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carioca1232001
09-01-2016, 08:55 AM
Both diesel engines on my boat are fitted with Johnson F-7B self-priming, raw-water pumps for engine cooling.

They had been fitted with GLOBE Works 'blue impellers' and worked flawlessly till of late, when the impeller on the port pump gave up while running on the hard (reduced flow of water in the supply hose).

Decided to change impellers on both pumps with JABSCO ones I had in stock, noting that the 'blue impeller' on starboard pump was still in perfect running order .

Turned on the engines again to verify satifactory operation when starboard pump with the new JABSCO impeller refused to draw water.

Put the the original 'blue impeller' in - and it worked perfectly !


Any thoughts ?

Could minor differences in impeller dimensions between GLOBE and JABSCO be the cause of this ?

More wear on the starboard pump housing and/or on the 'plate' that folds the impeller vanes ? ?

Breakaway
09-01-2016, 09:02 AM
Impellers have a direction. Did you put the replacement in the correct way?


Kevin

DeniseO30
09-01-2016, 10:15 AM
Most definitely impellers have to fit snug! I had the reverse problem with the blue impellers, they did not work in the pump on my boat's engine.

Usually the self priming is lost because of air getting past the ends of the impeller from a worn cover and or back plate or housing.

Figment
09-01-2016, 10:22 AM
Dad had the same problem a few years ago. In his case, one of the replacement impellers was about 3/32" narrower than the original (someone stuffed the wrong part in the box) and of course with the impeller blades not contacting the front and back of the pump housing, it was just whizzing the air around never priming. Made him crazy for two weeks until someone else noticed the size difference, his eyes just couldn't pick up on it.

Never blindly trust the part number on the package.

nedL
09-01-2016, 12:29 PM
Impellers have a direction. Did you put the replacement in the correct way?


Kevin


???? ..... Could you explain this?

Breakaway
09-01-2016, 12:37 PM
???? ..... Could you explain this?

If the impeller rotates clockwise, install the new one with the vanes pre-bent opposite the rotation. A little soap helps.

Kevin

willin woodworks
09-01-2016, 12:46 PM
Thats what I thiught you meant but the vanes are going to fold in the right direction as soon as they hit the cam anyway.

Check the cams. It is possible for them to get worn down to the point that they dont create enough pressure, or is it suction (?) to draw enough water.

nedL
09-01-2016, 06:43 PM
Yep, that's what I though you might mean too. Except I don't remember ever seeing a new impeller with any bias one way or the other to the veins.

carioca1232001
09-01-2016, 07:37 PM
Yep, that's what I though you might mean too. Except I don't remember ever seeing a new impeller with any bias one way or the other to the veins.

Am with you on this.

Actually, the new JABSCO impeller offered little resistance during installation in the stbd. pump, contrary to the port pump.

Could be that the stbd. pump body (circumference) and / or cam (plate) have seen excessive wear......need to look up manufacturer´s spec for the pump and take some measurements with a pair of calipers.

If the wear and tear is beyond repair, I´d be inclined to replace the lot with an equivalent OEM (JOHNSON) gear-driven pump and have a lathe shop do the needful (linking up with the engine gear-drive left over from the pneumatic brake pump).

If it is just the cam plate, may take the lazier route ;), although nitty-gritty parts such as cam plates etc. may be a PITA to locate.