Fun with Bilge Pumps

As I finish up the bilge pump for my upcoming project I figured I would share some of my progress and testing. For whatever weird reason I really enjoy putting the pump together and getting it wired up. I also really like how there are so many little things you can do to modify or customize the pump itself to fit your boat's needs or to get a little more performance out of it. Based on some experience, but more on reading this forum and listening to the veterans at battles I would like to share what I've put together.

Major components:
-Traditional BC large pump
-RS-550s 18v brushed motor
-Turnigy 30A brushed ESC
-12v power source
-Flysky FS-i6X Tx



Pump Modification:

Starting with the resin cast large BC pump housing I bored out the pump outlet to make room for 3/8" copper tubing and a 3/8" 90 degree elbow. The copper tubing was soldered together and at the end of it is the standard BC 1 unit restrictor. This is the part that will protrude from the deck (premeasured for height to deck and any intruding superstructure). The reason for the immediate 90 turn to the vertical was to hopefully reduce priming issues (having air stuck in a horizontal plumbing component).

The next modification was to move the priming hole from the side to the top of the housing. Again, this is to help with priming. This modification along with some of the other items in this write up are thanks to the www.portpolarbear.com article: "How to build an awesome pump". To complete the move the hole in the original priming hole and set screw access nut was soldered over. The nut is still removable of course to access the set screw in the impeller. However, now that the priming hole was moved, a small high pressure stream of water leaves the housing at a 45 degree angle or so. I didn't really want water spraying all over the inside of the boat if it could be helped so I designed and 3D printed a diffuser that attaches to the exterior of the pump housing:



Testing has shown that this works well and a small fan of water sprays downward right next to the pump to be "re-sucked".

As far as other modifications go you can see from the above picture I added an aluminum heat diffuser to help with heat dissipation. This will be probably be unnecessary but in preliminary testing with the standard Johnson motor that comes with the pump it got very hot. I'm not so sure it would of been able to run at 12v for an extended period of time so I switched to the RS-550S 18v. The motor also has screen attached around the large opening to prevent debris from entering the pump during a sink and causing subsequent problems. I also plan on having the extra tubing attached to the end of the outlet that will be above the deck. Weather this actually improves output performance I don't know but it does keep the stream height to a minimum and angles it slightly overboard.

Pump Construction:

When assembling the pump I used RTV silicone to seal all the gaps. This included placing some around the motor and in the screw holes when attaching the motor to the upper housing. I then tested the motor to make sure I didn't over do it and get any silicone in any moving parts. I should have taken a picture during this process but I didn't. Again, portpolarbear has a great article on this process. Then the bottom housing and outlet tube got some silicone before being mated to the upper housing. Its good to test motor and impeller rotation after each of these steps to make sure everything spins freely.

The last item was to add the pump screen. This is so important! Lack of a screen is asking for pump failure and its a matter of when not if. Even if you operate in a really clean pond its your own balsa that's been shot into your hull that will be your demise if a proper screen isn't in place. Not to mention bbs! One inherent problem with just placing a small piece of screen over the pump inlet: enough debris build up and your inlet size has drastically reduced! You need to expand the protected area so that even with debris pulled against the screen there is still room for the water to be ingested. I found a hollowed out rectangle fish filter at a pet store that does this. I cut a 1/4" slice of it and added another screen to the hole. Now water can come in from all sides and still be filtered. My testing has shown that this particular filter does not impede the pump's ability to ingest water.



Pump Operation and Test Data:

One thing I read was that high RPM pumps can have a lot of trouble priming. Knowing that my FS-i6X had rotary knobs I did some testing to see if I could plug an ESC into the appropriate channel and use the rotary knob to control the speed. This was successful and as a result I can ramp up the speed of the pump to minimize priming issues. The ESC is a simple one-direction 30A ESC ($12) that can handle 12v. Before and after (added XT-60s and E6000 coating):


First test:
-Full throttle yielded 2.5GPM at 5amps
-Mid-throttle was less efficient and drew 13amps
-No priming issues if the water is there and the pump is turned on.

Second test:
-If the pump is running dry and water is introduced it has a very difficult time priming at full throttle. Throttle had to be reduced close to zero then re-applied after about 3 seconds and full pump stream was obtained.
-I determined where the highest amp draw was on the knob and marked it red. This is my "keep-out zone". Just under the red was about 1.0GPM and 2.5amps so that will be my "I'm not hurting yet but need to keep the water out" zone.



Well that's about all I have for now. Critique is always appreciated and if anyone wants to share additional info to help make a more reliable or better performing pump that is always welcome! As a final note I personally believe there is such thing as too much performance. I don't want to patch that many holes and watching my boat sink after a hard fought battle is still entertaining!

 

2.5 gpm is great at 5 amps. Best I got using the flow meter was 3.2 gpm, using 10 volts, with a 2 kv brushless motor. It was drawing 19 amps. Not bad really, very close to what a Stinger brushed draws.

Using a brushed motor the best I could get was 2.9 gpm, but at 42 amps draw, tried another motor, drawing 82 amps, and it would only do 2.94 gpm. The higher turn motors drew less amps like yours, and were about the same 2.4 to 2.6 gpm on the flow meter at less than 10 amps.

3.2 gpm seems to be about the limit out of the 1/8 outlet.

 

I have a brushless ESC (https://hobbyking.com/en_us/hobbyking-30a-boat-esc-3a-ubec.html) that I'm hoping to use for my pump motor; one of the programming options is Start Mode (Punch) - I believe it controls how fast the ESC ramps up the speed of the motor. I'm theorizing this can be adjusted to allow the pump to effectively prime before reaching max speed, as well as avoid current spikes, but I have yet to experimentally prove this...

 

You could use a model powerboat auto-bailer glued on the prime hole to stop the spray altogether and increase outlet pressure further.

 

Pump update. So the above pump lives in my Bayern. Although it pumps like an SOB it does have some serious priming issues. The one test I cannot get it to pass is thus:
1) boat on bench completely dry
2) turn on pump (I’ve tried multiple speeds since the pump is ESC controlled)
3) start pouring water into the hull
Desired result: pump begins pumping under load with full stream once water covers pump inlet.
Actual result: minimal pump stream with little change in load on motor. Essentially it’s not priming. It takes far too much water before the motor loads up and the stream really goes. Now I can get it to prime if I turn the motor off, wait a few seconds then turn it back on. What I’ve found however from a practical standpoint is that once it does prime it pumps the water out in a hurry and then looses prime until more water enters the boat. So with moderate damage I’m constantly trying to pump out then re-prime, etc. Bottom line is it’s taking away from my ability to pay attention to battling. I need it to be able to self prime as the water rises on its own at a decent water level.

The first post in this thread is the original pump build. Changes I’ve tried since then: removing fish filter and just putting the pump in a screen sack. Added about 1/8” worth of washers to raise the inlet of the housing off the bottom of the boat. Changed the priming outlet from the top corner as recommended by port polar bear and went back to the original side outlet (I think this helped a little for some reason).

The pump sits in a 1/4” water channel. Perhaps it needs to be deeper? When the pump does prime it gets almost all the water out until loosing prime, but again, it seems to take far more to get it re-primed.

Anyone have any other thoughts I could try?

 

Have you sealed the bushing of the motor to the pump housing with RTV? That has helped priming issue in the past.
If you used the “corner” vent hole did the vent hole in the side get sealed. Once you opened the side vent back up did you seal the corner one.
Have you tried balancing the impeller? The set screw on one side make the impeller pretty heavy on that side. I balance mine by carefully drilling out some plastic on the top of the impeller near the set screw. Very carefully.

 

Thanks for the responses guys. The motor was sealed to the upper housing using RTV. RTV was applied to the screws, shaft base (bushing?), and the perimeter of the motor can itself. The two halves of the pump housing were also RTV sealed. When I initially moved the vent hole to the upper corner of the pump housing, yes, the original vent hole was sealed with solder. During my recent testing I actually tested with the old horizontal vent hole open along with the upper corner vent hole. There seemed to be some improvement, but probably a loss of overall efficiency. I then e6000’d over the drilled corner outlet so currently the only vent is the original horizontal one.

The one thing I have yet to do is the balancing. Perhaps given the higher RPM this plays a fairly large roll? I know Charlie has a video on how to do it and PPB has some guidance too so I can certainly get that done.

Greg, do you have a picture that would better explain this “dead air cavity”? Where is this hole on the backside of the impeller drilled? In the housing somewhere? Is that the same vent that BC has in their pump housing or are you talking about something different?

Thanks again for your help

 

I’m curious to know how you get this resolved. I have the exact same issue. Toggling the pump on and off is a pain.

 

Some more pictures that might help with diagnosis.




The only thing so far that comes to mind as a source of trouble is that there was a pretty large gap between the top of the housing and the impeller which can be kind of seen in the last image.

 

The higher RPM might be making the wate cavitate too much. Air bubbles are bad.

 

Sucking air down the shaft bore, not a good thing. Nick might want to edit that?
Too long a run of outlet hose causes airbind in some cases?
I like to go up and out, like the photo.

 

I like that pump. It’s shiney and chrome looks fast. Do you build those for purchase?

 

This years run is spoke for. I do run production once a year, starting in December.

 

I've had a lot better luck with the new injection molded BC pumps. Have you been using a solid 10-32 plug? Using the drilled plug in addition to vent hole you have at the top can help

 

That is my back up plan, I’ve already got the new BC pump ordered. Question is, will it get here in time for the next SCRAP battle on Feb 1.

I’ve got the impeller pretty well balanced and I’m going to try some other tests on this pump in case I don’t get the new one in time.

 

Just from my personal experience I had the same problems from the new BC pump. I Still have to toggle the pump on and off.

 

what motor/voltage combination are you using? Multi-B to switch it on or ESC or other? Curious to see if there are similarities to my set up.

 

I’m running brush set up 550 motor. Pump switch from the B-board with 3s lipos.