Swallow Yachts Forum > Technical

BC26 (and possibly other boats) ballast pump problem

<< < (2/2)

Nick Orchard:
Well the pump is all back together again now, and reinstalled on the boat yesterday. Turning it the other way up was slightly more involved than it should be on other boats as I have my fridge compressor mounted on the bulkhead and it gets in the way of the inlet hose. Without the compressor in the way you should be able to just turn it 180 degrees upside down and screw it back in the same holes. I had to glue another pad on a bit higher up, and it's also angled to give a better run for the hoses - see photo. When you turn it the other way up you will need to change the direction of pumping. You can either just switch the 12v wires round so the motor runs the other way, or you can turn the pump head 180 degrees. Switching the wires might sound easier, particularly as you may need to add more wire with the motor being further away, but it could cause confusion in future with the black supply wire connected to the red motor wire. Turning the pump head is just a matter of removing two nuts, turning it round and putting it back on again, so pretty simple.
One thing that I've noticed over time is that the system leaks air, so I have to prime the pump using the hand pump first otherwise it fails to suck the water up high enough to get to the pump. I think some air is getting in via the ballast/bilge changeover valve as you can see bubbles in the pipe, and also air is being drawn backwards through the Whale hand pump, and this is in spite of me installing a non-return valve in the line. Once it's sucking water it's ok, but it still slowly sucks the water back from the hand pump until after about 5 minutes it's just sucking air again and needs another few pumps on the handle. It takes about 20-25 minutes to empty the tank, but I seem to remember when new it took 15-20. 
If you want any info about refurbishing the motor then let me know.

(For some reason the thumbnail photo is rotated 90 but it's the right way up when you click on it for full size?)

Sea Simon:
Imho...Given that this pumps duty is to empty a ballast tank (and so, it's planned to run it dry at some point?), I'm  not surprised that this type of flexible lobe pump is starting to struggle as it ages. Never mind the inverted fitment causing sealing issues too!

These pumps depend almost entirely on the flexibility of the vane materials to operate, although casings will wear if pumping gritty/sandy water. I was astounded how much sand came in with the water ballast on my BRe, particularly when I  inadvertently left the fill/drain plug out while moored over sand for a few tides. So much sand that I  needed to actively flush the tank with a hose, while the boat was on a concrete slipway. Not that the Bre had a pump to fret about, but sand is HEAVY!
All vanes also need to be intact. If a vane is shed, try to find it!
These pumps are known to have relatively low suction capabilities.

Try fitting a new impeller? Apparently there are two different materials used, nitrile rubber or polyurethane. The polyurethane  impeller being preferred for self priming duty.

Copy parts are cheap enough (buy several, you'll need them if you plan to run it dry), they are imho acceptable for this non critical  duty (although I wouldn't fit some of these knock-offs to the similar pumps fitted for diesel engine critical cooling systems),   and they are easily fitted with simple tools.
An occasional dob of silicon grease (or Johnson pump lube - glycerine) thru that brass plug on the suction port might help lengthen service life?

Try and seal the suction line that is drawing air.

Perhaps fit a foot valve to the suction line, to try to keep fluid in the pump after it stops. The Whale bilge suction strainers can come with a foot (non return) valve incorporated.

AndyB:
Thanks for the advice Nick.

I have the same problem with the pump needing priming. I have only done this once but it is a shock the first time.

Navigation

[0] Message Index

[*] Previous page