Explaining an Airlock in a Bilge Hose

Jeff: Thanks for watching jabscotech.com, I'm Jeff Lander.

Mike: And Mike Irving.

Jeff: And today, we're going to talk about Rule bilge pumps and avoiding dips and sags in your discharge hose line.

Mike: And the big thing is when you install your rule bilge pump it has to go continuously upward.  That discharge line, if it has any sags in it, it's going to create a water trap. We made a cool fixture to show you exactly what's going on.

So this is pretty cool. We have got some clear PVC hooked up to a 500 gallon per hour bilge pump and we've made it so that we can raise and lower the pump to simulate the water level dropping in the bilge. So when the water level goes down, the float switch shuts the pump off. Residual water in the line drains back down through the system. Now what happens is some of the water remains inside this little valley here, and there's a whole bunch of air that goes from here all the way up and over to the underside of the pump, actually to the underside of the impeller cavity. Now as the water level raises again, you still have that air bubble that goes from here up and over till just about there where that water level is. Pump switch turns on but it can't pump the water. And that's because these pumps are centrifugal style pumps; they’re are not self priming, which means the water has to be in contact with the impeller to be able to pump the water out.

That's a great example of an airlock right there. See that big air bubble on the underside of that running pump? That air cannot move through the system because of that trap right there. That water's got it stuck. It can't push through the system because of that valley; gravity is pulling that water down to the bottom of that little valley there and this air can't go anyplace. So the pump’s running but it just can't displace that air.

Jeff: So there you have it. We just showed you what happens when your Rule bilge pump has dips and sags in the discharge hose line.

Mike: Now the big take away is running that discharge line continuously upwards. If you have any valleys, that's where water is going to collect and you could cause an airlock. Well, my name is Mike Irving.

Jeff: I'm Jeff Lander. Thanks for tuning in to this episode of jabscotech. Hopefully it was helpful illustrating what could happen when dips and sags are in your discharge hose line come. Back soon we'll have more videos for you.