The Steamboating Forum

Hi Deitrich,

How much vacuum do you anticipate from these pumps? As best I can tell from Google, they seem to max out at about 12" of vacuum. Are you making any modifications to increase the vacuum, or is the intent just to pull enough vacuum to clear the condensate?

Cheers,
Scott

Hi Scott,

thanks for your question, but unfortunately I can't make sense of the specification "12 inches of vacuum" since I live in the "metric empire", where atmospheric pressure is 1 bar and a complete vacuum is 0 bar. For me, inches are a unit of length.

I'm hoping to achieve a vacuum of 0.8–0.9 bar during operation.
To be honest, I was inspired by the design of the Stuart Swan because I liked it and wanted a different solution than the one I used on my 2 hp steam engine. The cylinders of the Stuart 1 are slightly smaller than those of the Swan, so it should work.

The photo shows the vacuum achieved during the test of my large steam engine with hand-tightened connections.


I'll probably do it the same way as on my large steam engine. There, the condensate flows into a collection container and is then pumped out using a condensate pump.


Regards
Dietrich

A specification of 12" of vacuum almost always means inches of mercury in a manometer. Now, 29.92 in Hg == 1 bar. So a 12" vacuum means 12/29.92 bar vacuum or 1 - 2/29.92 absolute pressure.

- Bart

That flat plate heat exchanger looks quite interesting; they are very compact for the surface area provided. How does one choose the appropriate size of unit to avoid excessive back presure?

Hi Bart,

thank you for the explanation regarding the 12 inches.

I used the smallest heat exchanger I could find. Because the exhaust steam is completely condensed and the condensate is then pumped out, no back pressure is expected. At least that wasn't the case with the condenser of my large steam engine. I will take advantage of a meeting in May and then conduct tests on the loaded machine.

Some more data can be found here.


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Dietrich

Thanks, Dietrich, for the information. I'm considering switching Otter's (our little 19' steamer) hand-fabricated shell and tube feed water heater I made many years ago with one of these units; the shell and tube is about 18" long and hides nicely under the boiler, but is quite difficult to purge for winter time in that position. We moved to Lopez Island, WA during the pandemic, and can freeze hard here, so getting the plumbing empty at the end of the season is important.

Hi,

i've made some progress. The hand lever and the pump diaphragm drive were removed from the shaft for manual pump operation, and the shaft was then reinstalled.


The diaphragm drive rod will be made from 10 mm round stock. This rod will be guided by a shaft seal in the housing. This seal will be secured in its seat with a washer.


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Dietrich

Hi,

some more pictures.
The oil seal is inserted into the seat in the housing.


View from the membrane side


View from the drive side


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Dietrich

Hi,

I removed the riveted diaphragm rod.


To ensure the full stroke (7 mm (9/32")), I flattened the head of the mounting bolt and reduced its diameter so that it is only slightly larger than the original rivet head.


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Dietrich

Hi,

to test the pump's proper function, I installed it and measured the flow rate using a measuring cup.


The maximum stroke of 7 mm was achieved; the pump's stroke in the steam engine system will be 6 mm.
During the test, 30 strokes delivered a volume of 475 cm³.


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Dietrich