water pump impeller

[harrytom 648]

replaced my impeller  and have done  it in after 20hrs running,took back to manufacturer and they gave a bit of a run around.

Last sunday motored down panmure river water coming out of exhaust,ran for 1.5hrs,  2 hrs later started motor up and no water,bugger,pulled pump apart and found when turning pump impeller stayed put but shaft and brass insert of impeller turned,what would cause this?

luckily member of c/g and towed us home and safely on mooring,(wind and outgoing tide same way so sailing up not really a option)

Manufacturer said worn (really 20hrs)overheated no water?something lodged in impeller(no we have a onboard strainer)

 

check water from seacock plenty coming in,checked strainer inside,full of water,checked inlet water,checked outlet water.disconnected outlet and blew, motor clear.

brought new and fitted new impeller and no problems now.

 

Suspect manufacturing fault?

Thoughts please.

 

 

[ballystick 73]

I had that happen to my Bukh and I was advised that problem was from a blockage on the inlet side. I inspected the intake hose carefully and it showed signs of collapsing, I replaced it with a fully reinforced hose and there has been no problems for a couple of years.

[Island Time 1,239]

Yep, usually caused by blockage. Can be seacock wasn't on, physical obstruction, or, as above an overly soft intake hose collapsing under suction. The heat buildup causes the vulcanising to fail.

Of course it could be a crap impeller, but unlikely if it was a factory one.

[wheels 543]

Restrictions on the suck side tend to damage Impellers. Pressure not so much. Except if the pressure side restriction stops the pump. However, a restriction on the pressure side can cause the pump to not be able to pick up the water fast enough and the Impeller can over heat.
Make sure the input to the heat exchanger is free of bits of Rubber from the old impeller.
 

[harrytom 648]

was unsure how old the previous impeller was so fitted a new one,same connections on suck/outlet,cannot understand why new impeller only lasted a short time.

 

yes water was on as we had motored for 1.5hrs,sat at rest for 2hrs so cannot understand why? only thing that comes to mind is a bag or something got stuck on inlet under hull when started motor? tend to think manufacturing fault but who knows one of life's little mysteries

[Marshy 30]

There was a batch of dodgy volvo impellors - we had one on Cosa Nostra's old motor do exactly the same thing - was it Volvo per chance?

[harrytom 648]

no it was fynspray on a yanmar $94 for new impeller.crazy

[Island Time 1,239]

Visually check the hose from the seacock to the raw water pump, while the engine is running at maximum rpm. If the hose is at all out of round, replace it. They can suck closed when old and soft, and bounce back to normal when the revs are low or motor off.

[harrytom 648]

thanks I/T will check,no harm in replacing hose.

[wheels 543]

There was a batch of dodgy volvo impellors.

 

I can remember there being a problem, but a long time ago now. Way back when I was on CF. And it was not just a Volvo issue. I remember Yanmar being affected as well.

It comes down to what engine used the particular Pump I would expect, because the pumps are not made by the Engine maker. The issue was that the Bronze centre of the Impellor would let go of the Rubber and spin without driving the rubber. Of course as per usual, the manufacturer declined there was any problem, but the issue became a very wide spread problem and discussion at the time. We never did come to any conclusion as to what the problem was, if it were a faulty batch or some other issue causing the Impellor to fail. So I really can't say for certain it was a faulty batch. It may have been some other situation that simply puts too much load on the impellor (like a plastic bag as suggested) and this particular type of impellor fails at that point.

[too_tall 15]

On a related note, what sort of pressure is going to be on the output side of the pump? I am guessing only .2 bar or thereabouts? After all, there should be not much restriction through the exchanger or injection to exhaust. But no doubt there is enough that a suitably sensitive pressure switch could be installed to sound an alarm should the pump not be pumping sufficient water for whatever reason?

[harrytom 648]

just checked fynspray site for my pump,30 seconds dry impeller then stuffed,not a lot of time to stop motor.raw water pump also feeds water to dripless gland. .going down today and replacing hose from cock to strainer and strainer to pump and pump to engine.might disconnect pump and force water through engine(fresh) and give strainer a good clean.

giving myself bet chance of avoiding another failure.

[Romany 162]

related post too - anybody able to advise how to withdraw shaft etc as shown on photo? Yamaha 2hp with FUBAR impellor.

[wheels 543]

 

On a related note, what sort of pressure is going to be on the output side of the pump? I am guessing only .2 bar or thereabouts? After all, there should be not much restriction through the exchanger or injection to exhaust. But no doubt there is enough that a suitably sensitive pressure switch could be installed to sound an alarm should the pump not be pumping sufficient water for whatever reason?

That's one way to do it TT, or use a flow switch. It's a simple little paddle that moves with the water flow, but if the flow stops, the paddle comes back center and trips a magnetic switch.

 

Harrytom, when you fit the new impellor, use so KY jelly to lube it up real good. Damage can be done to the impellor the first time you start up before it gets water to the pump.

[wheels 543]

 

anybody able to advise how to withdraw shaft etc as shown on photo? Yamaha 2hp with FUBAR impellor.

It should just pull out of the box.

[harrytom 648]

That's one way to do it TT, or use a flow switch. It's a simple little paddle that moves with the water flow, but if the flow stops, the paddle comes back center and trips a magnetic switch.

 

Harrytom, when you fit the new impellor, use so KY jelly to lube it up real good. Damage can be done to the impellor the first time you start up before it gets water to the pump.

little bit ahead there,gave the whole pump to shop and showed which way of rotation and got them to fit it knowing how tight they are.  yes I/T?intake hose was collapsing,had a kink so replaced.pumps well,2hrs motoring up/down river seems ok.

[Romany 162]

Thank you Wheels. Anybody else? I will say (and accept that I did not before) - it seems not to withdraw easily as most reasonable folk would expect.Even gentle (& I do mean gentle) persuasion from my old mans engineers hammer seems to make no difference.

 

I have read somewhere that there were some models where you had to remove a circlip from the bottom of the shaft (i.e. inside the 'gear' box - not

that this O/b has more than 1 gear). To get to it involved more stuffing around than is reasonable and I guess its fair to say the Yammy engineer who designed it may have had better days.

 

I'm hoping this isn't one of those motors.

[Island Time 1,239]

That's one way to do it TT, or use a flow switch. It's a simple little paddle that moves with the water flow, but if the flow stops, the paddle comes back center and trips a magnetic switch.

 

Harrytom, when you fit the new impellor, use so KY jelly to lube it up real good. Damage can be done to the impellor the first time you start up before it gets water to the pump.

flow switch is the way! On engines equipped with temp gauges and heat exchangers, it is possible to overheat them and stuff them without gauge or alarm sounding.

 

This happens when, for whatever reason, the fresh water side looses all it's water and the temp sensor is no longer immersed. No alarms, first thing is seizing, melted exhaust riser, or even a fire!! It can happen really quickly, and the only way to know is a flow switch, or perhaps a pressure switch.

Some reasons for a failure of this type can be a failed hose, frost plug etc. Can be a very expensive failure.

[too_tall 15]

That's one way to do it TT, or use a flow switch. It's a simple little paddle that moves with the water flow, but if the flow stops, the paddle comes back center and trips a magnetic switch.

 

Harrytom, when you fit the new impellor, use so KY jelly to lube it up real good. Damage can be done to the impellor the first time you start up before it gets water to the pump.

 I had not thought of a flow switch. I have many of them in differing applications around the farms too. Very simple and effective. Not the requirement to know the exact pressure first. Only downside is a pressure sensor could ( if it has 2 setpoints or is analogue ) sense both low pressure ( no flow ) and overpressure, indicating potentially a blocked exchanger. Getting a bit pricey to go to an analogue type setup though.

[wheels 543]

flow switch is the way! On engines equipped with temp gauges and heat exchangers, it is possible to overheat them and stuff them without gauge or alarm sounding.

 

Yes, but this can also be an improved system by using a Temp switch. Similar to a Temp switch used to turn on a Radiator Fan. You fit this into the exhaust just after the point the water is introduced. So with water flowing and cool, the switch remains open. But as soon as the water stops, the switch almost instantly closes because of the hot exhaust and the switch is connected to an alarm.

The issue I now have is one alarm and too many switches. If the Alarm goes off, I have to work out what set it off and by then the damages is likely too late