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[HelgeBe]

Hello everybody

I have a Proteus engine which causes me some challenges. Since there are so many experts on this forum I hope there are someone who can help me find a solution.

After a few minutes when the engine has been run hot I experience that it is difficult to get it to self-start. Sometimes I have to give full throttle to get it start, resulting in max rpm, in other cases I have to turn it a little by hand. It then feels like it hangs on some internal friction. In some cases everything is so stuck that the servo do not manage to move the reversing handle. It looks like it is the same point of rotation it hangs on every time. When the engine is cold and I am turning it by hand it is not possible to identify any extra resistance at any point.

I have taken the engine appart but could not identify any faults. Everything moves freely in their bearings. I have changed the O-rings on the pistons. I found that the timing was not precisely set and have slightly adjusted it, the result remain the same.

Any advise on how I should proceed?

Thanks.

Regrads
HelgeBe

[Ivor Bittle]

When I had a problem like this I consulted a friend who had driven a shunting engine. He just said "water". He was really telling me to look for a hydraulic lock, that is, for a position of the crank when water is trapped in the cylinder.
Take the cover off the steam chests and look for yourself.

I remember one of the chaps at Martin, Howes and Bayliss saying that when they made their first engine six weeks elapsed between the engine running on compressed air and getting it to run on steam.

Try my web site at WWW.ivorbittle.co.uk

Ivor Bittle 

[gondolier88]

Hi Ivor,

You may be right- the symptoms described sound very much like condensate in the cylinders- however the problem described becomes worse with heat- as you know cylinders get less condensate in them the hotter they become.

Greg

[Bunkerbarge]

It sounds like a tight spot as a result of either not being properly run in or a misalignement.  Do you know whether the engine has been correctly run in?  My suggestion is about 3-4 hours on air, lubricating regularly, say every 10-15 minutes to start with.

[Bee]

How about gently warming it up to running temp but dry using a paint sripper gun. This would eliminate the condensate aspect. It could be differential expansion making the piston tight, or if at top or bottom actually hitting the cover. Then the bedplate might warp itself or what it's mounted to misaligning the shaft. We assume it is lubricated.

[bogstandard]

As Bee has suggested, it definitely points to heat expansion causing the problem.

Just make sure that things like piston rod threads haven't wound out slightly. It is fairly easy to check if piston stroke is causing the problem. Take off the top cylinder caps, make sure there is a little oil in the cylinder, to prevent sticking, and pop a tiny ball of blutack in there, put caps back on and turn over by hand. Even when cold you should see if you have enough top clearance.
Look at the thickness it has been compresed to. If it is still rather thick compared to the other one, it might be bottom stroke that is causing it, so needs the rod extending a bit. If one looks ok, but the other is very thin, then suspect the upstroke on that cylinder, in which case half a turn on shortening might do it.
They should both be very close to the same thickness, and you need to end up with both strokes in a neutral position.

Don't forget to remove the blutack after you have finished, it would make a terrible mess inside the engine if you run it in there with steam.


Bogs

[HelgeBe]

Thanks everybody and a special thanks to Ivor for providing links to his very extensive articles.

Based on your input I have done some more investigation:
I dismantled the cylinders and measured the available space for piston movement, it is 20.5 mm, hight of the piston is 7.5 mm and stroke lengt is 11 mm. This gives a clearance of 1 mm on top and bottom, which there is. The piston rods have threads in both ends but do not have a looking nut. You simply screw them to the bottom of the threads and you then get the clearance of 1mm. I think we then can disregard material expansion due to heat.

The plant was bough second hand a few year ago complete with the ABC unit. I did not have any signs of ever being run. When i inspected it I found that the timing was set to something different than 90° so I changed it to 90° which I at that time believed should be correct. With this set up I had the engine running at some exhibitions at low steam pressure and at low rpm for some 30-40 hours total. It should therefore properly be run in.

At high rpm the engine runs fine when it is hot. It is at very low rpm the engine can have a tendency to stop and be difficult to get to self start again in eather direction. When I inspected the slide valves the first time I adjusted the timing so the steam ports start to open at TDC/BDC. The engine then had a very smooth running at high RPM but the problem with looking got worse at low rpm or when attempting to reverse the engine. This led me to compare the settings of my engine with the principles outlined in in Ivor's articles.

I have attached a picture of the dismantled D-slide valve. As can bee seen there is a significant overlap on the steam side but no overlap on the exhaust side. I have taken some measurements and transfered them to the same sort of diagram as in Ivor's articles. As can be seen if point A is at TDC then there is a high risk of getting water trapped in the cylinder. If timing is set at 90° so point D is at TDC then there should not be possible to get water trapped in the cylinder. My next attempt will now be to readjust the timing as precisely as possible to 90° and run the engine again.

HelgeBe

[HelgeBe]

Hmmm

I see the pictures are missing. Can anyone tell me how to get them in?

HelgeBe

[Proteus]

how did it run when you first got it and before you altered the timing ?because I don't think they should be set at 90deg, I remember hearing what it was and someone queering it.

Proteus

[Martin (Admin)]

Have a look at:
 http://www.modelboatmayhem.co.uk/forum/index.php?topic=16854.msg168401#msg168401
 http://www.modelboatmayhem.co.uk/forum/index.php?topic=2277.0
 http://www.modelboatmayhem.co.uk/forum/index.php?topic=23.0

[HelgeBe]

New try for pictures....

[AlexC]

 

HelgeBe,

Your slide valve is designed with LAP.

Lap is the amount that the steam edges of the valve extend past the outer edges of the steam ports when the valve is in it's MID position.

See attached Fig 9a..... LAP (steam) = dim (e)..... a and d are the steam edges.... b and c are the exhaust edges.... f = exhaust lap (but you probably don't have any, so ignore it and edges b and c will be in line with the inside edges of the steam ports (SP))..... EP = exhaust port.

In order to set this for correct operation the ECCENTRIC must be set to a greater angle of advance than the 90 deg you are using.
See attached fig 11 and 11a.

The 90 deg advance is only correct for valves with no LAP. See attached fig 10.

However in order to get things right you will need to use the 90 deg position to start with.... as below.

To set yours correctly you must first get the valve in the correct position on the valve rod (distance from eccentric centre to valve centre is critical).

Proceede as follows: -

Place the reversing gear in FULL forwards position.

Put one piston at top dead centre...... adjust the eccentric to be exactly 90 deg ahead of the crank..... adjust the d-slide valve to overlap BOTH steam ports by exactly the same amount (valve is now centred)..... lock the valve to the valve spindle in this position.

Repeat for the other cylinder and valve.

Once you have both valves centred...... put one piston at TDC and adjust the engle of advance of the eccentric such that the top steam port is just about to open. (outer edge of valve dead in line with outer edge of steam port)...... lock the eccentric in this position (from your diag this would be approx 113.6 deg in advance of the crank).

Repeat for the other cylinder.

This should get you where you need to be.

I attach a couple of diagrams that may be of help... these show the different eccentric settings required for a valve either with or without LAP.

Hope this gets you sorted.

Best regards.

AlexC 

EDIT... the term LEAD refers to the amout the steam port is open to steam when the piston is at TDC (or BDC) but in your case you can ignore this.

[AlexC]

 

Hi Guy's,

I have just noticed that I posted a duplicate of diagram 11a.

And missed diag 11.

Here is the missing one....

Sorry about that... must go and kick myself.

Best regards

AlexC

[HelgeBe]

Proteus,

I did not run it with the original timing. I just realised it way off 90°. Can you estimate what it is set at at your engine (approx)?

AlexC,

Your procedure is exactly what I did last I run it. With this timing the exhaust port closes before TDC and if there is some water there it do not get out.

HelgeBe

[AlexC]

 

Helgebe,

I appreciate your problem, however, such is the nature of this type of valve.

If your problem is water/condensate remaining in the cylinder then you must find, and eliminate the cause of this…. changing the valve timing is not the way to do it.

If you adjust the timing such that the exhaust port remains open until the piston reaches the end of it’s stroke then the steam port will not open until the piston is well past TDC or BDC… approx 23.6 deg in either case.
This will certainly give you starting problems and will also cause pressure surges in the steam chest…. It will also make steam CUT-OFF late, by the same number of degrees; hence little or no expansive work will be done and the benefits of the more advanced type of valve gear will be lost.

The whole idea of the exhaust closing before TDC/BDC is to allow some compression of any remaining steam to bring it back up to something approaching boiler pressure in order to eliminate/reduce these pressure surges.

Unfortunately you can’t have it both ways with that valve design…. The only type that will give you a fighting chance of both would be the Line-on-Line type as shown on my diagram Fig 10 but you will not be able make use of steam expansion.

This would also mean modifying the valve, which I do not recommend.

I would recommend you set the valve gear as detailed, which is the correct method for this type of valve gear, and then seek to find alternative solutions for the water /condensate problem.
 

There are many causes for water/condensate remaining in the cylinder including: -

The use of wet steam at too low a pressure. (Which will be at a lower temperature to start with)

Engine too cold or cooling down too much whilst running (e.g. stopping for too long before re-starting)

Running too slowly, especially with wet steam at too low a pressure, since this will allow more time for the heat (in the cooler steam) to escape from the steam/engine resulting in condensate.



Possible remedies.

Use higher steam pressure, which will then be at a higher temperature to start with.

Fit and use a steam dryer (what Cheddar call a super heater).

Try not running too slowly, especially if you are not using dry (super heated) steam.

Don’t stop the engine for too long before restarting.

Lag the outside of the cylinders to retain heat; also the steam feed pipes feeding the engine from the boiler.


Best regards.


AlexC. 

[HelgeBe]

Thanks AlexC,

I agree that adjusting the timing so the steamport opens at TDC will give the best efficiency and if I can get rid of the water some other way I will do so.

The boiler is the Cheddar Proteus Boiler that came with the engine. This has a superheater. According to the instruction the maximum working pressure is 90 psig but on my boiler the safety valve starts to open around 60 psig. I have therefore set the pressure controller to just below 60 psig. I do not know whether the pressure indicator is correct or if the safety valve is correct so I do not feel I should play with the safety valve. It is therefore little I can do with the pressure.

Originally there was some white cotton tread around the steam tubes from the boiler to the engine. Unfortunately this got burnt on one of my first attempts to lit the burner. I therefore removed it. It is an easy job to put it on again and I will do so with even thicker layer.

Not running slow is not an option, that is actually what I am aiming for. The plant sits in a tug boat and I would like to do some carefully maneuvering with this.

HelgeBe

[AlexC]

 

HelgeBe,

The stated 90psi max pressure is the absolute max pressure for which the boiler is designed and tested for.

In actual practice this limits the actual working steam pressure to 81psi since the safety valve test rules (part of the boiler test regulations under STEAM TEST) state that the boiler pressure shall not rise more than 10% above chosen working pressure whilst it is in the OPEN position and with MAXIMUM FIRING applied. (Gas burner control would be disconnected)
If the pressure did rise more than this then the safety valve would be failed and would require replacement.

If the safety valve were to be set for 90psi and the boiler pressure increased by any amount above this, when the valve was open, then you would be beyond the maximum design pressure.... again a failure.

The design maximum pressure does not mean it has to be run at this pressure and 60psi is the usual level that Cheddar used to set them up for.


I agree, if you have not got an accurate (certified) large ‘test standard’ pressure gauge to refer to then under no circumstances should you try and adjust the safety valve.
The small pressure gauge fitted to the boiler should only be regarded as a guide, unless it has been calibrated against a known certified ‘test standard’.

Your SLOW running requirement may be more easily solved by fitting a gearbox between the engine and the prop shaft (say 2:1 or even 3:1 ratio) since this will allow the engines speed band to be increased to a level where low speed condensation in the cylinders will not be an issue. Additionally, the lower overall loading on the engine will help in starting.
 
The maximum speed (RPM) available from the Proteus should be more than enough at 60psi to give you the required prop shaft speed and you will have much more TORQUE available at the prop shaft meaning you can drive a larger or higher pitch prop, or even one with more blades.

I agree that this would require more steam, to accommodate the higher engine RPM, however, this in itself may also have a hidden benefit….. Namely, it would also mean that the burner would be at a higher level for more of the time and the super heater (more like a steam dryer in Cheddars case) would at least be working more effectively.

With your current set up, where the engine is running much too slowly and not using very much steam, the burner would be at it’s low setting most of the time… resulting in the super heater not getting much heat and therefore not doing much. In such an instance it becomes little more than an extension of the steam feed pipe and allowing WETTER steam to get through to the engine.

As with most things there are often trade off’s to be made.

I hope you find a suitable solution.

Best Regards.

AlexC.