Brass or Stainless steel Raw water pump?

[BartW]

Have been doing service on a raw water pump from our toilet flush system;
Replacing a worn seal

I was wondering,
These pumps are 26year old (the IT pump manufacturer told me)
And seem in fairly good condition,
Not much growth inside.
And there is NO anode inside.

This pump has been filled with sea water permanently since 25years,
She might have had some service before my ownership, but is still working perfectly,
All original raw water pumps in the boat are brass.

The rawwater pump from the airco,
I have replaced that, during the first season that I owned the boat,
with a ordinary domestic 230V Stainless steel centrifugal pump.

Two questions,
- is it adviseable to use a stainless steel pump for raw water ?
- how come there is so little growth inside these pumps, ? no light ?
so far I never had to clean one of them,
there are quite a few; toilet flush(2), airco, anker shower, fire extinguishing, water maker (but that one is flushed after use),

thanks for advice

 

[Nick_H]

I recently stripped my airco pump, because like yours there's no anode in the raw water system, so I wondered if the impeller may have corroded away after 11 years. It had only minor corrosion, but the seal was leaking so I replaced them both as the service kit was cheap anyway. Mine has a SS shaft, with a bronze impeller and housing. I certainly wouldn't want to use brass, and it seems that the marine grade pumps are usually bronze, not SS.

 

[BartW]

I recently stripped my airco pump, because like yours there's no anode in the raw water system, so I wondered if the impeller may have corroded away after 11 years. It had only minor corrosion, but the seal was leaking so I replaced them both as the service kit was cheap anyway. Mine has a SS shaft, with a bronze impeller and housing. I certainly wouldn't want to use brass, and it seems that the marine grade pumps are usually bronze, not SS.

I think mine are also bronze, not brass,
sorry wrong wording

 

[MapisM]

Two questions,
- is it adviseable to use a stainless steel pump for raw water ?
- how come there is so little growth inside these pumps, ? no light ?

I believe bronze is actually better than s/s, B.
In fact, I've seen some MTU engines still running on their original bronze raw water pump impeller after 25 years, and counting...
Ref the lack of growth, I believe it has to see with both the lack of light and flow.
I mean, aside from when flushed, the sea water is essentially enclosed and stagnating in the circuit, and I think marine growth prefers a nicer environment, so to speak...

 

[QBhoy]

Lack of oxygen (or less than exposed to atmosphere anyway) would see to the lack of corrosion and lack of growth may be down to marine growth not getting through filter/strainer and not particularly being suited to settling on bronze type alloys ?
My thoughts anyway...