The Steamboating Forum

Hi,

Unless I want to wait a long time for enough water to accumulate in my condensation system to be pushed through to the hot well, I assume I need to pre-fill the loop with fresh water. Do I make a provision in the circuit inside the boat to do so ? Also, do I need to have a check valve on the exhaust side of the engine ?

thanks in advance for the help, I know I am a nuisance

jon

Jon, perhaps you meant to say this, but your condensor should be a vacuum. That's the whole idea of condensing - besides, of course, re-circulation of the feedwater. Vacuum eliminates back pressure at the exhaust cycle of the (last) cyclinder, getting power (heat) out of the last vestige of steam's expansive properties. Historically, this was achieved on launch engines through a crosshead-driven air (vacuum) pump mounted off the LP crosshead. Some fellows use other arrangements now.

A large, surface condensor situtation would chill the exhaust sufficiently to create a vacuum from the inverse property of the nature of the expansive power of steam, with the feedwater then emptying into the hotwell. We can't quite get these economies of scale on our launches. So most use a keel condensor to chill the exhaust at a sufficient slope so that the the suction on the air (vacuum) pump is at the bottom of the slope, and yet not too far from the air (vacuum) pump. I trust that makes sense, and others will weigh in with things I may have missed. Oh, and most use some kind of check to maintain the integrity of the vacuum along with the working of the pump.

On my crude (simple?) little boat with a simple (single expansion) engine I have no vacuum pump or check valve. The exhaust just goes into the keel condenser. condenses to hot water, drains to the low point in the condenser where the resulting back pressure pushes the condensate up to the hot well. The back pressure runs about one inch of mercury. Two p.s.i.

I'm sure that I will have an attack of remorse some day and fit a vacuum pump but it runs now. The pump is down the list below an exhaust feed water heater and an economizer.

Lopez Mike wrote:I'm sure that I will have an attack of remorse some day and fit a vacuum pump but it runs now.

Friend, be at peace ...

Lopez Mike wrote:... The back pressure runs about one inch of mercury. Two p.s.i. ...

Ya got it backward Mike - two inches of mercury = 1 psi.

Wup! Right you are.

To clarify the installation, the engine exhaust has to raise the condensate a maximum of two feet. 24 inches of water = two inches of mercury = one psi. All approximate, of course.

Doesn't seem to make that much difference to this engine with 100 to 150 psi in. As I said, it will be after a bunch of attention to insulation, an exhaust feed water heater and an economizer that I get around to a condensate pump.

I'm trying to stay with reciprocating pumps so that I can run in reverse as long as I please without a hassle.

Lopez Mike wrote:... I'm trying to stay with reciprocating pumps so that I can run in reverse as long as I please without a hassle.

Mike, I strongly recommend using "plunger" or "ram" (not piston) pump for your feedwater - no need for rings, etc. and the US Navy type air pump as discussed here recently. Do a stepdown reduction from the crankshaft - about 3 : 2 (cuts down the possibility of "air hammer" in the water delivery line) - turning an eccentric with strap and short rod(s) to drive pump(s). Makes for a very compact and quiet unit.

The two designs that look best to me so far are either the Edwards type or a version of the Navy pump. The built up one in S & MSL by Dave Fogg looks like it could be scaled for various bore/stroke combinations without too many difficulties.

As I said, though, this is all down the road a bit.

Edwards is what we are reproducing: http://www.thesteamboatingforum.net/for ... 6&start=40

Den (farmerden) has one on his boat and some time when he is looking the other way I'm going to whack him behind the ear with a Stilson wrench and steal his long enough to take off dimensions.

The 'navy' pump design like Dave Fogg's uses the same theory of operation but is double acting.

Has anyone ever successfully used a diaphragm pump such as a bilge pump to pull a vacuum? They have a lot of inherent springiness that would probably be a problem. Nice short stroke though and no cross head needed for eccentric drive.