Originally Posted by Steelaway35
I'm leaning towards the spring loaded poppet because it can be installed at any angle while the swing check valve's are specific to certain orientation (vertical/horizontal).
I'll be using a variable speed water pump with no accumulator tank and will have the pressure relief valve plumbed into the bilge
to deal with excessive pressure build up.
Use a swing check. either in upright or horizontal is fine, just not down. pressure from the water heater will keep it closed.
Not a big fan of using T&P reliefs to relief pressure. Oh it will work fine. But two things worry me. First the T&P may get a piece of mineral stuck in the seat and not reset, which could lead to a bilge full of water or an empty water tank.
Second I don't trust the typical aluminum
used in the cheap marine
heater. I'm thinking that repeated cycling of the tank pressure that normally sees 40-50 psig to 80-100 psig would tend to weaken the tank seams and cause premature tank failure of the aluminum tanks
. That's not a problem with the better, IE more expensive glass lined steel
tanks of the higher end marine
If it were me, I'd put a thermal expansion tank somewhere down stream of the check valve and that will prevent excess pressure on the water heater tank. I know the marketing
hype of the VSD pumps say you don't need one and you don't for the pump. But they also act as a thermal expansion tank too and if you have a check valve on the heater, (oddly enough sometimes required by the VSD pump) then prudent design would have a expansion tank on the heater too.
Now as someone who has designed 1000's of hot water heating
systems up to 1000 GPM (steam fired on that one and no its not a typo) over 30 odd years, I would not put a check valve on the water heater. Well not on a boat. But then I'm not that fond of using small VSD pumps, that cost more and tend to fail faster, due to the more complicated electronics
on the VSD side either.
If you don't have a VSD pump you don't need a check valve at the water heater. Worst case,you just need a heat trap (vertical 12" ish U Bend) on the cold side. Simple and nothing to fail.
Check valves fail so if you can avoid using one, its always better....