Problem connecting small propane generator to 120 gal tank

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  #1  
Old 01-15-14, 02:54 PM
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Problem connecting small propane generator to 120 gal tank

Hi - I have a 3500W Gentron propane generator that I want to connect to the 120 gal tank that we use for cooktop and hot water. ( I know - it's Chinese mfg, but that's all I saw for sale in small propane models at the time).
The generator is designed to connect to a 20# BBQ tank. The line then runs directly to something that looks similar to a Garretson regulator, but it's a Chinese version that takes tank pressure at the inlet. The outlet then goes directly to the carb.
My propane supplier thought he could give me a hookup like for a gas grill so he put a T on the big tank with a regulator that outputs low pressure (11" WC). He insists he can't run a tank pressure line to the generator.
So now he wants to modify the generator. My question is - what mod would work? I think he wants to put in a safety valve and then run right to the carb. Would this work? I don't understand what mechanism changes the propane supply in response to the load. Or should I replace the Chinese regulator with a Garretson?
I really will appreciate advice.
 
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  #2  
Old 01-15-14, 04:48 PM
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Have you used the generator with a 20# tank at all? Also, what happens when you try to use the gas grill hook up? Does it start at all? Run a tiny bit?
 
  #3  
Old 01-15-14, 09:51 PM
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What you are calling a regulator is actually a zero-pressure governor. Some ZP governors, like the one you have on your generator, will allow for full tank pressure on the inlet whereas many will only allow for a maximum of 1/2 psi inlet pressure. Some even allow for liquid (at tank pressure) inlets and these commonly have a water jacket to provide the necessary heat to vaporize the liquid propane. The heated water is from the water cooling system of the engine.

I don't know why your propane dealer cannot supply a full pressure tap from your tank unless it is a matter of local code and regulations. Or maybe he is not allowed to run tank pressure piping any distance. There should be no reason that I am aware of why he couldn't install a tee with a standard POL or ACME connection that your generator would connect to at the tank. This would, of course, mean that you would have to have the generator at the tank and run the electrical connection from there.

Yes, You could change out the current ZP governor for a model that used a lower inlet pressure, it might require a medium (10 psi) regulator at the tank and a secondary (11 inches WC) regulator at the inlet to the ZP governor. Doing so would require in addition to the new ZP governor re-adjusting the maximum fuel metering device on the engine carburetor or ZP governor.
 
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Old 01-16-14, 07:45 AM
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Yes, it runs fine on a 20# tank. I just wanted to be able to run it off my larger tank for use with a more extended power outage.
 
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Old 01-16-14, 07:54 AM
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"Doing so would require in addition to the new ZP governor re-adjusting the maximum fuel metering device on the engine carburetor or ZP governor."

Thank you for the reply. Could you explain the above a little more? At a glance I don't see anything to adjust. In normal operation is it the ZP governor itself that allows more propane flow in response to a heavier load on the generator? If not, what accomplishes this?

By the way, what he has installed now is a tee on the tank with a regulator that supplies 11 in WC and then about a 8 ft line to a box where I would have a quick connect to the hose to the generator.
 
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Old 01-16-14, 02:59 PM
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Since yours is a factory modification it may not have the adjustment, normally called a "load block".

The zero-pressure governor is a sensitive valve that is actuated by the vacuum developed by the carburetor. As the mechanical load on the engine increases the airflow through the carburetor venturi increases and that causes the ZP governor to open the fuel valve a bit more feeding more propane to the carburetor. It is a delicate balancing act and it all works very well except that it CAN feed an excessive amount of fuel under some conditions. This is where the load block comes into play. The load block is nothing more than a restriction in the fuel line between the ZP governor and the carburetor's fuel tube (in the venturi) that limits the maximum fuel flow. It could be a screw adjustment in the carburetor body or an orifice somewhere in the fuel line. Most common in aftermarket conversions is simply a tee that has a bolt threaded in one side that restricts the passages.

Because the ZP governor is so sensitive to minute pressure changes it is also pretty intolerant of too high a pressure inlet. High inlet pressure inlet will tend to lift the valve off its seat and overcome the mechanism that controls the valve opening via the carburetor vacuum. To get around this problem an additional high-to-low pressure regulator is installed prior to the inlet of the ZP governor. In your particular case that high-to-low pressure regulator is built into the same housing as the ZP governor but having a separate regulator is also common.


If you could post a few pictures of the regulator/valve/disconnect that you have at the large tank I might be able to make some suggestions. This is not rocket science.
 
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Old 01-16-14, 05:38 PM
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Thanks again. So far nothing has been modified on the generator, but obviously something will have to be changed since the factory regulator/ZPG expects tank pressure at the inlet and I am only going to be able to supply 11"WC.
I'm not at home right now, but I'll post some pics when I get back on Sunday.
Thanks for your help.
 
  #8  
Old 01-19-14, 02:35 PM
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Generator pics

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I'm still thinking I need a Garretson type device in place of the existing ZPG, but is there another alternative? Seems like I need something to stop gas flow when the engine stops. And to vary the flow according to electrical load on the generator?

See if the pics help.
Thanks again.
 
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Old 01-29-14, 04:38 AM
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Sorry to have taken so long in getting back.

It is too bad that your dealer couldn't simply install a POL fitting, regular (brass) ell, a tee and then the original regulator and an additional ACME connector for the generator as that would have been the easiest. The biggest problems are going to be clearances from the fill valve, allowing the hose and fittings clearance through the guard ring and keeping the original regulator inside the guard ring. I suspect that the reason why the dealer did what he did is that he wanted to keep all the high-pressure fittings inside the guard ring.

This page: Brass Fittings, Valves, Brass Nipples, Disposable Cylinder Adapter, Gas Orifice, Gas Manifold Parts shows various fittings that could be used to allow both the original regulator and the ACME connector on the generator to be used at the same time. Do a Google for propane fittings and you can see lots and lots of suppliers of various fittings. The things to remember are that the tank valve is a POL type, the regulators are now using POL pigtails (these can be changed) and the generator uses an ACME connector.

Ideally you would have a separate valve between the tank valve and the ACME adapter but it is not absolutely necessary since the ACME connector has a self-closing valve that closes when disconnected. You would not need anything extra for the generator as the ZP governor installed will shut off the gas flow when the engine is not running as well as metering the correct gas flow depending on the generator's electrical load.
 
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