to be permanently mounted and permanently connected to the gas line? Taking out permits, getting it inspected? If that is the goal, then it would seem logical that it should be hooked up with the appropriate sized gas pipe. (1" ?) That could be black pipe, CSSC, etc depending on where it's being installed and local codes. Usually you select a reasonable location, for the appliance, then run whatever pipe size you need. For say 30ft, it's not all that much different running 1/2" or 1" is it?
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wrote:

You have a picture or a link. I want to see what it looks like. ================================================ http://www.generatorsales.com/order/Honda-16kw-Propane-Generator.asp?page=H04599
additionally modified by them for gasoline, as well. No other options, except for the propane regulator hose.
Looking at the specs, they specify a 3/8" connection, quite a bit smaller than 3/4" Altho, that diaphram pressure reg. you see attached to the base actually has a 3/4" thread, which the company bushes down to 3/8 -- but I think that 3/8" is just for the propane, and you would use the un-bushed 3/4 for nat gas.... Now ahm gettin it.... LOL
Note the small overall size of the unit...If you re-locate the pressure reg, the actual footprint of the unit is 30 L x 21 H x 16 D -- small indeed. "Only" 245#, but goddamm, a heavy 245..... holy shit.... Much lower power Generacs et al are the size of a goddamm garden shed!! And not honda powered, either.
So it seems I will have to go with 3/4" pipe, which I thought I might avoid. So be it. Let the next storm/outtage come!!
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wrote:

Looks like a really nice unit to me. People swear by Honda engines for generators, compressors, etc. I've never pulled one apart to see for myself. I don't like Honda's car engines because if you overheat them they have no material in the head and the head warps. Very easy to do if an electric fan breaks or shorts. As soon as you notice it, it's too late. I stick with GM / GMC trucks now. Obviously this isn't an issue here. Just wondering what makes the Honda engines for this stuff so good that people rave about them. Probably cast and machined very well with a lot of attention to detail. ====================================================== That, and that the other engines that Generac et al uses are crappy, lot of complaints. Briggs&Stratton generators ought to have an OK engine, don't know about Kohler and other brands.
What I think is happening is this: When you buy a generator as a deducated standby back up generator for a house, these companies are *banking* on the fact that in the next 10 years, you will run the generator a whole 50 hours. So that's what they build the engine for. And mebbe not even that.
Otoh, if you buy a *multi-purpose* unit like mine, they proly account for the fact that you will be beating the shit out of the unit with lots of use, and make it stronger. Ergo, the Honder engine.
This Maine company doesn't manufacture stuff per se, they put these units together from various suppliers, seems to be OK. They also modify the Black Max 8,750 W unit for tri-fuel, that you find at Sam's club (gasoline only) -- which also has a Honda engine.
Generac et al has a lot of bells and whistles, but not intrinsic quality, as per the above. I just went for simple and lotsa power. They're all goddamm noisy, until you get to water cooled units, Onans, etc. Much bigger $$ tho. Even a lower rpm jobby air cooled jobby cost substantially more money. Run of the mill are all 3600 rpm.
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wrote:

I agree with your assessment. Sure looks to me like you did your homework and ended up with quality. ================================================== Well, time will tell on the quality. I chose that company because they seemed like, well, a *real company* , as opposed to some fukn investment scheme of a bunch of CPAs and lawyers. You can actually talk to good ole boys there.
Much of that homework was a number of very good threads on alt.home.repair on the whole back up power issue, ranging from types of generators, to battery/inverter backup, to car-inverter backup. All have some level of viability, and I keep a big-azz marine battery/1500W inverter in m'truck (for other purposes), which, in a pinch, could provide not even 1 kW of power, but enough for basic basics. The alternator is the real bottleneck. We talked about high-output alternators as well, but anything really practical, power-wise, gets into $$.
That marine battery really came in handy, the other day. For some reason, the truck batt was deader'n'a doornail, so basically, I was able to give myself a jump!!! Hilarious....
Also, those ahr threads showed that what seems like a good idea, a slam dunk, often is not.
I think a great solution to power back up would be an option for vehicles for an *additional* super-high output alternator, that could be "levered in" to the belt system, when it's needed. But then, this adds year-round weight to the car, and it is still gas-dependent. But mebbe the better option for some. And hybrids almost have this solution *built-in*!! Just not the right voltages.
Ultimately, a noisy genset is Da Bomb, raw watts-wise, and nat gas makes it an even more usable strategy, esp. for long outages, or, in Sandy's case, where gas lines were city-blocks long. The problem with nat gas is the pita installation. But another very real advantage to nat gas is not having to worry about carburetor problems, or old/bad gas, or varnishing. That reliability factor is a big biggie.
But a good nat gas installation can equal, double, or even triple the cost of the unit itself, for a non-diy-er. Even for a diy-er, it's a fair-sized pita -- for something that you may NEVER use!!! Dats the kicker.....
So I most likely over-bought, but with the shop and all, and with Sandy (and Irene, and that 2011 Halloween nightmare ) just scaring the effing bejeezus out of me, the peace of mind will hopefully be worth it. They are saying Sandy knocked out power for 8 million people, many of them for WEEKS, and that Halloween snowstorm knocked out power for a few million, and many in CT were without power for a MONTH, in NJ for a cupla weeks. Just too much bullshit around here now.... We're even having *tornadoes* touch down!!!! goodgawd....
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"Existential Angst"

Don't know where you are located but following Katrina all the utilities, gas, water and electricity were cut off until there was an inspection.
We had NG for part of the day following land fall but ran on LPG/gasoline for several weeks. Keep that in mind if you expect a disaster to effect services.
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If you buy a Mitsubishi I-miev electric car, it has a "home power station" option. The traction battery can be used to supply the home. 15Kwh if fully charged.
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wrote:

If you buy a Mitsubishi I-miev electric car, it has a "home power station" option. The traction battery can be used to supply the home. 15Kwh if fully charged. ==================================================== That's good to know! But, iirc, the I miev is all electric, right? So in an extended power outtage, you may be stranded as well!
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A lot depends on if you want a natural gas generator installed as a permanent installation or if you leave it as a portable. Personally, I'd opt for about a 5KW portable. It's light enough to be able to move easily and enough power to run the loads you want in a typical house. If you leave it as a portable, all you need is a length of gas hose with quick connects on either end. You would need a place at a gas line to connect it. But in many cases that should be easy. Either a point where maybe an outside gas grill is attached, or a pool heater. And if not, you could put a fitting inside, say the basement by the furnace or water heater, then just run the gas hose outside to the generator when needed. That is a very easy install.
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Question can you run the gen set with a very short supply line? I ask as the problem may not be the line from the outlet to the gen set but the line and any regulation from the utility at the street than anything you have provided.
A friend built himself a furnace to cast bronze parts. Found out the utility had installed restriction for a standard house that would not feed the furnace.
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That would be my luck!! But it doesn't appear to be so, in this case. My original gas meter was proly slated for a large bakery, but wound up in my house. I wonder why the utility bothered with such a restriction -- mebbe he's in a semi-industrial area, and they are paying more attention to zoning issues?
I'm looking forward to seeing just how much of a bottleneck 50 ft of 3/8" hose will be on that genset, loaded. Should give me a better idea of which of those links I provided is more accurate ito pipe size..
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It will only be a bottleneck if you require full power.
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It will only be a bottleneck if you require full power. ===================================================== Or near-full power -- I aim to find out tomorrow. I don't have any convenient way of fully loading the genset right now, but I do have small Miller welder (165 A, over a 50 A draw with a heavy arc), that should load the genset pretty good. Insufficient gas flow should just cause a voltage drop, I'm sposing, and if it's not too bad, I'll go with the smaller pipe. Will be inneresting to see what actually happens.
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On 1/9/2013 2:11 AM, Existential Angst wrote:

You can always hook up a manometer an watch the gas pressure in inches/water column as the generator runs then is put under load. I own several manometers that I use to test NG and LPG equipment with. ^_^
http://inspectusa.com/gas-manifold-pressure-kit-gpk035-case-tubing-adapter-p-802.html?osCsid 103f0855021829fa52db73ca719353
http://tinyurl.com/awrxxvf
TDD
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On 1/9/2013 12:11 AM, Existential Angst wrote:

I've found it useful to measure/control the thing you really care about. So, what do you care about?
If it were me, I'd care about the air/fuel ratio across the full load range.
So, what makes that happen? If it's a converted open-loop carburetor, the A/F ratio might be very pressure dependent. The only acceptable pressure drop might be "none".
If it's an injection system with feedback from the exhaust sensor, it might be relatively insensitive to supply line restriction.
The whole concept of "see what happens" falls apart if you can't actually see the thing you care about. In this case, it might be more appropriate to "hear what happens." After writing that, it occurs to me that I have no idea whether a natural gas engine exhibits knock when you run it lean.
Measure what you care about.
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That's a good point, and quite apropos of DD's manometer -- which I wish I had. And even if I did have one, what I really care about is voltage under load. If my welder drops the voltage by only a few %, I'll be a happy camper.
The listening advice is always good -- I don't want constant voltage with load if it's going to burn out the engine because of fuel issues. Funny, I tell that (about listening) to the guy that works with me, all the time: LISTEN to the machine (lathe, milling) -- it's your first indication when shit ain't right. That, and smoke/sparks..... LOL
Tonite is the night I start kluging stuff together electrically, see what happens. And hear what happens.... :)
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On 1/9/2013 1:15 PM, Existential Angst wrote:

Then you're good to go. For me, I'd like the engine to run cool and have LOOOOONG life.
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    [ ... ]

    Something you can make easily -- especially for the pressure levels involved in natural gas.
    Get some clear plastic hose/tubing.
    Get a board about four feet long or so, and mount it upright.
    Attach the tubing to the board to form a 'U', with the open end of the U facing up.
    Keep one end totally open, and the other end connected to your gas feed pipe. (Probably fix things up so you can connect it at either the supply end or close to the generator -- or even make two of them so you can measure both at once.)
    Pour enough water into it so you have at least as few inches of water as the maximum pressure from the gas company's regulator. (This is actually twice as much as you need, but reduces the chances of things spraying out during a pulse of pressure.
    Mount a yardstick between the pipes which can be slid up or down, so the zero point can be lined up with the water level in the lower of the two pipes.
    Then measure the inches from the top of the low end to the top of the high end, and that is your pressure in inches of water.
    For higher pressures, you either need a longer board and tubing, or to replace the water with mercury (there about 29" is equal to atmospheric pressure).

    You'll need to continue that arc for a while, to allow the pressure in the pipe to adjust to conditions -- it won't be immediate, as the pipe will act as a reservoir for a while.
    Good Luck,         DoN.
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