Converting PSV capacity from one fluid (vapor) to another

[colemanstoops]

My memory is a bit fuzzy here: I believe that if one has the capacity of a PSV in mass/unit time for (let's say) steam, the corresponding capacity for (again, let's say) Dowtherm A vapor at the same set pressure is obtained by multiplying the known steam capacity by the square root of the ratio of the molecular weights. That is, if we have:

X lb/hr steam as the known capacity
18 as the molecular weight of steam
166 as the molecular weight of Dowtherm A

Then the Dowtherm A capacity would be X*(166/18)^½, or so I believe. Correct? If not, would you please set me straight? Thanks.