Boiler install questions

[DetroiTug]

Getting ready to install the boiler on the tug and I have a few preliminary questions.

First off:

I'm installing a water leg VFT boiler and it has a 3/4" NPT blow down on each side for the mud ring. The hull is steel, the plan is to weld two 3/4" bosses in the bottom near the boiler. How should I attach these? I was thinking rigid pipe with unions. Or should I just use a flexible marine grade hose? One idea I had was to incorporate the water pick up tee'd into one of these blow downs, reason for that, it it gets plugged, it can be backflushed with a blow down valve. Bad idea?

Also, the steam line from the boiler to the engine: What is best here? I have seen pipe, copper tube, braided hose, etc. It seems schedule 80 pipe would be best. I'm trailering this tub and the boiler is tall and heavy (24" diameter and 48" tall) and I'm concerned about the boiler shaking in transit and fatiguing rigid connections.

I'll make all efforts to hold the boiler steady, but it's heavy (around 700 pounds) and mass is mass and inertia is inertia. Not sure it can be held perfectly static, no matter the mounting and bracketing to the existing construction. Probably over thinking it as usual.

-Ron

[farmerden]

I would absolutely have a flexable line. Both to the engine and from the engine. I don't think the blow-downs should be rigid either. Go to your local hydraulic hose shop and have them make something up that will handle steam. Get them to use brass or stainless fittings as the steel ones I originally had started to rust -oh yeah it doesn't rust where you live does it? Den Also somewhere I read an article about blowing down below the water line and I think it was frowned upon but I can't remember why.Could be as simple as having the boat sink if a line ever broke! Maybe someone smarter than me can jump in here![that should include just about everybody!]

[DetroiTug]

Den,

Flexible is best, that is sort of what I was thinking. This engine is pretty well balanced, but it is still two heavy objects, engine and boiler mounted independently of one another.

Ha, yeah it rusts around here, My pickup is blooming nicely with age

I'll confess, I had to Google "Rustmoth".. I fell for that one.. Reminds me of the time I went snipe hunting..

-Ron

(Sorry about putting this thread in the wrong section of the forum, if you want to move it, feel free)

[fredrosse]

Flexability is needed between the boiler and engine, between the boiler and hull. Low pressure exhaust lines can use good automotive heater/radiator hose and hose clamps. Anything over 10 psi can use stainless braided flex metal hose, good for high temp & pressure. I have two of them on my main steam pipe, 1/2 NPT x 12 inches long, about $22 USD each from WW Grainger.

High pressure steam hose is also available, but very expensive, and with a short life.

[artemis]

Getting ready to install the boiler on the tug and I have a few preliminary questions.

First off:

I'm installing a water leg VFT boiler and it has a 3/4" NPT blow down on each side for the mud ring. The hull is steel, the plan is to weld two 3/4" bosses in the bottom near the boiler. How should I attach these? I was thinking rigid pipe with unions. Or should I just use a flexible marine grade hose? One idea I had was to incorporate the water pick up tee'd into one of these blow downs, reason for that, it it gets plugged, it can be backflushed with a blow down valve. Bad idea?

I've never particularly liked blowdown exhausts below the waterline - or any "hole in a boat" below the waterline. But if you must, use a proper "seacock". This is a combination of thru hull fitting with a shut off valve (ball valve is fine). If the pipe inside of the thru hull/shut off valve should leak, the shut off valve takes care of the problem. Won't sink the boat that way. Always remember to open the "sea cock" before opening the blowdown. Blow downs are like pressure relief valves, they should not share service connections with other "pipes". I think there is an ASME regulation against that. You can avoid this whole problem by exhausting well above the waterline with a 90deg. fitting and a short pipe nipple on the outside of the hull pointing downwards.

Also, the steam line from the boiler to the engine: What is best here? I have seen pipe, copper tube, braided hose, etc. It seems schedule 80 pipe would be best. I'm trailering this tub and the boiler is tall and heavy (24" diameter and 48" tall) and I'm concerned about the boiler shaking in transit and fatiguing rigid connections.

I'll make all efforts to hold the boiler steady, but it's heavy (around 700 pounds) and mass is mass and inertia is inertia. Not sure it can be held perfectly static, no matter the mounting and bracketing to the existing construction. Probably over thinking it as usual.

-Ron

I've always used a flexible braided steam hose (buy it from any steam supply house in Detroit). Best installed where the steam line makes the 90deg. turn to the engine. Look for it online if all else fails. Grainger is a good bet.

[87gn@tahoe]

At the steamboat meet I just attended one of the boats had the main steam line break due to a lack of flexible connection between engine and boiler.

[mcandrew1894]

At the steamboat meet I just attended one of the boats had the main steam line break due to a lack of flexible connection between engine and boiler.

And there you go...get ye some braided stainless steel line!

Dave

[DetroiTug]

Wes,

That is about as definitive an answer as I could receive.

I looked on line today, it appears that McMaster Carr has the braided hose. It's funny the 1/2" Npt to 1/2" NPT version is rated for 1187 PSI, the 1/2" NPT to 1/2" integrated union version is rated at only 300 PSI. Must be the rating of the integrated union connectiion.

On the underwater thru-hull fittings. That I'm pretty comfortable with, my old Chris-Craft has the water pickup and even two 2.5" exhaust outlets submerged, all connected to marine hose. Never been an issue with any of them. I usually leave it in the water all summer. A lot of boats are set up that way. One of the reasons I want to blow down under the water is, this boiler probably holds around 40 gallons of water. If I'm alone, I won't know if someone is near the outlet outside the boat when that much scalding hot water is released. Someone might call the fire dept too

That's another question, when I get to the lake, the boiler will be empty, whats the best way to fill it before firing? Is it advisable to have a small electric pump? That would be a lot of manual pumping.

Using one of the blow down outlets for a water pick-up sounds as though it may be out.

Thanks for the info, Ron

[mcandrew1894]

You could fill it to half full to minimize the load and then use an injector once you got up steam...........just thinking out loud..

Dave

[artemis]

You could fill it to half full to minimize the load and then use an injector once you got up steam...........just thinking out loud..

Dave

When lighting off a vertical fire tube boiler, the boiler should be totally filled with water before the fire is lighted. Once steam begins to form, the water should be "blown down" (here's where a surface blow down valve/connection is desireable) to the correct level. The area of the tube(s) above the water is now partially protected by steam. Your VFT boiler will last much longer is this rule is observed.