Motor flusher question

[boscoe99]

Can someone please explain how a rubber impeller, single stage centrifugal pump, AKA a water pump on a outboard.....can be also a positive displacement pump?

I am not following that....never heard that before.

I am not understanding the centrifugal part. The positive displacement part I am.

Second diagram below is from Yamaha.

https://www.castlepumps.com/info-hub...ler-pump-guide

[99yam40]

when you spin it fast enough, the vane tips are no longer in contact with the cup outer diameter.
So it is no longer a positive displacement pump it is a centrifugal

[boscoe99]

I don't see a positive displacement pump becoming a centrifugal pump just because the vanes may not contact inner wall of the cup.

Centrifugal force should be acting to hold the tips of the vanes to the inner wall of the cup. And I can see the tips of the vanes riding on a thin film of water such that they are really not in contact with the cup.

But I don't see centrifugal force acting on the water to facilitate the flow of the water. The inlet port of the pump is becoming larger as the pump turns and the outlet port of the pump is becoming smaller as the pump turns no matter what the speed is. The outlet of the pump is not positioned at the point that it would be if it were a centrifugal pump.

Guess it goes to show how we can see the same thing and come up with different opinions as to what it is. Race, politics or pumps.

[99yam40]

I picked up some sea weed once and over heated a motor
alarm went off and I shut it down ,waited for it to cool off, and fired back up no water from tell tail.
played around for awhile fishing etc. but never could get a flow at low RPM.
had a line of storms heading my way and I could see the beach so I headed in to at least get into the river and land.
to my suprize when I opened up the throttle I had water flow out of the TT. and it did not over heat all the way back to the launch.
At home when I took it apart the impeller was about 1/2 the size it use to be,
and no way anything was touching the outer part of the cup.

I have faith that it acted as a centrifical pump.

but then someone could cut off part of the vanes on a pump and run it to see for themselves.

I see no way that rubber pump would not flex away from the cup when pushing that much water at high RPM

[Warren60]

Ok,the pissing contests need to stop please. The reason i asked about the motor flusher was to get the engine up to normal operating temp without putting it in the lake.
I had a hot soak fuel concern at the eletric fuel pump.(yes i am a mechanic). I found the positive wire going to the pump from the main relay in the main junction box was crushed. someone prior to me didn't route it correctly and i guess over time and a lot use the wires would seperate when hot.
I took the boat out yesterday and ran it,shut it down and fished and started again several times with no more issues. i believe I have it corrected but only time will tell.
Thanks again for all the help.
Warren

[boscoe99]

Ok,the pissing contests need to stop please. The reason i asked about the motor flusher was to get the engine up to normal operating temp without putting it in the lake.
I had a hot soak fuel concern at the eletric fuel pump.(yes i am a mechanic). I found the positive wire going to the pump from the main relay in the main junction box was crushed. someone prior to me didn't route it correctly and i guess over time and a lot use the wires would seperate when hot.
I took the boat out yesterday and ran it,shut it down and fished and started again several times with no more issues. i believe I have it corrected but only time will tell.
Thanks again for all the help.
Warren

Not much pissing going on here. If you want to see some pissing in action then head on over to The Hull Truth. Them boys like to piss like the proverbial race horses.

[pstephens46]

Ok,the pissing contests need to stop please. The reason i asked about the motor flusher was to get the engine up to normal operating temp without putting it in the lake.
I had a hot soak fuel concern at the eletric fuel pump.(yes i am a mechanic). I found the positive wire going to the pump from the main relay in the main junction box was crushed. someone prior to me didn't route it correctly and i guess over time and a lot use the wires would seperate when hot.
I took the boat out yesterday and ran it,shut it down and fished and started again several times with no more issues. i believe I have it corrected but only time will tell.
Thanks again for all the help.
Warren

These aren't pissing contests. Many regulars here debate back and forth while waiting for OP's to respond. In the process, such as this thread, things are learned. Especially by noobs such as myself.

Now over at THT you can observe some real pissing matches. Nobody is learning much over there. Most have no interest in learning anything.

[boscoe99]

I see no way that rubber pump would not flex away from the cup when pushing that much water at high RPM

If the water outlet was blocked or severely restricted then I could see that happening. The tips of the vanes flexing away from the inner wall of the cup that is. Such as might be the normal situation no matter what, where the vane tips ride on a surface of water. Kinda like a bearing floats on oil and does not actually contact metal.

Positive displacement pumps generally are not happy if the outlet is blocked or severely restricted. A piston type positive displacement pump can damage stuff if its outlet gets blocked. With a flexible vane type displacement pump the vanes moving away from the cup wall may act as a sort of pressure relief mechanism to prevent damage.

[99yam40]

I look at it as the pump is designed to give enough flow at idle to keep it cool.
when RPM rises the pump out put increases along with the heat from burning more fuel.
there is only so much water that can pass thru the cooling system so pressure builds to a point that the vanes will be pushed away from the walls.
Some motors have water pressure relief valves and some do not, but the pressure builds up to some point where it stops being positive displacment
the centrifugal part is the water being spun and moved by a rotor that is not touching the walls

[panasonic]

I am not understanding the centrifugal part. The positive displacement part I am.

Second diagram below is from Yamaha.

https://www.castlepumps.com/info-hub...ler-pump-guide

Sorry I got that backwards, meant to say flexible impeller is positive displacement pump not the other way around, as I posted. Was going on memory...see how good that is now.

I don't understand how it changes to centrifugal pump at higher speed either.

[panasonic]

at low speeds the blades make contact with the cup.
as impeller speed increases the blades actually fold back away from the cup and it is now centrifugal.
fairly simple concept that most outboards have used since the 40's. some old mercs and british seagulls did not use the two stage but used a centrifugal.

That sounds like a reasonable explanation and can see how that works Rodbolt. Learn something new everyday.

[boscoe99]

I thought you might have had it bass ackwards.

I suffer from Lysdexia from time to time myself.

[panasonic]

I think that the fwd motion of the engine as rpm increases is then forcing water in through the inlets and up to the WP inlet will have an effect on how the pump operates. Thoughts on that?

OP no pissing match going on here...we just like to debate the crap out of everything...and try to keep it civil as possible. Sometimes it becomes a pissing match, not often though.

[99yam40]

With the inlets on the side of the leg and screens on them I do not see water being forced up to the pump

[DennisG01]

Ok,the pissing contests need to stop please. The reason i asked about the motor flusher was to get the engine up to normal operating temp without putting it in the lake.
I had a hot soak fuel concern at the eletric fuel pump.(yes i am a mechanic). I found the positive wire going to the pump from the main relay in the main junction box was crushed. someone prior to me didn't route it correctly and i guess over time and a lot use the wires would seperate when hot.
I took the boat out yesterday and ran it,shut it down and fished and started again several times with no more issues. i believe I have it corrected but only time will tell.
Thanks again for all the help.
Warren

Glad to hear you got it all worked out. Good find on that hot wire!