Tiny Hole Theory: Defeating Airlock on a Rule 800 w/Check Valve

[vanilladuck]

NOTE: If the ideas below seem reasonable, I'm contemplating a blog article to memorialize the findings. I've seen this forum thread, but didn't want to add to it as the content here is slightly askew from the goal of that thread.

With the number of rain storms coming through the SF Bay area recently, it's given me a good opportunity to see how the bilge pumps on SV Rumour are working -- and not. I realized a while ago that the shower bilge wasn't automatically pumping. No big deal -- water never goes down the shower drain in the floor of the head, so why would that fill up? Turns out with enough rain water down the mast and even without a redirecting gutter at the mast step... lots. Enough that it overfills the shower sump compartment and spills into the main bilge and forward into those ridiculous pockets under the forward cabin sole. The squishy cabin sole in the v-berth was a little unnerving.

The float switch was broken, but the pump worked when manually triggered. It was an old Rule 400. It would evacuate the shower sump and then all the water left in the red hose would drain back into the sump nearly filling it again (but not quite all the way). That seemed inefficient. Maybe I could improve the system, I thought. I know, a new pump & a check valve!



Ew, and gross.

I collected some parts after reading some threads and blogs around EY.o:

• Non-automatic Rule 800 centrifugal pump
• Water Witch Model 217
• Some hoses, new Scandvik clamps, host connectors
• My wiring tools, heat shrink butt connectors
• JBL speaker to play some shower sump blues

After wiring everything up, the new automatic system with the Water Witch worked perfectly. The first time. After evacuating the water and sucking some air, the Rule 800 would become air-locked and, when triggered again, would just spin pointlessly without moving any water.

Then I found this thread: https://ericsonyachts.org/ie/threads/factory-original-bilge-pumps-in-32-3.20451/ (wow!)
Then I found this blog article: https://ericsonyachts.org/ie/threads/factory-original-bilge-pumps-in-32-3.20451/ and related comments

So my choices are:

1. Leave the check valve in and risk airlock, thus disabling the effect of my handiwork
2. Take the check value out and let the water in the discharge hose drain back to the sump

I chose Option 3: Go fish

After a beer and a lot of searching on the internet, I came across some random post from a forum far far away which described these small holes on the sides of the newer models of Rule pumps. Or maybe I passed out in the port berth and was visited by an angel. Anyway, these tiny holes were designed to vent enough air so that the pump could defeat airlock. Check it out:



But these tiny holes are covered up with the blue tabs of the strainer which mounts on the bottom of the pump. I'm not sure they're actually doing anything when the strainer is installed. I decided to try a test, so I left the strainer off the pump and put everything back together WITH the check valve. Low and behold, after sucking all the water and some air, the Rule 800 was able to self-vent and pull itself out of airlock. Notice the jets of water directed sideways toward the end of the video clip:

I tested it repeatedly and then left this for a few days and a couple bouts of heavy rain. Went back to the boat and found:

• the shower sump only partially full of water
• the main bilge pump had not fired at all (previously it would have gone off 1-2 times with the same amount of rainfall)
• the forward cabin sole in the v-berth was not squishy (previously it would have been squishy)

So, I present these facts, unaltered and without reservation for peer review: is leaving these tiny holes uncovered a horrible idea? I think I'm getting everything I want... an automatic shower bilge, no runback, no airlock, no potential for dying float switch.

Some extra information:

• Yes, I have anti-siphon loops in the stern near the exit thruhull for the bilge pumps
• Yes, I have a centrifugal Rule pump in the main bilge - contemplating a move to a diaphragm pump though for the main bilge
• Yes, you can try and convince me that a diaphragm pump for both bilges would be better, and you're probably right But really I want to evaluate the efficacy of The Tiny Hole Theory
• Yes, if I leave it this way I will probably drill a tiny hole in the blue tab and reinstall the strainer

 

[jtsai]

I wonder if the blue plastic strainer is asymmetrical and the air lock preventer hole is exposed if the strainer is flipped. It is puzzling why Rule would build in this feature then blocks it with a strainer cover.

I am 1,500 miles away from my boat visiting daughter in San Francisco for few days, yes, it has rained a lot. Beautiful area!

 

[G Kiba]

Excellent write up as usual Bryan! I have been fighting my own bilge wars as well. That with poor wiring from a previous owner shorted out my float switch and melted it. Glad there was no fire.

 

[Kenneth K]

But these tiny holes are covered up with the blue tabs of the strainer which mounts on the bottom of the pump. I'm not sure they're actually doing anything when the strainer is installed. I decided to try a test, so I left the strainer off the pump and put everything back together WITH the check valve. Low and behold, after sucking all the water and some air, the Rule 800 was able to self-vent and pull itself out of airlock. Notice the jets of water directed sideways toward the end of the video clip:

Yeah, I think you totally cracked the code on Rule's new pumps.

The "tiny hole" or priming hole is something I read about a while back on another boating site where someone was trying to explain how to get around the problem of air-locking with check valves. They relayed a story about a sump pump setup in a commercial building. The installers were scratching their heads over why the system wouldn't pump. Then, the "old guy" asks if they remembered to drill the priming hole at the bottom, which, of course, they had forgotten. With the priming hole drilled, they system worked as advertised.

I bought one of the new Rule 500s (with check valve and vent holes) earlier this year so I was interested in the new configuration. I found that if you block the intake port at the bottom of the pump and blow into the exhaust port, you can hear air passing through the vent holes with or without the blue strainer in place. Your video shows that (although they should work either way) the vents are likely more effective with the blue strainer removed. I suspect Rule's decision to hide the vent holes behind the strainer is a bit of slight-of-hand on their part. I.e., if people witnessed their pumps spraying water out the side, how many would return their "leaky" pumps, or perhaps, try to plug the holes for better output. So, Rule chose to pump the vented water into the sides of the strainer so you can't see it "leaking" and refilling the bilge slightly as it pumps. Since the vent holes are located behind the push-in (disassembly) tabs of the strainer, the holes should only be blocked while pushing in on the tabs, but not while the strainer is locked in place.

I actually think a vent hole(s) would be most effective located just outside the pump, at the base of the discharge nozzle, since the vent hole is trying tease the flow of water in the proper direction through the pump until full-flow pumping can be achieved. Instead, Rule placed the vent holes at the top of the pumping chamber (at the same height as the discharge nozzle). Apparently, this is sufficient to encourage the proper flow pattern while still allowing them to "hide" the holes behind the strainer.

The vent holes likely do reduce pump output a bit, but in setups like our Ericson's, I'll bet this is a much lower efficiency drop then it was to have the whole length of the hose backflow into the bilge.

Also, note that if you're mainly dealing with fresh water in the mast bilge, Water Witch float switches have a warning that they sometimes fail to trigger in rainwater.

 

[Marlin Prowell]

Our boat has two bilge pump switches. The primary switch is a Water Witch and up higher is a traditional float switch. Perhaps a PO was solving the problem of the Water Witch not always triggering when gallons of rain water came down the mast.

 

[Kenneth K]

Our boat has two bilge pump switches. The primary switch is a Water Witch and up higher is a traditional float switch. Perhaps a PO was solving the problem of the Water Witch not always triggering when gallons of rain water came down the mast.

Do both switches activate the same pump?

 

[Marlin Prowell]

Do both switches activate the same pump?

Yes. I have three short busbars near the bilge pump: ground, unswitched +12VDC, and bilge pump. The pump is connected to the ground busbar and the bilge pump busbar. Each bilge switch is connected to the +12VDC busbar and the bilge pump busbar. When either bilge switch activates, it provides power to the pump.

There’s even a wire coming from the bilge pump toggle switch near the nav table and it is connected to the bilge pump busbar. Flipping that switch to Manual puts +12VDC on the wire and this also activates the bilge pump.

 

[Kenneth K]

Yes. I have three short busbars near the bilge pump: ground, unswitched +12VDC, and bilge pump. The pump is connected to the ground busbar and the bilge pump busbar. Each bilge switch is connected to the +12VDC busbar and the bilge pump busbar. When either bilge switch activates, it provides power to the pump.

Sounds like a good setup. Better than the factory original.

 

[vanilladuck]

Tonight I went to examine the strainer a bit more. The inside of the tabs is completely smooth.

I drilled a hole in each side to match the hole on the side of the Rule 800 pump and reinstalled the strainer. Several tests proved it all works as before with the strainer removed. Woo hoo!

 

[Kenneth K]

Interesting. So, is what you're saying that:

Straight out of the package, the pump doesn't actually work. One either has to remove the check valve (and accept flowback, like the old pumps), or enlarge the vent holes (drill through the strainer) to get the check valve to work?​

​

That would be a brilliant failure on Rule/Xylem's part.

And, if one were to remove the check valve (which also opens the inner diameter of the pump nozzle by about 50%), they would be better off blocking the vent holes as well, which effectively turns the new pump back into the old pump which it replaced.

 

[Tin Kicker]

Slight tangent but since the Ericsons always have a bit of water in the bilge, note that DIY Dry Bilge systems are very easy to put together for $50-ish or less.

A dry bilge for $50

Water in the bilge, even small quantities, is a recipe for bad smells and generally unpleasant results. Every boat I've owned accumulated water somewhere that a traditional bilge pump couldn't entirely remove. I've long been aware of commercial kits designed to completely dry bilges, but the...

panbo.com

Or you can pay up to $1,000 for a commercial unit.

 

[Loren Beach]

Or, for usually $5 to $7. :

"Batteries not included" Or needed.

 

[Kenneth K]

A dry bilge for $50

Water in the bilge, even small quantities, is a recipe for bad smells and generally unpleasant results. Every boat I've owned accumulated water somewhere that a traditional bilge pump couldn't entirely remove. I've long been aware of commercial kits designed to completely dry bilges, but the...

panbo.com

Interesting pump. Uses 3/8" dia hose so it might make adding a new thru-TAFG installation simpler. It's low output, but that would be fine for water entering through the mast. I hadn't heard of Seaflo until recently, but now I see them a lot more, mostly via Amazon.

SEAFLO: Most Professional DC Pump Manufacturer in China for 13 Years

SEAFLO specializes in the R&D, manufacturing and marketing of micro pumps, blowers, pressure system, fluidic devices, sprayers, blow-mould kayaks and accessories, which are used in yachts, RVs, Industrial, Agricultural & Water Sports applications.

www.seaflo.com

 

[vanilladuck]

Interesting. So, is what you're saying that:

Straight out of the package, the pump doesn't actually work. One either has to remove the check valve (and accept flowback, like the old pumps), or enlarge the vent holes (drill through the strainer) to get the check valve to work?​

The pump works fine as long as a specific condition is met: the pump must never be allowed to run completely dry. If the check valve is installed and this happens, airlock is induced. If the check valve is removed, the pump should be able to re-prime itself.

The problem with the setup on Rumour is that I'm not able to get the pump to run automatically and not run the shower sump dry. This is due to the timing on the Water Witch switch.

And, if one were to remove the check valve (which also opens the inner diameter of the pump nozzle by about 50%), they would be better off blocking the vent holes as well, which effectively turns the new pump back into the old pump which it replaced.

I don't know about that. Saying that a 800gph pump is the same as a 400gph pump would be empirically false. I don't have a measurement for how much water exits the vent holes either ¯\_(ツ)_/¯

 

[Kenneth K]

I don't know about that. Saying that a 800gph pump is the same as a 400gph pump would be empirically false.

Yeah, sorry, I wasn't referring to your specific installation here. I was referring to the "evolution" (or lack thereof) of the new Rule pumps.

If the Average Joe is now forced to remove the check valve to get his pump to work, then Rule has really made no improvement versus the old pump.

 

[Kenneth K]

The pump works fine as long as a specific condition is met: the pump must never be allowed to run completely dry. If the check valve is installed and this happens, airlock is induced. If the check valve is removed, the pump should be able to re-prime itself.

The problem with the setup on Rumour is that I'm not able to get the pump to run automatically and not run the shower sump dry. This is due to the timing on the Water Witch switch.

Well, the important thing here is that you figured out how to make it work.

The rest of this is purely academic, but my understanding of things might be a little different from yours. Here's my take: These pumps can't really ever "run completely dry." Not only are they "submersible," but they actually must be submersed (both inside and out) for them to do anything at all. So, at the end of the pump cycle, the pump isn't actually pumping any air into the lines--centrifugals can't pump air (so it's not creating an airlock). The pump body is still full of water that is just "hovering" above the spinning blades. The discharge hose is also still full of water. Only when the pump stops spinning, and gravity pulls the remaining water out of the pump body (and the hose, up to the point of the check valve), does air enter the system. Then, on the next pump cycle, even though the bottom of the pump is now submerged again, the check valve has trapped the air that entered the pump body after its last shutdown. The pump blades are likely only partially submerged due to the trapped air. This is the first purpose of the "tiny vents"--to allow that trapped air to escape the pump body as the pump begins to fill (from below) with water. It should only take a "tiny" hole to vent the air, especially in slowly rising water, and, thus, this should not have required drilling through the strainer.

So now let's say we're back at the start of the second pump cycle again--this time, the pump (and now the blades) are both submerged, as the vents have let the air escape the pump body as the water level rose. Once the pump kicks on again, there is still a second problem--the check valve is holding, say, 3ft of water pressure behind it. Before the pump can start moving water again, it must overcome this back pressure, but that's a hard thing for the pump to do. All the blades of the pump really do is push water outward (thus, the name centrifugal). The cylindrical pump body converts the outward flow to an upward flow, but the backpressure prevents the upward flow from exiting the pump nozzle--so the blades just spin the water without pumping it. This is the second purpose of the "tiny vents," to give the upward flow of water a place to go until the water flow gains enough momentum to overcome the check-valve's backpressure. I would guess that this is the reason you had to drill through the strainer; with the strainer in place, the vents were insufficient to pass enough water to establish a flow pattern that could overcome the check-valve's backpressure. Funny that Rule wouldn’t have figured this out before manufacturing.

Or something kinda vaguely similar to that.....