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Cody Killgore

Adjustable propane regulator. Does inlet pressure matter?

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Hey guys. Having a 500 gallon propane tank put in today. He's running 10 psi from the tank which is more than I need. I'm wondering if I can still use the 0-60psi adjustable regulator I was using to drop it from the smaller propane bottles. 

Basically, does it matter that the inlet pressure is only going to be 10 psi? My regulator is one from hightemptools. 

Edited by Cody Killgore

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Holy a 500 gallon tank?  You must use propane for heating and your stove.

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That shouldn't be a problem.  Regulators only really care if there is too much (or I guess possibly too little) pressure.  Since yours obviously works above the 10, and can accurately read below to the ranges you want, you shouldn't have a problem.  There is a chance that it may not read 100% accurately, but I can't imagine it being unsafe at all.  So worst case scenario you need a better tuned regulator.  Which is way better than worst case scenario being "BOOM".  

*I'm not a regulator expert.  This is just my understanding of it.  

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Hey Jerrod. Thanks for the reply. It does appear to be working as intended. The propane guy has not been the most helpful guy. He had taken a lunch break and I was trying to sort out how I wanted it all plumbed up and was crossing my fingers that was going to work.

@AndyB this tank is mostly for forging but gave me the added benefit of being able to (finally) put a nice heater out in the shop for when it cools off in the winter.

This whole propane tank thing has been a bit of an adventure for the last couple months. The first time he came out to set the tank, he showed up and told me that he couldn't run more than 11 in w.c. (about 0.4psi) inside a building due to national fire codes. Seein as he was the propane guy, I felt obligated to believe him. We called the company later to try and figure out some way to make it happen and then he claimed he could do up to 5psi inside a building, which is just a little low (I can just barely get to welding heat in my big forge at 5psi). After sifting through the NFPA 54 and 58, I saw that there was a restriction on 5psi inside a building unless it met any of a bunch of criteria. One of which was simply that the pipe joints are welded/brazed. Basically, if you follow the code, you can run up to 20psi in a normal building. I had even asked him the first time he was here if he could just stub it up outside and I'd run a hose around the corner. He basically said no because "you'd still be hooking into my tank" since we are renting, I suppose.

Still didn't get him to run it in the building. But finally convinced him to stub it up just outside. At least I've got propane now.

Looking forward to this weekend. Haven't been able to get out and forge for a couple months now while I was waiting for that tank. And I didn't really want to pay double price for propane and go get my other tanks filled up thinking I would get the 500 gallon any day now.

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Dang well youll be set once you get that one in.  I still have to get my 100 pounder and thats about as big as I can get here where I live lol.

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It will "probably" be fine, but with caveats.

Inside the regulator, a plug moves in and out of a hole, controlling the amount of gas getting through. The plug is attached to a diaphragm and this works against a spring. The gas, downstream of the plug and hole, presses on the diaphragm and spring. As the pressure rises, the plug moves into the hole. As the pressure falls, the plug moves out of the hole. The steady state is where the pressure on the diaphragm balances against the pressure of the spring. Adjusting the spring preload adjusts the regulator pressure.

The size of the plug and hole are important. These are fixed in your regulator. If your regulator is rated for use with, for example, 50 PSI upstream pressure and 5 PSI downstream pressure and will allow 5 lb/hr of Propane to flow at those pressures, the pressure available to drive the flow is 50-5=45 PSI. The regulator can control the flow to less than 5 lb/hr by moving the plug into the hole, but once the downstream pressure drops below 5PSIG and stays there, the regulator will be fully open and the size of the hole is what matters.

If you now supply the regulator with 10 PSI gas instead, the pressure available to drive the flow is 10-5=5 PSI. Only 1/9th of the original pressure. Flow through an orifice varies as the square root of the pressure, so the maximum throughput the regulator could provide would be the square root of 1/9th: 1/3rd of the design flow or 1.67 lb/hr.

The numbers I used were chosen because they are easy numbers. However, the vapor pressure of Propane at 30 degF, just below the freezing point of water, is 51 PSIG. At -20 degF, it is 11 PSI. Both are similar to my easy numbers. The effects of Propane cylinders "freezing" are well known/documented in smithing circles. 

Be aware that you may find yourself seeing identical symptoms to cylinder freezing as a result of using a, now too-small, regulator fed from a 10PSI supply.

 

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Thanks for the additional info. Nothing left to do but try it and see how it goes at this point. They are out there filling up the new 500gallon right now. 

I was having a lot of trouble finding any kind of adjustable high pressure regulator that wasn't intended for coming straight off a cylinder at relatively high pressures. Not sure if one meant for lower inlet pressures even exists.

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Give it a try and see if there is a problem.

As you will have a regulator in the system already, a local shutoff valve and a needle valve to control the flow to the forge would probably get the job done.

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