How big is your priming hole? It's possible that is too small. To find out, you'll want to pour-test the pump without the #10-32 side plug installed. If it works just fine like that, then your priming hole is too small. Re-install the #10-32 plug and start drilling the plug with larger and larger drill bits, repeating the test each time until it consistently primes.
This sounds promising. The current priming hole is 1/16”. I’ll try leaving the 10-32 out and see how it does and go from there. Thanks for your input.
How far off the bottom of the hull is the base? About 1/8-1/4" lets a nice puddle of water stay under the impeller. If you're sucking really hard you can create a void in the gaps that the water can't fill simply by dribbling in when you're not heavy on the damage. I've sometimes had to just leave the priming plug off on BC pumps when I don't do the top primer hole. Why? No idea. Voodoo I guess. Balancing the impeller is money because you don't wear out the bushings as quickly and get that SCCWWWEEEEEE as fast.
Well, starting to run out of ideas on this one. I tried a different outlet design by going to the more traditional sweeping tube as opposed to the 90 degree elbow to see if that changed anything. I tried leaving the 10-32 plug completely out. I even drilled 2 more vent holes in the top of the housing in each quadrant. So 4 total vents. All with no luck. My only guess is that this design can’t handle this high of an RPM and self prime. Like I mentioned, it will prime but it requires me to run it, then turn it off for about 3 seconds, then back on again. Or, have a significant amount of water in the boat before turning the pump on. Here is a picture of the bottom. The pump sits about .15 inches from the bottom of the boat. I’ve also tried combinations of no washers putting the base at about 1/8” from bottom and 4 washers putting it at 1/4” from bottom. No real differences in regards to priming ability noted. Here is the pump operating in the non-primed condition. Water was added to tub after pump was on. You can see water escaping from the extra vents I drilled. The big problem being the vortex of air that you can see in the clear outlet tubing. I have a slower RPM 12v motor coming today that I hope to test. Otherwise I’m still waiting for the new BC pump to arrive.
I am very curious about how to balance impellers, since early bearing failure was one of the many pump issues I ran into last year. Reducing the top speed of your motor will limit your pumping capacity, so how about throttling speed with an ESC? Plug it into a channel with a three-position switch or a dial, and then throttle your pump as needed. Run the pump at half-power until that's not enough anymore, then kick it up to full throttle.
Most rc airplane shops will sell an inexpensive propellor balancer. Basically a rod with little friction (magnetized or similar) that you put your impeller on. You let it settle then you remove material by drilling shallow holes from the rim of the heavy side until it is completely balanced. That was easy with resin impellers, not sure about plastic. Just google RC propellor balancer and you will get the idea. Not sure if helps though. Good luck John
http://www.portpolarbear.com/reports/How to Build a Pump.docx Also on the BC website if you click on the new BC large pump Charlie has a video on how to balance an impeller.
So here is a video of the test... View: https://www.youtube.com/watch?v=3sKp-o6CTVc There is initially some water in the boat and the pump is getting about 6v. I started adding more water and there isn’t much of a change. I add enough water that most of the pump is submerged and start adding power to the pump, probably up to 10v which for that motor is probably in the 12k RPM range. Still not a great improvement in pumping. Then I drop the voltage to zero and reapply, and off she goes.
You're describing how the pumps with big power generally work. They need some water to prime and they don't like "dry" priming ie running, then adding water. They like to stop, be wet, then prime and pump like a banshee. It looks fine to me, you might look at a deeper well for the pump to sit in so it collects more water locally to prime easier.
Here is my first pump test fail, I think I needed more power. If only Bob had helped me it would have worked. View: https://www.youtube.com/watch?v=UeCHrdeE1ys
Now that’s the good stuff! At this point I’m guessing it has to do with the housing or impeller design of the BC pump that has trouble dry priming at high RPMs.
one other thing to keep in mind. if there is insufficient volume to pull from, a high powered pump will generate an air path from the surface of the surrounding pond to the inlet of the p;ump. may look like it is not priming, when in actuality, it is just pulling air from the pool around it. see image here https://www.sciencedirect.com/topics/engineering/suction-pipe
I think I’ve finally had some success with the priming issue. The answer was actually already on this site, a drawing by SteveT showing pump outlet orientation. I had seen it before but it didn’t actually “click”. The pump outlet was too low in the housing, so I used a Dremel and took out some material and then filled the bottom portion in with Free Form Air epoxy dough and sanded as needed. The pump quickly primed from dry and running with water added to the bucket. She also primed quickly sitting in the boat as water was added. I may have to tweak which priming vent holes I want to leave open since I drilled a bunch of them .
https://rcwarshipcombat.com/threads/priming-hole-for-pumps.444968/#post-511154 My pump was literally an exact example of the “bad” pump outlet position.
Oh ya I’m definitely checking my pump! Bet it has the same issue. Wonder if enlarging the discharge out let would do the same thing?
When I first put this pump together I actually did enlarge the outlet from what BC had by just running a bigger bit through the existing hole. I’m not sure if the bit floated down or that’s just where the original hole was drilled but it was still too low in the casing. I should have taken a picture of the inside of the casing after I moved the outlet upward but I’d say the top of the new outlet was 1/32” to 1/16” from the very top of the inside of the pump housing. Originally it was well over 1/8”.
