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robbin
Mod
join:2000-09-21
Leander, TX

robbin to wth

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to wth

Re: Check my math - Propane vs. NG cost comparison for BBQ

said by wth:

said by LazMan:

said by wth:

As for refilling a propane tank, I get mine refilled for $14.88 AND that's for 20 lbs of propane. You may want to check with your refiller or exchanger as some places are only putting in 16-18 lbs in the tank to increase profits.

That's the law, actually... Not allowed to fill past 80% by volume, as to allow expansion and vaporization room... 18# would actually be overfilled on a 20# cylinder in most circumstances.

I just assumed that even with the current specs for 20# tanks (the ones with a float valve in them) would still allow a legal 20lb fill.

They do or they should although OPD valves can stick and are not a reliable way to fill a tank to capacity.

"By the way, if your tank has an OPD or Overfill Protection Device, do not let your propane supplier convince you that the tank need not be weighed simply because it is full when the valve closes. This isn't necessarily true! These valves are notoriously unrepeatable and you will have no idea how much propane is actually in the tank. While the tank is full in that no more propane can be placed into it, it doesn't mean that you have received the maximum amount of propane that the tank was designed to hold (i.e. 42% of WC). Make them weigh the tank before AND after the fill."

As noted in the above quote, the correct way to calculate tank capacity is based on the WC number stamped on the tank. That number is how much water the tank holds in pounds.

"To fill the tank properly, the dealer must calculate the maximum safe fill from the Water Content (WC) value stamped on the tank. The maximum amount of propane that can be placed in the tank is 42% of the WC value. This ensures adequate room for the propane in the tank to expand safely. The empty (tare) weight of the tank is also stamped on the the collar and allows the dealer to calculate a full or gross tank weight."

As an example, I have a 20 lb cylinder that has a tare of 17.0 and a WC of 47.6. Multiplying the WC of 47.6 by 42% gives me a propane capacity of 19.992 lbs. Adding the tare of 17 shows that my tank should weigh 36.992 lbs when filled to safe capacity.

Above quotes taken from this webpage.

Alternately, the propane company uses a propane cylinder filling chart as shown below.




49528867 (banned)
join:2010-04-16
Fort Lauderdale, FL

1 edit

49528867 (banned)

Member

said by robbin:

They do or they should although OPD valves can stick and are not a reliable way to fill a tank to capacity.

OPD’s have two common problems, the dangerous one is if the valve has been used repeatability as a re-fill shutoff it may begin bleeding allowing an un-weighted tank to be capped out with the operator shutting the fill down upon noticing (hearing) the pump going into bypass, and if not resolved this sends the customer on his way with a 100% filled tank, which if you will pardon the pun is not too cool as once that liquid warms up the over pressure valve begins venting.

The other problem with OPD’s is shutting down a fill before the tank is to capacity leaving the owner with two decisions, use the less than full refill and return the tank for another one or just put up with a pound or so loss.

Wayne