Boat Plumbing - Potable Water - Backflow Preventer Before Heater?

[jviss]

My previous boat had a backflow preventer between the pump and the water heater input. My current boat doesn't.

I am re-doing some plumbing on the new one, de-Rube-Goldberg-izing it, I think is the term, and noticed no backflow preventer. While ordering some additional Parker "O" Ring/Grab Ring Tube Fittings (which I really like, by the way), I ordered a check valve that I plan on installing before the water heater.

Parker fittings:
https://www.usplastic.com/catalog/default.aspx?catid=676&clickid=popcorn

Check valve:
https://www.usplastic.com/catalog/item.aspx?itemid=36847

I was just wondering, is this the correct way to do this? Is a check valve recommended, necessary?

Thanks.

By the way, the Parker fittings are really great. The current boat has polybutylene tubing, which is a problem in houses, apparently, but no issue in boats. It's unavailable now, so I purchased some LLDPE tubing, "linear low density polyethylene," which is food grade, good for drinking water, etc. $18/100'. It is available in colors, and cuts very easily with a tubing cutter tool, as what is used for PEX. The Parker fittings go together without tools very quickly, and hand tight is water tight, no tool needed or recommended to make them up. Highly recommended. I hate the nylon-reinforced vinyl tubing in the old boat, as it can kink, and it hardens with age, making it very tough to undo, remove from a hose barb, etc. This LLDPE and Parker is a huge upgrade for folks who do their own maintenance and upgrade work.

 

[justsomeguy]

which is a problem in houses, apparently, but no issue in boats.

Prolly because there aren't enough plaintiffs to get the lawyers salivating.

 

[Ken Cross]

Why do you need a backflow preventer for a hot water heater?
Normally they are used to prevent contamination in water systems should the pressure fail (such as in a lawn sprinklers so debris and fertilizer can't siphon into the water system.) I just don't understand the need for the application you described.

Ken

 

[jviss]

Why do you need a backflow preventer for a hot water heater?
Normally they are used to prevent contamination in water systems should the pressure fail (such as in a lawn sprinklers so debris and fertilizer can't siphon into the water system.) I just don't understand the need for the application you described.

Ken

I don't know, that's why I'm asking. My theory:

• if the water heater fails, and engine coolant leaks into the potable water side, the backflow preventer would prevent contaminating the water supply.

 

[jviss]

Found this:

Water heaters have four threaded ports. The tank inlet connects via a tee-connector to the outlet hose from the pump. A check valve is required in this line or in the heater to prevent hot water from migrating back toward the pump.

http://www.boatus.com/boattech/casey/boat-plumbing.asp

And also this:

...in potable-water systems, check valves are often used on the supply side of a water heater to prevent it from inadvertently draining and burning out the electric heating element in the event of a leak in the incoming line.

https://www.cruisingworld.com/how/get-know-your-check-valves

Force 10 Water Heater Manual:

Connect cold water supply and hot water outlet to the heater as indicated on the
front of the tank. (The tank is supplied with 1/2” NPT Female fitting) Force 10
recommends the installation of a check valve on the cold water inlet. Seal all pipe
fittings with Teflon tape or Loctite thread sealant.

http://www.marlow-hunter.com/wp-con...xport/Vendor-Manuals/Force10 Water Heater.pdf

 

[Skipper]

A check valve is to keep heat-pressurized hot water out of the cold side. You don't want to turn on the cold side and unexpectedly get a burst of engine-temp water.

 

[nat55]

JVISS- I hadn't seen those before, I've used the Seatech products. I agree with Ken, don't bother with a backflow preventer, I was reading the specs on the US plastics and notice that the temp range on the PP version is 32f - 212f while the nylon is rated @ -40f - 200f. I hope you are using the nylon?

 

[jviss]

JVISS- I hadn't seen those before, I've used the Seatech products. I agree with Ken, don't bother with a backflow preventer, I was reading the specs on the US plastics and notice that the temp range on the PP version is 32f - 212f while the nylon is rated @ -40f - 200f. I hope you are using the nylon?

That is a good catch, Nat, I confess I never read the specs.; I bought the nylon ones 'cause that's what was already used on the boat. I don't anticipate a problem, though. I'm not sure what they mean by "temperature range," but as a former spec writing engineer, I take it to mean that the other specs, the operational specs, like pressure, apply only over this range.

 

[jamhass]

What are the downsides?
Installing the check valve costs a few $$.
Not installing risks the issues noted above.
Which would you rather live with?

 

[jviss]

What are the downsides?
Installing the check valve costs a few $$.
Not installing risks the issues noted above.
Which would you rather live with?

$7.28, plus maybe a couple of 1/2" NPT fittings.

 

[Bob J.]

Potential downside to the check valve, water expands when heated. If the expansion has no where to go the relief valve on the water heater may drip. If you're replumbing might consider installing a tempering/mixing valve on the hot water outlet. In doing so you can set the temperature leaving the heater so you don't have 160 degree water coming out of a faucet when the engine's running. It also gives your water heater a little more capacity.

 

[jviss]

Thanks Misfits, yes; there's an overpressure relief valve with a hose barb on it, I may attach a piece of vinyl tubing and lead it to the bilge. There's no tempering valve. I hadn't thought of that.

 

[Ron20324]

ANY part of the water system may burst and drain the water tank. How often does that happen, as compared to check valve going defective and block ALL of you water needs? Just today I finished installing a hot water tempering valve. Nice thing to have, but I guess 4 crew this weekend will have their comments.

 

[Ken13559]

A check valve is to keep heat-pressurized hot water out of the cold side. You don't want to turn on the cold side and unexpectedly get a burst of engine-temp water.

Not likely to get much back flow from heater side as there finite expansion when heated and the cold water would dilute it to luke warm water. Further more the pump is on cold water side.

 

[kloudie1]

@jviss Yup.. full ratings at that temp range.. my bet is not much water is going to be flowing below 32F..

 

[thinwater]

This is a backflow preventer. The OP is talking about a check valve. Not the same thing. You can buy small backflow preventers for hoses, but they can also discharge water on the ground, which is not what you want.

 

[SG]

This is a backflow preventer. The OP is talking about a check valve. Not the same thing. You can buy small backflow preventers for hoses, but they can also discharge water on the ground, which is not what you want.

VERY, VERY, correct and cute, Thinwater. ;^)))

I think that it will do no harm, the 200 degrees rating for the fitting shouldn't be a problem -- unless your engine overheats or is running hot. (I've only had the expansion valve trip in one series of episodes when my heat exchanger wasn't working right and I was running the engine at 2,8000 for an extended period of hours, not minutes. The solution for me, after I noticed that the waterpump and bilge pump was cycling, was to tool back to 2,300 rpm. That lead to another long story.)

I don't think most boats have a CHECK VALVE to LIMIT the backflow -- but it won't hurt anything, should conserve water, will keep the inside of the boat cooler (my a very, little bit), etc., etc.

The expansion of the water as it heats should be taken-up by the hoses and other fittings -- or you are running a pressure vessel, which should only occur if the safety valve doesn't "release" temporarily.

 

[jviss]

Well, yes, it's not a proper backflow preventer, it's a check valve. It will provide a degree of protection of the water supply should the water heater fail internally. It's recommended by Force 10, in their installation manual, and by other authoritative sources (quoted above). And, if I install it "in line,", in a plumbing line, it can quickly be removed and replaced with a union, without tools, should it fail closed (which is highly unlikely, in my opinion).

I'm not following the temp discussion, this is on the feed side. I imagine the side towards the heater could warm up eventually with no flow, but not so much that it would damage the valve. What's the maximum the water will get to, either by engine heat, or AC? The maximum operating temperature of this valve is 140º F.

 

[SG]

The pressure release valve on mine is a lot higher than 140 degrees. I think it is Aird at precluding the water heater from becoming a pressure vessel. That would be a closer to the boiling point of water (which varies by elevation above sea level).

The electric heating function should be thermostatically controlled, but the heat exchanger is not — except by the engines cooling system and heat loss in the hoses.

 

[Skipper]

Not likely to get much back flow from heater side as there finite expansion when heated and the cold water would dilute it to luke warm water. Further more the pump is on cold water side.

The pump is on both sides. Feeding cold and heater simultaneously. Otherwise one side would get no input pressure.
When the heater pressurizes with heat, especially from the motor, hot water can travel backwards to the cold side when a valve (faucet) is opened, without ever touching the pump, which may have its own check valve or enough resistance to cause the hot water to take the path of least resistance: the open faucet.
Mine did this years ago. Troubleshooting found the bronze check valve stuck slightly open.