Bilge hose "plugged" no discharge

[daviddp]

This is strange. I installed a new 1000 GPM Johnson pump recently thinking the old pump was bad. Several times prior I found the old bilge pump submerged. A week later I tried to manually start the new pump by holding my fingers on the test buttons when I found the pump submerged. The pump would run but no discharge of water out the thru-hull. The bilge is clean and set approx 3/4" off the floor on starboard. I don't think it is "picking up" foreign matter, the impeller is not blocked. I checked the thru-hull to be sure it was not plugged @ the exit. While I had the discharge hose off the thru-hull I blew into to it forcing air back into the pump and felt it clear and free flow after blowing hard into the pipe, it started pumping fine. 2 weeks later and the same problem again. The total run of the 1" corrugated pipe is approx 6' and approx 3' rise above the pump. Does the pump lack adq head pressure? The pipe has a few low spots based on how it gets out of the bilge and up to the thru-hull.

 

[Ron20324]

Google your pump model and see what the rise specs are.

 

[jviss]

If a 1000gpm pump can't pump over a 3' rise, then I don't know what you got. Corrugated hose is not the best, better off with a smooth bore.

Take the hose off your pump and stick it into an air horn and pull the trigger. That should clear any junk that's in there.

 

[dlochner]

The typical centrifugal bilge pump can not pump air. The hose must run up hill all the way, if there is a dip in the hose the pump will airlock and not pump anything. Make sure there are no dips or low spots in the hose.

 

[daviddp]

Thanks David. That makes perfect sense and sounds like an ez fix. I took the joker valve out thinking that was restrictive. I'll put that back in to assure a column of water and check the hose alignment. So I understand, when I was blowing into the discharge end of the hose to clear it when I removed it from the thru-hull I was pushing air out on either side of a water column?

 

[jviss]

What joker valve? And, if it had one, how could you have blown air in the reverse direction?

 

[dlochner]

What joker valve? And, if it had one, how could you have blown air in the reverse direction?

New bilge pumps often have a check valve (joker valve) built into the outlet. The stops the perennial problem of water back flowing from the discharge hose into the bilge. This would often start the pump cycling, water was pumped up and out the hose, the pump stopped, water flowed back down the hose and into the bilge starting the pump working again.

I was blowing into the discharge end of the hose to clear it when I removed it from the thru-hull I was pushing air out on either side of a water column?

Probably you moved enough water out of the way to let the air go through.

 

[JamesG161]

1000 GPM Johnson pump

You meant 1000 GPH or gallon per hour and NOT M=Minute
That pump does have a back flow preventing check valve, that is removable.
I don't have one installed, because I like the slight back flow to clear the slotted screen on the pump.
It would take a very long 3/4" line, back flowing, to have a continuous cycling.
So, if your last pump didn't cycle on and off, No worries about your line length.
______
A centrifugal pump suction needs to be submerged, but the float switch assures that it true.
______

if there is a dip in the hose the pump will airlock

I normally agree with Dave, but not here. The Johnson pump manual does say that. Airlock is a bad term.
If the "joker valve" is removed, this is not true.

Discharge hose "Dips" will hold a bit of water, but will not airlock. [They might prevent a bit of back flow, if you you use the "blow in end" method of testing]
______

2 weeks later and the same problem again

You have a dirty discharge hose and/or something restricting the slotted suction screen.
Jim...

 

[odaydokay]

Loose hose clamp somewhere?

 

[Pirate Dave]

Air lock. Get you garden hose and shoot a stream down it until the water exits then reconnect. Problem solved

 

[jviss]

Air lock. Get you garden hose and shoot a stream down it until the water exits then reconnect. Problem solved

Explain to me how there can be an airlock on the output side of a centrifugal bilge pump.

 

[Pirate Dave]

Read his first post. He blew the water out..

 

[JamesG161]

Explain to me how there can be an airlock on the output side of a centrifugal bilge pump.

I can, if there is a check valve and a BIG Dip.

The Dip can act like a "P Trap" and that Dip creates a big back pressure. The discharge pressure needed may be too large to overcome.

Like I said, Airlock, is a bad term to use.

 

[dlochner]

Explain to me how there can be an airlock on the output side of a centrifugal bilge pump.

Here's the answer:

The hose must run up hill all the way, if there is a dip in the hose the pump will airlock and not pump anything. Make sure there are no dips or low spots in the hose.

The dips work like the trap on your kitchen sink. The pump is not sufficiently powerful enough to push the water out of the trap. Bilge pumps are high volume, low pressure pumps. If the pump was a diagpham pump, the air lock would not be an issue.

 

[FastOlson]

(opinion) Small and even mid size centrifugal bilge pumps are marketed on price and misleading performance hype.
Get a positive displacement (multi chamber) bilge pump. And as already pointed out, use only smooth-bore hose.
Our boat came with a pair of Jabsco 37202 pumps. Always reliable. They actually put out their "rated flow".

Aside: if your existing bilge hoses are over 20 years old, there is a chance that they are cracked and have some leakage also. Safest to replace 'em.

 

[JamesG161]

The dips work like the trap on your kitchen sink.

Now Dave and I agree!!!

The Dip can act like a "P Trap" and that Dip creates a big back pressure.

 

[jviss]

The pump is not sufficiently powerful enough to push the water out of the trap.

I'll take your word for it, Dave, but I still find it hard to believe. We know, for example, that the pump is powerful enough to move ALL of the water that's in the output hose, which, in my C36, could have been as long as 20'. That's a lot more water weight, going uphill, than one would encounter in a short down-dip.

 

[JamesG161]

It is the Check Valve, "Joker Valve", that is the problem with the DIP'ing.
Remove that valve, no problem with a DIP.
Why?
Then you don't have stagnant water filled discharged line that grows "stuff" in it.
____
Normally at such low flow, even friction loss from a corrugated pipe is no issue.

Only the height of water from discharge to thru hull, is the resistance.
Jim...

 

[jviss]

Normally at such low flow, even friction loss from a corrugated pipe is no issue.

Not so. See this:
https://www.boatus.org/findings/14/

 

[JamesG161]

I did all these calculations for a Rant by MaineSail and will find at link on a Rule Pump curve.
Search SBO for Rule Pumps.
Jim...