Why Do Doubles Always Cost Twice as Much to Fill?

[jim T.]

I've never gotten a clear explanation from dive shops about this.
I've heard everything from, it's a charge for the "hook up" to fill.
But doubles are filled from one post/valve only...
to "They're twice as heavy to lift into a wet tank". (I mostly go to shops who fill on the floor (dry). I also go out of my way to supply my own hand truck and lift/move the tanks myself.

So...if I have HP100s (3442 fill pressure)with 1750 remaining gauge pressure, I've used the contents of "one tank" only. Why are we charged for the amount to fill two tanks?

Am I missing something obvious or this really the "rip off" it seems to be? Could shop owners/LDS posters fill me in on this please? How does it cost the shop owner more to fill "half" of a doubles set than a single tank?

I've only found one shop that charges based on the actual amount of the fill needed.

Thanks.

 

[DBailey]

Does this shop charge you 1/2 the cost to fill a 1/2 full AL 80?

 

[Bryan]

Maybe if you trick them and put them into a single fiberglass enclosure?

Spoiler

 

[jim T.]

Yes they do. They tongue in cheek-ily call it "a pony fill".

I see a basic difference here though. An average dive is going to be approx. 45 min. to an hr. for a single tank. With a doubles set, if you get to only do one dive (one tank) but your next dive outing is for two dives (maybe a boat/wreck dive) you'll need a full set.

If you're only getting one tank's "worth" of refill (one half of total doubles set fills)
why are you getting charged for two? I don't see this as "half a tank"
I see it as an empty (single) tank banded to another full tank.
I see it as paying (at least) twice for a full tank I've already purchased from this (any) shop. I find this kind of confusing. Maybe there's some valid economic reasoning for the LDS but I need to understand what it is, I guess.

 

[Mack Diver]

Basically, each shop has to determine the cost of fills and therefore how much to charge for a fill. Besides the cost of the compressor and electricity to run it etc, there is also the labor involved in performing the fill. For whatever reason, the LDS you mention has decided it costs twice as much to fill your doubles (slower fill rate combined with added air( 100 > 80)).

It sounds like you have found one shop that has been able to calulate down to a cuft rate. I'd like to know the math they used to do that.

 

[Belmont]

Shut your center valve and drain only one tank then tell them you want one tank filled but don't bother about the "pony"

 

[Jim Lapenta]

Do what I did. Become a DM. I have not paid for an air or nitrox fill locally in 3 years. Only thing I pay for is trimix.

 

[jim T.]

I'm not sure what calculations are really necessary in the case of half gauge pressure for a doubles set. The shops charge a certain amount for an AL 80 fill, a certain amount for a 95-100s fills, a certain amount for 120s to 130s. It's right up there, posted on the wall. So what's the math needed to fill what amounts to one empty HP 100?

Fill express in Fla. fills to just what is needed and charges based on that amount only. There may be an additional "starting" hook up fee but it's been posted here on another thread that less than a certain amount/top offs are free.

I realize that shops make almost no money on fills after compressor and filter expenses. I'm not asking for anything less than they need to make an honest profit for their business. But charging for a two tank fill when only one tank('s worth) is needed seems wrong to me.

If math is indeed "the problem" how hard is it to make up a one time chart for the tank fillers to use based on increments of CF? On a computer it would only need to be done once and then updated as inflation, etc. rears it's ugly head.

 

[H2Andy]

So...if I have HP100s (3442 fill pressure)with 1750 remaining gauge pressure, I've used the contents of "one tank" only. Why are we charged for the amount to fill two tanks?

honest shops will charge you for the actual amount (in cubic feet) of gas dispensed

so ...

draw your own conclusions about your shop

 

[Lock Down]

I understand your issue but i think there is more to it than that. I'm sure not everyone lifts their own doubles into and out of the fill sstation and some people need more air than others. so in the shop owners eyes he needs to pay for the future back injury of his employees. plus their time and the cost of equipment. In the end it's up to you to decide where to go. If you believe that a shop charges unfairly you have the ability to go somewhere else. Although if that is the nearest shop to you then maybe you should look at it as paying for the convienence. just my .02...