Water Tank Management

[Blackacre]

1986 Hunter H34:

I'm looking to modify my water tank supply system in order to feed water from both tanks simultaneously. The current configuration allows me to feed from either the aft tank or the starboard tank or shutoff. I'm curious as to the advantages and disadvantages of doing this as well as the best method of reconfiguring the system.

Pro's
- Convenience of not having to switch tanks manually
- less likely to run the water pump dry

Con's
- possible uneven feed from tanks
- possible air entering the line
- possible cross tank contamination if not isolated
- other unknown possibilities

Whats the best procedure for accomplishing this? My current assumption is that replacing the current three way valve with a valve which allows the use of either tank 1 or tank 2 or both or shutoff. I'm not sure how best to describe this type of valve. Other ideas would be to splice into the tank supply lines which feed the valve and insert a bypass with a separate one way valve in order to connect both tanks together.

 

[Jackdaw]

Replace the single valve with a 3-tap manifold with valves on the two intake taps. Google 'water tank manifold' and you will get lots of pictures/ideas.

 

[Stu Jackson]

That's the answer.

KISS.

The benefit of using one tank at a time is that you KNOW when one's empty and have a backup.

If you draw from both always, you either run out at a most inconvenient time or you need gauges and sensors, which are overkill for most coastal cruisers.

 

[Blackacre]

Thanks for the input. So I see a lot of custom setups but I can't seam to find a similar replacement valve that will allow both tanks to feed simultaneously. Does anyone have a product description or pictures of a installation.

It's beginning to look like I'll need to make a custom setup. I'm surprised that there isn't any off the shelf valves that do this.

 

[Bill Roosa]

All you need is a tee and two valves. the flow will be from tank 1 to valve to tee to pump. The flow from tank 2 will be tank 2 to the second valve to the tee to the pump. lets you feed both at the same time (not recommended for several reasons see below) or individually.
For the life of me I can't see that messing with a valve once in a while is nearly as inconvenient as running completely out of water. Also, running the pump dry will not hurt it at all.
using the configuration that connects the two tanks will cause the following to happen. The two tanks are at different levels and have different water surface levels. The tank with the highest water level will pump by gravity to the lower tank (through the tee) till the levels are equal. If you try this with full tanks some of the water will be pushed out the lower tank vent if it is below the level of the top tank. As you use water out of the tanks the one with the highest bottom will empty first and if the tee is not sufficiently lower than that level air will get sucked into the pump. This all assumes that the boat is not heeled. If you heel the boat all the levels change and water starts flowing and you get really weird boat balance problems as the water drains to the low side. Kinda like having your rail meat sit on the leeward side instead of the windward side.

 

[Blackacre]

The two tanks are at different levels and have different water surface levels. The tank with the highest water level will pump by gravity to the lower tank (through the tee) till the levels are equal. If you try this with full tanks some of the water will be pushed out the lower tank vent if it is below the level of the top tank. As you use water out of the tanks the one with the highest bottom will empty first and if the tee is not sufficiently lower than that level air will get sucked into the pump.

Thanks for the info. I have a few questions though.

- Wouldn't the lower tank feed water back into the upper tank rather then overboard since the vent for both tanks are at higher points then the tanks themselves? Both tanks are near centerline and the lower tank is midship.
- I understand the pump is capable of running dry but it will run continuously if gone unnoticed. Is there an alternative solution for this?
- If the top tank is empty would the pump just suck air rather then water from the lower tank? Kind of like using two straws to drink with but one straw is outside the glass.

 

[Terry Cox]

Fresh Water Management

Our P42 came standard with two water tanks. Each tank feed has a screen type filter to catch any debris before entering and damaging the water pump. After this screen each feed enters a dedicated valve so that the owner can select either or both tanks. I normally alternate tanks during the course of a season in order to keep the water fresher.

After each shutoff valve the feed joins to a tee fitting, then into the pump. After the pump the feed goes to another tee; one side feeding the cold water supply the other to the hot water tank for the hot water supply.

I like the way Hunter set it up on our boat. It has worked well for us over the years. Nothing has come up yet where I would want to make a change. If you need a source for Zern/Qest PEX type fittings, see the link below.

https://www.plumbingsupply.com/polyb.html

 

[Blackacre]

Thanks for the link Terry. I'm a little confused as to how the sizes work. All of the hoses on my boat have an OD of 1/2". Can I conclude that I need 1/2" fittings as well?

 

[Terry Cox]

Fresh Water Management

Ours is all 1/2" OD tubing as well. I have never ordered from this site so I would pose that question to them before ordering. You might find a local RV or marine chandlery that still has the fittings you need in stock. Most are moving away from this older style to the newer quick connect type.

If you do order from them, please let me know your experience. I found what I needed from our local marine discount store. Also have some extra parts as spares.

 

[Blackacre]

I placed my order today. The sizes are very confusing and took some time to get right.

I plan on just adding to my current configuration for simplicity. I will create a new line with a shut off valve that connects the two tanks together when opened. this way the tank selector will still work as normal but I will also have the option of feeding the aft tank to the forward tank.

I will post some pictures of the modification when its complete.