General Outboard Motor Water Pump Description and Operation

[boscoe99]

I wonder where Mercury got their data from?

If from Yamaha then why is it not in the Yamaha book? Probably because some yahoo would install a pressure gauge and complain that his motor was deficient by about a half psi at 2000 RPM and demand a new motor.

Would be expensive for Mercury to perform tests to come up with pressure curves on their own.

If I had a Yamaha motor and Mercury branded that motor as their own I would surely have the Mercury manual over the Yamaha manual.

Question for fairwinds. Does the Merc manual show torque in lb-ft or ft-lb? I suspect that I know the answer but would like it to be confirmed.

[fairdeal]

Does the Merc manual show torque in lb-ft or ft-lb? I suspect that I know the answer but would like it to be confirmed.

[boscoe99]

Thanks much.

[robert graham]

http://www.tuthillpump.com/dam/2525.pdf

I would consider the Yamaha water pump to be a positive displacement pump and not a centrifugal pump. I guess others will see it differently.

I agree, Yamaha's description sounds like a positive displacement.....unless at higher RPM's the rubber vane tips ride up and away from the metal cup on a wave of water???

[zenoahphobic]

What Yamaha has to say:

Water Pump
The water pump is a rubber bladed impeller mounted in a housing and driven by the drive shaft. The top and bottom of the impeller create a seal against the surface of the housing and plate. The impeller blades also seal against the housing side and end surfaces. It is essential that no water leaks between these surfaces for efficient operation. The impeller is eccentrically aligned or off center in the pump body, and the impeller blades fluctuate as the impeller rotates. As the blades pass over the intake port, water is drawn into the pump. The blades are compressed during rotation due to the off set as they get closer to the housing wall. The water is discharged under pressure through the discharge opening.

Pressure Control Valve (PCV)
Since a higher degree of heat is generated in midsize and larger engines, the water pump facilitates a higher cooling system capability. Even when the thermostat is closed, the water pump operates and water is being pumped resulting in an increase in cooling water pressure. Due to this increase in pressure, water could start leaking through weak spots, such as gaskets. Should the water pressure rise beyond a certain point, a PCV valve has been incorporated which opens and dissipates the cooling water through a bypass passage to control the cooling water pressure.

Descriptions never describe properly what actually happens! The diagram also defies physics!!!
Remember we understand water does not compress, so why is the picture (and description) showing us that the water is being compressed - going from a large space into a smaller space? Absolute nonsense

These pumps are simply displacement pumps then become crude centrifugal pumps; the rubber vains must leave the walls to allow the uncompressible water to occupy exactly the same volume all around the pump.

[cpostis]

Descriptions never describe properly what actually happens! The diagram also defies physics!!!
Remember we understand water does not compress, so why is the picture (and description) showing us that the water is being compressed - going from a large space into a smaller space? Absolute nonsense

These pumps are simply displacement pumps then become crude centrifugal pumps; the rubber vains must leave the walls to allow the uncompressible water to occupy exactly the same volume all around the pump.

Well, looking at the link Boscoe provided http://www.tuthillpump.com/dam/2525.pdf beginning on page 40 of the document, in particular "Positive Displacement Pumps, Vane Pumps", It looks to me that Yamaha's pump design reflects such a pump. Rather than having "sliding vanes", Yamaha's has "flexible impeller blades" that in effect, perform the same function.

So I agree with Boscoe. And I believe Robert Graham's is close, however I don't believe the impeller blades will ever have a gap between the housing (Insert) IMO.

[boscoe99]

Perhaps it is semantics. Perhaps the better word would have been to say that the blades are creating a low pressure in the pump inlet and a high pressure in the pump outlet.

The vanes, being made of rubber are certainly compressible.

Water is considered to be virtually in-compressible but compressible it is, however slight it may be.

Low pressure in the pump inlet contributes to higher pressure water outside of the pump moving into the pump. High pressure in the pump outlet contributes to higher pressure water moving up the water pump tube to the block.

I love physics. Wish I had paid more attention back in school instead of looking at Peggy's tits all the time.

[boscoe99]

A centrifugal pump does not change the geometry of the vanes/blades. The positive displacement pump does.

The centrifugal pump depends upon centrifugal force to create water pressure. The positive displacement pump depends upon the creation of a low pressure area and then a high pressure area (depending upon whether the area is being increased or decreased by the position of the vanes).

The Yamaha pump is clearly a positive displacement pump. Nothing centrifugal about it. IMO.

https://en.wikipedia.org/wiki/Flexib...eller_pump.gif

[fairdeal]

I have to agree with Zeno's observation that the pump illustration appears to show a physical impossibility:



The cavity "E" just after the vane passes the intake opening appears clearly larger than cavity "A" - before the discharge opening is reached.

As he says, this is a physical impossibility unless some water has "leaked back" over the top of the vane from A to E.

But this is an "artist's conception" - not a technical drawing.

If, rather, the cavity volume decreases only while the discharge opening is exposed

then the vanes never need to "leave the walls".

And the pump is doing exactly as a positive displacement pump is defined in the link Boscoe posted:

"operate on the principle of filling, trapping, transporting, and forcing out "

[zenoahphobic]

A centrifugal pump does not change the geometry of the vanes/blades. The positive displacement pump does.

The centrifugal pump depends upon centrifugal force to create water pressure. The positive displacement pump depends upon the creation of a low pressure area and then a high pressure area (depending upon whether the area is being increased or decreased by the position of the vanes).

The Yamaha pump is clearly a positive displacement pump. Nothing centrifugal about it. IMO.

https://en.wikipedia.org/wiki/Flexib...eller_pump.gif

I like that big writing reference to tuthill pumps. In it it says centrifugal forces are also present in vane pumps (IMO it also has to be).

That Boscoe Yamaha diagram shows the vane after passing the intake fully extended, my experience with these is that all the vanes are bent back significantly (at varying stress due to the "o"centricty of the design). So I suggest the vane(s) in the "transport" phase is/are bent much further back to equalize the volume in the chambers before being discharged.

I might also suggest that it is the spring in the flexing of the vanes that pushes the water out. This is the only way it could work if you believe no centrifugal forces are involved (but they are).

Not many tits in my physic's classes!

[fairdeal]

I might also suggest that it is the spring in the flexing of the vanes that pushes the water out. This is the only way it could work if you believe no centrifugal forces are involved (but they are).

I think the "spring" is essential for the recovery of the vane back to "intake position".

What pushes the water out is due to the eccentric positioning of the impeller in the housing -

the cavity of water between the vanes, is made to "disappear" as the vanes are bent back.

[zenoahphobic]

The Wikipedia pump, although again not a very good animation as it shows the same vane positions over the openings, clearly shows the centrifugal departure of the water (I know it did not mention this force).

[rodbolt17]

dunno.
do the maint or pay the repairs.
the pump housing in the picture is a scrap housing though.

[cpostis]

dunno.
do the maint or pay the repairs.
the pump housing in the picture is a scrap housing though.

Yep, replaced with complete kit after nephew decided to run the engine and drive the boat off the trailer at ramp before submersing the lower unit. Live and learn. 30 seconds max before I put my truck in park set the brake and yelled at his ass before he shut the motor down. My fault, I was the captain.

[robert graham]

Well, I thought I understood....but now I ain't so sure....but the pump works fine and that's what matters most to me!...