General Outboard Motor Water Pump Description and Operation

[99yam40]

why do they insert the statement
"If the impeller blades are short, they remain in contact throughout the RPM range, supplying full pressure."
if it is acting as a centrifugal at higher speeds by the vanes bending back away from the housing?

[boscoe99]

It is a stupidly simple speed volume system. The faster the speed the greater the volume.

I been studying water flow since I was in kindergarten.

[robert graham]

I understand that the pump acts as a positive displacement pump at lower RPM's and a centrifugal pump at higher RPM's....seems like an interesting item...

[fairdeal]

great theoretical issue!

now be prepared for Rodbolt to check in and tell us that its a stupid simple mechanism and you just need to replace the impeller regularly.....



"maintains an equal volume of water flow at most operating speeds" is an interesting statement.

Seems that is saying less about the pump and more about it discharging into a (largely) fixed restriction.

I do marvel at the very idea of driving the same pump (and expecting satisfactory results) at 650 rpm AND and 6000 rpm

[cpostis]

I'm posting this to get some feedback, also not so into watching the Dolphins getting slaughtered by the Patriots.

Per Seloc Marine Repair Manual:

"The water pump uses an impeller driven by the driveshaft, sealing between an offset housing and lower plate to create a flexing of the impeller blades. The rubber impeller inside the pump maintains an equal volume of water flow at most operating speeds.
At low speeds, the pump acts like a full displacement pump with the longer impeller blades following the contour of the pump housing. As pump speed increases, and because of resistance to the flow of water, the impeller vanes bend back away from the pump housing and the pump acts like a centrifugal pump. If the impeller blades are short, they remain in contact throughout the RPM range, supplying full pressure."

Now, if this is true, and knowing something about pump dynamics, this makes sense to me. Also, the operation of the pressure control (relief) valve as well.

Positive comments please.

Thanks all!