Transition from hard copper to thru hull fittings

[JonRiley56]

All,

I am going to have two thru hull connections on my set up. The first will be my blown down line. I will be coming off my boiler with 3/8th inch copper with a shut off valve and a check valve in line between the boiler and the hull. I dont think that usine a flexible line is an option for this one because of the pressure and temperature. (I guess I could use braided stainless........but it is pricey) Can I run copper most of the way and then just include a small length of flexible line, or will I run into problems ? I am nervous about this run since it exits below the water line.

The second one will be a feed line coming in to my water loop to allow me to pull water from outside of the hull if I am running on fresh water.
I am considering using flexible ine on this one, that way I could just use a thru hull with a hose barb on it.

comments ?

jon

[Lopez Mike]

By the time the steam in the blowdown line gets to the thru hull fitting it ill almost certainly be at low pressure and 212F and thus ordinary rubber hose should handle it easily as a coupling between hard lien and the thru hull. Maybe some extra hose clamps on everything for piece of mind.

3/8" line seems small though. The smallest diameter in my blowdown line is 1"

The suction line has no pressure, of course and with small diameters and no sharp bends to kink it, ordinary rubber fuel line hose should serve.

Mike

[fredrosse]

The blowdown pressure existing just before the thru-hull fitting & hull valve can be considerably above atmospheric pressure for certain piping arrangements. Braided stainless hose rated for the boiler temperature/pressure is available from Graingers at about $30 for a 12 inch long piece, with pipe threaded ends.

If you plan on using something like automotive radiator hose as the flex just before the thru-hull valve connection, you should reduce boiler pressure to about 15 PSIG before blowing down. That will assure temperature/pressure less than 15 PSIG/250F. What Mike recommends is generally true, and the thru hull connection pressure is probably close to atmospheric pressure, but the word "probably" involves some risk. I can imagine several piping arrangements where the pressure close to entering the thru-hull valve is nearly the boiler pressure during blowdown.

You can also consider using no specific flexible connection, by having a loop in the copper line, so it becomes flexible enough to take care of any movement due to thermal expansions. Can you send a picture of your arrangement, identifying the boiler blowdown connection, as well as the thru hull valve and connection?

[fredrosse]

Some additional stuff reguarding the blowdown & feedwater connections:

I believe the boiler code requires two blowdown isolation valves in series for any blowdown line. As to the check valve, what for?

Is it correct to assume there will be an isolation valve located immediately inside the hull at any thru-hull connection? This valve would be in addition to the blowdown isolation valves and check valve.

[JonRiley56]

Hi Fred,

I have been having trouble trying to upload a pic of my water circuit. As always, your thoughts are appreciated.

jon