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another propane convention question on dual[ing] bulk tanks
Having established 10 lbs as the standard frst stage pressure (except maybe for blueberry processors who use 5 frequently) in a previous thread I'm on to the next convention. . . speaking of conventions, just got back from the world of concrete in las vegas, but thus missed the chicago show but I digress.
Have installed twin 1000 gallon tanks at our farm, mostly for storage capacity, but if the power went out on the coldest days of the year and the tanks were down to 10% full (gotta figure the murphy factor here) then we would need the vaporization rate of both tanks to run the boiler and the generator at the same time.
So the industry standard to take advantage of vaporization from both tanks is to pipe the tanks together at tank pressure to a tee and then a common first stage regulator. The purpose here is to drain the tanks more or less evenly and take full advantage of the vaporization rate from both tanks.
On the other hand, the industry standard for single tanks is to mount the first stage regulator right under the tank cover and thus never have tank pressure running out from under the cover. vapor pressures aren't so crazy in the winter but they can stabilize at almost 200 lbs. in the summer.
So I'm trying to reason through what would happen if I put a first stage regulator on each tank and then tee them together. The obvious problem that leads to use of a single regulator for both tanks is that no 2 regulators are going to be precisely identical in output pressure and you are going to tend to feed from one tank only or much more from one tank because one of the regulators will always be putting out a slightly higher pressure.
On the other hand, if I use two regulators and start to draw down one tank more than the other then the wetted surface will be reduced in that tank and its vaporization rate will slow. my guess is that as long as the regulators are tuned reasonably close to one another that this lower vaporization rate coupled with the significant demand from the boiler would lower the delivery pressure enough to trigger delivery from the second regulator, thus see-sawing delivery of gas and somewhat evenly emptying the tanks.
This would allow for no tank pressure piping other than the 6" presto-lite whip to the regulator.
The simplest alternative if I'm going single regulator is prestolite by flare adapters and leading copper to a prestolite tee between the tanks that feeds the single regulator. The service pressures aren't any problem for that setup with a 3 times safety factor even for summer vapor pressures, and the only likely physical disturbance is when the tanks are filled and we deliberately located the feed several feet away and in back of the approach for the fill guy. So this means maybe a 6 foot run at tank pressure to the common regulator between the tanks which are about 3 feet apart.
But since i'm applying the murphy factor to the btu requirements, I reckon I could at least think of worst case scenarios, e.g. tree limb blowing into exposed copper piping and try to reason out whether I could regulate both tanks and keep the tank pressure confined under the covers.
Right now I'm just operating off a single tank at a time while I reckon the best approach here.