Vacuum Pump / Condensor

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Anne from Little Britan
Anne from Little Britan
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Vacuum Pump / Condensor

Post by csonics » Wed Nov 18, 2009 5:07 pm

Posted on behalf of Waterlily:

Waterlily
Just Starting Out


Joined: 16 Jul 2008
Posts: 2

Posted: Wed Jul 16, 2008 6:07 pm Post subject: Vacuum Pump / Condensor
Hi; I have a Semple single in my Elliott Bay hull and only seem to get about 9" of vacuum. Could it be pump speed issue or something? Any comments welcomed.

Cheers Waterlily :
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Maltelec
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Joined: 23 Sep 2007
Posts: 156
Location: Cumbria, UK
Posted: Thu Jul 17, 2008 5:04 pm Post subject:
Hi

The best thing to do is to take some measurements and do some calculations.

1st of all the water return from the condenser must be cool. If its too warm the steam will not condense - remember that water will flash at a much lower temperature in a higher vacuum.

2nd of all you must make sure the pump is adiquate for the job. To do this you need to work out the ammount of water the engine uses (steam at a specific pressure and volume is equivelant to a specific volume of water).

A general rule of thumb is the air pump wants to move 20% of the volume of the LP cylinder (or the only cylinder in your case). I.e. if the LP swepped volume is 1 litre, the air pump should be 0.2 litre.

If your air pump is driven at 1/2 engine speed, the swepped volume should then me 0.4 litre etc.

Unless you get all the variables correct, increasing one area with another still at fault will not rectify the problem.

According to t'interweb, as you approach a complete vacuum, the boiling point of water drops dramatically. How accurate this is I don't know, but it would sergest that you want the condenser to cool the water as much as possible.

Other factors you should look at are the obvious really. How good are the seals, is the pipe blocked (daft as it may sound, I've known a copper pipe collapse before). If the pump getting too hot, is it running too fast and not able to draw in the water before the piston returns? If you've got little pressure in the condenser trying to push the condensate into the relative vacuum in the pump and it is restricted by a tiny pipe, that won't be doing it much good.

I hope that has given you some pointers.
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Waterlily
Just Starting Out


Joined: 16 Jul 2008
Posts: 2

Posted: Thu Jul 17, 2008 6:40 pm Post subject: Condenser Issues
Thanks for the ideas. I'll work away on it and let you know if things work out. At first I thought I wasn't getting a good connection to the condensed steam but as i get no back pressure and some vacuum (9") it must be getting something. Will haul her out and look at the piping. I know I had a pinhole leak in a joint when I first made it but I i was sure on the rebuild it was tight - pressured it up and saw no leaks.
Will investigate all this tomorrow.

Thanks and still open to ideas

Waterlily
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artemis
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Joined: 24 Sep 2007
Posts: 19
Location: Portland, OR, USA
Posted: Wed Jul 30, 2008 1:35 pm Post subject:
There are so many variables involved that's its absolutely freaky.

Artemis was a 26' Navy motor whaleboat hull converted to steam (this has been done to several). The engine was a compound of 3" + 6" x 4.5". Since the amount of steam used by the engine is what is admitted to the HP, the engine was close to the Semple single (which is, as I recall, a 3" x 4"). I knew the boat for many years in the Puget Sound area and purchased her in 1995 many years after I had moved to Portland, OR, on the Columbia River.

I had the engine rebuilt (while I was rebuilding the hull and installing all new piping, etc.). She was originally fitted with a keel condenser which I retained. Running her for the first year I had varying results with the vacuum, with no apparent cause but definitely fluctuating from 21" at low rpm to 2psi back pressure at 280rpm. I did much checking of the plumbing, making sure there were NO leaks on the vacuum side (a very LITTLE air leak destroys a LOT of vacuum). The air pump I was using was a copy of a Bailey (or US Navy) style, 1.625" bore x 1.25" stroke double acting. I did the calculations and found that it should be more than adequate (you can have an air pump TOO big) and in the process learned that the size of the pump is not governed by the water consumed, but rather by the amount of air entrained in the steam (leakage past pump glands, valve and piston rods, poor piping connections, etc. ALL affect this quantity). It ran at 2/3 engine rpm, which seemed to be the right speed.

All of the above was happening in 1997. In mid August of 1998 she was trailered to Olympia, Washington on Puget Sound (her original body of water) for the Annual NWSS Meet - where she operated very well, maintaining a steady 20+" of vacuum no matter what. Well, of course, the transport over Washington State's bumpy roads "knocked something loose". Back down to the Columbia River a week or so later. Guess what? Problem is back. Time to engage brain again. Hummmm. What causes the condensation. Why the water the boat is in. What's the difference between the water in Puget Sound in August and that of the Columbia River. Ahhhhhh! Puget Sound is 51F + or - 1 deg year around. The fathometer on Artemis (don't navigate ANY Western River of the US without one) also had a temperature sensor. Temperature of the Columbia River in August (after traverling several hundred miles through the hot, east side of Oregon/Washington) was 76F. There wasn't enough surface area to condense the steam in August. A larger condenser was needed for the summer. There was not enough space to comfortably accomodate a proper size overboard condenser (nor did I want ice cubes going into the "hot well" in winter months), so I opted for an inboard (shell) condenser. Thus by altering the flow of cooling water, I could control the temperature of the water going back to the hotwell and also the vacuum. I found that a condensate temperature of 130F also let me consistently maintain a vacuum of about 20". The 130F kept the water in the hot well de-aeriated and improved fuel consumption - the feedwater was now 60+F hotter than on Puget Sound.

Would I use an inboard condenser again. YES! Not only did it give better control, but removing the outboard consdenser also improved the handling/steering qualities of Artemis. The cost was not great and an inexpensive baitwell pump provided a centrifugal pump to bring water from overboard to the condenser.
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daysaver1
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Joined: 03 Sep 2008
Posts: 2
Location: Livermore, California
Posted: Wed Sep 03, 2008 6:17 pm Post subject: Building a new vacuum pump
I'll be installing my boiler in my 16' lifeboat hull in the next month. Can someone please lead me to construction drawings for a Baily type vacuum pump so I can get some more chips made in my garage? Thank you.
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My hull is a 16 foot steel lifeboat. Don Mentzer of Medford, Or built my 2.5x3 engine and I helped him build the 40 sq ft Roberts type boiler. I've set a schedule to have the boat under way at the Rocky Point, Oregon steamboat event June 2009.
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artemis
Just Starting Out


Joined: 24 Sep 2007
Posts: 19
Location: Portland, OR, USA
Posted: Wed Sep 03, 2008 9:26 pm Post subject:
There is an excellent article by Dave Fogg in Steamboats and Modern Steam Launches, March-April, 1963, pp 25 & 26 on a well functioning Navy (Bailey) air/condensate pump. No castings involved, just tubing and bar stock. The one I mentioned that Artemis used was a smaller version of this one (dimensions are in my post of July 30).

John York made patterns and sold castings for a good version of the same. Andrew Van Luenen (AVL Machine Works) has the patterns and now sells the kits. Read the article and you'll see that this is a very robust, US Navy seaman proof, piece of machinery and operates from any position - horizontal, vertical, 45deg angle, up-side-down...
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