Dang, you are so right on the 1 3/4" already being on the van.  I
confused myself.  Mine has already been converted to the manual fill system.
Edward

At 08:56 PM 1/9/2012, you wrote:
>Erm...what you already have on there is a 1 3/4" Acme valve, unless
>someone has been seriously messing with things.  It's *not* the same
>as what's on a 20 lb BBQ tank.  That's Acme but much smaller
>diameter.   I initially thought that the valve you pointed to was of
>this smaller size (one-inch?) which is why I responded as I did.  If
>you have the OEM valve still present, it has an automatic stop
>facility which makes it more complicated and expensive - the tank
>fitting that acts as a level gauge (by passing liquid instead of
>vapor when the tank is filled to 80% of its "water capacity") is
>plumbed into the side of this valve which detects the passage of
>liquid and closes against the incoming fill.
>
>The valve you're looking at doesn't have this complication and
>requires the operator to observe when liquid starts coming from the
>opened gauge valve and stop filling at that point.  If he doesn't
>stop immediately you then have to continue bleeding off the liquid
>until you get back down to vapor coming from the valve.
>
>New ASME tanks (the kind we have, stands for the American Society of
>Mechanical Engineers) have a float-type shutoff similar to the ones
>now required in DOT (Department of Transportation, BBQ-type)
>tanks.  Unlike the DOT tanks however there is no requirement to
>retrofit such valves to existing ASME tanks, nor is there any
>requirement for periodic testing/recertification of ASME tanks which
>are constructed much more heavily than DOT tanks.  If you bought a
>new tank from Manchester Tank it would come with the float-type shutoff.
>
>But regardless, all these tanks (manual shutoff, liquid-flow
>shutoff, float-type shutoff) are filled from the same hose, or the
>same adapter if it's an outfit that primarily fills DOT tanks.
>
>If you *were* to put a BBQ-tank valve onto one of our tanks you
>would have to remove the Overfilling Protection Device (float-type
>shutoff) from the valve, and would be in at least a questionable
>area regarding whether the tank would still be considered certified
>as an ASME tank.  In practice I think you would have difficulty
>finding people willing to fill it for you, though that is a
>guess.  And you'd still have to install and use the manual gauge
>valve.  If  you *did* find people willing to fill the tank I think
>there would be an increased risk that the operator would fail to
>open the gauge valve, since they're spring-loaded by now to expect
>the BBQ tanks to shut themselves off without any operator intervention.
>
>Purely by the way - the Acme designation no doubt comes because the
>external thread used to couple the fill hose onto the valve has the
>"Acme" thread form which is commonly used for leadscrews on lathes
>and similar machinery and other power-transmission uses.  It's a
>modification - stronger and easier to machine - of the square thread form.
>
>Yours,
>David