Sea water pump impleller

[paulga]

This is a jabsco sea water pump on a sp135 port side right below the fuel injection pump. The impeller was last changed two years ago, with less than 100 hours usage since then. Is the impeller still good for one or two seasons?

 

[Bmarler]

It’s a crapshoot. Sometimes they’ll be ok, sometimes not. I change every two years regardless of engine hours.

 

[paulga]

It’s a crapshoot. Sometimes they’ll be ok, sometimes not. I change every two years regardless of engine hours.

Is it usually changed together with the v belt, for the same purpose to avoid overheating?

 

[Bmarler]

That’s good practice, but I monitor my belts and change when I see signs of wear. They can last several years if they are not stressed.

 

[paulga]

That’s good practice, but I monitor my belts and change when I see signs of wear. They can last several years if they are not stressed.

To change impeller on this pump, is removing the 6 screws cover enough, or does it require a jabsco impeller puller to take it off and put the new one in?

 

[Bmarler]

I don’t have a Lehman, so I don’t know exactly, but I think it may be possible to remove without the puller if you use two screwdrivers to pry it out. Be sure to pad the shafts where they rub on the pump housing so you don’t damage the sealing surface.
Of course a puller is easier.
Be sure to inspect the whole thing for wear, or signs of seal failure.

 

[CharlieO.]

I am able to remove mine with needle nose pliers.

 

[twistedtree]

Be sure to shut off the sea cock first, and then don't forget to reopen it before starting the engine.

 

[paulga]

Thanks for all your input. I will check the impeller first.

 

[psneeld]

After 2 years of low use I would change it.

Many (not all depending on manufacturer composition) will start to take a set and the blades with the greatest bend for the longest time may be weakened even though not showing damage or cracking.

Lehman impellers are inexpensive in the big scheme of diesel impellers.

I had a pair of long handled, long 90 degree bend, needle nose pliers (cheap from Harbor freight) that always got my impellers out without prying or damaging the pump.

An trick an old time fish boat engineer told me that if you don't have a new gasket, just put a solid piece if a paper grocery bag over the in place impeller place the cover over it and gently push on the machine screws to find the holes and tighten the scews, Trim the excess paper off with a razor knife. Once the screws are tight the paper that is against the impeller will be shredded off a dissolve in no time.

I have done it several times and it worked well. Eventually I would just use construction paper, even copy paper from a household printer where I just copied the gasket onto it and cut out the center and punched out the fastener holes. Kept a half dozen on board with my impellers in case I had to do multiple change outs when troubleshooting.

See Boomerang's thread for an unusual impeller situation.

$10 at Harbor Freight and very handy on a boat.

 

[Greg QS]

I have found I can reliably get 2 years out of impellers, main Engines and gensets, regardless of hours. At 3 years impellers start to come apart. It sucks pulling apart the cooling system looking for missing impeller bits.

If you guys ever have missing bits on a impeller, Go looking for the parts. They are down stream in the system clogging your cooling system.

 

[paulga]

I did the impeller change today. The existing impellers are still in good shape though they have been in service for years, especially the one on the genset. I replaced both.

The new impeller on the main engine- in the end, one vane is not in the same direction as the others. This though does duplicate the pattern of the vanes on the old impeller. Is the clockwise orientation important?

The impeller on the genset- I did pushed it to the bottom, however it still seemed a tid bit protruding out of the cavity, so it will be squeezed by the cover plate when the cover plate is tightened. Is this because the flange has been sanded down many times? Does it affect the pump function?

 

[Iggy]

It’s a crapshoot. Sometimes they’ll be ok, sometimes not. I change every two years regardless of engine hours.

I do the same. Two years ago, I pulled mine and it looked new. Out of the box new. Just last week I changed it again thinking it was going to look new again. One fin was ready break off.

 

[Bmarler]

When installing the impeller you need to orient the vane direction to replicate the one you took out. Some say they will reorient themselves but I don’t take any chances. One errant vane shouldn’t be a problem, it’ll likely fix itself on startup.
The new impeller protruding a bit is pretty normal. It helps it seal when you install the cover plate.

 

[paulga]

When installing the impeller you need to orient the vane direction to replicate the one you took out. Some say they will reorient themselves but I don’t take any chances. One errant vane shouldn’t be a problem, it’ll likely fix itself on startup.
The new impeller protruding a bit is pretty normal. It helps it seal when you install the cover plate.

I watched these two videos for tutorials-

youtube.com/watch?v=bJ3K2V6OY6E
youtu.be/G-BHHa-1oF8?si=Ug-JL7IJa43Cykue

The first video says the screws on the cover plate should just be "snugged up" instead of going berserk, as the pump casing is just brass.

when driving these screws, what's the spot of "just snug up"?

 

[Pprior]

A smidge before too much. It's a feeling in the soul.

Tighten until snug, then a quarter turn more—unless you're a rookie, then it’s snug, snap, and replace the part.

 

[paulga]

A smidge before too much. It's a feeling in the soul.

Tighten until snug, then a quarter turn more—unless you're a rookie, then it’s snug, snap, and replace the part.

it's a gradual progress of increasing torque before the thread or screw is stripped. The required tightening extent also depends on the base material, eg steel or brass

 

[Mac2]

Using Superlube on the inside of the housing, shaft and faceplate will help with the install along with keeping things cool till the water starts flowing.

 

[paulga]

Using Superlube on the inside of the housing, shaft and faceplate will help with the install along with keeping things cool till the water starts flowing.

I used the Napa silicone grease. It was easier to put the new impeller in than pulling out.
After that, I applied Permatex #2 to the flange surface, and positioned the paper gasket on the flange. Then I smeared a bead of grease to cover the inside of the faceplate before assembling. Because the pattern of the screw holes are not symmetric, there will be no problem in lining up, he gasket can also stick to the faceplate first.

 

[O C Diver]

I use automotive hand cleaner WITHOUT pumice, all over the impeller and the barrel of the housing. It makes insertion a slippery piece of cake.

It doesn't matter which way the impellers face. Some engines, when they stop, will kick backwards maybe a quarter of a revolution or less. This kick back is a function of compression in the cylinder(s). As a result, the blades can reverse. So it may happen many times during the life of the impeller.

By lubing the blades (when the water pump is dry), the ones under compression will slip to where they're out of compression, before reversing. Once the pump is wet internally, it's not as abusive on the blades.

No, I've never run the water pump without the back cover, to observe this for myself. But I trust the guy implicitly who explained it to me.

Ted

 

[paulga]

I use automotive hand cleaner WITHOUT pumice, all over the impeller and the barrel of the housing. It makes insertion a slippery piece of cake.

It doesn't matter which way the impellers face. Some engines, when they stop, will kick backwards maybe a quarter of a revolution or less. This kick back is a function of compression in the cylinder(s). As a result, the blades can reverse. So it may happen many times during the life of the impeller.

By lubing the blades (when the water pump is dry), the ones under compression will slip to where they're out of compression, before reversing. Once the pump is wet internally, it's not as abusive on the blades.

No, I've never run the water pump without the back cover, to observe this for myself. But I trust the guy implicitly who explained it to me.

Ted

why does the raw water pump need to have a rubber impeller inside an non circular cavity? in comparison, the fresh water pump does not need this maintenance.

 

[jgwinks]

When the blades pass under the cam (the non circular part) they get squeezed against the hub, reducing the volume between the blades. When they return to the circular part the volume increases back to normal. This causes a vacuum or suction that allows to pump to self prime. It would not self prime without this feature. The fresh water pump doesn't need to do this as it's always full of liquid so it doesn't need to self prime.

 

[O C Diver]

why does the raw water pump need to have a rubber impeller inside an non circular cavity? in comparison, the fresh water pump does not need this maintenance.

A fresh water circulating pump can't create suction when dry. The pump must be mostly flooded to push water out, thereby pulling water into the pump by vacuum of the other water leaving. Most circulating pump impellers touch no part of the housing, because it's a closed loop system, mostly under pressure.

In many applications, a raw water pump must be able to pull water up to the pump. This can sometimes be a lift of several feet. As a result, the impeller blades must be mostly tight against the barrel, front pressure plate, and rear cover plate. Typically a raw water pump will hold some water (after the first time it's run) which creates the seal to lift the water, each subsequent time.

Ted

 

[paulga]

Thanks for your explanation.

The Jabsco impeller kit (main engine) has a rubber plug that is supposed to nest in the center of the impeller, as shown in the screenshot of a youtube video. What's the function of this plug? I forgot to install this plug.

The impeller on the genset does not have this center plug.

 

[Nick F]

why does the raw water pump need to have a rubber impeller inside an non circular cavity? in comparison, the fresh water pump does not need this maintenance.

The fresh water (antifreeze coolant) pump is always full of water. It is below the top of the water level in the engine. Because of this an impeller that works on inertial principles can be used. The specific type used in engines is a "centrifugal" impeller.

The raw water pump, by comparison, in many boats is above the seawater level and must be able to suck water up from this level. For this reason a "positive displacement" type pump is used. This type of pump does not depend on inertial effects and is able to pump air (although not very well) - in this way it can suck the water up to its level in order to start pumping the water. Note that it does not suck air very well if the rubber vanes are not at least somewhat wet.

There are many types of "positive displacement" pumps in existence but the rubber impeller (aka "Jabsco") type seems to be universally used on marine engines. It works by carrying pockets of liquid around the circle in the cavities between the vanes. The cavity is then squeezed to a lesser volume by the "bump" in the inner surface of the casing and the liquid is forced out through the hole in the casing which is located at the start of the "bump". In some pumps this "bump" is formed by a removable piece called a cam and in some newer pump designs the bump shape is machined into the casing block.

 

[tagillette]

For what it’s worth try using two long zip ties around both ends of the impeller to compress the vanes get started into housing with lube I like dish soap start onto splined shaft cut first tie push further cut second tie. On our cat engines it’s easier to remove entire pump and supply hose than to hang over engine

 

[O C Diver]

Thanks for your explanation.

The Jabsco impeller kit (main engine) has a rubber plug that is supposed to nest in the center of the impeller, as shown in the screenshot of a youtube video. What's the function of this plug? I forgot to install this plug.

The impeller on the genset does not have this center plug.

View attachment 164038

I don't know.

My assumption would be that the plug could add additional pressure on the front wear plate and the back cover plate to compensate for worn plates.

Ted