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Propane and Natural Gas Fuel Delivery and Tuning Discussion about the care and feeding of Propane and Natural Gas Engines.

Propane and Natural Gas Fuel Delivery and Tuning

Natural Gas Engines in Cold Weather


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  #61  
Old 11-19-2018, 04:19:16 PM
cornbinder89 cornbinder89 is online now
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Default Re: Natural Gas Engines in Cold Weather

You HAVE to use a demand regulator to control the gas to the engine, it is like the float in a gasoline carb, you can't take it out, you'd flood the engine.

Dry gas carbs are often called mixers because they don't have the metering equipment inside them, the metering is all done by the regulator, the "carb" just mixes the fuel with the incoming air.

---------- Post added at 02:19:16 PM ---------- Previous post was at 02:07:35 PM ----------

IIRC some of the reg's I worked on had two stages in one housing that was heated by coolant. I prevented the final stage from having to go from tank pressure to "negative" pressure (below atmosphic) in one shot. These were on engines bigger than small air cooled units. I still have my books somewhere but would have to searching for them.
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Old 11-19-2018, 04:27:25 PM
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by cornbinder89 View Post
You HAVE to use a demand regulator to control the gas to the engine, it is like the float in a gasoline carb, you can't take it out, you'd flood the engine.

Dry gas carbs are often called mixers because they don't have the metering equipment inside them, the metering is all done by the regulator, the "carb" just mixes the fuel with the incoming air.

---------- Post added at 02:19:16 PM ---------- Previous post was at 02:07:35 PM ----------

IIRC some of the reg's I worked on had two stages in one housing that was heated by coolant. I prevented the final stage from having to go from tank pressure to "negative" pressure (below atmosphic) in one shot. These were on engines bigger than small air cooled units. I still have my books somewhere but would have to searching for them.
Fair enough.

What's the difference between the demand regulators that regulate based on the vacuum on the fuel line vs ones that use a separate sensing line?

I've seen both. Unless I misunderstood something.
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Old 11-19-2018, 06:05:34 PM
cornbinder89 cornbinder89 is online now
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Default Re: Natural Gas Engines in Cold Weather

The ones with a separate vacuum line are still demand regulators, the vacuum line is there to cut off fuel when there is no engine vacuum. They are called vacuum lock-off type regulators. They need a stronger vacuum signal to open than the demand vacuum signal. in other words, manifold vacuum vs. venturi vacuum.
Some installs use an electric solenoid fuel lock. Duel fuel use this so no propane or NG will flow when running on gasoline. A simple vacuum lock would not know you are feeding gasoline, so when it saw vacuum it would allow gaseous fuel to the engine.
With the vacuum lock-off type regulator, it needs to see a manifold vacuum signal before it will allow the demand portion to meter fuel. even at cranking speed manifold vacuum should be higher than venturi vacuum. The advantage to this type is it doesn't require outside electrical power so can be used with mag's and hand cranked engines. As said before, it doesn't work when more than one fuel type is used, however.
When an electrical fuel cut off is used, a vacuum switch is used in place of the vacuum line to the regulator.
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  #64  
Old 11-20-2018, 01:42:28 PM
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by cornbinder89 View Post
The ones with a separate vacuum line are still demand regulators, the vacuum line is there to cut off fuel when there is no engine vacuum. They are called vacuum lock-off type regulators. They need a stronger vacuum signal to open than the demand vacuum signal. in other words, manifold vacuum vs. venturi vacuum.
Some installs use an electric solenoid fuel lock. Duel fuel use this so no propane or NG will flow when running on gasoline. A simple vacuum lock would not know you are feeding gasoline, so when it saw vacuum it would allow gaseous fuel to the engine.
With the vacuum lock-off type regulator, it needs to see a manifold vacuum signal before it will allow the demand portion to meter fuel. even at cranking speed manifold vacuum should be higher than venturi vacuum. The advantage to this type is it doesn't require outside electrical power so can be used with mag's and hand cranked engines. As said before, it doesn't work when more than one fuel type is used, however.
When an electrical fuel cut off is used, a vacuum switch is used in place of the vacuum line to the regulator.
Ah.

I'm asking because not all gasoline carburetors are created equal, some work fantastic, some work so so, and many work terrible.

I was curious if gaseous fuel setups are similar. Some being superior others being bare minimum to get the job done etc.
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  #65  
Old 11-20-2018, 04:13:43 PM
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Default Re: Natural Gas Engines in Cold Weather

With dry gas, the demand regulator meters the fuel based on what the mixer is telling it via the vacuum signal. The better the mixer is at detecting the air flow, the better the system will be.
In Gasoline carbs, the carb does both the supply of gas and the metering. With dry gas the regulator does the supply while the carb does the mixing. Single purpose dry gas carbs will do the best when compared to a spud in the intake of a gasoline carb.
Every LP or NG system needs some sort of fuel lock. It can be electrically operated or can be vacuum operated. The fuel lock must not allow fuel to the engine when it is not turning. The demand portion of the regulator is not a fuel lock, so either a 2nd vacuum line from the manifold is used or an electric lock controlled by a vacuum switch is used. Either will meet the requirement.
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Old 11-22-2018, 08:45:28 PM
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by cornbinder89 View Post
Every LP or NG system needs some sort of fuel lock. It can be electrically operated or can be vacuum operated. The fuel lock must not allow fuel to the engine when it is not turning. The demand portion of the regulator is not a fuel lock, so either a 2nd vacuum line from the manifold is used or an electric lock controlled by a vacuum switch is used. Either will meet the requirement.
Treat THIS as if it is the BIBLE! your life, barns, and home depend on it!!!

When the engine is NOT running, the fuel MUST be POSITIVELY cut off... 'locked' off... and the best way of doing it, is as CLOSE to the fuel source as you can get.

There are a few older systems around that were developed EARLY in the gaseous fuel metering years... that used a dedicated vacuum demand signal (ported vacuum... meaning... not manifold vacuum, but vacuum from within the venturi) that controlled the diaphram of an early demand regulator. This is not a concept used much anymore, if at all.

The idea was that the demand regulator would be strong enough to cut off fuel when the engine stopped, but sensitive enough to flow fuel under idle conditions.

In theory, it makes sense... but in practice, it didn't work so well... because in order for a demand regulator to respond well at small demand, it has to be extremely sensitive... and at high demand, it has to flow lots, and be responsive... and at no demand, totally shut off.

That 'totally shut off' part, can be very difficult to achieve, when ordinary atmospheric pressure changes... like wind blowing across the top of your exhaust stack... causes airflow through the mixer. The demand regulator WILL respond, and flow fuel ;-)

What developers found, is that expecting a demand reg to 'lock off' was asking too much to result in a dead-simple and reliable system, so now we have vacuum lockoff (by virtue of direct manifold vacuum) or electric lockoff valves, and these valves, located in higher pressure spots... provide reliability and safety, without interfering with the sensitive response curve of the demand regulator.

And yes, the demand regulator DOES cut off fuel when there's absolutely no demand... but asking it to be the last bastion of fuel containment safety, is perilous.

This is also one of the reasons why I advise people to NOT mess with the adjustments on a demand regulator... if the engine's not running right... first, because it's typically NOT the demand reg, and second, if it IS, the better move is to just replace it with a new one- they're too inexpensive to warrant the risk.

Also- Binder's note about -23F being 'too low' for liquid delivery... that refers to Propane's pressure-temperature curve. At -23F, a common propane fuel system would not be regulated to 10psi... because the fuel is only at 9psi, and from that temperature down, the only pressure available, would be that shown on the curve (-36F = 3psi, -38.46= 2psi, and -43.74 = 0psi.

The reason why many make this note, is because most large-flow liquid devices in rural service, are grain dryers, and those dryers are equipped with fuel pressure sensors, and regulators with minimum pressure and excess flow valving that do NOT cope well with such low temperatures.

on a gaseous fuel generator, there's rarely a regulating issue at such low temperatures... a 10psi regulator doesn't cut off flow BELOW 10psi... it is instead, a 'pressure limiting' valve... so let's say you're at -29F outside... the tank will show about 6psi... your line pressure downstream of the 10psi regulator will be... 6psi.

Now, if you look at a, IMPCO Cobra, you'll see that it's advertised as being high pressure (up to something like 250psi) on the inlet, and the outlet connects to your mixer. That product is a 'combination fuel controller', and it accepts liquid or gaseous propane... on the high pressure side. It has threaded ports and passages though which you can flow liquid coolant, or even bypass a little exhaust through them... to provide heat to evaporate liquid propane. After that, is a regulator system that drops it down to 11" W.C. inside, and then, has an integral demand regulation feature... it's a clever all-in-one package perfect for mobile equipment and vehicular applications.

In MY experience, the Cobra and it's relatives work darned well for small and mid-size portable generators running vapor withdrawl (the evap scroll basically doing nothing... or larger generators, forklifts, and bigger moble equipment with liquid-withdrawl tanks (with evaporator heat). Machines like floor scrubbers and power trowels, Zamboni ice polishers... being operated inside buildings... propane is the better solution because the carbon monoxide levels can be made much lower.

For stationary systems from very small (2hp) up to pretty darned big (70hp), a large stationary tank with first and second stage regulation... I use the Garretson KN. My farm's emergency generation system consists of 3 stationary engine-driven generators, all fed from the same line, vapor withdrawl from a pair of 1000-gallon tanks. 10psi regulator at the tank, an an electric lockoff valve, then 11" w.c. regulator on the outside of the building, a 3/4" pipe across the ceiling with drops above each engine, and a hand-valve prior to the Garretson KN on each engine. It's been well below 20F here, and never had any problems fueling my machines... if they only grant me 1psi, that's still 27.6" W.C. available at my 11" w.c. regulator... that makes my drop-off temperature about -42F...

And yeah, I DID consider stray propane with the STERNO can trick... but at that low a pressure, my regulators don't vent much... and it's a fair distance from any stray to that sterno can. An alternative would've been to slap a 250W magnetic engine heater to it... but that assumes you have electricity. ;-)

This is all moot for our OP, though- he's talkin' about Natural Gas, which is a no-brainer. You have 11" w.c. coming into your house- T off there, run it to a fuel lockoff solenoid, then to a hand-valve, then Garretson KN demand regulator, then to the venturi of your mixer or dual-fuel carb, and you're done.
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  #67  
Old 11-22-2018, 09:22:52 PM
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Default Re: Natural Gas Engines in Cold Weather

Quote:
Originally Posted by dkamp View Post
Treat THIS as if it is the BIBLE! your life, barns, and home depend on it!!!

When the engine is NOT running, the fuel MUST be POSITIVELY cut off... 'locked' off... and the best way of doing it, is as CLOSE to the fuel source as you can get.

There are a few older systems around that were developed EARLY in the gaseous fuel metering years... that used a dedicated vacuum demand signal (ported vacuum... meaning... not manifold vacuum, but vacuum from within the venturi) that controlled the diaphram of an early demand regulator. This is not a concept used much anymore, if at all.

The idea was that the demand regulator would be strong enough to cut off fuel when the engine stopped, but sensitive enough to flow fuel under idle conditions.

In theory, it makes sense... but in practice, it didn't work so well... because in order for a demand regulator to respond well at small demand, it has to be extremely sensitive... and at high demand, it has to flow lots, and be responsive... and at no demand, totally shut off.

That 'totally shut off' part, can be very difficult to achieve, when ordinary atmospheric pressure changes... like wind blowing across the top of your exhaust stack... causes airflow through the mixer. The demand regulator WILL respond, and flow fuel ;-)

What developers found, is that expecting a demand reg to 'lock off' was asking too much to result in a dead-simple and reliable system, so now we have vacuum lockoff (by virtue of direct manifold vacuum) or electric lockoff valves, and these valves, located in higher pressure spots... provide reliability and safety, without interfering with the sensitive response curve of the demand regulator.

And yes, the demand regulator DOES cut off fuel when there's absolutely no demand... but asking it to be the last bastion of fuel containment safety, is perilous.

This is also one of the reasons why I advise people to NOT mess with the adjustments on a demand regulator... if the engine's not running right... first, because it's typically NOT the demand reg, and second, if it IS, the better move is to just replace it with a new one- they're too inexpensive to warrant the risk.

Also- Binder's note about -23F being 'too low' for liquid delivery... that refers to Propane's pressure-temperature curve. At -23F, a common propane fuel system would not be regulated to 10psi... because the fuel is only at 9psi, and from that temperature down, the only pressure available, would be that shown on the curve (-36F = 3psi, -38.46= 2psi, and -43.74 = 0psi.

The reason why many make this note, is because most large-flow liquid devices in rural service, are grain dryers, and those dryers are equipped with fuel pressure sensors, and regulators with minimum pressure and excess flow valving that do NOT cope well with such low temperatures.

on a gaseous fuel generator, there's rarely a regulating issue at such low temperatures... a 10psi regulator doesn't cut off flow BELOW 10psi... it is instead, a 'pressure limiting' valve... so let's say you're at -29F outside... the tank will show about 6psi... your line pressure downstream of the 10psi regulator will be... 6psi.

Now, if you look at a, IMPCO Cobra, you'll see that it's advertised as being high pressure (up to something like 250psi) on the inlet, and the outlet connects to your mixer. That product is a 'combination fuel controller', and it accepts liquid or gaseous propane... on the high pressure side. It has threaded ports and passages though which you can flow liquid coolant, or even bypass a little exhaust through them... to provide heat to evaporate liquid propane. After that, is a regulator system that drops it down to 11" W.C. inside, and then, has an integral demand regulation feature... it's a clever all-in-one package perfect for mobile equipment and vehicular applications.

In MY experience, the Cobra and it's relatives work darned well for small and mid-size portable generators running vapor withdrawl (the evap scroll basically doing nothing... or larger generators, forklifts, and bigger moble equipment with liquid-withdrawl tanks (with evaporator heat). Machines like floor scrubbers and power trowels, Zamboni ice polishers... being operated inside buildings... propane is the better solution because the carbon monoxide levels can be made much lower.

For stationary systems from very small (2hp) up to pretty darned big (70hp), a large stationary tank with first and second stage regulation... I use the Garretson KN. My farm's emergency generation system consists of 3 stationary engine-driven generators, all fed from the same line, vapor withdrawl from a pair of 1000-gallon tanks. 10psi regulator at the tank, an an electric lockoff valve, then 11" w.c. regulator on the outside of the building, a 3/4" pipe across the ceiling with drops above each engine, and a hand-valve prior to the Garretson KN on each engine. It's been well below 20F here, and never had any problems fueling my machines... if they only grant me 1psi, that's still 27.6" W.C. available at my 11" w.c. regulator... that makes my drop-off temperature about -42F...

And yeah, I DID consider stray propane with the STERNO can trick... but at that low a pressure, my regulators don't vent much... and it's a fair distance from any stray to that sterno can. An alternative would've been to slap a 250W magnetic engine heater to it... but that assumes you have electricity. ;-)

This is all moot for our OP, though- he's talkin' about Natural Gas, which is a no-brainer. You have 11" w.c. coming into your house- T off there, run it to a fuel lockoff solenoid, then to a hand-valve, then Garretson KN demand regulator, then to the venturi of your mixer or dual-fuel carb, and you're done.


I could use some ideas for a lockoff solenoid.
I've got a Garrettson KN and was going to use a simple ball valve before it. But this wont interrupt it if the engine stalls for some reason and I'm asleep or not home.

The engine does have a built in alternator. I think both an AC side for a headlight and a DC side for battery charging.

My first thought, not knowing any other solutions is to wire a 12v solenoid to the alternator so if the engine dies so does the solenoid. But I'd need a way to start it. Either a manual valve is a way to open the solenoid until the engine gets spinning.
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  #68  
Old 11-23-2018, 09:40:36 PM
cornbinder89 cornbinder89 is online now
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Default Re: Natural Gas Engines in Cold Weather

A lock-off for NG is going to be different than one for LP most times. This is because LP is supplied either in the liquid form or as high pressure vapor, so the volume of the lock-off has to pass is small, where as NG is supplied as a low pressure gas so the lock-off has to flow a large volume.
So I guess what I am saying is you need a NG lock-off, not one for LP.
If this is your 1st "rodeo" you should be working with a NG fuel system supplier who can recommend what demand regulator and lock-off would meet the engines needs.
You are not likely to find what you need by looking at propane stuff on E bay or the like. While the demand reg section will work on LP or NG, how the gas is supplied to the demand reg differs from NG and Propane.

A vacuum lock-off is the simplest to plumb, is reliable and meets the requirement of being fairly fool proof.
An electric lock-off allows you to shut the engine down by cutting fuel (electrically), while leaving the spark on to burn any fuel drawn into the engine. You can do the same thing with a ball valve ahead of the vacuum lock-off, while still maintaining automatic lock-off if the engine stops running at any time. So you can shut off the fuel, then when the engine stops, shut off the ignition.
An electrical lock off can be controlled by an oil pressure switch or a Vacuum switch, either should be a SPDT switch where the common is connected to the lock-off and the NC is connected to a isolated starter feed, and the NO is connected to ign on. This way it will supply gas when cranking. It isn't 100% required, as the vacuum or oil pressure switch should eventually close during cranking, but it does make the engine start easier. However, you need to design a circuit that is "fail-safe such that a failure in part doesn't back-feed and defeat the lock-off function. This is another reason to work with a NG engine supplier for your 1st go around. A vacuum switch will react to cranking quicker than an oil pressure switch will and is less effected by cranking speed.
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  #69  
Old 11-27-2018, 08:17:33 AM
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by cornbinder89 View Post
A lock-off for NG is going to be different than one for LP most times. This is because LP is supplied either in the liquid form or as high pressure vapor, so the volume of the lock-off has to pass is small, where as NG is supplied as a low pressure gas so the lock-off has to flow a large volume.
So I guess what I am saying is you need a NG lock-off, not one for LP.
If this is your 1st "rodeo" you should be working with a NG fuel system supplier who can recommend what demand regulator and lock-off would meet the engines needs.
You are not likely to find what you need by looking at propane stuff on E bay or the like. While the demand reg section will work on LP or NG, how the gas is supplied to the demand reg differs from NG and Propane.

A vacuum lock-off is the simplest to plumb, is reliable and meets the requirement of being fairly fool proof.
An electric lock-off allows you to shut the engine down by cutting fuel (electrically), while leaving the spark on to burn any fuel drawn into the engine. You can do the same thing with a ball valve ahead of the vacuum lock-off, while still maintaining automatic lock-off if the engine stops running at any time. So you can shut off the fuel, then when the engine stops, shut off the ignition.
An electrical lock off can be controlled by an oil pressure switch or a Vacuum switch, either should be a SPDT switch where the common is connected to the lock-off and the NC is connected to a isolated starter feed, and the NO is connected to ign on. This way it will supply gas when cranking. It isn't 100% required, as the vacuum or oil pressure switch should eventually close during cranking, but it does make the engine start easier. However, you need to design a circuit that is "fail-safe such that a failure in part doesn't back-feed and defeat the lock-off function. This is another reason to work with a NG engine supplier for your 1st go around. A vacuum switch will react to cranking quicker than an oil pressure switch will and is less effected by cranking speed.
Well,

Here's a quick childish doodle I did this morning for a lockoff.

Thoughts?
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  #70  
Old 11-28-2018, 12:06:26 AM
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Default Re: Natural Gas Engines in Cold Weather

That will work. You'll need a lockoff valve designed for low pressure (high volume) gas service.
I have to admit I am not a fan of using diodes to isolate critical circuits that would cause serious harm if the diode shorted. I know that with the proper selection of the diode the risk is minimal. I have just been around a few failures that put me off it.
A double pole start button would be a way around it, or another relay to provide a positive block in the starter circuit .
I've seen some really high cap NG valves that used a small hyd pump to open against a stiff spring and a large dump valve to slam the valve shut. Opened slow and would shut in a hurry if need be. Used Skydrol for operating fluid. Don't think you are running anything that big, are you? I don't think you said how big an engine you are going to run off this.
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Old 11-28-2018, 02:40:33 PM
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Default Re: Natural Gas Engines in Cold Weather

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Originally Posted by cornbinder89 View Post
That will work. You'll need a lockoff valve designed for low pressure (high volume) gas service.
I have to admit I am not a fan of using diodes to isolate critical circuits that would cause serious harm if the diode shorted. I know that with the proper selection of the diode the risk is minimal. I have just been around a few failures that put me off it.
A double pole start button would be a way around it, or another relay to provide a positive block in the starter circuit .
I've seen some really high cap NG valves that used a small hyd pump to open against a stiff spring and a large dump valve to slam the valve shut. Opened slow and would shut in a hurry if need be. Used Skydrol for operating fluid. Don't think you are running anything that big, are you? I don't think you said how big an engine you are going to run off this.
I could use a double pole switch for the start, not a big deal.

The engine size is small, 18HP. These are also temporary units connected via a hose with a quick disconnect.
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Old 11-28-2018, 10:47:10 PM
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Default Re: Natural Gas Engines in Cold Weather

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I could use a double pole switch for the start, not a big deal.

The engine size is small, 18HP. These are also temporary units connected via a hose with a quick disconnect.
Your way will work also, I was just stating my preference. When working with gases, it is best to try and think out every way a failure can happen and what the unintended results would be.
Everything can fail, a double pole switch can short internally, but is less likely to do so than a diode that is subject to inductive load voltage spikes.
I once had a relay with a short between the control coil and one of the load terminals, it cause all kinds of problems that weren't obvious because of how the relay was being used.
Just look for the likely failures and try and build in failsafes.
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  #73  
Old 12-02-2018, 01:29:18 AM
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Default Re: Natural Gas Engines in Cold Weather

Actually, if you've got a hydraulically opened, spring closed lockoff, you can just tap off the engine's oil gallery...
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Old 12-02-2018, 12:00:55 PM
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Default Re: Natural Gas Engines in Cold Weather

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Actually, if you've got a hydraulically opened, spring closed lockoff, you can just tap off the engine's oil gallery...
I haven't seen one, but it sure doesn't sound like a cheap item.

---------- Post added at 11:00:55 AM ---------- Previous post was at 10:59:52 AM ----------

Also, how would you start it unless it opens at a very low pressure?
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Old 12-02-2018, 06:12:38 PM
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Default Re: Natural Gas Engines in Cold Weather

Yeah, many reasons not to go that route. The one I worked on was for a large NG fired boiler. They wanted a slow open and fast shut for that application.
An oil pressure lock-off would take a fair bit of cranking to open the gas valve. Electric over vacuum or pure vacuum would be quicker to act.
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Old 12-05-2018, 11:06:26 AM
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Default Re: Natural Gas Engines in Cold Weather

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Also, how would you start it unless it opens at a very low pressure?
It would be very low pressure... 2psi or so, and it would take a few turns of the crank... but it takes at least one full rotation of any cylinder to have fuel, and in order to present vacuum, it requires those turns anyway. Added bonus is that it'd shut down if you ever had an oil pressure loss... with no additional critical circuitry required.

Vacuum and electric are more common.
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Old 12-05-2018, 11:27:44 AM
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It would be very low pressure... 2psi or so, and it would take a few turns of the crank... but it takes at least one full rotation of any cylinder to have fuel, and in order to present vacuum, it requires those turns anyway. Added bonus is that it'd shut down if you ever had an oil pressure loss... with no additional critical circuitry required.

Vacuum and electric are more common.
Can you recommend a 3/4" or 1" gas valve equipped as such?
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Old 12-06-2018, 12:17:27 AM
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Default Re: Natural Gas Engines in Cold Weather

I have this one mounted in the main line that feeds all three of my generators:

https://www.propanecarbs.com/impco/f...y-shutoff.html

It's on the low-pressure side of the gas line... it is NOT intended for the high-pressure side of your fuel supply... so it goes downstream of your 11" w.c. regulator, but BEFORE your fuel controller/zero governor/negative pressure regulator.

Even though my system is all propane, it is same plumbing plan as your NG, in that fuel gas comes to the machine from a final-stage 11" w.c. regulator, and this type of lockoff goes right after that regulator.

I see a 1/2" NPT version of similar, and a 90-degree turn type also, but all the rest of the lockoffs, including the vacuum lockoffs I see are for high-pressure side operation- they are not suitable for your NG system.

Century shows this one:
https://centuryfuelproducts.com/part...solenoid-valve

I'm actually surprised that all the vacuum lockoffs are high-pressure only... that is curious.

It was either Century or Zenith on the hydraulically-piloted lockoff operated by engine oil pressure... was a Government contract... part of "LongLines"... cold-war microwave link... really cool stuff.
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Old 12-06-2018, 09:07:00 AM
cjjmw cjjmw is offline
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Default Re: Natural Gas Engines in Cold Weather

Where's it best to vent the demand regulator?

All of the conversion kits I see just have it exposed but it seems like it would actually do better if it was vented into the air filter housing of the engine. No?

That way it sees the same pressure the carburetor inlet sees?
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Old 12-07-2018, 01:47:02 AM
dkamp dkamp is offline
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Default Re: Natural Gas Engines in Cold Weather

No, it needs to be vented to atmosphere external to the engine... totally ambient...

And just in case someone's wondering... no fuel gas vents through the vent- the vent's purpose is to allow the demand regulator's diaphragm to modulate properly. If it was sealed in a cavity, the pressure inside the cavity would prevent the diaphragm from moving in response to demand vacuum... on a cold day, pressure in the cavity would 'lock off' the fuel supply, and on a warm day, pressure would be so low, that it'd flow fuel with no engine operation.

If you look at the Garretson KN, you'll see that one of the features is a 'primer' button. This is generally used to purge air from a propane line when an exchangeable bottle is used... everytime you remove the fuel hose, propane in the hose wanders out, and air wanders in... when you reattach the tank, air in that hose has to get pulled out... and it takes lots of cranking to get it started up. Press the PRIME button for a little bit, and all the air will be purged out. Well, if you look closer, you'll see that the vent is not far from that purge button... and the purge button simply presses on the diaphragm.

The fuel controller works on the principle that air pressure inside the VENTURI of the carb (the part where it's narrow... where a liquid fuel's main jet would normally be found) is LOWER than ambient pressure.

Realize that a carbeurator works because the pressure drop inside the venturi LIFTS fuel up from the carbeurator bowl, because ATMOSPHERIC pressure is in the bowl, pushing DOWN on the fuel level. If you were to plug off the carbeurator's vent... or connect it to some other partial-vacuum location, then the fuel draw from the bowl would be incorrect, and worse yet, unstable... so your fuel mix would be likewise errant.

The fuel controller (zero governor, negative pressure regulator) takes place of the liquid fuel's float bowl level... and the needle and seat... in one simple component.

And as an aside note... the 'power valve'... the large adjustable valve between the fuel controller and the venturi feedpoint... has NO control of the mixture at ANY point other than full throttle. It simply limits fuel at full throttle. At any other speed, it's the fuel controller's gain adjustment, which is essentially linear, based on the difference between ambient atmospheric pressure, and the demand pressure signal it senses in the venturi.
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