What causes normal performance degradation of flexible rubber impeller pump?

[sarah321]

Hello,

I know that over time a rubber impeller is going to get worn down and therefore performance of the pump will drop, which is why there is a recommended about of hours before replacing an impeller. But, what is the actual reason for this normal performance loss?

I would assume the rubber just gets worn down by the friction on the cam and then there is less compression between the impeller and cam and therefore decreased performance?

Thanks

 

[moltenmetal]

The volumetric efficiency drops due to wear and compression set on the elastomeric components. They stop being quite so "rubbery" and combined with wear, they no longer seal very well.

 

[EdStainless]

You have both the mechanical degradation (wear, compression set) as well as a degradation of the rubber (ageing and hardening or softening).
If it hardens you will loose flex and sealing, if it softens it will tend to tear easier.

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P.E. Metallurgy

 

[itsmoked]

What happens is the impeller starts losing arms!
I've seen many when you open them up and two or three arms are missing. As you can imagine each loss causes a step drop in performance.

Which brings up another point. Whatever is being supplied by a rubber impeller pump needs to deal with passing impeller arms. Either it can't care or you need a filter or screen to catch them.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TugboatEng]

I feel that cross-linking is the primary cause. Cross-linking causes the rubber to harden so that it cannot conform to the housing and causes it to get brittle and break vanes. Both of these are failure modes for flexible impeller pumps. Running it dry will cause premature failure every time but all flexible impeller pumps suffer from a short lifecycle.

 

[btrueblood]

Hm. Never seen an arm fail before loss of head/flow due to leakage. But then, we were using the pump to push pretty dirty water with sand and fibers in it.

 

[itsmoked]

Rubber impeller pumps are de rigueur in boats. They pump the water thru the exhaust manifolds for cooling and often the galley faucets. Half the time you open one arms are missing. LOL

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TugboatEng]

They're very sensitive to dry running and that's not uncommon for boats that are in and out of the water or operating in areas that have lots of fouling potential.


However, there is one engine manufacturer that insists on using flexible impeller pumps for closed cooling circuits and those do start shedding vanes after 3000-5000 hours in service. Their centrifugal pumps only last about 8000 hours so I guess the flexible impeller pump is lower cost over the lifetime.

 

[itsmoked]

They're often very easy to change out. If that's the case then you can change them every X oil changes and avoid shed arms all together. If they're in a lousy location and a problem to change then you'll be haunted.

Keith Cress
kcress -

http://www.flaminsystems.com