Resources/Information for Crank Lubrication?

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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gondolier88
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Re: Resources/Information for Crank Lubrication?

Post by gondolier88 » Sun Mar 18, 2018 9:07 pm

DetroiTug wrote:Greg, Great post!

I think the biggest issue with a compound in a small boat where the load is varying wildly, is having a fixed cutoff on the LP. On large ships, I read and heard that every time a compound powered steam ship left port to make a long distance trip, the engineer would pull an indicator card on the LP and balance the cutoff to the load and speed for highest efficiency. I've heard reports of engines equipped with a pressure gauge on the receiver, that 0 psi was observed underway at certain speeds.

-Ron
Ron,

Yes, the biggest difference between commercial vessels and private steam was the availability of professional full-time engineers, who (hopefully) knew valve gear well and could coax the most out of the steam for days, sometimes weeks, at a time where the opportunity to monitor an engine could be done in scientific manner. There are stories of engineers long in the tooth who would have their own little tricks for accruing the best performance out of the engine on their shift, some legitimate, some not so...!

I haven't yet managed to find any contemporary material on the design of receivers- the best Triples almost all used cast-in receivers, and I can't help feel that the volume of these is crucial- the balance between back-pressure and vacuum is a tricky one, and is definitely a good reason to use piston valves which can totally isolate the receivers- a pipe from slide valve HP chest onto a LP slide valve chest is simply a communication channel, not a precision vessel for holding steam pressure for a pre-determined amount of time. This would be greatly improved by having a piston valve on the HP and slide valve on the LP, an arrangement not uncommon on compounds of all sizes, and those I've observed modify their ST 6A's to this arrangement report a quite a difference in engine characteristics.

Greg
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Re: Resources/Information for Crank Lubrication?

Post by PeteThePen1 » Sun Mar 18, 2018 10:21 pm

Hi Folks

I have been greatly enjoying this thread and much admire anybody with the courage to design their own engine. However, since I come from the 'quick & dirty' end of the hobby, could I interject a request to Lopez Mike? Sir, could you start a thread to show us details of your old and new hulls? We need folk who can design engines and folk like Lionell who can do us engineering porn, but how about some inspiration for those of us who are boaters first and only steamers because we have a few friends that know what they are doing and got it fixed up for us... Let's see the non exhibition boats.

Regards

Pete

I am re-plumbing Frances Ann to include the condenser. Talk about a 3D jig-saw puzzle for which I keep on having to go off and buy bits I didn't realise I would need... Perhaps I'm part of a new category - 'Slow and Dirty'
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Re: Resources/Information for Crank Lubrication?

Post by Lionel Connell » Mon Mar 19, 2018 2:14 am

Greg,
In terms of steam usage- the most efficient way to run a HP twin is a boiler WP of around 120-150psi, with throttle cracked open to allow 25-35psi of chest pressure- which usually results in a cruising speed of around 70-80% of hull speed and a measurable amount of real throttle superheating.
Are you saying that the most efficient way to run a twin is to wire draw a 75% pressure drop across the throttle valve?
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Re: Resources/Information for Crank Lubrication?

Post by fredrosse » Mon Mar 19, 2018 2:19 am

Looking at the Simpland Strickland Catalogue, the organization that was a strong advocate of Quadruple Expansion launch engines about 100 years ago:

Their smallest engine, with two crank throws in tandem/cross compounding arrangement, is described for 250 psi steam, rated 10 IHP @ 600 RPM.
2.00 x 2.75 x 3.75 x 5.00 with 3 inch stroke on all cylinders.

They made 11 Quad engines of this type in the catalogue, with the largest rated at 200 IHP.

They have a brief discussion about the four crank quad racing engine, making 19 knots in a 30 foot open launch, and quote: "The standard types of this engine are designed for 350 lbs. boiler pressure, but if required they can be made for as low a pressure as 200 lbs. below which it is scarcely worth while to quadruple."

Their catalogue also has numerous watertube boilers, however I see no superheaters, and no discussion about superheat in the catalogue.
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Re: Resources/Information for Crank Lubrication?

Post by fredrosse » Mon Mar 19, 2018 3:21 am

From Greg: "In terms of steam usage- the most efficient way to run a HP twin is a boiler WP of around 120-150psi, with throttle cracked open to allow 25-35psi of chest pressure- which usually results in a cruising speed of around 70-80% of hull speed and a measurable amount of real throttle superheating."

Actually running an engine at 35PSIG vs. 150 PSIG in the steam chest (wiredrawing) will result in around 20% of rated (150 PSI) power output, and that will give a little less than 60% of the speed attainable with full steam chest pressure.

Steam flow with that condition will be about 25% of rated steam flow, and will result in lower efficiency in terms of heat units required per horsepower output. When hand firing, running a boiler at 25% of rated capacity is far more easily accomplished, everything has more time available for operator actions.

Perhaps a better way of describing this running condition is "the most comfortable way to run", but not the most efficient, and certainly not 70-80% speed, but still a comfortable cruise for many of us.
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Re: Resources/Information for Crank Lubrication?

Post by fredrosse » Mon Mar 19, 2018 3:53 am

From Tom: "Also, I'm really not familiar with any applications of steam reheat on reciprocating steam engines, so that should be interesting because as far as I can tell it really isn't seen much."

Yes, while steam reheat is quite normal in the present commercial power industry, it is very rare in reciprocating steam engines. Note however that the fastest steam yacht, the "Arrow" of the very early 20th century, made 40 knots with quadruple expansion engines, 400 PSI, and with reheat between every expansion!
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Re: Resources/Information for Crank Lubrication?

Post by marinesteam » Mon Mar 19, 2018 1:24 pm

gondolier88 wrote:
.... Oh, and he's in total silence while sipping a G&T in elegant steam style! ....

Greg
Doh! This is the whole reason I'm building a steamboat, but I decided to build a compound engine, guess I need to scrap the dang thing.

Ken
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Re: Resources/Information for Crank Lubrication?

Post by DetroiTug » Mon Mar 19, 2018 2:00 pm

Quote: "I decided to build a compound engine, guess I need to scrap the dang"

Absolutely nothing wrong with a compound in a small steamer and no one is suggesting that they should be abandoned, we are just debating the often-heard claim that they are far superior due to their much better efficiency over a simple engine. They do use less fuel overall (from my observation), but being relegated to lower RPM's they typically aren't as fast as a simple engine which can enjoy lower steam pressure at higher volume for the same amount of work. As I mentioned earlier, I think the issue is fixed cutoff on the LP, now if one does a lot of cruising and can adjust the cutoff on the LP in relation to the HP at cruising speed, they will see a higher efficiency and possibly more speed overall.

I think most compounds, the timing is set on the bench at assembly and never touched again. The way to tune it would be with a gauge on the receiver or LP steam chest and try to attain about half of the HP steam chest pressure for optimal performance.

I plan off and on for a modern steam car (tubular aluminum chassis, carbon graphite body)and the plan presently is a 4-cylinder compound with two HP's and two LP's clocked at 90° to make it self starting without the need for simpling - and smoother running. The "plan" is to digitally control the cutoff on the LP's logically actuated from a pressure value off of each receiver, continually tuning the LP's.

-Ron
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Re: Resources/Information for Crank Lubrication?

Post by Lionel Connell » Tue Mar 20, 2018 12:59 am

From Greg: "In terms of steam usage- the most efficient way to run a HP twin is a boiler WP of around 120-150psi, with throttle cracked open to allow 25-35psi of chest pressure- which usually results in a cruising speed of around 70-80% of hull speed and a measurable amount of real throttle superheating."

Actually running an engine at 35PSIG vs. 150 PSIG in the steam chest (wiredrawing) will result in around 20% of rated (150 PSI) power output, and that will give a little less than 60% of the speed attainable with full steam chest pressure.
Why would we bother building engines with expansion links if we intend to ignore the reason for their existence, the efficient way to run if we don't need all of the available power is to cut off earlier, not to run at a reduced throttle opening. There is a simple rule of efficiency in this case and it is written and rewritten every where in steam engineering manuals ; there should be no drop in pressure unless it is a result of doing work.

Also, there is no reason that a compound engine cannot turn as fast as a twin if it is designed to do so, not at 10,000 RPM but most certainly to 600RPM with small launch engines. It is not common to see a compound with larger balance weights on the LP throw, but it can most certainly be done.

For anybody that has seriously studied Stephenson's valve gear using simulation it is very obvious that any engine that is fitted with side suspended Stephenson's links is never going to run well at anything but one particular setting. The Stuart 6A standard link arrangement is so bad that under simulation it is in fact difficult to believe that it could be so bad. The magic of the Sephenson's link ONLY works when the link is center suspended and when the suspension pin is in exactly the correct offset relative to the slot. If you find that your twin runs better with the throttle reduced than it does with the cut off made shorter, the reason will lie with the valve gear. On a standard 6A, if you set the valves at full gear and then cut back to what you would expect to be 40% cut off. what you actually get is 30% cut off in one direction and 50% cut off in the other. To make matters worse, the compression ( exhaust lap) is also put into terrible imbalance in the same manner. This is caused by the side suspended link. It's no wonder they run roughly. I spent a month running simulations on the 6A, needless to say I build my engine with center suspended links. Lionel
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Re: Resources/Information for Crank Lubrication?

Post by Lopez Mike » Tue Mar 20, 2018 1:10 am

If i send you the information on my valve gear will you run it on your simulator? It's single expansion single cylinder and runs well but I'm consumed with curiosity.
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