Propane System - Pressure question

[Ironhorse74]

Originally Posted by osirissail

jeesh - go away for 10 years and they change everything . . . . again

Point of clarification - is this new connector attached to the tank itself or to a regulator that is attached to the tank? Or is it on the hose from the tank to the regulator?

It is in the hose connector. It used to be only the ones that were hand tightened (inside threads) A couple of years ago they started putting them on all propane connectors, inside and outside threads.

[osirissail]

Part II - you'all got me interested in what this new connector system is all about - so with a little searching I found an RV/Motor Home site with an explanation of how that new connector flow limiter - QCC connector works or is supposed to work. If the OP has one it might be malfunctioning.
From: Propane 101-The basics

"Now to the new style excess flow check valve on the Acme nut that connects to the DOT cylinder's OPD valve. It is really a simple device. Inside the Acme nut, there is a ball bearing check valve that almost shuts off momentarily when full pressure is released by opening the cylinder valve. You should hear a click at that point. It doesn't shut down completely, as that would negate its ability to detect leaks and excess flow from a leak or major line break, and no gas could flow. It closes just enough to allow a bypass of gas that is very slight, about 10 cubic feet or less per hour (cf/hour) flow, as opposed to the max flow of 200 cf/hour. The bypass gas goes into the propane system, and if there are no leaks or broken pipes, it backs up and builds pressure in the gas lines in the RV. When it equalizes on both sides of the valve, the valve opens to allow full pressure up to about a max of 200 cf/hour at 100 psi. Then if you were standing there, you would hear a second click. Using all of your propane appliances should not exceed 100cf/hour. If there is a leak or a broken pipe, the pressure can't build up and the excess flow valve doesn't open up all the way thus limiting the gas output to about 10 cf/hour, or less. It is important to note that propane, like gasoline vapor, has narrow ignition requirements as far as air fuel mixture is concerned. So if you lit the leak (Don't try this at home!) it would show a flame at the leak in the air, but the concentration is too high in the line for it to ignite. In other words the fire can't run up the line to the cylinder or tank to ignite it. Want to see it in action? Watch your gas range work. Why doesn't the flame travel up the tube it comes out of to the burner? Same thing."

[cfarrar]

...it appears to me to be a flow sensor that will trip if a large amount of propane gas starts flowing. Very much like "fluid fuses" that allow small to moderate fluid flow (like gasoline fill hoses/nozzles at a service station), but if a large flow is sensed they shut off the flow.

Exactly! I keep a spare connector-hose-pigtail on board in case the valve or hose goes bad.

[cfarrar]

It closes just enough to allow a bypass of gas that is very slight, about 10 cubic feet or less per hour (cf/hour) flow... and if there are no leaks or broken pipes, it backs up and builds pressure in the gas lines in the RV. When it equalizes on both sides of the valve, the valve opens to allow full pressure up to about a max of 200 cf/hour at 100 psi.

Thanks, Osirissail. It sounds like the OP and I did not experience this because we didn't wait long enough for the pressure to equalize. Instead, my experience is: 1) I turn on the tank valve too quickly, 2) the safety valve closes, and 3) when I light the burner I get a miserable little flame that won't toast bread. As long as the burner is lit the pressure won't equalize.

[Dennis.G]

As you would likely have the solenoid valve off when opening the tank valve, might then expect this excess flow valve in coupling to close when switching the solenoid valve on. Then need to wait again to equalize pressure before turning the stove on or will end up with less than 10 CF/hr gas flow.

This is new info to me (and thanks for posting the propane 101 stuff), but I am thinking that my connector to the tank does not have such a flow limit gizmo in it.

[cal40john]

Originally Posted by cfarrar

Thanks, Osirissail. It sounds like the OP and I did not experience this because we didn't wait long enough for the pressure to equalize. Instead, my experience is: 1) I turn on the tank valve too quickly, 2) the safety valve closes, and 3) when I light the burner I get a miserable little flame that won't toast bread. As long as the burner is lit the pressure won't equalize.

This happens a lot on our club trips where we bring 3 burner 40,000 BTU cookers to use on the island. Open the tank valve quickly, turn on a burner soon after and you can barely keep it lit. Open tank valve slowly, or wait awhile and it works.

Also my boat has one of these that I discovered years ago the hard way. Disassembled everything before I found the excess flow valve. This was on the system when I bought the boat over 8 years ago, attached to a POL.

But I don't think any of this has anything to do with the OP's question.

John

[osirissail]

How's this bite your butt - You can find/get the POL fitting with the "excess flow" feature installed inside the fitting. I found several sources selling them. Here is what one looks like - (virtually identical to the "old" POL fittings).
See: Gas Excess Flow Valves - Natural Gas and Propane Gas Shut Off Valves
and
Excess Flow Valves

Here is an extract from a technical bulletin from manufacturer of the valves on how to operate an EFV equipped valve: http://www.squibbtaylor.com/subfiles...ssflow7.96.pdf

"B. PROPER OPERATING PROCEDURE
1. All valves on the upstream or downstream side of an excess flow valve must be in the full open position. Partially opened valves will restrict the flow and not allow the full flow closing rate required to shut the valve in the event of an emergency.
2. Pinched or partially cut hoses, or small ruptures in piping or fittings will not allow sufficient discharge of LP-gas or NH3 to close an excess flow valve. It is therefore imperative that all operating personnel be familiar with the location and mode of operation of all ESV (Emergency Shutdown Valves) in the piping system.
3. How an excess flow valve works: When a line or a hose is completely broken, the spring loaded check disc immediately moves to form a metal to metal seal with the valve body. At this point most of the LP-gas or NH3 liquid flow will cease. The valve will remain closed until the pressure on both sides of the check disc is equalized via the bypass hole through the check disc. At this time the spring will automatically reopen the valve. When a line is completely severed, pressure cannot equalize and the excess flow valve will remain closed until the line is repaired. The bypass hole in the check disc will allow a small amount of product to discharge, and a cloud of vapor will be seen even though the valve has closed properly. An Excess Flow Valve is not intended to shut off bubble tight when closed, but only to reduce the flow of vapor to a manageable amount until a shut off valve or ESV can be safely closed."

The last image shows a cut-away of an EFV. It works by a spring, shaft, and a disc with a little hole in it. Excess flow on the supply side forces the disc to compress the spring and the disc closes off most of the flow. When the flow "leaks" through the bypass hose enough to equalize the pressure on both sides, the spring moves the disc back to it "open" position. The strength of the spring would determine how much flow is needed to close the valve.

Seems that, IMHO, this feature is of only marginal value to a cruiser or a small boat installation. As stated, a total rupture or cutting off of the hose is necessary to active the "safety feature." A fitting or hose leak (puncture or torn hose) that remains below the flow limit setting of the EFV will not activate the valve and you boat will fill up with propane gas just like it would in the "olden days" with the ordinary original POL valve.
In a cruising boat (and others) the propane hazard is caused by the accumulation of the gas in the bottom of the boat (bilges, etc.) and then a spark sets off the massive fire that destroys or severely damages the boat.

[MarkSF]

Originally Posted by Ironhorse74

Only a problem if you are not conscientious about your propane plumbing.

When will the nanny state decide it is to dangerous to go boating? You could drown or get lost.

A good system is designed to be tolerant of error, within reason. The archives abound with stories about people who thought their propane installation was safe, just before they were blown 100ft into the air and scattered over a wide area.

Don't forget amongst the people who use propane are some pretty dumb ones.

Not to mention the "professionals" in the industry.

They overfill the bottles leading to explosions, necessitating the new overfill valve.

Recently I had to go to two places to find someone with the IQ to fill a bottle, and had to argue with them about whether you should purge new bottles (you should, btw). If you don't, the oxygen in air degrades the "stink" compound and the gas then has no smell.

The first tech sent me home with the bottles in the trunk and one of the purge valves left open. I could have been blown to kingdom come. Good thing I'm paranoid and left all the windows open and the back seats down for ventilation.

From the interweb :

"According to recent statistics from the U.S. Fire Administration, a division of FEMA, some 6,500 barbecue grill fires injure Americans accounting for property loss of over $27 million annually. Nearly a third of these gas grill fires occur in the backyard on a patio or terrace, and another third of these grill fires takes place in America’s backyards. The overwhelming majority of these grill fires result from accidents related to malfunctioning propane gas grills. Mechanical failure or malfunction is by far the leading cause of propane ignition. BLEVEs (boiling liquid expanding vapor explosions) are pressure-release explosions that occur when propane tanks are heated to combustion temperature, and are extremely dangerous."

[kiltym]

Just a quick note on this topic.

It seems that finding a POL valve that does not have the Excess Flow feature is becoming harder and harder to find. For a typical installation, should not be a huge deal.

For my use, as I need to make a hose and fittings to allow me to gravity fill my tank, an excess flow POL will defeat my goal. Outside of the US, with international fittings, it's the only reliable way. For this use, you need a full-flow POL valve.

One source (although not necessarily marine approved):

Products page