The Steamboating Forum

Is it possible to set up the vacum to the exaust side of an engine so that it is adjustable?
In the past I have achieved a primitive sort of adjustment on my old portable by pumping feed water from the make up tank through a jacketed condenser. Do you guys think this would work in a marine application? And would this effect the vac pump in any way ? The guys at the Threshers Association are starting to think Im a little crazy , but as this is sort of a givin I dont mind. The above technique does not produce a large boost ,but it seemed to make some difference. This difference was on the order of roughly 3-7# on the gauge. As always your thoughts and suggestions are greatly appreciated.

Not sure where you are coming from here? I think you have been reading too many philosophy books?
If you have a vacuum then you want the best you can get, It won't be great on anything short of a turbine. Any ingress of air will reduce it significantly as will an increase in the condensate temperature. Its a balancing act between a good vacuum and condensate that is as hot as you can get away with.
Regards Jack

steamboatjack wrote:... If you have a vacuum then you want the best you can get, It won't be great on anything short of a turbine. Any ingress of air will reduce it significantly as will an increase in the condensate temperature. Its a balancing act between a good vacuum and condensate that is as hot as you can get away with.
Regards Jack

If you're a perfectionist. If you're not, as is the case with many of us, any vacuum above 10" (or 10psia) will result in a noticeable increase in rpms/engine performance.

After rereading my original post ,I see that it is not really very clear. What I am really trying to get my head around is the size of vacum pump in use ,how one finds the optimum size for the pump and how one gets the very best results. Now I've been told I am one of the best IC mechanics in this part of the country . I have been building racing engines and hot rod motors for 30 years. However my experience with steam engines is limited to simple and single cylinder double acting engines ,all of them non condensing engines that exaust strait to atmosphere. You see in an IC engine I have several ways to make adjustments to how the vacum pressure in the engine acts, valve events , length of stroke intake sizes,and a few other things. But here I find myself in a position where all of my knowledge about how to manage vacum pressure is useless. Its an apples and oranges kind of thing. I badly want to get the steam plant right . tho I will probably start with a small boat , I want it to be the very best little boat that it can be

The great thing about a steam engine is it will run with any load it can start...which makes it very forgiving.

Most boats have one of two different types of condensors, but they are both surface types

Keel condensor

Shell and tube condensor

The shell and tube is very similar to your current one on your stationary engine ..I think as I haven't seen it, just read the description.

The Keel condensor has a pipe running along the keel that is cooled by the water your sitting in.

Running a vacuum is great on recips but up to a point, as you can end up drying the cylinder out and it will squeak.
20-25 in Hg seems to be the practical limit though I am sure someone will argue with me.
I run no internal lubrication...as does a bunch of steamers I know, without issues.

A keel condensor is very simple....a shell and tube very flexible in operation. Run whatever you like as your the Captain!

Dave

I would agree that 20-25ins is a good vacuum I have never been on a boat with more. There are so many things which influence this, most of which restrict the vacuum.
There are many types of air pump in use, all work to some degree. Assuming a single acting reciprocating pump is used it should be about one sixth of the total cylinder volume (or the L.P.in a compound) but this figure can vary enormously. If the engine runs fast, then a bigger pump geared down is best. Also I believe a vertical single acting pump with the flow from bottom to top is best as this ensures there are no air pockets and the pump gland is at the top in the delivery chamber so has less chance of spoiling the vacuum.
The Edwards type pumps are good but they should only be used with an inboard condenser where the pump base is the lowest part of the system, yes I know there are some in use with outboard condensers which apparently work ok.

Regards Jack

1/6 th the size of the lP is about right....I'm about 1/10, but I need to be very sure I don't have any air leaks..then the vacuum good (10-16 in hg).

Dave

I 'm interested why Edward's style don't work to well with outboard [keel] condensors. Do they not lift too well? Here's some pics of mine apart. Den

[/img]

These are called Edwards air pumps in the UK after the inventor. The idea is that the condensate runs into the bottom chamber where the bucket descends and pushes the fluid around into the cylinder above the bucket without shock, the bucket then carries the fluid up and through the delivery valve plate. If you are then having to “suck” up the next charge this cannot be as good as a conventional pump with foot valves??
I am not saying they are no good, just that people use them for what they are not designed to do. If they work well then fine.
Regards
Jack

A common misunderstanding is that a vacuum pump "pulls" fluid into itself. It is common in industry to say that a vacuum "pulls" fluids, however this is simply not true. In fact, fluids (including the air and non-condensables and condensate going to the vacuum pump) must be "pushed" by fluid pressure upstream, or caused to flow by gravity. When you suck on a soda straw, you do not "pull" any fluid up the straw, it is the upstream pressure (atmospheric pressure) that forces the fluid up the straw.

With a very good vacuum, there is little pressure to force fluids into the vacuum pump, hence the Edwards pump would only be able to function if it was mounted where gravity flow could do the job of getting fluid into the pump. In our steam launch applications, there is usually nothing near a perfect vacuum, so there is enough pressure in the condenser to push the fluids into the pump, so any reasonable vacuum pump may work OK without the help of gravity.