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Dick Bennett recently sent me this photo of an "unmolested" cylinder from a 5-Gallon Correct Measure pump. The cylinder size is not one that I had included in my chart of cylinder sizes. This got me to thinking about a question Roger Goodwin recently asked, " I've never understood how 10 gallon pumps all have different sizes, how does that work!"

I decided to put some of my old high school geometry to work and calculate the actual gallon capacity of the cylinders. The results are rather surprising.

Bear in mind that the actual capacity that a pump could hold was affected by a number of factors other than just the outside dimensions of the cylinder, such as:

The volume of gas held in the bottom plate and plumbing below the bottom of the cylinder all the way to the shutoff valve.
The volume within a sight-glass.
The amount of gas displaced by any internal tubing, rod and indicators.
The height of the overflow tube.
The thickness of the glass. (For my calculations I used a glass thickness of 7/32" or a total of 7/16".)

Correct Meas cylinder.JPG Cylinder Capacity.jpg
Last edited by Tim Rohr; Wed May 01 2013 12:07 PM.
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Fascinating ! Ed Shaver


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Tim your calculating should be real close & almost impossible without having every cylinder to check the Inside of the cylinder & as you stated the other factors [recess in castings, pipes, over flow, wet/dry hose, etc.]. City, County & State Weights & Measures would check & an affix a sticker &/or wire seal jar lid/calibration screw to insure the customers were getting the correct amounts they were paying for just as they do today. Any company/station caught cheating were/are issued a stiff fine.


Last edited by Dick Bennett; Wed May 01 2013 03:53 PM.
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Thats why some Ohio visible pumps were made with the taller more slender cylinders (10 x 37 1/2), people felt that when the sun came up in the morning and shined on the glass, that they were getting cheated. Scott Anderson wrote an article about it in Check the Oil. And boy have I found tons of that particular size here in this state.

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I used to test tanks many years ago and one of the most important considerations was the temperature of the gas itself. We spent up to an hour getting the gas to circulate in the tank to stabilize the temp. It's very temperamental and expands quickly with heat. We used a stand pipe similar to a visible cylinder and had to shade it from direct sunlight. Long story short the longer the gas sat in the pump, the more (or less) it would expand, adding to the inaccuracy of any given cylinder.

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Goober,
Because the taller cylinders exposed more surface to heat, and the gas would expand faster? Sorry I don't have the article to read. I'm sure that would explain your statement.

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I notice a small error in my original calculations and have corrected it. At the same time I have showed how variations in the glass thickness affect capacity. In the original chart I used 7/32".

I purposely did not list gas temperature as being a variable because from a "strictly mathematical" point of view the "Volume Capacity" of the cylinder does not change. It can either hold 5 gallons of warm gas or 5 gallons of cold gas.

Cylinder Capacity.jpg

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