Marcher twin cylinder marine steam

[Team ricky]

It’s certainly not bad but could benefit from some more power if used in a boat !

When the boiler primed a bit of water I could still see blow past the valve to the underside (above eccentric)

And a bit of water bypassing to exhaust! So definitely a little more to go….. with the correct throw on the crank I’ll get a bit more torque also

[paul gough]

If you are only running on air or low pressure steam then graphite loaded teflon has shown itself a satisfactory material for a small piston valve. Might have to experiment to get a good seal and running fit but somewhere near smooth light push fit should come close. Regards, Paul Gough.

[MJM460]

Hi Ricky, congratulations on getting it running well.  Clearly the valves were a big part of the problem.

Now it is running, the new crankshaft will increase the power, remember the formula Power is proportional to P x L x A x N with a constant to allow for the irrational units usually used for these quantities.  You can see Power (and Torque) are directly proportional to stroke.  Increasing the stroke from 7 to 11 mm will give over 50% increase in torque and power, without much increase in steam consumption due to the increased efficiency with less clearance volume.

Looking closely at your drawings, the ports are specified as 3/32” not 1/8” per your earlier post.  And the piston valve lands must match the port width at 3/32” as shown on your drawing extract.  So the eccentric throw will still not completely open the ports.  However, the ports are shown as 1/4” wide, so do not need to open much to give a similar flow area to the passages in the steam chest which are only 7/64” diameter.  Increased flow area beyond this has diminishing returns.  Increasing the valve stroke increases dimensions of the valve chest and around the eccentric strap, so no need to make it larger than necessary.  I suspect this is the answer to your earlier question on not opening the ports completely.

In the original magazine write up, John Bertinat explains that the piston valve layout is for radio controlled reversing by an external valve which reverses the steam and exhaust connections.  For this configuration, the valve movement has to be symmetrical with no lap or lead and the eccentrics at 90 degrees to the respective main cranks.  The drawing then shows only .005” of lap each side of the port, which means slightly late steam valve opening, but probably a good compromise.  Remember the valve is only in that position for a tiny fraction of the revolution so steam leakage there is not a big factor.  The 90 degree crank orientation of the crankshaft should ensure self starting.  Its worth rechecking the port and valve dimensions, and the port locations if you still think the performance could be improved.

The condensate formed when warming up the engine has to be drained so a little valve leakage is good, indeed essential as John says above, but the lower end of the piston has no gland, equivalent to the valve rod gland on the normal slide valve configuration, so leakage is expected.  If it is too objectionable, a grove in the bottom land of the piston valve with a wrap of packing would reduce that.

Then perhaps a little fine tuning of the valve timing until you are satisfied.  If you are planning on running on steam, particularly if your superheater is good, I would not bother with the Teflon sleeve.

If I understand correctly you are also making a slide valve version.  Comparing the two will be interesting.

MJM460

[Team ricky]

Thanks for the reply’s gents

All good for thought !

Unfortunately the second engine has been ported for piston valve use so I don’t think the slide valve would work properly or at least not to drawing!

I am building a bigger all cast iron (where possible) Borderer slide valve which I think will be more interesting and looks wise be a lot more scale than Gun metal

I will at some point build the second Marcher using what I’ve learned so far….

If it’s possible to buy precision hollow shaft (Id being precise too) this could be a possibility as a piston valve chest/housing as reaming however careful seem to give a very slight taper if you have run out in the reaming operation, The hollow shaft can be silver soldered to a brass plate for mounting..

All options I’d like to explore before finishing the Borderer piston valve engine that at this stage in build

[MJM460]

Hi Ricky, that will make a nice group of engines and will allow you to experiment with various features to help you optimise the performance.

Looking forward to following your progress.
MJM460

[Team ricky]

Here’s the reverse valve and manifolds done ✅

Well to a degree!

The threads are under size so I need to make two stand pipes tighter to rescue the part …. These will be epoxy onto the threads and give a decent pipe for the nut and Union to bolt to…

I have also some Teflon so in investigating leaks I’ve decided to make two rings for the lower part of the piston valves as they leak pretty badly from the bottom , I’ll leave a gap for some water to escape but nothing like as much as present .

[Team ricky]

Well all a bit odd with this engine….

It ran well on compressed air without the reverse valve, fitted the valve and it rams both ways pretty well still no power but the new crank will help a little there …

During the run I put a little oil into the intake and after a minute or so it ran badly, would not reverse and is pretty much un usable….

So I made the grooves for the Teflon rings and fitted those to both cylinders… I noticed the previous Nickel plate on the one test valve all stated to come off !!

So I think I’m back to badly sealing piston valves … I ran the engine again on steam and it will run fast but zero torque, Ut didn’t clear anything or run better.

I think I’m going to have the valves professionally plated then I can polish each valve to suit its hole !!


Very disappointing set up with these valves since the home machinist can only ream a hole and buy ground stock and hope ! Well it’s less than ideal and I’m my case produced a scrap engine..

The only good thing to come out of the last day is my tap follower I made to fit my mill for hand tapping 7-8Ba

[crueby]

When I've done spool valves, the trickiest bit was getting a good slid8ng fit. Rather than depend on reamers and ground stock to match up, I started with the next size bar up and turned the spools down to size, taking very light cuts to sneak up on the size, lots of testing it in the bore, and leaving the bar in the chuck the whole time. To test, I  back up the cross slide out of the way to get room to test it in the bore. Final cuts were spring cuts, taking passes without advancing the cross slide in. Even then, sometimes had to start over. I much prefer d valves, but sometimes  a spool valve is what the design needs.

[Team ricky]

I may well have a go at that tomorrow
No harm trying one ☝️

I think what’s needed and if it’s possible to get could be precision tube (I’d) and I’d bet it would be alot easier to get a good fit with ground bar ! I’m pretty confident the reamer didn’t cut a totally parallel bore …. This is definitely giving trouble, So last resort and probably last thing this engine gets I 6mm reamer and another two new valves , failing that I’m not carrying on with it

[crueby]

If you have a good small boring bar, that can give you a good tube cut to the size needed to fit the ground rod. The tube walls need to be thick enough to chuck up without deforming for that to work (had that happen, learned that the hard way)

[Team ricky]

Thanks for the tips there

I patiently made my stock from 5.5 mm 316 stainless ,As you said crept up to dimension for each valve chest and then ground down till they both fitted very close indeed , They need care to break the burr on each part of the valve you need to do so,

A good learning curve because I had to further set up the accuracy of the tail stock to get pretty much perfect cuts over 3” or so and using spring passes to confirm the accuracy..

All in the engine now runs great again on my rubbish tyre emergency air pump (14 psi)


I’ll next re-establish the reverse valve then wood cladding then the new crank which should give a usable model

Oh and I think I’ll buy a small quiet compressor for running things in ect !

[crueby]

Excellent!




One compressor  type worth looking at is the line of small ones from California  Air Tools, quiet enough not to need earplugs like most. I  got mine years ago, there may well be other brands as quiet now.

[Kim]

A second vote for the California Air Tools compressors.  It's very quiet compared to my other compressor.  I certainly wouldn't call it silent, but it is orders of magnitude quieter than a standard compressor!  I've also had mine for many years.

Kim

[Team ricky]

Cheers for the heads up


I’ll have a look around , my constraints are living on a boat so it will have to be small !

I did finish the lagging and the wood cladding bar two brass strips !

Looks good , runs both ways on low pressure compressor so I think just a crank when I’m ready and hopefully it’s usable

[Admiral_dk]

A fine looking little Engine 

Will it be mounted in a boat ?

Per