An electric pump instead of the Jabsco impeller??

[Idaho]

I opened my seawater pump this morning. The impeller looked nearly new. I filled the voids with glycerin lubricant from the pharmacy, so it doesn't run dry the 1st go.

Glad I had a look.

[Stu Jackson]

Originally Posted by Jolly Roger

.................
The pump ran dry, and all—I mean all, the vanes broke and tons of muck went first through the oil heat exchanger, then into the engine heat exchanger, then who knows where in the block. I even found a bit in the exhaust water jacket.
....................

I am having a great deal of difficulty one the words after "...heat exchanger..." How can bits end up in those places?

[s/v Jedi]

Originally Posted by Idaho

I opened my seawater pump this morning. The impeller looked nearly new. I filled the voids with glycerin lubricant from the pharmacy, so it doesn't run dry the 1st go.

Glad I had a look.

Take the hose off the outlet as well to check for obstructions. For older boats it’s a 50/50 bet something is stuck there.

[Idaho]

Originally Posted by s/v Jedi

Take the hose off the outlet as well to check for obstructions. For older boats it’s a 50/50 bet something is stuck there.

I took the pump off the engine to open it on the bench. Inlet & outlet were clear.

I busted a hose clamp putting it back on, so it was good to find that weak link and fix it.

[Jolly Roger]

Here is a shot of all the broken impeller bits I found in the oil cooler, which is the first thing after the seawater pump outlet on my engine.

[Cheechako]

Originally Posted by Simi 60

Yeah, can't say I agree

Our mechanical pump on the Genset failed a couple of times a year - impeller
Blood and swearing was involved to repair.

Electric pump has been in 5 years, zero issues.
Same pump I have used in another application has many more years again on it.

Iwaki MD 30 clone on eBay for $140.

Yeah I did one on a home made diesel 12V gen set, but didnt long , was just worried about reliability, but it made the build much easier to do. But some factory Gen sets are known for spinning impellors, so I get it. I think they sit too high in the boat making pulling water or lack of prime an issue. ?

In 50 years of diesel boat engines I have spun an impellor twice I think; once I had the seacock closed, the other time the mechanic was working on the engine.

After clearing the impellor debris I put a nice little bronze sea strainer right after the pump output to end that problem. That engine was convenient to do it on though.

In that 50 years of boating I have probably replaced 8-10 electric water pumps of various sorts. Not to mention a diesel engine will run while sinking with the engine impellor pump up and until the seawater reaches the engine intake. Which is a nit I suppose....

[Tudorsailor]

I have wondered about putting in a Y strainer to catch any broken vanes from the impeller on my Onan. This one has a little inspection window.
I have not yet got around to measuring the space
Here is one

[Cheechako]

Originally Posted by Tudorsailor

I have wondered about putting in a Y strainer to catch any broken vanes from the impeller on my Onan. This one has a little inspection window.
I have not yet got around to measuring the space
Here is one

Seems it could work. I will say though, in industrial applications, I have seen grey PVC, even schedule 80 fittings, break from vibration.

[Sailorman97]

Originally Posted by Jolly Roger

I have just had to completely dismantle all the raw water system on my Perkins 4.236, due to the inlet getting clogged, which caused the Jabsco impeller to run dry, and shred all its vanes into the engine.
I want to replace it with a separate electrical pump, preferably a diaphragm type.
Has anyone done this, and if so, which pump is best?

Nothing good will come of this. The better idea is that you put a flow switch.

This will do.




Wire it up to an alarm


Then to stop your impeller ending up in the heat exchanger insert one of these immediately after the raw water pump.




Al your problems have disappeared.

[col50]

Originally Posted by s/v Jedi

Here’s how to do that. The inner part I made from thin wall PVC pipe. The largest opening is smaller than the channels in the heat exchanger.

If you see impeller parts, you replace the impeller

Great idea. Might have to clean the bowl occasionally to maintain visibility.

[smacksman]

Changing from a Jabsco direct driven pump to an electric/hydraulic/steam driven pump will not help if the inlet is blocked. I always fit a steam strainer downstream of the Jabsco to catch impeller bits. The mesh is coarse enough to cause little back pressure to the system.

[Shaneesprit]

Originally Posted by nuku34

I agree that an external electric fixed-output raw water pump is not an option.

I'm assuming that the OP's engine water temp alarm either was not working, he didn't hear it, or by the time the engine overheated, the impeller was toast.

A flow alarm is a good fix to this problem. Commercial one's are expensive, but goboatingnow might share his DIY design?
The built-in engine temp alarm on the engine control panel is sensing the fresh water temp INSIDE the engine. This temp will take a minute or more to rise hot enough to trigger the alarm, during which time the impeller has already burned up.
To get an almost instant alarm when the raw water flow stops:
Fit a "snap disc" temp switch on the external surface of your wet exhaust elbow just after the water injection point. These snap disc switches come in various temp ranges and are very cheap, around NZ$7. Get a normally open, 70 degree C disc. The disc is about 30mm in diameter. Make a simple mounting band to hold it tight against the wet exhaust elbow and put a bit of heat transfer grease under it. Connect the switch to a loud buzzer (12vt pizzo buzzers cost about NZ$4). Now, when the raw water stops flowing, no water is injected into the exhaust elbow, and within 10-15 seconds the elbow heats up to over 70 degrees (because uncooled hot exhaust is flowing through it), the switch closes and the buzzer says "no raw water shut engine down NOW".

I wouldn’t say an electric pump is not an option, I have spent over a decade working on engine systems with their manufacturers cooling pump removed and an electric one in place, even changing running pressures and Temperatures of the Engine to 135C + so it’s not a non starter but it does require some design and planning, but it’s possible - I am not recommending it though.

[Sailorman97]

Originally Posted by s/v Jedi

Here’s how to do that. The inner part I made from thin wall PVC pipe. The largest opening is smaller than the channels in the heat exchanger.

If you see impeller parts, you replace the impeller

What did you use for the housing itself?

[skenn_ie]

Originally Posted by goboatingnow

why not fit a simple raw water flow meter , I made up one from a few parts

I put an adjustable pressure switch immediately before the heat-exchanger. Switch is closed with static water head to outlet, open when there is flow pressure My outlet is about 3 ft above the h/e.


In answer to the OP, the reason that almost everyone uses a Jabsco type is that, assuming there is water available, it will self prime. Adding another thing to go wrong (electric motor) seems daft to me. I avoid electrics or electronics on primary systems, even the fuel enable solenoid. A stop solenoid is OK.

Personally, I wouldn't use a diaphragm pump. I suspect that they aren't intended, or expected, to run for long periods. You could put a centrifugal pump in, as long as it is below inlet water level, AND there is an automatic bleed system. The freshwater is, after all, circulated by a centrifugal one.

[Jimmyhenry]

I have installed the Aqualarm. Brilliant. Extra easy to install.