Thru hull blow down conection

[johnp]

Do I need to put a check valve on the blow down thru hull conection?

[barts]

Only if it is below water line.... and I don't recommend this, because you'll suck silently salt as the boiler cools if the check hangs.

- Bart

[johnp]

Thanks, it's in the transom with an isolation valve, i'm in fresh water and I'll add a check.

[Dhutch]

We have a 'sea cock' on the hull leading to a T peice, straight ahead is plugged and reserved for rodding an obstruction, with the other connection being piped by a short pipe to the boiler, which then has a quater turn blow down valve. No check valves.

That said, we have never used the rodding access, and infact, rather naughty, rairly use the sea cock at the end of a days boating.


Daniel

[daysaver1]

Dhutch claimed: "and infact, rather naughty, rairly use the sea cock at the end of a days boating."

It's my understanding one blows down only in the morning after the boiler has had an opportunity to settle all the particles into the mud ring which were suspended in the boiler water while the boat is bobbing up and down while under way.

Also, the rational for putting the blow down "through the hull" below the water line is the ability to see what you are blowing down. With the outlet above the water line all one can see is a cloud of steam, where if the outlet is a couple inches below the water line one can see when the crud has blown out and its time to close the blow down valve.

[Dhutch]

The morning after we typically have no steam to blow anything anywhere!

Typcially we will blowdown of an evening, and hour or so after tying up, with the pressure at around 50 (200psi WP) as recommended by our boiler inspectors, although occasionally, espcially if I know its a little dirtier than normal and there is a opertunity when the pressures a bit down and we have been sat for a while, I will blow down in the middle of the day as well.

I hadnt really thought of its coming out underwater as giving a better indication of the leval of sludge present, it proberbly would in clear water, although in most UK canals it simply makes it more user/public freindly.


Daniel

[gondolier88]

No you don't need a check valve- a seacock on the hull with a globe valve on the boiler is sufficient- seacocks are designed to be hull-pressure tight. A globe valve, arranged in the usual fashion with seat closing with pressure on the bottom is perfectly adequate, and when the boiler goes into vacuum it seats even harder as the it is pulled onto the seat.

On Gondola I use two globe valves- replacing two quarter-turn bronze valves which wore down every season and leaked past. They are both rated to pressures and temperatures far in excess of what they see in service, and with both arranged with facing the 'right' way, when closed the hull valve has the pressure of the water on top of the seat, the boiler valve has vacuum on the underside of the seat, and as yet I haven't seen or heard any evidence to say there has been any leaking past the valves.

Greg

[Lopez Mike]

We are sooo lucky to have decent feed water on both our condensing and non-condensing boats. I have personally seen a 700,000 pound locomotive in the U.S. midwest do a blow down after a 300 mile run using local water. Really hard stuff. The steam column exiting the side of the firebox was clearly brown for the first few seconds. And people drink this stuff!