Perko Fresh Water Strainer # 493

[puff6022]

I keep loosing prime to my water pump on my Yanmar 2GM20 Diesel ( Island Packet 27). The inlet is shared with the head. I replaced head and still loose prime. The strainer is probably the culprit right? Do I replace gaskets in Perko # 493 Strainer or just trash it or is that the problem at all? The problem started when I replaced my water pump and put it back together. Help, Witts end

[sailingdog]

Puff-

It is a raw water strainer... a fresh water strainer would generally refer to something in your boat's water system... the water coming in from outside is raw water—fresh or salt.

The Perko is a good strainer, and one that is generally trouble free. Unless the basket on the Perko is covered with stuff, I doubt that it is the problem.

A few questions I'd ask first... How big is the inlet? Also, have you checked the outside of the throughhull? Does it have barnacles on it??? Finally, where is the head located with respect to the engine—this is probably the culprit in my book.

If you're losing prime, it could be because the water pump on the engine is sucking in air via the hose going to the head. Generally, I recommend keeping the engine raw water intake separate from all the other raw water intakes, since that tends to reduce the number of problems on a boat considerably.

[camaraderie]

I would guess the tap is responsible for losing your prime too but since that wasn't a problem before you replaced the pump, I would focus on proper pump operation first.
Suggest you remove the hose at the T-valve and stick it in a bucket of water and see if your pump is working correctly.
I doubt it is the Perko but you could have an obstruction in the line BEFORE the Perko which is blocking your water flow. We had kelp in our intake line once which did this.

[Valiente]

I've got that strainer...I love it! Do you know where your waterline is vis-a-vis the strainer? Is your strainer on the centerline or offset, and do you lose prime on one heel or another?

I agree that it's likely a blockage or an air leak somewhere, but it's worth consideration.

[sailingdog]

Cam-

Don't you have an exterior strainer over the raw water intake through-hull???

[puff6022]

Sailing Dog, Thanks , It is the raw water strainer. I can pump the head and it is fine bringing water in. I don't loose prime until I am sailing on a Starboard tack at a good heel. The inlet is on the starboard side near the centerline of the boat. I have not checked the inlet but I get good water flow when the boat is idle. This all started when I had the water pump rebuilt and I opened Strainer to get the prime back after dre installing the water pump.

[sailingdog]

It sounds like you may be getting air in through the through-hull. I would check to see how well the water pump is working per Cam's suggestion. If it seems to be okay and generating enough suction, I would see if there's anything obstructing the outboard side of the t-fitting to the exterior of the boat. Maybe you have kelp or something else growing or stuck in that side of the hose. Also, double check all the hoses, just in case.

If the pump isn't faulty, then there has to be an obstruction, and when you're on a heel, the head* on the through-hull lessens, reducing the water pressure at the through hull. If the flow is restricted enough, this may be causing the engine to suck air from the head side of the t-fitting. BTW, this might have become a problem because the new water pump is working much better than the old one—since it would demand more water, it would pull on the hose leading to the head more strongly than the old pump, increasing the likelihood of getting air via that hose. Hence, my argument for leaving the raw water for the engine on a dedicated raw water through-hull.

After trying the water pump in a bucket, I would try connecting the hose directly to the seacock, and removing the t-fitting. If it doesn't lose prime after that change, you know it is sucking air in via the head hose, and that the through-hull or outboard side is probably obstructed to some degree.

* head is also a term used to describe the amount or height of water at a specific point.

[puff6022]

Originally Posted by Valiente

I've got that strainer...I love it! Do you know where your waterline is vis-a-vis the strainer? Is your strainer on the centerline or offset, and do you lose prime on one heel or another?

I agree that it's likely a blockage or an air leak somewhere, but it's worth consideration.

The Strainer is about 18" Higher than the waterline and about 12" outboard of centerline on starboard side about 48" forward of transom

[camaraderie]

SD...yep..that is what I would suggest also. And in answer to your question, no i do not have an external screen. The issue occurred on my last boat due to an ELBOW in the incoming line getting blocked. My present boat has a straight 1.5" wide feed to a large filtered "water closet" type manifold so I have no need for an external strainer.

PUFF...one more question. Is the Perko BELOW the height of the water pump? It should be. I also prefer to mount them below the water line as well to insure there is always a full prime. Your last post got me thinking that you are sucking air on a starboard tack as the INLET is coming out of the water when you are heavily heeled because this is not happening on the other tack. Maybe it is just a question of not running your engine when you have that much heel under sail??

[sailingdog]

Elbows in raw water lines for the engine are bad... especially upstream of the strainer... I like the manifold idea on larger boats, as it allows you to keep an eye on things and can reduce the number of holes through the hull.

My boat is too small to need a manifold... in fact, the only saltwater through hulls on it are for the head.. 1.5" out and a 1/2" in... Since it uses an outboard as the auxiliarry power, no raw water for the engine needed.