Propane System - Pressure question

[sf-robert]

We always turned off the propane valve when leaving the boat or at night when sleeping aboard. In other words, I don't just count on the solenoid to shut off the system.

Recently we decided to "burn off" the pressure in the system as well. Basically, I turn off the tank valve, head inside and light a burner until it dies out. This was only taking seconds, until I had the fiberglass propane tank refilled. Since then it takes nearly two minutes for one burner to burn off the propane in the lines.

This doesn't make sense to me, but I'm not a propane expert.

Can anyone enlighten me?

Thanks,
Robert
Wanderlust, Gulfstar 37

[Duke 48]

P1V1=P2V2

Pressure one X Volume One = Pressure Two X Volume Two

Could it be the captured pressure between the valve and the tank is increased since the bottle was refiled?

[djmarchand]

Robert:

As long as there is still liquid propane in the tank (and there will be until it is almost empty) then the pressure in the tank is solely dependent on the temperature of the tank. It will be 110 psig at 70 deg F.

But maybe your tank was almost empty and it was only full of gas and the pressure in the tank was very low. That is why it burned off in a few seconds. When you refilled the tank the pressure went up to the liquid vapor pressure and it took longer.

Having said that I am really surprised that it took ten times longer to burn off. That doesn't make sense.

And FWIW why don't you trust the solenoid valve, particularly if you burn off the pressure once you trip the solenoid. Beats going outside and turning off the valve each time.

David

[Ironhorse74]

I am going to assume something here and you know what they say about assuming. That you have an OPD valve on the tank and are here in the US. Just got your tank refilled and you have low pressure? The reason for this is that when you open the tank fast, it makes the OPD valve think there is a leak. Especially when it is filling a long low pressure hose. The trick is to close the valve and remove the connector from the tank. Reattach and then just barely "crack" the cylinder. Filling the low pressure hose. Once this is done you can open the valve all the way up.

Pain in the A$$ but the nanny state says it is for our own safety.

[stacy]

After reading many reports concerning explosions with propane systems on boats I have adopted a very conservative approach and would never trust a solenoid valve. We always turn off the valve at the tank.

[thinwater]

Originally Posted by stacy

After reading many reports concerning explosions with propane systems on boats I have adopted a very conservative approach and would never trust a solenoid valve. We always turn off the valve at the tank.

Another good reason to do what DJ said; it checks the solenoid valve function.

Close the tank valve also, if you like or when leaving the boat.

[osirissail]

Originally Posted by Ironhorse74

. . . The reason for this is that when you open the tank fast, it makes the OPD valve think there is a leak. Especially when it is filling a long low pressure hose. . . .

Huh? where did that come from? OPD is "Overfill Protection Device" and only has to do with refilling the tank. It is a simple "float valve."
See: Propane OPD - Overfill Prevention Device Cylinder Valves

"An OPD Valve is easily identified by having a triangular knob with the words OPD marked on the valve itself. Overfill Prevention Device fitted valves are the result of extensive research into improving gas safety for you and your gas tanks. The new OPD valves prevent overfilling of gas cylinders, making filling and using gas cylinders safer than ever before. They are also compatible with your current gas appliances so it is easy to upgrade. Older style valves were more susceptible to overfilling which leaves no room for the liquid propane to expand. As a result gas may escape, creating a potentially hazardous situation. OPD valves solve this problem by using a special float (shown right) which rises during refilling to block the filling process when the tank is 80% full."

"Because the OPD valve is not designed to restrict flow out of the cylinder, it's only designed to stop flow into the cylinder during the filling process. OPD equipped propane cylinders will allow liquid propane into gas lines and hoses if tipped over or inverted. Overfill Prevention Devices are not a safety mechanism used or actuated during cylinder usage."

The newer version of the OPD valve has added a valve like a tire stem valve that must be depressed by the attachment hose fitting before propane can be removed/allowed out of the tank. This may be causing the problem the OP mentions. See: http://www.propane101.com/valveopennopropane.htm

The first photo is of the new horizontal propane tank with an OPD valve. Older horizontal propane tanks are exempt from have to have an OPD installed. But new horizontal tanks do have an OPD and they have added a gas outflow valve (yellow) that is piped to the "top" of the space inside the tank so that propane gas rather than liquid propane flows down the supply hose.

[cfarrar]

you have an OPD valve on the tank...

We have a valve in our connector, not the tank. It closes if the flow rate is too high. Maybe your newly filled tank creates enough of a pressure differential to trip the valve, whereas it didn't when the tank was nearly empty. Just open the tank valve slowly.

Colin

[cfarrar]

Our connector is the one pictured below. If I remove the hose from the regulator and blow hard into this connector the safety valve closes, and I turn blue in the face. If I blow gently the safety valve allows the air to pass. If I reconnect everything and open the tank valve too quickly I can actually hear a click as the safety valve closes. I suffered through a few cold dinners before I figured this out!

[Ironhorse74]

Originally Posted by osirissail

Huh? where did that come from? OPD is "Overfill Protection Device" and only has to do with refilling the tank. It is a simple "float valve."

Along with the OPD valve came a new connector like cfarrar described. Along with the connector came the leak detector. Before OPD valves there was no valve in the connector.

The point is you don't have the connector with the valve without the OPD valve.

Still the nanny state making sure we are safe.

[Ironhorse74]

Originally Posted by cfarrar

Our connector is the one pictured below. If I remove the hose from the regulator and blow hard into this connector the safety valve closes, and I turn blue in the face. If I blow gently the safety valve allows the air to pass. If I reconnect everything and open the tank valve too quickly I can actually hear a click as the safety valve closes. I suffered through a few cold dinners before I figured this out!

What you are pointing at is the vent for the valve. If you have to blow into the vent to reseal the valve, you have a bad connector. There is a spring in there that should reset the valve when it is removed from the tank.

[MarkSF]

Originally Posted by Ironhorse74

I am going to assume something here and you know what they say about assuming. That you have an OPD valve on the tank and are here in the US. Just got your tank refilled and you have low pressure? The reason for this is that when you open the tank fast, it makes the OPD valve think there is a leak. Especially when it is filling a long low pressure hose. The trick is to close the valve and remove the connector from the tank. Reattach and then just barely "crack" the cylinder. Filling the low pressure hose. Once this is done you can open the valve all the way up.

Pain in the A$$ but the nanny state says it is for our own safety.

Yeah, I can't believe they took away our freedom to be blown to bits in a horrible fiery death.

[cfarrar]

If you have to blow into it to reseal the valve, you have a bad connector. There is a spring in there that should reset the valve when it is removed from the tank.

Exactly! The valve resets as soon as you close the tank valve. I was blowing from the connector towards the regulator, simulating gas pressure, to demonstrate (to myself) how the valve works. Cheers, Colin

[Ironhorse74]

Originally Posted by MarkSF

Yeah, I can't believe they took away our freedom to be blown to bits in a horrible fiery death.

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.

[osirissail]

Originally Posted by cfarrar

Our connector is the one pictured below. If I remove the hose from the regulator and blow hard into this connector the safety valve closes, . . .

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?

That particular connector uses the outside threads on the OPD valve. The old "normal" (POL type used by the rest of the world) still uses the "inside" threads on the OPD valve and the old connectors. A photo of the "old" POL-type is below.

Technically, the OPD valve only has the float and this new stem valve inside that must be depressed to allow propane to exit the tank. However, your fitting/connector is something "else" and not part of the OPD valve. As mentioned by others 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.

I am kinda with Ironhorse74 on this "new" addition. You could just get rid of the new and go back to the "old" - if you can't get the "new" to function properly. . .

P.S. that "copper crimped hose clamp" that is shown holding the hose onto the "new" connector/fitting looks like a future problem waiting to happen. The copper gets eaten away by the salt water atmosphere and then the hose is no longer clamped to the connector/fitting . . .