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I have an adjustable propane regulator that I plan to have up to 10 PSI maximum. It's got a POL fitting, and works fine on a regular barbecue tank. However, rather than connect to the tank directly, I want to have a dedicated pipe coming through the wall for propane with the tank outside. I have a 20 PSI regulator attached to the tank on the outside for the purpose, so it looks like:

tank -> 20PSI regulator (with 3/8" hose) -> 3/8" to 1/2" adapter -> 1/2" pipe -> 1/2" ball valve -> (my regulator goes here)

What I'm unsure about is what fitting I can use to go from POL to the ball valve. My basic understanding says something like this: https://propanewarehouse.com/shop/fittings/pol-fittings/female-pol-x-14-mnpt/

I'm concerned about the pressure though. My understanding is that POL valves are meant to take the high-pressure gas from the tank. But rather than high-pressure gas, I've got a max of 20 PSI coming in (probably less because we're going from 3/8 -> 1/2 on the input). So I have two questions: 1) Is this the correct fitting? 2) Is the pressure here okay? Is it valid to go from a 1/2" pipe at relatively low pressure (compared to tank pressure) to POL? Will it cause me to lose appreciable pressure?

Assuming I can't do this, what's my next option? Remove the POL fitting from the regulator and use something else?

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Simply changing pipe size does not affect pressure. Flow affects pressure: for a given pipe size, pressure drop increases as flow rate increases. Likewise, for a given flow rate, pressure drop increases as pipe size decreases. We can't say anything at all about the pressure drops that might occur in your system without knowing a lot more about the flow rate, ie the consumption by the gas appliance.

My first reaction is that the whole project has the suspicious feeling of being built on some false premise. I feel this way because gas appliances typically require an inlet pressure around 11 inches water column (about 0.4 PSI). It strikes me as "wrong" to have plumbing bringing gas into a building at 20 PSI.

As to the shopping part of the question: it looks like you've chosen a part that matches your description, but the vendor might be in a better position to confirm that.

As to whether the adjustable regulator can work with just 20 PSI on the input rather than full tank pressure: charts of Propane vapor pressure on Engineering Toolbox indicate that propane's vapor pressure at 0 degrees F is about 40 psia, which is about 25 PSI gauge pressure. If that regulator works when the propane is very cold, either because of winter weather or because of prolonged use, there may be reason to expect it'll work in the setup you described.

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  • Thank you. The comment and link about the vapor pressure made me understand much better what's going on with the regulator. It should work fine then. – Surgo Jan 31 '20 at 6:05

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