Gauge Glass Safety Issue

[fredrosse]

This is a safety issue that became evident when I was getting my boiler ready for winter, blowing down all connections, etc.

I have an Ernst 300 PSI bronze gauge glass assembly mounted on the boiler water column. The Ernst Gauge glass assembly has isolation valves top and bottom, safety balls which instantly stop steam/water flow in the event of gauge glass breakage, and a small gauge glass blowdown valve at the bottom gauge assembly.

The bottom gauge assembly is schematically shown in Figure 1, with the safety ball in the proper position. Figure 2 shows the way it should work, if the glass breaks, the safety ball is pushed up by boiler pressure, and seats just below the broken glass, stopping hot boiler water from escaping and possibly burning anyone. The operator can then shut the gauge glass valves, and install a new gauge glass after things have sufficiently cooled down..

When I opened the gauge glass blowdown valve with pressure on the boiler, nothing came out. I thought it strange that sediment had so completely blocked this valve, but since it is a very small valve, I thought nothing of it. Later, with the boiler cool and drained, I removed the small blowdown valve, and to my surprise the safety ball fell out of the assembly!

At some time last year, I had the bright idea to remove the lower gauge glass isolation valve stem, and lubricate the valve threads with a graphite mixture, which I typically do to all valves in the system. Unknown to me, when I removed the valve stem, the safety ball dropped down into the lower area of the gauge glass body, and seated on the lower blowdown valve nipple, essentially stopping flow through the blowdown valve (Figure 3).

This condition resulted in absolutely no protection from hot water and steam leakage if the gauge glass were to break (Figure 4). Check to make sure your balls are in the right place!

All gauge glass installations should also have a clear plastic shield around the gauge glass to protect people from the broken glass and hot steam-water that may issue from the gauge glass assembly.

[DetroiTug]

Fred,

Great illustrations! That's a bad design. A captive ball - excess flow check right at the boiler connection would be much better. The fitting bored with a light spring and a roll pin to hold it all together. Could break the whole sight gauge off and it would still have some means to stop the flow. Due to gravity, they must have something different on the top valve? Maybe the ball is positive buoyant?

-Ron

[87gn@tahoe]

Not to nitpick but...

One should do a proper gauge glass blowdown at least once every steaming to ensure the glass is reading the correct level.

Proper procedure would have found the issue the first time out since the lubrication.

There have been many many boiler accidents partly due to operators failing to do exactly this.

[gondolier88]

Not to nitpick but...

One should do a proper gauge glass blowdown at least once every steaming to ensure the glass is reading the correct level.

Proper procedure would have found the issue the first time out since the lubrication.

There have been many many boiler accidents partly due to operators failing to do exactly this.

Second that absolutely.

Also recommend Reflex type gauges as I have never heard of one break (as in burst apart or crack and spurt water everywhere), they are far easier to read, cannot break with a light knock, in fact one steamboater recalled once that he had known Reflex glass being taken out of the gauge broken across, but hadn't been leaking at all under service! Having a flat plate of glass 1/2"-5/8" between the user appeals far more than a flimsy glass tube. Glasses, in the odd occasion it must happen somewhere, can be replaced without disturbing the gauge tails and their glands too, as well as spares being able to kick around in a toolbox with a bit of cardboard around them and show no signs of ware. The only downside is expense, but well worth the stretch of the purse if can.

[DetroiTug]

"We always blow the glass when the watch changes" Simon Oakland, From the movie Sand pebbles

[fredrosse]

The upper gauge glass assembly has a different arrangement, with the safety ball located upstream of the isolation valve seat. See Figure 5. I believe this is called a "rolling ball check". This safety ball is captive, and cannot fall out of place like the lower one.

Looking at the Ernst Catalogue for the sight glass, the following statement in the catalogue is noted:

Automatic gauge glass assemblies are furnished with ball checks that will seat in the event of glass breakage
shutting off the escape of fluid or steam.
(Note: Only the lifting ball checks are recommended for steam service; rolling ball checks must be
removed for steam applications.)"

I do not understand why Ernst makes this statement, although I know flashing steam/water issuing from the lower assembly is much more likley to burn a person than the steam only that would issue from the top assembly.

If the gauge glass breaks, when closing the upper gauge assembly isolation valve, the "rolling ball check" will be momentarily unseated before the manual valve seats. This momentary unseating as the manual isolation valve is closed would allow steam to escape, but probably not burning the operator. The lower "lifting ball check" will seat to stop the escape of flashing boiler water, and the manual isolation valve may be shut without unseating the ball. I think maybe this arrangement is to protect the person closing the isolation valves, but this is only a guess on my part.

Does anyone know the real answer here?

[marinesteam]

Not to nitpick but...

One should do a proper gauge glass blowdown at least once every steaming to ensure the glass is reading the correct level.

Proper procedure would have found the issue the first time out since the lubrication.

There have been many many boiler accidents partly due to operators failing to do exactly this.

Second that absolutely.

Also recommend Reflex type gauges as I have never heard of one break (as in burst apart or crack and spurt water everywhere), they are far easier to read, cannot break with a light knock, in fact one steamboater recalled once that he had known Reflex glass being taken out of the gauge broken across, but hadn't been leaking at all under service! Having a flat plate of glass 1/2"-5/8" between the user appeals far more than a flimsy glass tube. Glasses, in the odd occasion it must happen somewhere, can be replaced without disturbing the gauge tails and their glands too, as well as spares being able to kick around in a toolbox with a bit of cardboard around them and show no signs of ware. The only downside is expense, but well worth the stretch of the purse if can.

Who makes the reflex gauge shown above?

marinesteam

[artemis]

Don't know about that particular gauge, but http://www.mckenziecorp.com/boiler_gauge_glass.htm carries a selection, or go on line and google: boiler water gauge glass

[DetroiTug]

Tiny power sells that one, or one very similar in a kit.

http://www.tinypower.com/store.php?crn= ... how_detail

-Ron

[steamboatjack]

Reflex gauge glasses were originally (and still are) made by Richard Klinger & co. For those who don't know the corrugations on the inside of the glass cause the light to refract at a different angle in water as in steam, in water the light is absorbed, this causes a very good contrast in the appearance and so easily shows where the water is. Not that it bothers us much but they are only good for about 35 bar (500PSI) after which the glass tends to erode. In this case they use flat plate glass with mica sheets on the water side.
If designed sensibly the body to hold the glass can be made easily and so fitted between a conventional gauge glass cock set. The glass itself is not expensive considering its life although it is good practise to renew the gaskets if ever disturbed, they are available separately.
Regards Jack