Starting Valve

The starting valve on a compound engine is designed to admit steam direct to the low pressure cylinder. That makes sense. What I don't get is why my starting valve seems to massively vent out through the exhaust.

The amount of steam emitted does not seem to vary with the position of the reversing lever or with the position of the crank. I would have thought that the steam should be more-or-less contained within the cylinder, and be dependent where it is in the cycle.

Today was the first day I actually developed enough pressure to run. My starting valve tends to stick open, particularly at low pressure. I can get round that with a quick tweak of the long-nose pliers. But I'm concerned that the apparent through-passing of steam suggests something else isn't right in my cylinder block.

Can anyone put my mind at rest, or suggest why it seems to just blow out of the exhaust? Thanks.

Hi

The starter valve passes steam in to the LP steam chest. If then you get steam out the exhaust with reverse in mid gear. Your valve pucks are not sealing on to the valve faces. The usual culprit is over tightening of the nuts holding the puck on the spindle. These need to have a small gap so the valve can move out and in on the spindle to sit against the valve face and when under breaking the valve needs to be able to "flop" off the face to pass the over pressure from the cylinder to the exhaust.

The second could be the pucks are loose on the spindles but not close enough to the valve for the steam to shut them. Often new engines need help from a spring behind the puck to push the puck on to the valve face when starting out.

Check your valve spindle ends are not bent and are holding the valves off the face.
Check the puck has a good seat on the valve face. Using a little smear of engineers blue or a sharpie pen. Look for good even contact.
Check there is no burr interfering with the puck.

Thanks Lynn.

The valve pucks are just loose enough to move out from the face, without being sloppy. I might have a rummage through my springs bin and see what I can try.
Having removed the valve chest cover, I'm not so sure it's the starting valve anyway, 'cos I seem to get a load of air (running on compressor now) coming through the regulator port. Clearly I've still got some work to do...

Stu

Hi

Also remember Steam works completely different to air. It is wet so you get sealing where air will just pass by. Also air does not have the expansion ability of steam. So things act different under steam. Crystal leaked like a sieve and would not run on air at all. In steam she is powerful and non leaky.

Thanks again Lynn.
Ran it up on Sunday. A few fizzles as the pressure increased, then, as you suggested, it all sealed itself up.
My two main problems were the regulator, which I sorted with a bit more rubbing down, and that sticking starting valve. I've decided to leave it closed and just flick the flywheel to start it.

I even managed to get a decent fire and tested the safety. And drive it round the car park. Of course, everything's shifted due to the jolting around, so a new set of leaks to contend with!

Stu

Glad your getting progress. Yes it takes a few shake down steaming sessions to fully sort.