3 Boiler tri cocks ?

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Glenn Brooks
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3 Boiler tri cocks ?

Post by Glenn Brooks » Tue Sep 17, 2019 11:21 am

Hello All,

Hoping someone can enlighten me about old style boiler design. Iam getting ready to move forward with a new boiler for my 1904 era 12” gauge 4-4-0 locomotive. It presently has the original riveted, 14” boiler. See pics below...

I am confused why there are three pet cocks on the upper right hand side of the back sheet? And yet a fourth drain on the lower end of the sight glass- which is substantially lower than the lower right side pet cock.

Can any one explain the early day boiler design theory for this?

Thanks,
Glenn
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Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

steamup
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Re: 3 Boiler pet cocks ?

Post by steamup » Tue Sep 17, 2019 11:43 am

The petcocks are the backup for the boiler water level check. Sight glasses can be unreliable in dirty conditions. Hence there should always be a blow down on the site glass to clean it and the boiler tappings out. A plugged top or bottom tapping will give a false reading on the sight glass.

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cbrew
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Re: 3 Boiler pet cocks ?

Post by cbrew » Tue Sep 17, 2019 11:50 am

^^ What he said ,
imho, they are all but useless with these smaller boilers. unless you want them for the "look" I would replace them in favor of a second glass.
but with proper procedures a single glass will do the job
If it is not live steam. its not worth it.

Andy R
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Re: 3 Boiler pet cocks ?

Post by Andy R » Tue Sep 17, 2019 11:55 am

The top cock should upon opening emit steam.
The bottom should only emit water.
The middle - you guessed it - both water and steam if right at the water-steam interface.
There should be an inclined drain trough below the cocks connected to a drain line extending below the floor of the cab.

Glenn Brooks
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Re: 3 Boiler pet cocks ?

Post by Glenn Brooks » Tue Sep 17, 2019 12:36 pm

Thanks guys.

Kudos to Andy for mentioning a use for the middle cock. Some recess of my memory cells vaguely has opened up to recall the middle position as useful...now I know why.

One followup- the lower sight glass valve is mounted substantially below the lower pet cock. Is it true this was the old method? Maybe prior to an ASME rule change? Or is there some other early day reason for the low position?

BTW, years ago a state boiler inspector told me the pet cocks are/were a required S code boiler alternate to the sight glass. So that if the sight glass broke, or became unusable in some way, the engineer could still determine water level.

Ps, today Iam going to finish measuring the boiler- to determine where exactly the crown sheet is- seems like a lot of space between the pet cocks and the lower glass valve...

Thanks again,
Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

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cbrew
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Re: 3 Boiler pet cocks ?

Post by cbrew » Tue Sep 17, 2019 12:53 pm

Glenn Brooks wrote:
Tue Sep 17, 2019 12:36 pm
Thanks guys.

Kudos to Andy for mentioning a use for the middle cock. Some recess of my memory cells vaguely has opened up to recall the middle position as useful...now I know why.

One followup- the lower sight glass valve is mounted substantially below the lower pet cock. Is it true this was the old method? Maybe prior to an ASME rule change? Or is there some other early day reason for the low position?

BTW, years ago a state boiler inspector told me the pet cocks are/were a required S code boiler alternate to the sight glass. So that if the sight glass broke, or became unusable in some way, the engineer could still determine water level.

Ps, today Iam going to finish measuring the boiler- to determine where exactly the crown sheet is- seems like a lot of space between the pet cocks and the lower glass valve...

Thanks again,
Glenn
Glenn, the location of the three petcocks line up with the top, middle and bottom of the sight glass. the valve on the sight glass need to be lower then the bottom petcock due to physical layout.
the biggest problem i had with using petcocks is one most understand how to use them. if they are opened too much, the flow will draw water up to the petcock giving a false high.
in the case of a cracked glass. close the gauge valves, cut the fire and inject water. knowing your locomotive will tell ya how long to blindly inject water. then determent if you want to replace the glass hot or wait for cool down.
as i stated above. I would just replace them in favor of a second glass.
I used to crew a little 0-4-0 in poway cal. one morning we had the sight glass, we followed the steps above, replaced the glass hot and was able to having the locomotive in service with in an hour.
this locomotive has ~ 28 inch boiler and even on this boiler, it was easy enough to lift the water if the petcock/trycock was opened too much.
If it is not live steam. its not worth it.

steamup
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Re: 3 Boiler pet cocks ?

Post by steamup » Tue Sep 17, 2019 1:27 pm

Notes from the ASME high pressure stationary boiler code:

§ 14-9.18 Gage cocks.

(a) Each boiler shall have three or more gage cocks located within the visible length of the water glass, except when the boiler has two water glasses located on the same horizontal lines.

(b) Boilers not over 36 inches in diameter in which the heating surface does not exceed 100 square feet need have but two gage cocks.

(c) The gage cock connections shall not be less than one-half inch pipe size.

Glenn Brooks
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Re: 3 Boiler pet cocks ?

Post by Glenn Brooks » Tue Sep 17, 2019 2:02 pm

Good stuff! Thanks very much for the info - including the ASME code reference. This is my second year running steam, after a long hiatus. Lots to re-learn.

Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

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LVRR2095
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Re: 3 Boiler pet cocks ?

Post by LVRR2095 » Tue Sep 17, 2019 2:41 pm

Just as info.....the normal term for these valves were “Tri-Cocks” because there are three of them.

Keith

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LVRR2095
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Re: 3 Boiler pet cocks ?

Post by LVRR2095 » Tue Sep 17, 2019 2:43 pm

Also..have you done ultrasonic testing to determine the boiler sheet thicknesses?
If the sheets are not wasted you do not need to replace the boiler. Age alone will not condemn a boiler.

Glenn Brooks
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Re: 3 Boiler pet cocks ?

Post by Glenn Brooks » Tue Sep 17, 2019 7:49 pm

Thanks Keith, yes I’ve done an ultrasound in several places around the boiler. It’s lightweight steel .250”, so Lots of pluses, and minuses, with this one.

The boiler has only been fired half a dozen times, but it is 114 years old, or so. Tubes leak and it is riveted, with no materials specifications- so at best limited to 100 PSI operating pressure, because of the Wa state boiler code.

Also, the major impediment: the loco is gauged at 12 5/8” gauge. The boiler width at the fire box prohibits regauging to my standard 12” gauge track size. So all in all, l’ll need a new boiler to complete the restoration.

Glenn
Moderator - Grand Scale Forum

Motive power : 1902 A.S.Campbell 4-4-0 American - 12 5/8" gauge, 1955 Ottaway 4-4-0 American 12" gauge

Ahaha, Retirement: the good life - drifting endlessly on a Sea of projects....

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NP317
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Re: 3 Boiler pet cocks ?

Post by NP317 » Tue Sep 17, 2019 8:22 pm

And if you are providing rides to Friends and public, that old riveted boiler of unknown provenance is a huge liability in today's world.
RN

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