General Outboard Motor Water Pump Description and Operation

[zenoahphobic]

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!...

Well they(Yamaha pump) seem to work fine for most for a while but a large number of people have some difficulty with them. I don't know of any other pump out there that raises so many issues.

But I don't believe that anyone really knows how they work. The Yamaha description and picture is absolutely hopeless. If I am allowed to have a further comment on it, what happens after the vanes pass the outlet? What is in the spaces and what is happening to the volume? The more you look into it the less is understood. Why don't design engineers write and draw the description, why are these tasks given to zombies that haven't got a clue??

Interestingly I recently spoke with a pump engineer wanting to buy my mother in law's car. Taking the opportunity to question him about an issue with a diesel injection engine on our Prado, he had no clue.

I love Physics, and often resort to the simplicity of the subject to prompt thought. So I purport all pumps employ centrifugal force, no matter what the design.

What is centrifugal force? It is very simple: all mass moves, and moves in a straight line. That is the basis of Physics. There is only mass (OK it's energy but we will leave Einsteins Theory aside), and it travels (all of it) at constant speed (at great speed) forever. This is a concept that most of the human race does not know! There is no force required to maintain this speed. Force is required to alter this speed. (F=MA) This change is + or - acceleration. Centrfugal force is just a term we use to describe when this force direction is constantly altered around 360 degrees. A centrifugal pump simply accelerates the water mass which is then constantly deflected by the pump walls, then finding an outlet where it can continue to travel in a STRAIGHT line.

There is no pressure involved with a pump! Pressure simply is a mathematical invention; something to do with force over an area, stupid really, force can only apply to mass.

So the more we learn the harder we understand, or what we believed is not really how things work. Pumps hah!

[cpostis]

Well they(Yamaha pump) seem to work fine for most for a while but a large number of people have some difficulty with them. I don't know of any other pump out there that raises so many issues.

But I don't believe that anyone really knows how they work. The Yamaha description and picture is absolutely hopeless. If I am allowed to have a further comment on it, what happens after the vanes pass the outlet? What is in the spaces and what is happening to the volume? The more you look into it the less is understood. Why don't design engineers write and draw the description, why are these tasks given to zombies that haven't got a clue??

Interestingly I recently spoke with a pump engineer wanting to buy my mother in law's car. Taking the opportunity to question him about an issue with a diesel injection engine on our Prado, he had no clue.

I love Physics, and often resort to the simplicity of the subject to prompt thought. So I purport all pumps employ centrifugal force, no matter what the design.

What is centrifugal force? It is very simple: all mass moves, and moves in a straight line. That is the basis of Physics. There is only mass (OK it's energy but we will leave Einsteins Theory aside), and it travels (all of it) at constant speed (at great speed) forever. This is a concept that most of the human race does not know! There is no force required to maintain this speed. Force is required to alter this speed. (F=MA) This change is + or - acceleration. Centrfugal force is just a term we use to describe when this force direction is constantly altered around 360 degrees. A centrifugal pump simply accelerates the water mass which is then constantly deflected by the pump walls, then finding an outlet where it can continue to travel in a STRAIGHT line.

There is no pressure involved with a pump! Pressure simply is a mathematical invention; something to do with force over an area, stupid really, force can only apply to mass.

So the more we learn the harder we understand, or what we believed is not really how things work. Pumps hah!

Zenoahphobic:
Because you love physics...

Look at this link (full of good information, or not) and the associated links within.

Classifications of Pumps

Consider these basic definitions within the link page:

1). The centrifugal or roto-dynamic pump produce a head and a flow by increasing the velocity of the liquid through the machine with the help of the rotating vane impeller. Centrifugal pumps include radial, axial and mixed flow units.

2). A positive displacement pump operates by alternating filling a cavity and then displacing a given volume of liquid. A positive displacement pump delivers a constant volume of liquid for each cycle independent of discharge pressure or head.

Now, a few basic question on Yamaha's pump design:

Is the velocity being increased from the center of the impeller to the outside diameter of the impeller?

Are the voids between the impeller blades being filled up and emptied?

Is Yamaha's pump design a centrifugal pump, a positive displacement pump, or a combination?

We can go on forever!!!

[zenoahphobic]

Zenoahphobic:
Because you love physics...

Look at this link (full of good information, or not) and the associated links within.

Classifications of Pumps

Consider these basic definitions within the link page:

1). The centrifugal or roto-dynamic pump produce a head and a flow by increasing the velocity of the liquid through the machine with the help of the rotating vane impeller. Centrifugal pumps include radial, axial and mixed flow units.

2). A positive displacement pump operates by alternating filling a cavity and then displacing a given volume of liquid. A positive displacement pump delivers a constant volume of liquid for each cycle independent of discharge pressure or head.

Now, a few basic question on Yamaha's pump design:

Is the velocity being increased from the center of the impeller to the outside diameter of the impeller?

Are the voids between the impeller blades being filled up and emptied?

Is Yamaha's pump design a centrifugal pump, a positive displacement pump, or a combination?

We can go on forever!!!

That ref. Classification of Pumps, although mentions a vast variety of pumps, chooses to classify them as TWO.

Nothing there that I didn't know or disagree with, except for the explanation of "increased viscosity increases volume in a positive displacement pump"????

In answer to your two questions on Yam Pump design:
Yes, the velocity is increased from the center of the impellor to the outside. Simple mathematics tells you that. The water travels faster on the larger diameter than the water on the smaller diameter, because it has to travel a greater distance in the SAME time!

The voids will always have WATER in them (baring some cavitation that may pull some dissolved gases out). Because the pump is totally submerged in water. The volume of the voids are forced to equalise because water is incompressible; the vanes must distort to achieve this (including the forcing of water over the vanes).

Physics tells you this much. We don't have a model or 3 dimensional drawing to date!

The essence of this thread was a call for an output graph. Simplistically, if you want to call this pump a displacement pump then it would be easy to calculate, because the defined characteristic of such a pump is that the volume is constant for each revolution. So measure the displacement volume and multilply by whatever revolutions take your fancy.

You will quickly discover that the Yam Pump in practice will not correlate!

So it is a combination (Cpostis word) if you like.

[99yam40]

I have a feeling if the water did not get between the rubber vanes and metal cup and plate to help separate them from each other and lubricate ,they would wear down a lot quicker.
these pumps work well and can last a long time. Many have proved this, but run into problems after years and cannot get the bolts out when needed.

If running to shallow water where sand/mud is picked up with the water the cup and plate tend to wear more along with the rubber.
It is best to take apart as Yamaha recommends to help make sure the bolts do not seize up from years of corrosion and it costs just a little more to buy new water pump kit to make sure all seals up well and the rubber does not fall apart when you really need it to keep going

[zenoahphobic]

I have a feeling if the water did not get between the rubber vanes and metal cup and plate to help separate them from each other and lubricate ,they would wear down a lot quicker.
these pumps work well and can last a long time. Many have proved this, but run into problems after years and cannot get the bolts out when needed.

If running to shallow water where sand/mud is picked up with the water the cup and plate tend to wear more along with the rubber.
It is best to take apart as Yamaha recommends to help make sure the bolts do not seize up from years of corrosion and it costs just a little more to buy new water pump kit to make sure all seals up well and the rubber does not fall apart when you really need it to keep going

This a very interesting topic.
I have had decades of outboard experience, and as I have posted before have had no problems with O/B water pumps, having rarely replaced them letting them go for years (12 yrs on 115 2st Yammy no issue) .
My earlier years attitude was that as long as there is water pissing you don't have a problem, no-one emphasized that time had to be a factor in determining replacement, although functioning, also.
Longevity was also achieved by never running in shallow (very active on trim button), and meticulous freshwater flushing. And as you suggest, water flowing over the tips of the vanes would be the only way to provide significant lubrication preventing significant expected wear over that long period of time.

I just looked up an old Seloc manual 1965-1979 Mercury's (Seloc mentioned in this thread). No mention there of how these pumps work, but it does use the term impeller. I am thinking impeller also implies a centrifugal pump! Having looked at the pictures, I am sure those Mercury engines' pumps actually were centric and not eccentric. If they were centric then the flexible impeller was chosen for better efficiency, and made for small cheap and simple.
I have an old Yammy used impeller that has the permanent deformed bent back vanes and spun it on my bench grinder (4000rpm); those vanes straightened out. Observed by the diameter increasing as motor spun up.
So this suggests centrifical force on the vanes plays an important part in the
operation. For instance it would act against the bending of the vanes against the pressure of the water. It would act as a flipper throwing the water out the outlet.

Now the question is, if you were to rotate the Yammy pumps backwards (assuming they could comfortably do that), which way would the pump water flow? I suspect exactly the same direction (maybe not very well), because it probably is a function of inlet and outlet size and design (which has not changed significantly by reversing rotation).