Propane Excess Flow Check Valve

[colan]

In the propane appliance world whether dealing with a simple grill or a complete system a person frequently hears open the propane valve slowly or you will cause the excess flow valve to close.

Two things lead me to believe this oft repeated instruction is a lot like the take two aspirin and call me in the morning,

The first and least important reason for doubting the open slow advice is I’ve opened a lot of propane valves not worrying about how fast I open the valve and never had a lockup.

The second and most important reason for doubting the open slowly advice is knowing how the excess flow valve works. The excess flow is held open allowing gas to flow by the pressure in the propane system. If the pressure in the propane system drops below a set level like would happen with a large leak, the lack of pressure against the spring loaded valve causes it to close. To make this process work, the excess flow valve has a small hole to allow propane vapor to pass to the other side when the valve is closed (this is why a tripped excess flow valve will limit flow, but not stop flow; to stop flow the plastic nut at the tank melts at about 250 degrees).

When the tank valve is opened if the system isn’t at operating pressure the excess flow valve will be closed because of insufficient pressure (back pressure) in the system to overcome the pressure of the valve spring. The bleed hole in the excess flow valve allows gas to flow into the system until pressure in the system is sufficient to open the excess flow valve.

[howson]

...is a lot like the take two aspirin and call me in the morning,

Unless it was a military doc who'd prescribe motrin. (Vets will get it!)

When the tank valve is opened if the system isn’t at operating pressure the excess flow valve will be closed because of insufficient pressure (back pressure) in the system to overcome the pressure of the valve spring. The bleed hole in the excess flow valve allows gas to flow into the system until pressure in the system is sufficient to open the excess flow valve.

I'm sure you know what you're talking about Colan, so where (and why) do you think the advice to "open slowly" originated?

[Cate&Rob]

colan
Hi Colan . . . that is a very valid observation! Maybe we should start a "Myth Busters" section on this forum .

There was probably a time when excess flow valves did not have bleed holes to build downstream pressure and opening the tank valve slowly would be the only way to build system pressure without tripping the excess flow valve. (I don't know this to be true . . . just a guess)

Rob

[colan]

I was kind of hoping someone would tell me I’m mistaken and explain why.

I’ve read what seems like a zillion posts on the various forums where someone has a propane appliance not working and almost always someone will mention opening the tank slowly. I don’t think I’ve ever seen a response to the open slowly suggestion saying that resolved the issue.

[Country Campers]

I have had a couple experiences with this. A fellow camper in our group could not get his propane stove to burn on high flame. After hearing and reading some about the valves we un-hooked the hose connection and "banged" the cylinder on the ground , bottom of course , a couple of times and then re-attached and turned on , slowly this time , and we had a full flame , high , medium , and low. It is my understanding that when opening the valve too fast it will allow the internal safety to rise and slow down the exit of the propane. I also was under the understanding that this was an OPD valve , over fill protection device. Not sure if my explanation is correct but I have done this method a couple times and it has solved the problem. So , as a non scientific produced reason , I open any cylinder as slow as I can. If there is a leak downstream the 2 safety features built into the valve should take care of that.

Brian

[JeffC]

All I can add to this is the anecdotal evidence of seeing a number of appliances not work until the propane was turned off, bled, and turned back on slowly. So if it has no scientific basis, maybe it's voodoo.

[JCR GD]

After removing, filling and reinstalling my tanks when I open the valve for the first time I almost always hear a loud snap/ping so I close it and open it again slowly until the sound no longer happens. Seems to me that is the mystery valve closing.