Non-return valve

[NZL50505]

I want to install a non-return valve in the seawater pipe between though-hull valve and raw water pump/impeller on my genset. Purpose being to avoid pump/impeller running dry for first few seconds each time I start genset - which is reducing impeller lifespan.

Anyone else done this? And does it make any difference where in the pipe I install the non-return valve? High up close to pump or low down near through-hull? There’s a Vetus strainer in the system so my instinct is to install above that to avoid any leakage back through that (I know they are prone).

And finally what’s the best non-return valve to fit and where to buy?

Thanks

[Charlie-Bravo]

Hi, you might find an easier solution, whilst a non return valve might look like it will improve things, you must have wondered why there isn't one there in the first place .... I had similar thoughts ,but found that the seal O ring on the sea water strainer was letting in a tiny amount of air, it never leaked as it is under negative pressure, and the pump outlet pipe going from a lowdown pump then up to the heat exchanger makes a nice U bend on one side of things, .... anyhow, I smeared the filter seal with a little silicone grease and now the filter stays filled when the seacock is closed , and at about 1" deep with water when seacock is open despite the filter being a smidge higher than sea level.

Have a smear of grease at your seal, also work out how much higher than sea level your strainer is, it wants to be only an inch or two above sea level for optimum pump performance, but still work ok higher up.

CB

[rxc]

Remember that installing a non-return (check) valve provides a place for "stuff" to accumulate in the seawater side. You have a strainer for this, so if you install it between the thru-hull and the strainer, your check valve will likely start to catch stuff on its internals. It will also reduce the suction head to the pump, potentially causing problems with the pump impeller.

I had a problem with cooling of my genset that took 7 years to figure out, and it was due to a jellyfish quill (cartilege(sp?)) stuck in a right angle tailpiece installed on the thru hull valve. The rest of the jellyfish made it to the strainer, where I cleaned it out, but it took me 7 years to finally determine that the remains of the jellyfish inside the tailpiece were enough to starve the genset of water. It worked well in the cold NW European waters, but in Florida, the water is much warmer.

And the only way to verify that the check valve is clean is to remove it from the hose and open it up, which is not as easy as inspecting a strainer.

[NZL50505]

Yes I’ve added a smear of Vaseline to the Vetus strainer cap but even if that is airtight there’s nothing to stop the seawater draining back down because the genset (and it’s pump) are well above the waterline.

So I think my plan to tackle this is to progressively:

1. Remember to open/close seacock every time I start/stop genset
2. Try different brand of impeller (apparently Jabsco last best)
3. Install non-return valve (probably just above strainer sounds best)
4. Install an electric pump that activates during the 8-10s priming period when the genset is preparing to start. Apparently this is enough time for an electric pump to push water up to the raw water pump to ensure the impeller is wet if any water has drained back since last stopped. And I gather some people have even replaced their genset raw water pump entirely with an electric pump - which might be another final stage option.

[Charlie-Bravo]

Sorry, I mis read your post which clearly states genset..... my mind was on engine water, as you say , the genny being up higher is a different problem.

Your plans sound good, but choose the non return valve with care, a lot of 'plumbing' based nrv's are 'check valves' which do work preventing a large reverse flow, but do allow seepage backward over a little time, and might just hold the pipes full for a day.
And just another idea, you could install a solenoid valve that opens when you start the genny and shuts when you stop, or even a manual switch near the genny start, ... might be easier than grovelling in the bilge for the seacock , ...... more to go wrong as well I guess.
All the best with it.
CB

[rxc]

I agree with Charlie Bravo. It will be tricky to find a good check valve that will not impede the flow, and very few check valves are intended to prevent all backflow - they just prevent gross flow when subjected to sufficient back pressure. With little pressure, they are bound to leak back and leave you in the same position you are in right now. You also have to mount them in the right orientation so that they do not flop open as soon as the flow stops.

A pump requires electricity - maybe you could rig up a 12V bilge pump, below the water line so that it is always full of water. However, this still installs another (active) component in the flow path for genset cooling, which MUST work if you want to use the genset. Another point of failure. You don't want an AC pump, because this would mean that you need AC power before you start the genset - could be done with a dedicated inverter, but much more complex. A solenoid valve presents the same problems.

There are some new impellers (Globe is the name, I think) that can run dry. I have not tried them, but some people swear by them.

Question - where is your strainer located, relative to the thru-hull and the waterline? Is it far above the waterline, like our engine strainers are? They seem to stay full of water without a check valve, unless they get old and the gaskets dry out and harden. I have a Northern Lights genset that is about 15-20 ft aft of the thru hull, with the strainer about 3 ft from the thru hull, at just about the waterline of the boat, so it stays full.