Installation of Check-valve

ohaavik · #1 (**permalink**) 02-05-2009

So I was running the water maker (WM) the other day and found that my cockpit lockers appear to be doubling as additional water tanks!

It turns out that the inlet for the water maker has been t'd into the drain pipe from the cockpit lockers about 6" from the seacock. The lockers drain down about a 2' drop and rely on gravity and a 3/4" hose. The water maker intake t's off using a 1/2" hose down into the interior of Valkyrja.

When I was rummaging in the cockpit lockers for new filters for the WM I noticed there was a lot of fresh water coming in through the drain on both Stb and Pt sides (WM was running).

So, I figured I'd install a check valve on the drain from the lockers so that the back pressure in the WM will not cause the water to push up into the lockers. Yes, there is something wrong that isn't right with the WM since it's pumping all the fresh water back out rather than into my tanks

, but I'll get to that on the weekend.

Does anyone have an opinion on whether to install the check valve in the cockpit locker drain hose or on the intake to the WM? I thought it safer to hit the drain hose first since there's not much pressure there and leave the WM intake as a fall-back in case this didn't work. Anyone with any experience in this?

Thanks much in advance.

39512 · #2 (**permalink**) 02-05-2009

I have been trained to avoid using check valves on drains or discharges. I've also been trained to avoid combining intakes and discharges in most instances. Mixing potable water intakes with raw water discharges would be one of those instances.

The only safe use of check valves that I know of is for the intake side of a refrigeration pump.

JohnRPollard · #3 (**permalink**) 02-05-2009

I cannot comment about the advisability of installing a check-valve in your watermaker system, but I definitely would not put a check valve anywhere in the cockpit drains/scuppers.

RAGTIMEDON · #4 (**permalink**) 02-05-2009

IMHO one should never put a check valve in a deck scupper or cockpit drain. If you are anywhere near shore, there are likely to be trees dropping leaves on your deck, particularly during a heavy rain. A very small leaf can plug a very large check valve, causing a very large flood!

ohaavik · #5 (**permalink**) 02-10-2009

Thanks guys for feedback. Took me a couple days since I bought too big a check valve and had to re-order a smaller one.

Actually, the drains are from the lockers, not the main cockpit drains which run out (in the X-Yachts) in the wheel well. Since the lockers are dry and I have thought of further insulating them to make them 'waterproof' I think there is little chance of flooding there. The only time I have had them wet was when the watermaker for some reason pumped the fresh water back up there.

I know, the connection of intake to drain is really silly but I guess the PO figured the lockers were dry anyway and so could just T the intake to the thru-hull where there was no flow anyway...

I may have to re-think this one though...

xort · #6 (**permalink**) 02-10-2009

A check valve needs some amount of pressure to open. I would doubt the drains would exert enough pressure to open the check valve. So the only way this might work is to put a check valve on the watermaker to keep it from backing up into the locker.

ohaavik · #7 (**permalink**) 02-12-2009

Quote:

Originally Posted by xort

A check valve needs some amount of pressure to open. I would doubt the drains would exert enough pressure to open the check valve. So the only way this might work is to put a check valve on the watermaker to keep it from backing up into the locker.

Thanks Xort, yeah this is what I am thinking now...I thought I'd avoid messing with the watermaker intake. Then I thought, maybe I can just let the lockers drain into the bilge where I have up to 3 pumps that can pump out any excess moisture...I don't think they necessarily need a separate thru-hull and it could be dedicated to the watermaker intake.

And then I realized I have now spent close to $100 on 2 check-valves (with shipping) that I probably won't need

Deadeye · #8 (**permalink**) 02-12-2009

So I take it your locker drain through-hull is below the the waterline ?...just curious, but is it a realistic option to install a drain thru hull above the w/l and use the other one just for the WM ? I think all the ones I've put in wanted a dedicated thru hull just for the WM itself. What WM is it ?

If the WM has fresh water in its drain line, then it's rejecting the fresh ('product') water - maybe the salinity is too high. How old is the RO membrane ?
Most of the automatic ones do have an auto-backflush with freshwater to clear the brine from the outside of the membrane. That would put brackish water into the lockers - the flush cycle could easily have enough flow to overwhelm a 3/4" hose. But of course that would be coming out the WM's drain rather than its intake...

In your unit, do the intake and discharge use the same thru-hull ? I usually plumb the WM discharge into the sink drain if it's convenient and I don't think I've seen one back up into the sink.

Better to figure it out and fix the problem than to install a check valve to make the problem 'go away'. JMHO of course.

Rockter · #9 (**permalink**) 02-12-2009

Unusual to have a cockpit drain below the water line?

Most are above.

ohaavik · #10 (**permalink**) 02-23-2009

Quote:

Originally Posted by Deadeye

So I take it your locker drain through-hull is below the the waterline ?...just curious, but is it a realistic option to install a drain thru hull above the w/l and use the other one just for the WM ? I think all the ones I've put in wanted a dedicated thru hull just for the WM itself. What WM is it ?

If the WM has fresh water in its drain line, then it's rejecting the fresh ('product') water - maybe the salinity is too high. How old is the RO membrane ?
Most of the automatic ones do have an auto-backflush with freshwater to clear the brine from the outside of the membrane. That would put brackish water into the lockers - the flush cycle could easily have enough flow to overwhelm a 3/4" hose. But of course that would be coming out the WM's drain rather than its intake...

In your unit, do the intake and discharge use the same thru-hull ? I usually plumb the WM discharge into the sink drain if it's convenient and I don't think I've seen one back up into the sink.

Better to figure it out and fix the problem than to install a check valve to make the problem 'go away'. JMHO of course.

Deadeye; it's a Spectra 12V 24l/hr. You are probably right that the RO membrane may need to be changed - I am not sure when the PO last did it, but I have had the unit working well for the past year (intermittent use, admittedly) so it's entirely possible as you suggest that the WM is rejecting the water due to high salinity. I actually tasted the water in the cockpit lockers and it was fresh - I assume the slight salt taste was due to some salt having accumulated in the lockers from the ambient salinity of the air in the marina.

I have decided to get the WM overhauled instead of trying the check-valve plan. I think the brine is passed through a thru-hull in the galley after the secondary filter but, to be honest, I need an expert to go through the system to review and see what has happened.

Thanks much for the input though, very helpful indeed.

Best,
Odd