SOLVED: Sight Glass water drops during running

[cbrew]

Another possibility with that style water gauge, having glass end seals
in compression, is the seal material (O-Ring or Teflon washer) has
extruded under the compression from the clamping rods into the
water space enough to just about close it off. Happened to me once.
New seals and tightening only enough to seal cured that.

That the idea i had when i asked my last question.
I piece of Teflon tape can cause issue also.

[Dale_F]

Sight glass has o-ring seals. I will check them to see if they are overly compressed.

I will check the "slosh" this afternoon.

My plan for today is to fill boiler and pressurize with air, open throttle and observe glass.

If the pressure drops, try putting the glass from the Atlantic on and see if the behavior follows.

I will post all findings in a few hours.

Thanks.
Dale.

[Dale_F]

Test 1 complete - result is I am now cold and wet, and still bewildered.

I filled the boiler and moved the engine forward and back and the water sloshed the expected amount up and down in the glass. I stopped and the water stabilized where expected.

I put air in the boiler, blocked the engine up and ran on air. The water dipped slightly (maybe less than 1/4") but that could have been to do with a whole lot of things. The water did not drop out of the glass as I have seen in the past.

I guess the next thing is to move the engine to my backyard piece of test track - nothing more than some track where I can steam up and run back and forth. I am expecting the heat and steam are the factors here - I just do not know why.

I will post more after my test.
Dale.

[Phil P]

Hi

Posted in error.

[Fender]

I believe this problem has been described here before in an earlier thread. There is a phenomenon whereby rapid boiling around the firebox creates an upward flow of water and steam bubbles that can cause a drop in pressure in the lower opening to the sight glass. Thus the drop in the water level in the sight glass occurs when boiling is very vigorous in the boiler, and returns to normal level when the boiling subsides. The fix is to change the shape of the end of the tube going into the boiler backhead to avoid the venturi effect.

[Bill Shields]

What Dan (Fender) describes is real world in full-size boilers also.

As a youngster, I followed my father into a super-critical power plant where, on occasion any one of the 3 sight glasses would appear to INVERT - water on top, steam on bottom, depending on various conditions.

The problem was just as described - excess flow around the glass fittings was causing enough pressure differential to change the levels.

[Fred_V]

see this.

[tsph6500]

If it was vigorous boiling that is causing the dip, it would be possible to recreate the dip when the loco is stationary by over-firing.

If the phenomenon only occurs with throttle application it has to be due to the steam entering the dry pipe and leaving the boiler. Is the dry pipe located close to the pressure gauge fitting on the boiler? This might cause a situation similar to the gauge being plumbed to the turret, which we know is not correct practice.

[Dale_F]

First - thanks to everyone who has been helping. Your responses have all been helpful and thoughtful. I never thought my problem would go to 3 pages of responses - a first for me.

And, in all my years in this hobby, I never once thought I would ever have the opportunity to say ....

I'll put an angle on my spud and give her a steam first thing this afternoon.

I will post the results.
Thanks.
Dale F.

[cbrew]

If it was vigorous boiling that is causing the dip, it would be possible to recreate the dip when the loco is stationary by over-firing.

If the phenomenon only occurs with throttle application it has to be due to the steam entering the dry pipe and leaving the boiler. Is the dry pipe located close to the pressure gauge fitting on the boiler? This might cause a situation similar to the gauge being plumbed to the turret, which we know is not correct practice.

I don't think this is correct, all the over-firing will do is raise the temp/pressure, not a lot of "boiling" going on,
the boiling happen as steam is drawn from the vessel,
which
1) lowers the pressure (every so slight)
2) water reacting to the drop in pressure, flashing to steam (causing the boiling) as equalization of the system accrues
the faster the draw, the more violent the reaction, as any one seen the reaction to a boiler if the safety valves are too big for the boiler? its an amazing shower for all around)
3) pressure is maintained as you apply more heat,

this thread to discussing water drop in the sight glass not the pressure gauge.

[Fender]

Agree with Chris. A good test would be to over-fire while standing, and when the safety lifts, see if the water level drops.

[Dale_F]

The results are in - Chris was right.

I put an angle on the "spud" as described above and fired it up. As CBrew suspected, it made no difference. The water still dropped when the throttle opened. Further CBrew AND Dan were both right in anticipating that the water would drop out of the glass when the safety lifted. I took some video of the glass for both events on my phone. If it would be worth the effort, I can post them to YouTube with a link here.

One thing I have been wondering is if I should lengthen the nipple below the glass and above the return valve and connect the glass into the lower plugged port on the boiler - about 1" below the place the glass is connected now. You can see the plugged hole in the boiler in the attached photo. That would get the water return for the glass farther down in the water leg and possibly away from the turmoil around the top of the sheet.

Thanks.
Dale.