There is also the two-position version (no individual adjustment) and a third version of this demand regulator that has a needle valve type adjustment.

 

The LP nozzle is about a third of the way from the intake side of the carb throat. And yes, the demand regulator stops the gas from flowing whenever the engine shuts off.

Help me understand the following... (my notes in BOLD)

The main regulator attached to the LP bottle has the following specs: (Pretty standard, right?)

• Output pressure: 300mm. WC (about 11.8 in. WC or 2.94 kPa)
• Capacity: 1.5kkg per hour (or 3.3 lbs per hr)
• 3/8" barbed fitting

I'm using a 3/8" SS-reinforced LP hose from the main regulator to the demand regulator. It's 6ft long.

The demand regulator has the following specs:

• Fit for 5KW 5000W GX390 188F (My engine is the 188F and the power head is 5kW peak, 4.5kW running)
• LPG pressure range: 2.8 KPA ---3.8 KPA (Is this the allowable input pressure?)
• Pressure regulating valve closing pressure: 3.50KPA (Not sure what this means)
• NG pressure range: 2.0 KPA ---2.6 KPA (Ignore this, we don't have NG)
• Pressure regulating valve output pressure: 0.03-1.56KPA (see note below)
• 3/8" barbed fitting

Note: I believe this is adjustable by turning the screw in the middle of the orange (LP ↔ NG) knob. AFAIK, it regulates the gaseous fuel flow rate sent to the carb, much like an A/F set screw for gasoline. Would this be the equivalent of a load block?

 

The main regulator attached to the LP bottle has the following specs: (Pretty standard, right?)

• Output pressure: 300mm. WC (about 11.8 in. WC or 2.94 kPa)
• Capacity: 1.5kkg per hour (or 3.3 lbs per hr)
• 3/8" barbed fitting

Standard pressures though the use of barb fittings arent typical. NPT and flare fittings would be best.

LPG pressure range: 2.8 KPA ---3.8 KPA (Is this the allowable input pressure?)

Yes the numbers convert to 8.3-11.2 inHG

Pressure regulating valve closing pressure: 3.50KPA (Not sure what this means)

Im not sure either. 3.5 kpa is 10.3 inhg

• Pressure regulating valve output pressure: 0.03-1.56KPA (see note below)
• 3/8" barbed fitting

Note: I believe this is adjustable by turning the screw in the middle of the orange (LP ↔ NG) knob. AFAIK, it regulates the gaseous fuel flow rate sent to the carb, much like an A/F set screw for gasoline. Would this be the equivalent of a load block?

Definitely equivalent to a load block, similar to standby units that have a two position switch for NG or LPG fuel flow. In the case of a load lock for a typical tri fuel conversion the screw setting might be 6 turns out on propane, but 11 turns out on NG. With more fuel flow required when using natural gas.

I can’t tell from the angle of the photo is there is any adjustment built into the orange fuel selector.

 

yea....but you get a better signal on the down stream side of the venturi.

 

and soooo important that (the signal) or vac on the plate or injection on the carb setup is perfect and responsive.
it needs a good point that is responsive and fast reacting so the demand regulator can do it's thing.

best point is after the venturi on a carb....
just before the throttle plate...
but that is hard to do on some setups...
they have a dandy carb for the gx200 and another for the gx 390...

pm if you need links for those low cost universal setups.

 

best point is after the venturi on a carb....
just before the throttle plate...
but that is hard to do on some setups...

That is the ideal place, but as you noted it is hard to achieve on small carbs. My demand valve connection to carb is right after the choke plate...before the venturi.

 

Thanks. Just interested in the basic concepts. I just realized that the main regulator is just maintaining 11 in. WC but the flow rate will change depending on demand.

 

Let's assume for the moment that we have a main LP regulator that puts out exactly 11 in. WC with an unlimited flow rate potential (ideal).... just to put pipe diameter and other constraints out of the equation.

On the other end of the line is an LP appliance, a generator, that has a demand regulator and with the load block set to sustain the genny up to 100% full load.

Given that the demand regulator responds to engine vacuum (or lack of), does it also work to regulate the flow rate that's fed into the combustion chamber depending on the engine load?

Another way to put it, so if the load block was tuned to sustain the engine at 100% load, there's a certain flow rate associated with it. What happens to the flow rate when the engine ramps down to say, 75% load or 50% load.... does the flow rate:

a) Go down, or
b) Remain constant (as per load block setting)?

The thing I'm getting at is LP fuel consumption. Will a generator consume less LP when it is partially loaded VS fully loaded?

exact parts and part numbers always figure in to the equation.

yes on every thing matters.
every pipe and hose angle and length, hose, pipe and fitting diameter, gas pressure and flow volume , etc.
the demand regulator has orifice inside.
and there are different styles of demand regulators to select from. they all do the basic same thing.
but they have subtle ways of getting to the proper flow. as well as how the flow and flow volume is triggered.
and yes on the demand regulator setup doing the flow regulation to rpm and load.

now here is the kicker.
the fuel system needs to be engineered.
as every thing matters or makes a flow difference.
the whole picture needs to be viewed....
rpm and horsepower and cc's of the engine are all the big things that work in to a mechanical fuel system.

this is why i like the idea of electronic fuel injection.
an engineer sets up the system for narrow and wide band the computer program selects the proper fuel
it is all lambda.... air fuel spark.... and time is a big thing. that is where the computer map does the heavy lifting.
it takes the data from the sensors and calls for the exact mixture required for a perfect run.

for the fuel engineer
a flow bench helps with doing the AFR (air fuel ratio) engineering.
as well as a good grasp with the math ...
it is as close as you are going to get to a live system in the lab.

and yes real world is not the same as the lab.
you have all of the other things as variables like temperature, air pressure including altitude, and then the fuel delivery variables including quality.
that is where EFI (electronic fuel injection) stands above a basic fuel system.

 

Not sure what a load block is but I'll take a stab at your higher level question.

I would assume the demand regulator is connected to "ported vacuum" on the carb. That is a port that generates more vacuum as more air flows through the carb. As load increases on the gen, the throttle opens, more air flows thru carb and creates more ported vacuum. The increase in ported vacuum causes more propane flow, assuming the demand regulator is properly sized. The demand regulator doesn't really control the flow. The eng demand controls the flow via the demand regulator.

Gen will use less LP at partial load.