High vs Low Pressure Propane Generator

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  #1  
Old 02-04-14, 11:34 AM
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High vs Low Pressure Propane Generator

Hi - This is a small engine question, but propane. (I know this forum is mainly electrical, but I didn't see a better choice - if there is one please let me know).

So I have this propane generator designed to run on high (tank) pressure - like from a BBQ grill tank. I want to run it from my 120 gal tank that we use for cooking and hot water. The propane guy said it was against code to run a high pressure line to a box I would connect to, so he put another regulator on the tank and gave me a low (11" water) pressure connection.

The regulator/zero pressure governor on the generator needs high pressure, so I mounted a Garretson KN and connected the hose to the carb to the outlet of the Garretson. But it won't start. It only runs if I switch back to the factory setup and a BBQ tank.

My question is - do I need what is referred to as a load block adjustment on the outlet? And what is this device anyway? I can't find it as a part anywhere. Is it just a needle valve or flow controller? I can get one of those from Grainger.

Thanks very much for any help!
 
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  #2  
Old 02-04-14, 01:00 PM
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What inlet pressure does your generator need?

What pressure is "high pressure"? There is no defined standard for "high pressure" so we'll need a number.

All propane and the tank pressure is the same regardless of the tank's size. A 20lb barbecue tank has the same pressure as your bigger tank and is capable of providing the same pressures. The pressure in your lines/piping is controlled by the regulator. Most things like grills, stoves and furnaces operate off at 11" water pressure which I would call low.
 
  #3  
Old 02-04-14, 02:44 PM
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Again, the generator from the factory expects tank pressure, which I called "high". The number varies with ambient temperature and is usually something like 50 - 150 psi.
I want to run it from a "low" pressure feed - 11" water column or about 0.5 psi.

So I am using a Garretson KN in place of the factory regulator. Apparently I'm not getting the right air/fuel mixture, but I don't know if it's too rich or too lean.
 
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Old 02-04-14, 05:29 PM
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So, your generator was designed to be fed with liquid propane and you want to convert it to run on vapor. Have you calculated the btu required and will your house's gas lines be able to supply the demand?

You have not provided much information about your generator but each horsepower will take about 10'000 btu of propane. You'll need to make sure the regulator on your big tank and the piping into and through the house can supply the required volume... especially when the furnace is running.
 
  #5  
Old 02-04-14, 05:59 PM
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To answer your question, the load block is like a needle valve.

Are you using the primer button? Use only a short burst. You should get at least some popping out of it.

What size and how long is your supply? Generator specs do help.

I have converted two generators, both to low pressure propane, and have never had trouble getting them started.
 
  #6  
Old 02-05-14, 12:35 AM
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Did you read my response the other day I made to your original thread?

Have you asked the propane dealer to show you the regulation prohibiting a full-pressure connection for your generator?

How many times do I have to tell you that merely substituting a low-pressure Zero Pressure Governor for the original Zero Governor is NOT the answer? The original ZP governor does EXACTLY the same thing as the Garretson governor EXCEPT allow connection directly to the tank. If you insist on changing parts then the warranty on the generator will be voided AND you will be totally on your own. If this is acceptable then you MIGHT be able to get the Garretson to work with the additional pressure regulator that was added by the propane dealer IF that regulator can be adjusted down to a MAXIMUM of 1/2 psi. The Garretson ZP governor is limited to a maximum inlet pressure of one-half psi and if you are connecting it to a 10 psi regulator it is the same as not having any ZP governor at all.

OR, you could get the dealer to replace the incorrect 10 psi regulator with a 14 inch water column regulator and then use a significantly larger connecting hose to the inlet of the Garretson unit. A hose with at least a 1/2 inch inside diameter and as short as possible will be necessary.
 
  #7  
Old 02-05-14, 10:01 AM
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Pilot Dane - Thanks for your response but I don't think liquid vs vapor is an issue. The liquid is vaporized in the tank whether its a small 20# tank or the larger 120 gal tank. The propane guy put a T and a second regulator and line for the generator off the large tank. My issue isn't volume of propane but rather the air/fuel mix. This is a small (3500 W) portable generator and part of the problem is that it is a Gentron - I think it's a Chinese Honda clone.
 
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Old 02-05-14, 10:04 AM
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Yea, I'm catching on. I was trying to relate your generator to my forklift. After I posted I realized that a standard 20 pound cylinder does not have a liquid pickup.
 
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Old 02-05-14, 10:07 AM
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aandpdan - Thank you. This is a 3500 W Gentron which is not a conversion - that is, it comes from the factory designed to connect to a small (20#) grill tank. The connection I am trying has about 18 ft of 3/8" hose after the primary regulator on the large tank. This regulator steps the pressure down to 11" water column and that is what is going in to the Garretson. Right now I don't have a load block on the output but I guess that's what I need to try next.
 
  #10  
Old 02-05-14, 10:28 AM
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Furd - No, I hadn't seen your reply to my original thread, but thank you. I don't think I said anything about a 10 psi regulator. And I think you're right about wanting all the high pressure inside the guard ring on the 120 gal tank. He put in a T with a second (twin-stage) regulator that puts out 11" water column (0.4 psi) inside the guard ring. That's also the pressure I have going into my house (through the other line off the T). (Or so I was told - I guess I should confirm that). So the Garretson is supposedly getting the correct inlet pressure. I simply mounted the Garretson to the generator frame and moved the rubber line to the carb from the outlet of the factory regulator/ZPG to the outlet of the Garretson. (I can easily switch it back if I have to run off the small tanks). I guess I'm hoping that the addition of a load block will allow me to correct the air/fuel mix but I don't know why this isn't needed with the factory ZPG. I don't see any kind of load block in the factory setup.
 

Last edited by Windrider354; 02-05-14 at 11:49 AM.
  #11  
Old 02-05-14, 02:15 PM
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I looked up your generator so have a better idea of what you have.

How did you mount the Garretson? What position? It is important that it is mounted with the arrow pointing up and the diaphragm vertical.

Just to confirm, the line from the output of the 2 stage regulator on your tank is connected directly to the input of the Garretson?

I wouldn't worry much about not having a load block. Your engine was designed for propane, mine weren't. I had to adjust the load block for the engine to run correctly under load - but it DID run quite nicely even before I made any adjustments. Think of what you have as a sealed carb, one without a needle valve.

How are you trying to start this? Don't use the choke just the primer on the KN. I find 2-3 seconds and pull works great on my 7 hp even after just connecting the lines (full of air).

You are turning the ignition switch on too, right?
 
  #12  
Old 02-05-14, 04:23 PM
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Here is a picture of my generator that I converted to propane. Above the ZP governor you can see the Tee fitting that has a bolt out the top, that is the load block fitting and all it does is limit the maximum amount of propane when the generator is running fully loaded.

[ATTACH=CONFIG]26068[/ATTACH]

It is possible that your engine's carburetor has an orifice built in that acts as the limiting device. You DO need to have the ZP governor mounted vertically so that gravity plays no part in the diaphragm movement. You need to purge the air from the tank regulator and hose all the way to the ZP governor and on to the carburetor before attempting to start the engine. Different engines act differently but for mine I find that using about half choke and no primer it starts within a few revolutions (electric start) and then I slowly push the choke knob in. If you do not have the fuel at the carburetor it could take quite some time to move it from the tank to the generator so I always bleed the line at the generator inlet (not visible in the picture) before starting.
 
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  #13  
Old 02-06-14, 08:18 AM
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Thanks for the help, guys.

I do have the Garretson mounted as you said. One disadvantage I have is no electric starter. And with the small tank and factory configuration, both the mfg instructions and my experience is that I need to prime for a couple seconds and also choke it to get it to start - at least in the sub-freezing temperatures we have been having. And it takes several pulls.
I appreciate your suggestions for things to try - I'll keep experimenting.
Thanks again.
 
  #14  
Old 02-06-14, 08:25 PM
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With you now having a long(er) run from the storage tank to the engine it is entirely possible that you simply have not yet gotten the gas to the carburetor. I would try to use the primer until you smell the propane and then let it sit for several minutes until it clears. THEN try starting it in the manner that worked when using the small tank. Something else you might want to try is to re-gap the spark plug to about .020 inch gap as propane doesn't ignite well with a larger gap.

If you can get the engine to pop or stumble you at least know you have fuel, then it is a matter of getting the right mixture to keep it running. If it idles okay but won't "pull a load" then it is not getting enough fuel and this is where the "load block" adjustment comes into play.
 
  #15  
Old 02-07-14, 06:42 AM
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I'll play around more as soon as the weather gets a little better. Right now we have a foot of snow and temp in single digits or teens. Thanks again for the help.
 
  #16  
Old 04-30-14, 09:33 AM
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3500W propane gen hook up.

I think I may have a similar generator. Here's a pointer to the parts manual. http://images.palcdn.com/hlr-system/...0365_parts.pdf Page 36 shows the internal regulator/carb.
I just had a propane furnace installed and I'm having a 500 gal tank installed with a first stage regulator installed which I believe drops the pressure to 10psi. If a standard propane tank fitting were installed to this (so I can hook up the generator with out modifications) would the generator work with this lower initial pressure?
 
  #17  
Old 04-30-14, 12:44 PM
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CW - This looks like my generator except for the gizmo they call a magnetic valve (#8 on p 36). It's just a safety shutoff switch I think. I don't have it.
I don't think this will run on 10 psi input pressure because the regulator (#10 in the pic) expects to see full tank pressure - as you would get from hooking up a BBQ tank (or your 500 gal tank directly). You should be able to verify this by looking closely at the label on the regulator (which they call a decompression valve). It should state the expected input pressure, although you may have to convert the pressure units from MPa or kPa to psi to make sense of it.
 
  #18  
Old 05-07-14, 07:13 PM
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Hooking a generator to a first stage regulator

Thanks Windrider. I'll see if I can tear it apart tomorrow to get a look at it. I was just thinking (hoping) maybe the 10PSI first stage might look like an almost empty (forever) tank to the internal regulator.
 
  #19  
Old 05-08-14, 01:57 AM
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CW, how big is the 10 psi line from the storage tank? You will need about 65,000 BTUs/hr. to run that generator at full load. You need to add that figure to everything else in the house that might be using propane at the same time and then see if the 10 psi regulator and downstream piping will be able to pass that much gas. If not, then you will need to either upsize the piping or increase the pressure, maybe both.

You MAY be able to run the generator on a 10 psi inlet pressure, you will just have to try it. You may need to do what windrider has done and substitute a low pressure zero governor AND install a suitably sized intermediate regulator to lower the 10 psi to no more than 1/2 psi. Remember that as long as there is ANY liquid propane in the tank the pressure will be a function of the tank temperature. A pressure of 11 psi corresponds to a tank temperature of -20[SUP]o[/SUP] Fahrenheit
 
  #20  
Old 05-08-14, 06:30 AM
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Dang I took to long typing and was logged out. Gotta start over. OK I took the generator apart and the regulator says .2 - 1 MPa so if I read that right that's 29 PSI to 145 so I guess it won't work. There is no magnetic valve BTW the high pressure line goes direct to the regulator.
What is a low pressure zero governor and where in the system would it go. Would I still be able to connect the generator to a smaller tank if I needed it elsewhere?
The line from the tank to where the generator would be tied in would be about 25' and I think the size he was going to use was 5/8" type L. The over all length to the house and furnace would be around 125'
Thanks for your input.
 
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Old 05-08-14, 06:35 AM
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I've been up all night and I'm about to go to bed so I will have to get to you later.
 
  #22  
Old 05-09-14, 10:36 AM
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CW - There's a lot of info on the web about people converting gasoline generators to propane. Most use a Garretson KN regulator, also called a zero pressure governor, between the propane supply and the carburetor. These need low pressure at the inlet, usually quoted as 11 inches of water or about 0.4 psi. This is the common pressure supplied to appliances like a water heater or gas range. Your furnace requires more, so you have 10 psi going to it. The gas company could supply another regulator to step it down to 11 in water.
I mounted the Garretson on the generator frame. It would take the place of the regulator that is on the generator, but you could switch back and forth just by choosing which piece of tubing you connect to the carb - either from the factory regulator if you use a BBQ tank, or from the Garretson if you use a low pressure propane feed.
Of course this could all be avoided if you can work with the propane company to give you a way to connect your 500 gal tank directly to the generator. Mine wouldn't do it and it may be against code.
 
  #23  
Old 05-13-14, 02:07 AM
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I haven't given up on you guys, I'll be back tomorrow.
 
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Old 05-13-14, 06:00 AM
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I have a 6500 Kubota which is dual fuel. Off my tank I have a regulator that sends out 11" WC to everything. Straight to the generator, but further regulated to 10 psi+- for my gas basement "emergency" stove and gas logs. I'll post a picture of set up when I get back in town.
 
  #25  
Old 05-14-14, 01:11 AM
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ALL gasoline engines that have been converted to use gaseous fuel have a Zero Governor installed. This governor, also called a regulator, is a proportioning valve that allows a specified valve opening allowing the gaseous fuel to enter the carburetor based upon the vacuum developed by the engine. The primary difference between a low-pressure governor and a high pressure governor is the allowable inlet pressure.

The Garretson model KN is a low-pressure governor and has a maximum inlet pressure of about 1/2 psi; any greater pressure will cause the valve to lift off its seat and defeat the proper operation. Ideal pressure would be around 4 to 14 inches of water column pressure. Obviously this unit cannot be directly connected to a regular propane tank without an intervening pressure regulator.

IF you have a model KN zero governor then all you need is a standard propane regulator such as used with gas grilles and RVs connected between the tank and the model KN. Routinely the inlet to the standard regulator would have either a POL or Acme threaded connector to attach directly to the tank and then a low(er) pressure hose of sufficient diameter to pass the gas at the regulated 11 inches water column pressure to the model KN.

For connection to an intermediate pressure system, one that has a regulator at the large tank lowering the pressure to about 10 psi and then additional regulator(s) at either the house or the individual appliances that lower the pressure again to the 11 inches WC final pressure then you will need to get one of these intermediate pressure regulators (10 psi inlet/11 inches WC outlet) and connect between the 10 psi piping and the model KN.

Once a model KN is installed on the engine there is no reason to swap between the KN and the original high pressure zero governor.
 
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Old 05-15-14, 10:25 AM
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Thanks for the info. Don't think I have a KN etc. Here's a picture and the label on mine.Name:  propane genregulator2s.jpg
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Size:  31.2 KBName:  propane genregulator1s.jpg
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Size:  19.5 KB Not sure if that worked. Anyway I guess I'd like to keep mine stock if possible without spending a whole lot more on parts.
 
  #27  
Old 05-15-14, 04:38 PM
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Definitely not a Garretson model KN.

[ATTACH=CONFIG]31752[/ATTACH] (Garretson model KN image courtesy of propanecarbs.com)

Your governor has a maximum input pressure of 145 psi and a minimum input pressure of 29 psi. IF, and it is a big if, your propane supplier can raise the intermediate pressure between the tank regulator and the house (or appliance) regulator(s) to 30 psi then you could then connect directly to the intermediate pressure piping. Otherwise the best is to replace the governor with a low pressure model and use an additional separate regulator when using the generator directly from a portable propane tank.
 
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Old 05-16-14, 01:24 PM
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Thanks Furd. I'm hoping for the higher intermediate pressure so I don't need to mod the Geny. I see there are first stage regs adjustable in the 18psi to 50psi range so if OK that may be a possibility. Maybe as a byproduct smaller pipe from tanks to house and less $$
 
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