Raw water flow in strainer

[firstbase]

"Rebuilt" my old Groco SVS 1000 seacocks and strainers. Rebuild being cleaning/greasing and new gaskets all around. They appear in good shape but I am having an issue with both of them. they are on the ngine raw water intakes. I break the seal on the top and they fill up, no problem. As I run the water level in the strainer decreases until it is only filled about 1/3. Engine temps are fine but they should be full. Would seem like the only way that could happen is if air is being pulled in somewhere on the unit but....both at same time? I have tightened everything well but still same result. It's an open system so nothing to bleed. Anyone have similar experience? Take them apart and put back together and assume a gasket is out of line in some way on both?

 

[Gabe n Em]

You re definitely pulling air in. Are all the hose clamps tight between the strainer and the through hull?

Is there a normal amount of water in your exhaust outflow? "Engine temps are fine." Is this idling at the dock or out, under load?

 

[firstbase]

Temps normal under load for 3-4 hours. Will check all hose clamps but I didn't touch the ones between the strainer and the through hull. I did have a bottom job and they took the exterior strainers off but they were put back on. I don't remember (new to me boat) if they are the angled type. If they were and then put on reversed would that cause this? don't know why I thought of that but just wondered. Odd that it is both. Leads me to believe user error of some sort. Air from somewhere and I would think that has to be from the inside.

 

[boomerang]

Had you noticed this issue prior to rebuilding the strainers? Maybe it's a trait that's been there. If you run the RPM's up while the boat is at the dock & the level drops, it would seem to point to air being introduced on the inside of the boat. If they remain full when the boat is static but underway the water level drops, you have turbulence on the outside of the boat & are sucking up air there.

 

[Ex Sailor]

"Rebuilt" my old Groco SVS 1000 seacocks and strainers. Rebuild being cleaning/greasing and new gaskets all around. They appear in good shape but I am having an issue with both of them. they are on the ngine raw water intakes. I break the seal on the top and they fill up, no problem. As I run the water level in the strainer decreases until it is only filled about 1/3. Engine temps are fine but they should be full. Would seem like the only way that could happen is if air is being pulled in somewhere on the unit but....both at same time? I have tightened everything well but still same result. It's an open system so nothing to bleed. Anyone have similar experience? Take them apart and put back together and assume a gasket is out of line in some way on both?

My guess is that the engine pump is taking out more then it's coming in, I can't see incoming air having anything to do with this. Intake too small incl. supply hose, partially blocked outside strainer, ball valve restriction ??

just my .02 CAD FB

 

[firstbase]

Had you noticed this issue prior to rebuilding the strainers? Maybe it's a trait that's been there. If you run the RPM's up while the boat is at the dock & the level drops, it would seem to point to air being introduced on the inside of the boat. If they remain full when the boat is static but underway the water level drops, you have turbulence on the outside of the boat & are sucking up air there.

Thanks, will test that out this morning. This is a new issue, had no problems prior to my "fixing" things.

 

[firstbase]

My guess is that the engine pump is taking out more then it's coming in, I can't see incoming air having anything to do with this. Intake too small incl. supply hose, partially blocked outside strainer, ball valve restriction ??

just my .02 CAD FB

The hard rubber plug only installs one way/direction. Will play with the handle back and forth a little today and see if somehow it is off center but I can't see how that could be restricting. Again, with it being both sides, I am wondering what could have changed on both. If the exterior strainers were re-installed backwards, angled back, would that cause this? Seems to me the screw patterns would be different so it would be impossible to install incorrectly. not sure as you can tell. Of course I am back in the water so disassembly isn't going to happen. Can have my diver check for anything out side though. Have to be something I did. Story of my boating life....

 

[Ex Sailor]

The hard rubber plug only installs one way/direction. Will play with the handle back and forth a little today and see if somehow it is off center but I can't see how that could be restricting. Again, with it being both sides, I am wondering what could have changed on both. If the exterior strainers were re-installed backwards, angled back, would that cause this? Seems to me the screw patterns would be different so it would be impossible to install incorrectly. not sure as you can tell. Of course I am back in the water so disassembly isn't going to happen. Can have my diver check for anything out side though. Have to be something I did. Story of my boating life....

I would think that the exterior strainers backwards would be an issue while only under way ..... ( seems like most taper to allow for more water pick up under way ) If this is the first time you noticed this, it's hard to tell if maybe this was an ongoing thing if so ... then I'm back at too small of an intake, obstruction before the strainer and / or ball valve .... On my twin Cummins and even the Gen. there is some ? turbulence at the very top of the strainers but they are full otherwise ..... just sayn' FB

 

[Comodave]

Do they have an O ring in the top? If so maybe put some silicon grease on them. Maybe you aren’t getting a good seal.

 

[Pack Mule]

I was pulling air in my strainer and our own member here FF gave me some advice and it worked . I couldn't tell where the leak was. He told me to swob heavy wheel bearing grease around all the the connections all the way to the strainer and be patient. Watch the strainer level while running and the heavy grease will suck in and seal where it's leaking . Mine was at the strainer cap. The surface was rough even with new O ring I wasn't getting good enough seal. I pulled it back apart and slicked up the surface .

 

[Pack Mule]

Also when we were out getting bottom job my impeller dried out and a couple vanes broke and wasn't getting enough flow. I fixed that and then had the air problem with strainer , lost prime while underway and had to shut down, that wasted the new impeller.

 

[firstbase]

Thanks for the suggestion. I ran the boat up to temp while in the slip, 1200rpms and nothing. No loss or decrease in the water level at all. Flowing good out the exhaust. So I guess only under load with the boat moving. Hmmmm...

 

[HopCar]

Since the discharge is at the bottom of the strainer, air at the top isn't going to cause a problem.

I'm with Exsailor.

My first thought as that you were pulling a vacuum, not air, in the top of the strainer. That would indicate a restriction in the intake side. Some restriction would be normal but of course you want to minimize it.

Does it refill when you shut off the engine? That would indicate a vacuum to me.

If air was getting in, the strainer would eventually empty completely and the pump suck air.

For those not familiar with the SVS strainer, here is a picture and info.
https://www.groco.net/media/file/file/s/v/svs-series.pdf

 

[Pack Mule]

Since the discharge is at the bottom of the strainer, air at the top isn't going to cause a problem.

I'm with Exsailor.

My first thought as that you were pulling a vacuum, not air, in the top of the strainer. That would indicate a restriction in the intake side. Some restriction would be normal but of course you want to minimize it.

Does it refill when you shut off the engine? That would indicate a vacuum to me.

If air was getting in, the strainer would eventually empty completely and the pump suck air.

For those not familiar with the SVS strainer, here is a picture and info.
https://www.groco.net/media/file/file/s/v/svs-series.pdf

Thanks Parks , I wasn't paying close enough attention to the system fb has .

 

[firstbase]

Since the discharge is at the bottom of the strainer, air at the top isn't going to cause a problem.

I'm with Exsailor.

My first thought as that you were pulling a vacuum, not air, in the top of the strainer. That would indicate a restriction in the intake side. Some restriction would be normal but of course you want to minimize it.

Does it refill when you shut off the engine? That would indicate a vacuum to me.

If air was getting in, the strainer would eventually empty completely and the pump suck air.

For those not familiar with the SVS strainer, here is a picture and info.
https://www.groco.net/media/file/file/s/v/svs-series.pdf

Thanks Parks. The water remains at the lower level when I shut off the engines. They do not refill on their own. I have to crack the top of the strainer slightly and then water flows up to the top. I did think it strange that the water goes down to a certain level and then stops. 1/3 filled seems to be enough to cool the engines ok and it hasn't gone lower.

Not that it matters on this but I rebuilt another SV strainer for the A/C which is a stand alone strainer w/o integrated sea cock, and it is fine. Replaced a ball valve that fed it with a true sea cock but again, nothing to do with this.

 

[DavidM]

This is entirely normal, although you may have bottom paint build up or sea growth on the external strainer which makes it worse. The R/W pump is pulling a slight vacuum on the strainer, more if there is an external restriction.

The air bubble is either air being sucked in from outside or the slight vacuum is pulling air past the strainer cover gasket.

I would take a look at the external strainer and clean it if necessary. Otherwise fuggitaboutit.

David

 

[hmason]

I suspect your raw water pumps are failing. Simply changing the impellers do not necessarily fix a failing pump. When you are running under load the pumps may not be developing enough vacuum to keep the strainer filled.

I have had this experience with my domestic water system. The debris strainer would be filled to the top and when the pump ran the strainer would become half empty. A pump rebuild solved the problem and now the debris strainer is fully filled at all times. I also went through the exercise of tightening clamps and lubing o-rings to no avail.

 

[firstbase]

This is entirely normal, although you may have bottom paint build up or sea growth on the external strainer which makes it worse. The R/W pump is pulling a slight vacuum on the strainer, more if there is an external restriction.

The air bubble is either air being sucked in from outside or the slight vacuum is pulling air past the strainer cover gasket.

I would take a look at the external strainer and clean it if necessary. Otherwise fuggitaboutit.

David

Thanks David. The bottom was just done w/external strainers removed and cleaned. They were doing that while I rebuilt the strainers. I believe they put some bottom paint up in the intake for a few inches but they should both be clean, good to go.

 

[firstbase]

I suspect your raw water pumps are failing. Simply changing the impellers do not necessarily fix a failing pump. When you are running under load the pumps may not be developing enough vacuum to keep the strainer filled.

I have had this experience with my domestic water system. The debris strainer would be filled to the top and when the pump ran the strainer would become half empty. A pump rebuild solved the problem and now the debris strainer is fully filled at all times. I also went through the exercise of tightening clamps and lubing o-rings to no avail.

Well...if that were true wouldn't the water keep getting lower until no water? Why would it equalize? Everything was fine when they pulled the boat. 10 days later both have the same issue. Both pumps go, or start to go, at the same exact time? Is 10 days out of the water long enough to ruin the impellers?

 

[diver dave]

Thanks Parks. The water remains at the lower level when I shut off the engines. They do not refill on their own. I have to crack the top of the strainer slightly and then water flows up to the top. I did think it strange that the water goes down to a certain level and then stops. 1/3 filled seems to be enough to cool the engines ok and it hasn't gone lower.

OK, so the strainer top is below sealevel, it fills when the top is off.
You have an air leak at or below the strainer. The pump enforces flow up, so the pump can't enter air into the strainer. It must come from below.

The reason the strainer doesn't fill completely with air is because the air leak is fairly small and the pump volume is demanding basically a set amount of air plus water. I suspect there is a small whirlpool of air in the strainer at cruise that is admitting a small amount of air into the pump. You are losing cooling efficiency with air in the RW system.

Since the common denominator is the seacock rebuild, I would certainly look there for the air leak.

 

[HopCar]

Thanks Parks. The water remains at the lower level when I shut off the engines. They do not refill on their own. I have to crack the top of the strainer slightly and then water flows up to the top. I did think it strange that the water goes down to a certain level and then stops. 1/3 filled seems to be enough to cool the engines ok and it hasn't gone lower.

Not that it matters on this but I rebuilt another SV strainer for the A/C which is a stand alone strainer w/o integrated sea cock, and it is fine. Replaced a ball valve that fed it with a true sea cock but again, nothing to do with this.

That does sound like air is getting in. Still you'd think the strainer would eventually empty. Have you expanded the rubber plug with the T-bolt? Try cranking down on it. I hate to say it but at this age the rubber plug may be too hard to seal properly.

I think it's time to call Groco. They are really very nice to deal with.

 

[firstbase]

Yes, the guys at Groco are great. Spoke with them when deciding whether to rebuild or replace. The rubber plugs were in good shape, no deterioration, cracks etc. I have cranked them down but only by hand and at an odd angle due to placement. Can't say that they are REALLY cranked down. Hopefully that will make a difference. DJ mentioned "fogidaboutit" which I appreciate this is a new condition so I think I should keep trying before I call it a day and it is what it is. OF course I am back in the water now so there is only so far I can go with it and if the leak is below the strainer I'm out of luck taking it apart. I did put a new gasket underneath the whole thing but it has bolts going through it which hold the gasket in place so I would think they would be ok. Also cranked the bolts down more than they were originally. The exterior rods are cranked down well even to the point where I was worried I was going to far. Maybe take them all apart to the point I can, more grease and then back together to see if that makes a difference. Don't really know but appreciate everyones suggestions.

 

[HopCar]

Don't put a tool on the T-bolt, it's cast and you can break it. Finger tight should do it. If you can't open and close the valve without loosening the T-bolt, you're good. At this point, if you're not pulling air into the engine, I wouldn't worry too much and just keep an eye on it.