Check valve ghost

[Scott T-Bird]

There is no way to keep the sump completely dry. The shaft packing flow ends up there, and the ice box drains into it. There is always a half inch of water in there. There is no place for another, smaller pump at the bottom. There's already the sump pump at the bottom. There's nothing wrong with the float switch. I'm not going to manually pump it out - the ship's manual pump hose is at the same level anyway, and would do nothing. It's a deep sump, partially covered by a glassed-in shower sump. Manually pumping it with a portable is a PITA, with the discharge pointing out into the cockpit. Takes 3 hands. I'd have to do this multiple times a weekend if that were my process, and why would I if the original system that was designed and installed to prevent this is working properly?

I didn't mean to use a manual pump to pump it down ... I meant to use the panel switch manually to run the pump to draw water to a lower level. Once the float switches the pump off, I can still pump down about another inch of water. Even with a half inch in the bilge (about the amount that lingers after using the manual switch to pump it down), the water would have to rise about 3" to trigger the float on. If I come to the boat and see about 2" of water in the bilge from the ice box release, I switch the pump on at the panel and draw it down. The float switch isn't even involved. Can't you do the same thing?

I still don't understand why float switch should keep the pump cycling with the backwash. I actually watched mine operate just last night, as I had a significant amount of water in the ice box that I released into the bilge. Enough so the float switch was activated.

The float switch keeps the pump running long enough so that the drawdown is close to 2 inches below the level where the float would switch on again. The backwash isn't enough water to activate the switch. It is a small amount that causes a minimal height increase.

It seems that you must have such a large diameter hose or such a long length that the volume of backwash is too great. Or your float switch triggers off at the same height it triggers on, whereby the backwash triggers on. Float switches should trigger off at a lower level than it triggers on ... so the backwash doesn't affect it.

 

[Scott T-Bird]

Also, a deep bilge is a good thing for installing a back-up pump at a higher level. Why not install a small centrifugal pump with a proper float switch at the very bottom for normal use, and install the pump with the larger discharge on a platform at a higher level?

 

[Skipper]

I didn't mean to use a manual pump to pump it down ... I meant to use the panel switch manually to run the pump to draw water to a lower level.

Oh.
Yes, I do that. Doesn't help much. The characteristics\shape of the sump bottom are a factor - the float switch position enables it to kick off when the water is very low, so manual activation only get another cupful or so out. Anyway, it would fill again when I'm off the boat, from condensation, shaft drip, residual ice from the cooler, etc.

[/quote] It seems that you must have such a large diameter hose or such a long length that the volume of backwash is too great. [/quote]

Yes, long hose.

 

[nolasafari]

Interesting thread, I skimmed over it very quickly and may have missed something and I am not willing to enter in to the debate of to check vale or not to check valve. Skipper you did mention that it is a brass/bronze check valve, I assume with a brass/bronze flapper /clapper. I would find a lapping block or good substitute and some fine grit valve grinding compound and lap the flapper/clapper. I would also check and reface the seat for the flapper/clapper. The piviot points of the flapper/clapper may also have become worn over the years not letting the seat interface correctly with the flapper/clapper, in other words an out of control unlapped flapper/clapper. Put on your big eyes and look at the valve closely for signs of wear or warpping.

Jim

 

[tkanzler]

The characteristics\shape of the sump bottom are a factor - the float switch position enables it to kick off when the water is very low, so manual activation only get another cupful or so out. Anyway, it would fill again when I'm off the boat, from condensation, shaft drip, residual ice from the cooler, etc.

I had the same problem with my H340. The bilge was very small in plan, but deep, so a conventional float switch would close when the discharge flowed back to the bilge. Mine had a check valve, which worked perfectly for all the years I owned that boat unless the bilge pump was set low enough to draw air, in which case it had trouble getting past the check valve.

But a better solution, which I would have done had I kept the boat, would be as Scott suggested above - install a small pump at the bottom, with a small hose that won't backflow enough volume to reactivate the pump, and a large pump higher up, where the back flow is less likely to be a problem, as the bilge flared open as the water got deeper.

There are also switches that will run the pump for some predetermined time (seconds) below the cutoff depth, so it can be set high enough that, after the additional depth is pumped out on the off-delay timer, the back flow won't trigger the switch again. But I haven't researched them lately, as my boat doesn't even have a bilge, and lives on a trailer most of the time these days.

 

[Benny17441]

Shorten the discharge hose run. Re-route the discharge hose from the transom to the closest side of the hull. By reducing the length of the hose you reduce the volume of water that will flow back into the bilge. The use of check valves in bilge discharge hoses is not recommended. I know of one instance where a boat was almost lost due to a fouled check valve. An alternative would be to replace the float switch with one that has more travel to perhaps acommodate the larger volume of water before recycling.