Fitting a check valve

[Jklotz]

One of the water pumps on my boats' A/C's loses prime just about every time we go out. I know how to reprime the pump, and it's no big deal, but it's not a lot of fun after a long day of traveling, in a hot engine room. Plus it'd be nice to be able to run the A/C's underway (with generator, of course). Support guy from manufacturer recommended I install a check valve/back flow preventer somewhere between the thru hull and the pump. Doesn't sound all that tough, but it is below the water line, so it's critical that it is done properly. Anybody done this before care to offer some tips on best practices?

 

[READY]

Generally these pumps are best installed below the waterline. Check valve would probably fix your issue but might be a future problem/failure point. But if you go that route it is simple to put in a check valve as long as you can cut the hose and have a valve that matches the hose diameter. Secure it with good hose clamps, non perforated type is best.

 

[O C Diver]

If you put a flapper check valve before the pump, it should work. Be prepared to add water after the check valve if it sticks.

I installed a check valve after the pump, but I had a way to prime the pump.

A tip on check valves, the larger the sizes, the less pressure required to open it. If you can blow into the valve to open it, the opening pressure is 1 PSI or less.

Ted

 

[Jklotz]

Generally these pumps are best installed below the waterline. Check valve would probably fix your issue but might be a future problem/failure point. But if you go that route it is simple to put in a check valve as long as you can cut the hose and have a valve that matches the hose diameter. Secure it with good hose clamps, non perforated type is best.

Thanks for that. Reading between the lines, I feel like you are implying it's not the "proper" solution? Is there a better way to fix this that doesn't create a future point of failure?

 

[DDW]

How can it be losing prime, if it is below the waterline? Is there a hump in the hose between thru hull and pump? Might it be easier to get it to work correctly, than add another part?

 

[lwarden]

We just covered this priming issue in a recent thread a week or so ago. You might want to look that one up for ideas.

 

[twistedtree]

How can it be losing prime, if it is below the waterline? Is there a hump in the hose between thru hull and pump? Might it be easier to get it to work correctly, than add another part?

I'd also first focus on this. A typical AC pump has to be located below the water line because they are not capable of self-priming. And the inlet plumbing needs to be such that it ideally self-floods, or at a minimum remains flooded after initial prime.

 

[lwarden]

The issue with my setup, and it may be common to others is that the upstream lines are a complex maze of ups and downs and if the boat has motion and if there is some negative suction on the thru hull it can pull air down into the pump. So, even though the pump is below the water level, a bubble is trapped in the impeller due to the head column on top of it. This happens to my boat every time I get it up on plane.
A check valve which doesn't allow for the suction to pull air down into the pump should do the trick, but I know some are skeptical of having a check valve in the system.

 

[DDW]

Would be interesting to see a picture of the OP's installation. What you want is the pump close to the thru hull, and the run between the thru hull and pump all uphill. Anything else could be called a bad installation. Some installers, like many roofers, don't understand than gravity works - always.

 

[Datenight]

Jim,

We are 4514,so four boats earlier. Our ac pump is forward of the starboard fuel tank, inboard of the engine stringer. Where is yours located?
Rob

 

[Jklotz]

Jim,

We are 4514,so four boats earlier. Our ac pump is forward of the starboard fuel tank, inboard of the engine stringer. Where is yours located?
Rob

Interesting. I'm not at the boat right now, but ours is not mounted under the deck, with the cutout in the flooring, like yours is. Ours is mounted a bit higher. Not sure if this angle helps, but it shows where the previous owner installed a bleed valve. Next time I'm there' I'll try to get a better pic.

 

[DDW]

Seems like a lot of problems there. Hoses should go up not down after the pump. They have effectively mounted a centrifugal pump at the high point in a system. I might be tempted to try the following: T off a small line (like 1/4" or less) from the high point in that mess, and run it always upward and overboard somewhere. You will lose a very small amount of flow when the pump is running, but it should always run. Assuming the black hose goes down (and never up again) to the thru hull. No check valves and it should be reliable. You are just giving a path for the air to leave, pushed out by the seawater head. It will squirt water when the pump is running - a good tell tale that all is well.

If all that is below the waterline, best practice is two hose clamps on every barb connection, if the barbs are long enough.

 

[Datenight]

Jim,

…inboard of the engine stringer. Where is yours located?
Rob

Sorry, should have said between engine and fuel tank stringers.

Rob

 

[SteveK]

Interesting. I'm not at the boat right now, but ours is not mounted under the deck, with the cutout in the flooring, like yours is. Ours is mounted a bit higher. Not sure if this angle helps, but it shows where the previous owner installed a bleed valve. Next time I'm there' I'll try to get a better pic.
View attachment 165282

what is the red handle shut off for and is it going downwards?
I am trying to understand how a pump below water level can hold air even temporarily from motion to break the siphon effect.
Is it possible that it is not below water level?
A check valve would work until it didn't, I would not install it. By the time it sticks you have forgotten it is there.

 

[Jklotz]

what is the red handle shut off for and is it going downwards?
I am trying to understand how a pump below water level can hold air even temporarily from motion to break the siphon effect.
Is it possible that it is not below water level?
A check valve would work until it didn't, I would not install it. By the time it sticks you have forgotten it is there.

The red handle valve was installed by the previous owner to bleed the system. it does make it easier to bleed, I'm just wanting it to be properly installed so constant bleeding is not necessary.

 

[SteveK]

The red handle valve was installed by the previous owner to bleed the system. it does make it easier to bleed, I'm just wanting it to be properly installed so constant bleeding is not necessary.

OK, if the pump is below the outside water level then if you open that red tap outside water should flow to the bilge. (maybe just with motor running)
Can you explain how you prime the pump?

 

[Jklotz]

OK, if the pump is below the outside water level then if you open that red tap outside water should flow to the bilge. (maybe just with motor running)
Can you explain how you prime the pump?

Simple. I run the hose coming from the valve into a bucket, turn the handle, turn the unit on and wait for water to come out. Once it does, I close the handle and we are back in business, at least while we are docked or at anchor.

 

[Jklotz]

After some research, I am going to pull the pump and mount it in a lower location. Hopefully have enough hose to make the run. If that works, I'll remove that valve and put it back like it's supposed to be. Thanks for all the help.

 

[SteveK]

After some research, I am going to pull the pump and mount it in a lower location. Hopefully have enough hose to make the run. If that works, I'll remove that valve and put it back like it's supposed to be.

I think that would be best as I think pump is above water level. What you described for priming allowed the pump to bleed water easier instead of trying to compress the air in the closed line.

 

[DDW]

All a pump needs to airlock is be higher than the inlet and outlet hose. Even if well underwater. Any air that gets in, from whatever cause, collects at the impeller which is then ineffective.

Knowing what that T is for, here is what you should try. Turn the T pointing the branch up, and raise it slightly so that the T is the high point. Put a 1/4" barb adapter in place of the nipple and valve. Run a 1/4" hose overboard anywhere, keeping the run always sloped up. If you use transparent/translucent hose, as soon as you open the seacock you will see water rise in it to waterline level. Now it should be self bleeding. If you don't see a water level in the line, then the pump must be above the waterline, or there are more issues between the seacock and the pump that need addressing.

Lowering the pump will only work if you can lower it below the hose runs. You need the impeller to be the collection point for any water in the system, not the collection point for any air in the system.

 

[lwarden]

This 1/4” bleed line off the top of the pump as long as the pump is below water level is a great solution.