Stuart triple and condenser vacuum pump

[steamedlou]

I picked up a Stuart triple expansion engine on ebay and await its arrival. It is my intent to have it run on steam and want to build up a display that will have the engine and a boiler. I want to make whatever use I can of what comes with the engine even if its pretty much for show. The feedwater pump on the side of the engine is obvious. ill try and use it for a feedwater pump if it has the pressure. My big question is what to do with the conderser vacuum pump. How should it be piped? I'm thinking it should have its vacuum side piped to a closed condensate receiver so the engine exhausts into the receiver and the pump pumps out of the receiver to the open air. Does this seem right from anyones experience. Do these little pumps really work? will the pressure in the condensate tank be negative due to the pump or will pressure build up. If anyone has a clue how this is supposed to work I would love it. thanks.

 

[Charles Lamont]

If you are running on steam then for best results with a triple you should have a condenser. By exhausting the big low pressure cylinder into a vacuum, the power/efficiency of the engine is considerably increased, and it is doing what it is designed for.

It is the condensation of the steam that creates the vacuum, not the pump. Having said that, it is called an "air pump" because it is designed stop the vacuum being destroyed by air leaks into the condenser, for example from the LP piston-rod gland. It is intended to remove both air and condensate from the condenser. The air pump delivers into an open "hot well".

In a model, you may not want to pump condensate from the hot-well back into the boiler because it tends to be oily, and that is no good for the boiler.

Of course you will also need a supply of cold water to do the condensing. Condensers are of two basic types. The original form, going right back to Savery, is the jet condenser in which the steam is condensed by a water jet, so the cooling supply and the condensate are mixed, and both have the pumped out by the air pump. Later, and more efficient, is the surface condenser, which is simply a heat exchanger, typically a horizontal drum with the steam entry at the top and condensate outflow at the bottom and the cooling flow passing through it in tubes running between header chambers
at each end.

I do not know the design of the air-pump on the Stuart triple, but I would expect it would work.

For a full set of pumps you would also have a circulating pump for the condensing water, and a bilge pump.

 

[steamedlou]

interesting. So maybe the intent of the water pump on the Stuart triple is not to be a boiler make up pump, but maybe a circulating pump for some cooling water which might make sense and would require little or no pressure from the pump. It might be easy to have a not to exotic condensate tank with a few cooling tubes or even a spray system where cool water is sprayed in. Now its making more sense that the water pump be there for condensate cooling rather than boiler make up.

 

[Gedeon Spilett]

this thead deals with what you are planing to do:
http://www.homemodelenginemachinist.com/f31/compound-condensing-engine-14725/

drawings also are in the download section

 

[Charles Lamont]

interesting. So maybe the intent of the water pump on the Stuart triple is not to be a boiler make up pump, but maybe a circulating pump for some cooling water which might make sense and would require little or no pressure from the pump.

I am pretty sure the pump on the engine is intended as a boiler feed pump. I don't think there is any reason to doubt that it would perform that function.

 

[Gedeon Spilett]

The design of the pumps are all different for the feed pump, the circulating pump, the eduction pump, and the air pump, the later being much larger with a valve though the piston; if you add a bilge pump for a marine engine, it gives the opportunity to become an expert in pump making.

 

[steamedlou]

Got my hands on my triple and am exploring it. Im sure the water pump is for boiler feed. It's a plunger in a chamber next to a double ball ck. the air pump is quite strange. it has roughly a 1/2" piston which forces gases out through a circular multi hole flapper valve on top. On the down stroke it makes a vacuum in the cylinder until it reaches ports drilled in the side of the cylinder. there. air steam or whatever rushes in to fill the vacuum. Interesting.
Thinking about a surface condenser. Being lazy and a scrounge I went into my junk and found an old bellows seal valve. With modifications, cam make at least a cool looking condenser. My thoughts were to have the engine discharge into the side of the body and impinge on the copper bellows which is very thin and has a lot of surface area. I can pass some water through the bellows where the valve stem is now. Any thought if this might be useful at all, or just a show? Valve body is 1"x1"x3". Might be way to small for a triple.

 

[steamedlou]

I haven't started my renovation of my stuart triple yet but am still pondering the pump situation. I have taken both pumps apart and understand their operation. yes one is a boiler feed pump. the other is the "air pump". The design builds a vacuum and the discharge goes out though a round flapper sitting on many very small holes which to me is obviously meant to handle gas, not liquid. Hence my continued question. If its designed for gas I feel it should be piped to the top of a closed condensate receiver which in turn is piped to a condenser on the engine. This way the condensate will be drawn from the condenser by vacuum into the receiver and the air pump will not see liquid. Attached is a triple (not mine) where the air pump has been piped to the bottom of the condenser therefore seeing mostly condensate. To me this is just wrong. Anyone agree with me on this or maybe the volume of the condensate is so small it can go through the air pump and I'm being too anal. Would love some input.

 

[Charles Lamont]

From your more detailed description of the air-pump, it is clearly, as I suspected, of the Edwards type. It is meant to handle liquid and gas. See, for example, page 94 here: http://www.hnsa.org/doc/merchant/engineering/part4.htm

 

[rhankey]

Coincidently, the Stuart triple shown in the picture above has just been listed on eBay by a seller in the Netherlands for EUR5,000 (~$6,570USD)!!!

It is interesting how the air pump was plumbed in that photo. Not sure I agree with it either, but I'm not sure I'm not overly qualified in what is right or wrong, though I did recently build a Stuart triple of my own. I am not sure how Stuart intended the two pumps to be plumbed, as there are no clues offered in the drawings that come with the castings. I do like the simpling valve that was added to the engine in the photo, albeit a bit crude, allowing the engine to be self starting.

 

[steamedlou]

Great help guys. Charles, you hit it exactly. Is does match the Edwards scheme. So maybe I shouldn't worry about having the condensate go into it. thanks.
Rhankey: yeah that unit is a little overpriced. Even with condenser I wouldn't expect it to go over $4000-5000. Good luck with a self start. I'm still trying to get mine to run continuously. Spent hours on adjustments. seems to need about 35 psi steam to keep it running. Still takes 15 minutes of hand cranking to get it started. And your right. Stuart is useless. I have even written them asking about the piping and pump use. never really got an answer. You would think if they were going to put the pumps on the thing it would be established how to use them. this engine has remained unchanged for at least. 90 years. its in the 1923 copy of the catalog I have. They should be able to tell you everything by now.

 

[Mechanicboy]

I has Stuart compound steam engine and Stuart triple steam engine. The Edwards pump (vacuum pump) is connected after condensator to make vacuum and preventing air is entered into the low pressure steam cylinder/condensator and pumping the condensed water out of condensator. The waterpump is connected to condensator to keep condensator cooled down to example pumping cold seawater in a boat and after condensator seawater out of boat hence the steam is condensed to make better vacuum.

To self starting the compound steam engine, you need a simpling valve between hi pressure cylinder and low pressure cylinder, also add a simpling valve at steam pipe between hi/low cylinder (Triple steam: between hi/middle cylinder and middle/low cylinder). The simpling valve is connected to main steam pipe to make steam pressure in middle/low cylinder.

 

[steamedlou]

Mechanicboy, thanks. I thought the water pump on this engine was a boiler feed pump based on others comments. Actually makes more sense since its on the engine for it to be a circ pump for cooling the condenser although the flow rate for this pump seems low for cooling. Now your comments on the simpling valve have peaked my interest. Could I start easier with just feeding main steam to the low pressure cylinder at the same time as hi pressure? Will the timing allow this to work? it would be pretty easy to just tap into the supply line between the med and low pressure cylinders as long as I keep the valve close to the tap point(Im given to understand the volume in the supply pipe is a critical item on this design). Certainly the large diameter of the low pressure piston would be great for overcoming the high friction in this engine caused by all the piston rings. Once turning it would blow out all the starting condensate from the cylinders. using the cylinder drain cocks is one pain in the butt when all is hot. plus those lousy Stuart cocks never seem to seal.

 

[Mechanicboy]

steamedlou question:

Now your comments on the simpling valve have peaked my interest.

Could I start easier with just feeding main steam to the low pressure cylinder at the same time as hi pressure?

Answer: Yes.

Will the timing allow this to work? it would be pretty easy to just tap into the supply line between the med and low pressure cylinders as long as I keep the valve close to the tap point(Im given to understand the volume in the supply pipe is a critical item on this design). Certainly the large diameter of the low pressure piston would be great for overcoming the high friction in this engine caused by all the piston rings.

Answer: No problem, The timing is not affected by extra steam from simpling valve. The main steam who is entered into the second cylinder will not affect the first cylinder. Friction is not problem when the steam is ready mixed with oil from displacer lubricator. The simpling valve can be connected to steam pipe between cylindres or direct connected to steam steam chest at middle or low pressure cylinder. Most practical is connecting to steam pipe.

Once turning it would blow out all the starting condensate from the cylinders. using the cylinder drain cocks is one pain in the butt when all is hot. plus those lousy Stuart cocks never seem to seal.

Answer: Use cloves against hot drain cocks. Lap the drain cocks with very fine lapping paste to make them tight against leaks.

 

[steamedlou]

Well you have all helped. me. I believe the end result is 1. the air pump will be tied to a surface condenser and pump condensate and air. 2. since the flow rate is small and Stuart actually calls it a feed pump, the water pump will be a boiler feed pump with some other additional pump for a condenser cooling pump. 3. I'll tie a simpling valve into the steam line heading for the low pressure cylinder. Cool
One last question for you. No one commented on the proposed surface condenser that I posted earlier in this thread. Still wondering if anyone thinks the copper bellows shown would be effective at all in cooling the engine discharge. it does have good surface area and copper is a great conductor of heat but it is not large. would be really easy to modify by pumping cooling water through the center of the bellows and would look good. Just looking for some comments. If it looks useless ill forget about it. Of course in these models nothing is really critical but might as well make something that works or I'm wasting my time.

 

[Mechanicboy]

You need a large number of small copper pipe (let us say 2 mm/0,078" pipe) inside the condenser where cooling water circulating inside the pipe and exhaust steam between the pipes. The pipes is placed tight as possible between to increase cooling surface and the length must be large as possible. For a steam engine who has 1 1/4" bore and 2" stroke need a condenser at 3" diameter and 5" in length.

The problem is cylinder oil inside the condenser, better to use the adjusting valve on the displacer lubricator to control the amount of oil into the steam engine then the condenser will work effective. Due the oil is a barrier between steam and cooling pipe and the steam can not cool down quickly as possible.
In fact the real steam engine is oil amount not much, between 1-2 drops of cylinder oil for each pump stoke with the mechanical lubricator. In a model steam engine is also overlubricated, not so easy to control the amount of oil in the steam engine with the mechanical lubricator.

In the mechanical lubricator in the real steam engine has 2 pump for each moving parts such as cylinder, bearing etc. 1. The 1. pump is adjustable in stroke to give a required amount of oil and the 2. pump is to give a full stoke of oil into the cylinder and other moving parts in a steam engine. There is a small window in the lubricator who one can see how much drops oil is gived for each pump stroke and adjust in case too much or too little oil to a correct count of oil drops.

 

[steamedlou]

mechanicalboy: wow obviously my bellows wont cut it. the triple has a low pressure cylinder that is 1 3/4"x1". but for looks, I'm sure as heck not going to make a condenser 3x5 inches. It will look as big as the engine. Ill put up with a little inefficiency for the model looks. Plus it would be a pain to build. Im just figuring on maybe something like 1 1/4-1 1/2" in diameter and maybe 3-4" long. with as many small tubes as I can fit in that. Not going to try and solder a tube sheet for sure. J-B weld epoxy will take care f sealing that. thanks for the help.

 

[steamedlou]

Well after all the questions, answers and plans and even getting my Stuart triple to run, looks like I may not go full bore on the project. I just bought another triple on eBay. Though not named, it is obviously a Brunell triple which is larger and more complicated than the Stuart engine. Already has a surface condenser attached to the side. So I will probably finish and paint the Stuart and sell it. I don't need more than one triple in my collection. I'm anxious to see the "new" one to see any machining errors. lol always seems to be some. I do not that on one side of this engine the bronze columns don't seem to be centered on the base. Hope its cosmetic and I can do a little filling with some JB weld before painting. Hate thinks that don't look just right.

 

[Rivergypsy]

Now thats a very nice engine - I'm envious!
Just to offer, but if you decide not to sell the Stuart but just need extra storage space, then I'd more than willingly donate some shelf space

 

[steamedlou]

My new triple project arrived today. Its a beast! Didn't realize how big it is. I thought the Stuart triple was big weighing in at 11 pounds. this weighs 34. Makes the Stuart look like a wimp. I'm behind. haven't finished my Coomber rotary yet. These will keep me off the streets for a few months.