Sisson Triple

[MGMarine]

A most interesting discussion! May I declare an interest. At Markham Grange Steam Museum, Doncaster, we have what is possibly the largest collection of steamable marine engines under one roof (not in a boat).

Our current collection includes two Sisson triples, 6", 8", 11" x 8", both ex-Salters Steamers. No 2601 of 1927 (on loan from NMM, Greenwich) was in Mapledurham, and No 3113 of 1930/31 (on loan from Salters) was in Cliveden, both 105 foot boats. They have the Sisson version of J W Hackworth's valve gear, and three piston valves without rings. 2601 has run over 1000 hours here. 3113 has not been restored to steam.

The normal "rule" for the ahead direction of rotation on single crosshead guides is clockwise when the guides are on the left, the full area slide then being to the left or back side of the crosshead, and the edge-only slides being smaller in area are on the right or open side on which the edges of the crosshead slipper run in astern. This is so that the crosshead slipper presses mostly on the larger area, namely leftwards, both when the piston is being pushed downwards and the crank is moving away from the guide, also when it is being pushed upwards and the crank is moving towards the guide. If you draw a little sketch, all is revealed!

Now "our" Sisson engines are slightly different in that the guides are solid bars and the crosshead slippers are effectively lightly clamped around the bars. Because of this the pressures on the slippers, when following "the rule", is most heavily on the right hand side of the guides, ie the inside of the engine. And, lo and behold, at the bottom of the inside of each guide is a small oil-bath into which the crosshead slipper dips near bdc on each revolution. The outside of the crosshead slipper has a small trough into which is a generously-oiled pad, pressure on this side being experienced in astern.

The final quirk with the Sisson engines is that the guides are on the left and the rotation is therefore clockwise when looking on the barring hub. The drive coupling is at the other end of the crankshaft so that, for the ahead direction, when looking on the thrust bearing and propeller-shaft coupling, the rotation is anti-clockwise. The propeller obviously needs to match.

I assume that these features were standard Sisson practice. On the two engines here, the reversing lever and Hackworth valve sliders (and the pressure-relief valves!) and thus the operating position, were on the right when looking on the barring hub (on the port side of the boat), that is on the opposite side of the engine from the main crosshead guides. But this was not always the case, presumably the handing could be arranged on either side, to the customer's preference.

We have in the Museum three traditional marine propulsion compounds with 90 degree cranks. They can be very temperamental (that is very difficult) to start, basically because the cranks drop down to 45 degrees on each side of bdc, and there they sit - obstinate ( I won't elaborate on this here). By contrast, Sisson 2601 is very easy to start. By experiment we found that the crank could be carefully so positioned with the HP just off dead centre that it would not self-start, this setting being over only a few degrees of crankshaft position. A quick flick of the HP to MP bypass valve set it immediately in motion. Coupled with a triple's easy starting is also its beautifully balance running. (I don't like "lumpy compounds"!)

Digressing, on compounds, what is basically lacking is a true "simpling valve" which puts HP steam (maybe reduced in pressure) directly to the LP cylinder and, simultaneous turns the HP exhaust directly to the exhaust pipework. Thus, during this starting phase, the two cylinders would then be completely independent. Some compound locomotives were fitted with proper simpling valves but, as far as I know, it was not common marine practice. Why not?

[Lopez Mike]

I have a complete machined set of castings and parts for a compound articulated locomotive with the simpling valve in the rear (H.P.) cylinder assembly. I believe the popularity (in fact, necessity) of simpling in locomotive practice was almost entirely for starting heavy trains at zero speed, something we never see in marine practice. The high pressure and low pressure engines are quite separate from each other on american articulated engines. And each is a twin with cranks at 90 degrees

Anyone interested in a project, by the way. Northern Pacific RR 2-8-8-2 Z-3 in 1/8" to the foot scale. I will never get around to continuing work on this monster. Something my father started. Sigh.

[steamboatjack]

Marine engines were not fitted with a “simpling valve” as stated above, this is because they do not need one, the correct term for the valve fitted to a marine engine is an “impulse” or “starting” valve. I do get rather fed up with the term “simpling valve”.
They don't need one as the valves only function is to impart a quick high pressure thrust to move the HP off its dead area.
If you apply too much steam you would cause a high back pressure in the receiver which is self defeating and you may over pressure the LP components. The trick is to have a large area self closing valve, similar to a whistle valve, and to site it as near to the LP receiver or chest as you can. I usually supply a small “wedge”to allow the valve to be part opened for warming through.
Piston valve compounds are easier to start than slide valve engines as its the friction load on the valve which prevents ease of turning once steam is applied.

Simpling valves were fitted to White steam cars for the same reason as a locomotive.

Regards
Jack

[Lopez Mike]

My knowledge of marine practice just jumped about a mile. Thanks Jack.

Even in railroad use the engines were only run in simple (single expansion?) mode up to a walking speed or thereabouts. And yes, on these locomotives, the valve is opened when the cylinder cocks are opened to pre warm the low pressure engine as well as the high pressure one.

Compound engines in non-articulated designs were rare over here. And even compound articulateds were not that predominant. The demands produced by long distances, high speeds and huge trains meant that power and speed trumped efficiency. The last of steam power in North America was an object example of efficiency being subordinated to to power and speed. Killed it in the end.

[Mike Rometer]

My knowledge of marine practice just jumped about a mile. Thanks Jack.

Even in railroad use the engines were only run in simple (single expansion?) mode up to a walking speed or thereabouts. And yes, on these locomotives, the valve is opened when the cylinder cocks are opened to pre warm the low pressure engine as well as the high pressure one.

Compound engines in non-articulated designs were rare over here. And even compound articulateds were not that predominant. The demands produced by long distances, high speeds and huge trains meant that power and speed trumped efficiency. The last of steam power in North America was an object example of efficiency being subordinated to to power and speed. Killed it in the end.

Plus, you can't beat the simplicity of 'turn a key'. Even the miniature railways have discovered that.

[Scotty]

update

Last saturday we made a no-load testrun with the overhauled engine.
Works perfectly now, with very smooth running up to appr. 400 rpm.
Starting is still relatively easy without the impulse valve (this is fitted and works, but never used by me),
if the engine hangs it will start is with a quick reverse and back.

The rotation is definitely lefthand:
- Swallow (the sister ship) has a lefthand propeller
- the valve gear is optimized for lefthand turning
(as I found out during the measurements of the valve gear).

On last sunday the owner made a testrun of appr. 25 km (still with the righthand propeller,
as the new one has not arrived yet) with very satisfactory results:
- the boiler keeps up easily with the engine under full load
- speed still greater than 9.5 knots (this I want to measure myself)
- vacuum appr. 55 %
- condenser temp. very low (even with only one of two inlet valves open).

So we are now waiting for the new propeller for the final tests and the official commissioning of the boat.

The engine runs now again with the original adjustments, we copied the critical dimensions
of the HP- and IP-piston valves, the LP-piston valve is still original, the wear was lowest on this.

Greg, you will get my drawings and measurements of the valve gear when I'm finished with the documentation.

Scotty

[MGMarine]

In response to "steamboatjack", our experience with the three 90-degree crank compounds of three different sizes and manufacturers at Markham Grange Steam Museum is that they are all awkward starters. All three have LP slide valves. Two have hand controls, and steam pressure on the back of the (unbalanced) slide valve can clamp the control linkages and thus the control lever, making it impossible to move it without shutting off all steam to relieve the grip. Using the "impulse" or bypass valve does not get them started.

We have devised a "technique" to get the Yarwood engine away from rest, but it is, I am sure, most unorthodox, and it requires two people do do it. The Fleming & Ferguson engine has power control (which is strong enough to overcome the LP valve clamping effect), and unusually(?) no balance weights on the cranks. Its awkwardness to start was eventually overcome by fitting an (unauthentic) flywheel having balance weights inside which means that it usually comes to rest with the cranks not at the 45 degree bottom positions, and is able to be started.

As you say, if an impulse valve is left open too long, then steam backs up to the exhaust side of the HP cylinder, in opposition to the result you are trying to achieve.

A proper simpling valve should give the answer, that is a valve that makes the two cylinders truly duplex for starting, effectively completely independent. I did include the caveat that it might be necessary to include a pressure reducer when feeding the LP direct. However, if an engine with only an impulse or bypass valve fails to start and then locks up, then HP steam can reach the LP valve, and almost certainly the LP cylinder itself. So in fact any compound (or triple) needs to be physically designed to withstand full steam pressure at any point.

All-piston-valve compounds would not suffer from the lock-up problem, and might thereby be easier to start, but we don't have such an engine to prove or disprove the point. However, the power-operated Fleming & Ferguson which does not lock up would lead me to believe that an LP-piston-valve engine would be equally as difficult to start as an LP-slide-valve engine. In other words, our evidence indicates that a compound is awkward to start, and that the clamping of the LP slide valve is merely a secondary aggravation.

Three cheers for the lovely triples!

[Scotty]

Awkward to start engines usually have some design fault.

I have here a single-cyl. engine of 12.5 HP which starts very easily.
When locked (cyl. in top or bottom dead center) it can be moved easily by hand on the flywheel.
There is a special valve which connects top and bottom cyl.spaces for starting.
But then this engine has a slide valve ....
This engine is in commercial use for 25 years now and never a complaint from the engineer.

Scotty

[Lopez Mike]

What is this about connecting the top and bottom for starting? Like connecting the drain cocks together momentarily? I must think on this a bit. Tell me more.

[Scotty]

What is this about connecting the top and bottom for starting? Like connecting the drain cocks together momentarily? ....

Yes, on the left of the cylinder, with the handle pointing directly at the camera.



Don't get fooled by the looks, this engine has a piston valve.

Scotty