Sisson Triple

A special section just for steam engines and boilers, as without these you may as well fit a sail.
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Lopez Mike
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Re: Sisson Triple

Post by Lopez Mike »

Does this somehow allow the engine to start by simply opening the throttle? Or does this valve just relieve the cylinder pressures so that the operator can manually move the engine off center more easily? I've not seen this before.
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Re: Sisson Triple

Post by steamboatjack »

Please remember that the “dead area” of the HP piston is not just top or bottom dead centre, but includes the angle from the cut off point down to BDC and the same on the up stroke. The cut off point of the LP must be sufficiently late (in full gear) to “cover” this area. The same of course is true of a twin cylinder engine.
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Re: Sisson Triple

Post by MGMarine »

Hello again,

These digressions get further and further away from Sisson Triple!

However "our" Sisson and Plenty triples do have drain valves from both the top and bottom of each cylinder, then into a common pipe, in effect making a small-bore bypass round the piston. They help in getting warming steam through the cylinders. The engine should in fact be started, and will run, with these drain valves open, but it is not a very good use of steam once the engine is fully hot and rolling! If steam is likely to be very wet, it is a good idea to leave the LP drains open for a while longer. In an enclosed drainage system, a useful piece of kit is a sight glass in the commoned (ie shared) drain line; this allows the presence and very rough quantity of drainage water to be visually checked. Then by juggling the cylinder drain valves the source of the water may also be identified. Just little perfectionist refinements. An alternative is to lead the drains individually to a suitable tank, but the clouds of steam somewhat hamper inspection and, of course, the tank needs to be where the escaping steam will not be a nuisance. A lid on the tank overcomes that problem, but makes it more difficult to see the water. And the tank lid gets very hot (I know).

After warming an engine through, I shut off the steam, allow the pressure to die away (essential), and then bar the engine over a couple of times using a rod in the holes provided in the barring hub located at the opposite end of the crankshaft from the drive coupling, or in the drive coupling itself. If there is still water on the top of any piston, it can be felt as a resistance to turning. If necessary, the steam can be turned back on for some more warming time. I regard this procedure as essential (avoiding any risk of there being more water at the top of a cylinder than the clearance volume, leading to a demonstration of the Big Bang Theory!), but it is only practicable on an engine of small or modest size that can easily barred over. On a bigger engine that cannot be barred, warming has to be long enough to be sure all condensed water has re-evaporated. Feeling the outside of the casing lagging for heat is a helpful indication.

A single cylinder inverted vertical engine should always be warmed with the piston at TDC, but with a multi-cylinder engine having cranks not in line (eg at 90 or 120 degrees), only one piston can be at TDC for warming.

It should be noted that some vertical-cylinder engines have been made without any provision for drainage from the top of the cylinder, presumably on the assumption that nobody will try to start them with inadequate pre-heating, but I guess that is an exhibition of faith beyond what practical conditions might warrant.

A WARNING in passing: an engine should NEVER have a barring rod inserted while there is pressure steam in the engine.

Steam engines are friendly and kind (especially triples) and very pleasant to see running (none of that noisy "suck, squeeze, bang, blow" business), but they can bite if treated unsympathetically. And, just for fun, one double-acting steam cylinder gives two power strokes per revolution, whereas it takes a four-stoke combustion engine four cylinders to achieve that.
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Re: Sisson Triple

Post by gondolier88 »

MGMarine,

Vertical engines without top drains has little to do with misplaced professional confidence and much more to do with well thought out steam engine design.

It is almost certainly a trait that is attributed to engines with conical pistons and slide valves; with a proper over-run relief on the cylinder that is incorporated with the bottom edge of the steam port any condensate collects on the piston top and is blown out through the port with exhaust. However; this is a feature of engines that can be mis-used- on warming through- care must be taken that condensate doesn't form a plug of water that cannot escape quicker than the valve will allow.

It must be remembered that these features were not to be re-discovered by engineers in the future to be deciphered, but were well documented in manufacturers catalogues as well as the engineering press of the day- just as today in engineering profession, new features designed to make the engineer's job just that bit easier were pushed by reps and advertising to end users.

It is good to hear of good warming through practice- so much wear and tear happens within the first few revs, it is always a pleasure to see someone who knows nothing about steam engines to watch an engineer warm through an engine and see a silent and cold peice of metal come slowly to life with no noise or fuss or banging.

Perhaps you would post some pucfures of your Sissons engines?

Greg
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Re: Sisson Triple

Post by MGMarine »

Next instalment!

The steam port in a vertical cylinder is right at the top, just below the cover plate. Thus, if the piston is somewhere down the cylinder, then it is possible for water to be sitting on the piston of a greater volume than there is in the space above it at TDC. If the piston then rises sharply faster than that water can nip out of the steam port, then you have a close approximation to "an irresistible force meeting an immoveable body", and the result is a big bang. It has happened a number of times in history, and the velocity attained by the retreating cylinder cover and broken studs with nuts can be quite high, and woe betide anybody standing in the line of fire. Thus it behoves us to be sure that all condensed water has re-evaporated (or has been slowly squeezed out by hand barring) before spinning up the engine.

The Sisson engines we have are provided with spring-loaded relief valves, not in the cylinder walls (where one would think they would be most beneficial) but at the top and bottom of the valve chest. Why, I don't know.

"Our" two Sisson triples can be seen on our website: www.markhamgrangesteammuseum.co.uk. Sisson No 2601 is in Museum News for 2003, after our restoration, and No 3113 is at 2005 as it arrived from Salters and basically as it still is (so we have a "before and after"). The Plenty triple is at 2010, after our restoration (also belonging to Salters).

We had a nice run with 2601 today (August Bank Holiday Monday).

Regarding information in textbooks: first, the books tend to be scarce and expensive, also repetitive or overlapping; second, they don't usually go into the practical details, "the tricks of the trade", probably well-known to operators in "steam days", but maybe not known to writers of text books. When we were restoring the port side-lever engine from "Reliant" (also on our website news sections in various years) I had the utmost difficulty in obtaining useful information on vital points, and some of the little we found was clearly wrong, even nonsense (and had been transmitted from source to source as accurate). An engine shown in British Steam Tugs and claimed to be "Old Trafford"/"Reliant" is not, but it really did mislead us for a time. So, in practice, long after the steam age, and usually well after the companies had gone, and after (usually) most if not all records had been destroyed, we find ourselves starting at the bottom of the learning curve on every engine. Great fun in a way, but one's assumptions and conclusions may not always be correct. Books like Sothern are very helpful (one of the best), but whether he has selected "your" engine to give details is pure chance.

So there we are!
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Re: Sisson Triple

Post by Scotty »

Lopez Mike wrote:Does this somehow allow the engine to start by simply opening the throttle? Or does this valve just relieve the cylinder pressures so that the operator can manually move the engine off center more easily? I've not seen this before.
- NO (only if you are lucky)
- Yes, that is the intended use of the connecting valve
- As far as I know it was only realized on this engine


Note on Sisson cylinder drains:
MGMarine - have you dismantled the drain valves?
On our engine these have two sets of channels, so they are really two valves in one casing.


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Re: Sisson Triple

Post by gondolier88 »

MGMarine,

I imagine the Sissons engines you refer to will be piston valve on all cylinders? Relief valves on the cylinder covers on Sissons always looks a little odd doesn't it, a combined relief and drain fitting would make much more sense, although a lot more expensive to produce in different sizes.

Of course I referred quite specifically to slide valve engines in which it is nigh on impossible to create a hydraulic lock due to thier inherent lifting capacity.

The vast majority of cylinder failures were/are down to hydraulic locking in piston valve engines. Cylinder failure in slide valve engines, although rare, was usually due to abusive operating procedure or bad casting design.

With conical piston design, proper warming through procedure (there should never be any steam entering on the exhaust side of the piston when warming through, so I'm unsure where a plug of water enough to fill the cylinder on the 'cold' side of the piston could form from, nor am I aware of any engineer that would allow enough pressure to form on the 'hot' side that would suddenly cause half rotation fast enough to overcome the drain cock and the slide valve lifting) top cylinder drains are not a necessity. Of course in a marine, rather than demonstrative stationary context, the engine has instant load on it with the propeller/stern gland which dampens quick engine movements.

I agree, text books provide lots of useful theory and facts, but magazines such as 'The Engineer' and other such publications provide insights into design quirks and prototype ideas. I haven't a copy of Sothern, but R.Sennet's Treatise from 1875 and Audels guides from 1914 and 1918 provide interesting comparisons in engine design and operation differences- although nothing beats getting to grips with as many engines as possible and broadening experience of what works and what doesn't.

Greg
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Re: Sisson Triple

Post by MGMarine »

Curiouser and curiouser, as said Alice (in Wonderland, or was it Through the Looking Glass?)

To Scotty -

Yes "our" Sissons have the interesting multi-valves, which we last stripped way back. I am at home now and cannot see them! But they are arranged so that they are shut, or both top and bottom open, or either open, ie four positions.

To gondolier88 -

These Sissons have piston valves on all three cylinders (without rings, and we set them with slight endways clearance so that they can "float" sideways in the bore). There are no relief valves in the top covers. The drains are through the cylinder sidewalls.

There is no set crank position recommended for warming through (not that I've ever heard of or read of, and have not seen any markings on engines). When warming "our" Sisson through, all the drain valves are open, also the HP to IP/MP valve chest bypass and the IP/MP to LP valve chest bypass. When the steam supply valve is cracked, the steam goes where it will, determined by all those small-bore interconnections, and also by the positions of the three main piston valves. At least two of the pistons must be not-at-TDC, and there will be empty space above them, regardless of the piston shape. The point I am making is that if the engine is started before any excess-to-clearance water is removed (which any top drain cannot do on low pistons) then the undesirable condition is "primed", and ready to act. I agree that in principle slide valves should lift and relieve the pressure (whereas piston valves cannot), this release happens, or not, determined by the volume of excess water, the speed of the piston movement, the cross-sectional area and length of the top steam port, and the inertia of the slide valve and any restraint it may have. The bottom line, the moral of the story, for any steam engine, with any sort of valves, is to be absolutely sure that there is no more water that can occupy the cylinder clearance before full steam is turned onto the engine. To me, possible or notional mitigating factors are irrelevant. Anyway, Mr Sisson fitted drains to the tops of his cylinders, and when his engine is barred over by hand, if water is still present it can be felt, and can be pushed out of the top drains (and/or warming steam turned on for a few more minutes). For all that circumlocution(!), I think we are actually agreed on the basic principle - eliminate the water before starting.

I have Sennet & Oram, also Audels 1, 2 and 3. All very good, but they don't usually answer the awkward questions. It would certainly be nice to have a bound indexed set of "The Engineer" or "Engineering" from about 1880 to 1925; a few libraries have them, but in practical terms (unless one lives very near) they are inaccessible (and in effect don't exist). Or is there an accessible (free) set on the Internet? So, in the meantime, back to the bottom of the learning curve.
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Re: Sisson Triple

Post by steamboatjack »

These books are fine, I have them too, but no amount of reading is a substitute for experience of operation of large steam plant.
I have never seen a large marine engine (100 IHP+) without drains at both ends of the cylinder and the valve chests and without adequate cylinder relieve valves where required.
Souvenir d' Antan's engine (20 IHP built 1901) which I have just overhauled has no top drains and flat top pistons so than blows that theory out of the water.

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Jack
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Re: Sisson Triple

Post by gondolier88 »

MGMarine,

It wasn't so much a question of disagreeing with you, merely providing an explanation as to why some engines weren't provided with top drains according to what I have learnt along the way. We are certainly in agreement as to the importance of proper warming through, however I believe I pointed out that only well engineered designs would have negated the requirement for a top valve- vaguely I admit, but I was drawing attention to the fact that with decades of engine manufacture to their name the more sophisticated engine designers had banks of data gathered on test engines that allowed them to offer an engine with the very real issues that you raise above properly addressed.

Perhaps if you have a curator at Markham they could research whether a public archive of engineering magazines is available- something that the SBA or similar organisation could perhaps take responsibility for to the benefit of it's members?

Jack,

That is very interesting- it's a while since I was on Souvenir, but if I remember right the engine was built by Burgoine's? It would be interesting to compare other engines of his, if any exist? Or even photos. Perhaps as it was an overhaul you may not have had chance to check, but do you know the difference in the free space above the piston at TDC compared to that below at BDC as it would be good to compare to a comparitive size engine with top and bottom drains?

Scotty,

Sorry for digression, again!

Greg
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