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Old 13-11-2019, 19:13   #1
Han
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lpg pressure gauge after solenoid?

All the references I can find say that the pressure gauge must be the first thing in line downstream of the propane tank. However, our (recently acquired) boat has the solenoid first followed by the pressure gauge, and I'm stumped as to why this is any worse than the reverse order. We can still test the system by closing the tank valve and watching the pressure. All the reading I've done says it must be pressure gauge first, but no one says why exactly. Can anyone here enlighten me?

Thanks!
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Old 13-11-2019, 19:43   #2
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Re: lpg pressure gauge after solenoid?

I assume because that way you can test the solenoid? Then open the solenoid and test the lines and the stove valves?
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Old 13-11-2019, 19:59   #3
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Re: lpg pressure gauge after solenoid?

^^^
he's got it.
To clarify, with solenoid closed you open the tank valve and read pressure at gauge. Then close tank valve and then go to the stove and open burner valve as if lighting burner. The line between solenoid valve and stove should then have no pressure. Check the pressure gauge at tank - assuming solenoid valve is not leaking the pressure should not drop. Check again in an hour or so. If solenoid valve is leaking pressure will drop. This test requires the gauge be installed before the solenoid valve.
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Old 13-11-2019, 21:10   #4
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Re: lpg pressure gauge after solenoid?

Ok, that makes sense. I hadn't considered needing to test the solenoid itself.

Thanks for the quick and helpful replies!
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Old 13-11-2019, 21:23   #5
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Re: lpg pressure gauge after solenoid?

Great! My properly setup dual tanks feed a dual regulator and gauges, followed by the solenoid. We experienced a failure of the dual regulator and dumped 15 pounds of propane into the locker. Fortunately, the locker seal and vent kept the gas out of the interior. We were on the hard where the gas cloud could have been easily ignited.

These things have a finite life. BTW the hose from the tank to regulator is dated and should be replaced. Recommended three years. They are cheap. A new dual regulator was about $120. The tank valves also go bad. When you hydro the tank, replace the valve. It’s removed for the test anyway.
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Old 13-11-2019, 21:43   #6
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Re: lpg pressure gauge after solenoid?

Quote:
Originally Posted by Dennis.G View Post
^^^
he's got it.
To clarify, with solenoid closed you open the tank valve and read pressure at gauge. Then close tank valve and then go to the stove and open burner valve as if lighting burner. The line between solenoid valve and stove should then have no pressure. Check the pressure gauge at tank - assuming solenoid valve is not leaking the pressure should not drop. Check again in an hour or so. If solenoid valve is leaking pressure will drop. This test requires the gauge be installed before the solenoid valve.
This is such a nice thought, but it will not actually work as described...

Running the stove with the solenoid off will drop the pressure in the line to 0 PSIG. When the stove goes out, it's flame sensing safety will then shut off gas flow.

Here is where the problem comes in. The pressure in the line after the regulator is TINY, about 4 inches of water, gauge. The pressure at the solenoid is about 100 PSIG. If the solenoid was leaking, it would take pressurize the line to the stove and then everything would stop. The amount of gas to bring the line back up to 4 inches of water is very small, and would make a fairly small change pressure at the gauge, which would then stop changing. Especially if the line to the stove is short, any pressure change at the gauge is small enough it could easily be lost in temperature changes. Do the PV=nRT calculation and you'll understand the problem.

Unless you figure out a way to continuously bleed the stove line of gas, this description of a solenoid leak test will NOT work as described.

But it does sound good, doesn't it?

Having the gauge DOWNSTREAM of the solenoid would actually be a BETTER solution to test for a leaking solenoid. Like this:

1: With burner running, and solenoid open, close tank valve.
2: When flame goes out, gauge should read zero. Close solenoid.
3: Open tank valve.

If pressure gauge rises--at all--with solenoid closed, solenoid is leaking.
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Old 13-11-2019, 21:53   #7
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Re: lpg pressure gauge after solenoid?

Would two gauges rectify this issue? One on the inlet side capable of the higher pressure directly from the cylinder and one on the downstream side of the regulator which can read much lower values? Could I then leak test both sides of the solenoid simultaneously? A timely thread as I am about to start the installation of our new propane system on our catamaran rebuild in the next month or two. Thanks to all for the insight and lessons.

Safe Journeys,
~Jake
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Old 14-11-2019, 10:43   #8
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Re: lpg pressure gauge after solenoid?

Replaced my propane line last year. If memory serves, regulations stipulate that solenoid is first in line after tank. Tank—>solenoid—>gauge—>regulator. BTW, the heavy yellow teflon tape for this application calls for three full wraps around the fittings. Two is not enough.
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Old 14-11-2019, 10:53   #9
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lpg pressure gauge after solenoid?

Actually if you look at this all in one sold, youíll see itís tank, gauge, regulator and on the low pressure side, the solenoid. This doesnít have the solenoid, but itís obvious where it would go.
Usually after the regulator there is hose that then connects to a solenoid often mounted to the wall of the locker and connected to a hard line, often copper.
https://www.defender.com/product.jsp...76254&id=59327
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Old 14-11-2019, 10:56   #10
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Re: lpg pressure gauge after solenoid?

Quote:
Originally Posted by Nicholson58 View Post
Great! My properly setup dual tanks feed a dual regulator and gauges, followed by the solenoid. We experienced a failure of the dual regulator and dumped 15 pounds of propane into the locker.
Solenoid is first in line after tank to prevent this potential tragedy. Per ABYC:
1.5.2 Each system shall be fitted with a pressure gauge. The gauge shall read the cylinder pressure side of the pressure regulator.
NOTE: Tile purpose of the gauge is to provide a quick and easy way to test the system for leakage.
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Old 14-11-2019, 11:01   #11
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lpg pressure gauge after solenoid?

You can test the whole system by turning on the tank with the solenoid off, pressurize the system, turn off tank valve and wait to see if pressure decreases, if not go below and try to light the stove, it shouldnít of course. Then look to see if there was a pressure drop, there shouldnít be.
Your HP side and everything up to the solenoid doesnít leak and your solenoid does prevent any leakage in the off position.
Then energize the solenoid, and re-pressurize the system and close the tank valve, wait and see if pressure drops, if it doesnít then you know your whole LP side doesnít leak and neither do any of your stoveís valves.
Turn off the solenoid valve.

Now this is just my opinion, but I donít think you should leave a solenoid energized for a long period of time without gas flow, a solenoid of course gets hot, and itís my belief that the normal flow of cold gas cools it, no gas flow, no cooling.

But that is just my belief, I have NOT seen that in writing anywhere.
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Old 14-11-2019, 11:10   #12
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Re: lpg pressure gauge after solenoid?

I did not see any reference in the ABYC propane recommendations section about the proper positions, but all references as mentioned above have the gauge first, then regulator and solenoid as in the picture below.
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Old 14-11-2019, 14:50   #13
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Re: lpg pressure gauge after solenoid?

Don't know about that, tank pressure is always at 35psi. That is the boiling point of liquid propane. When the fuel level gets really low the pressure will bleed down indicating it is time to change the tank.
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Old 14-11-2019, 14:59   #14
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lpg pressure gauge after solenoid?

Quote:
Originally Posted by jmschmidt View Post
Don't know about that, tank pressure is always at 35psi. That is the boiling point of liquid propane. When the fuel level gets really low the pressure will bleed down indicating it is time to change the tank.


No, the tank pressure will vary with temperature, but itís usually about 120- 140 PSI, maybe itís 35 after the regulator, but that still sounds high for the low side?
Tank pressure will remain stable, varying only with temp until the liquid propane is gone, then it will drop rather quickly as you run out, that is why you canít use pressure as a fuel gauge, you have to either weigh a tank, or some I believe even have a float fuel gauge, but Iíve never seen one.

Now as the propane boils off the tank will get colder, and the drop in temp will cause a small drop in pressure, but it will return when the tank warms up.

Here is a propane vs temp chart, three actually
https://www.engineeringtoolbox.com/p...re-d_1020.html
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Old 14-11-2019, 15:31   #15
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Re: lpg pressure gauge after solenoid?

Quote:
Originally Posted by jmschmidt View Post
Don't know about that, tank pressure is always at 35psi. That is the boiling point of liquid propane. When the fuel level gets really low the pressure will bleed down indicating it is time to change the tank.
???

First, the internal pressure of a propane tank of ANY size will typically be between 100 and 200 psi, and dependent on temperature.

To say that 35 psi is the boiling point of propane (or any other liquid, for that matter) is just wrong. If I don't explain it well enough below, google Boyle's Law.

The boiling point of ANY liquid is completely pressure dependent, in other words a temperature AT a specific pressure. For example, water boils at 212 F. at sea level, AKA one atmosphere, AKA ~14.7 psi (absolute). Enclose the water in a pressure vessel and apply heat, and the boiling point increases with the temperature, e.g. at 15 psig it has climbed to 250 F. Apply a vacuum down to 30 mm Hg, and it drops to 79 F.
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