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Old 13-01-2010, 18:18   #1
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Air Conditioning Raw Water Strainer?

Hi Everyone! I'm getting into the reassembly of our air conditioning system (a Cruisair Zephyr) and they are recommending a raw water strainer before the March cooling pump. Am I alone in dreading a stainer BELOW the waterline? My engine Raw water strainer is slightly above, and I'm having trouble committing to this below-the-waterline's bad enough that the March pump has to be below! Anyone have any experience here? The only strainer I like for this is the grate over the thruhull!


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Old 13-01-2010, 18:33   #2
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Thousands of boats here in the south have strainers below the water line. In 30 years I only know of 1 boat that took on water from a failed strainer and that was an old design with a center bolt that is no longer used. They are very safe if installed properly like most things on boats common sense applies

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Old 13-01-2010, 19:02   #3
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Old 13-01-2010, 20:28   #4
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The reaon the the filter has to be below the waterline as well as the pump is that the AC pumps are not self priming
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Old 14-01-2010, 05:06   #5
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I second the Groco idea.

I've had the marelon / plastic Forespar units and had one disintegrate just from turning the knob to open the basket. I just rebuilt / cleaned a big Groco ARG-1500 (yes it's below the water line and services the AC circ pump) using just 2 gaskets and replacement crush washers.

Don't be afraid of these below the water line. Get a good unit and keep your seacocks maintained. Parts are everywhere and relatively cheap.

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Old 14-01-2010, 05:34   #6
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Chief is right. Filters feeding non-self priming pumps have to be below the waterline. Mark is right as well. "Get a good unit and keep your seacocks maintained." But good boating pratice is to keep the thru hulls closed when you leave the boat anyway. If I remember right most boats are sunk at the dock.
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Old 14-01-2010, 05:35   #7
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I agree with your fears. I recently installed a March pump to supply raw water to my genset with the same instructions. I used a Vetus fliter with both the input and output at the bottom of the filter. I aligned the top of the filter to be just above the waterline. It seems to work ok.

I'm now thinking of moving the filter well above the waterline and making sure the filter is "primed" prior to starting. If the pump is below the waterline, I don't see it running dry. A loss of performance is to be expected but I'm not sure it will be significant.
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Old 14-01-2010, 05:54   #8
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groco bronze strainer. the thing that worries me about the march pump is the nylon hose fittings. but what are you gonna do?
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Old 14-01-2010, 06:52   #9
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I have also had no problems w/ below waterline filters; one added comment: you might want to consider installing a T / garden hose connection inline before the pump, this will provide an access point for fresh water flush and/or a chemical cleaning of the system. I usually perform this once a year or as needed; am overnight soaking w/ white vinegar seems to do a good job of cleaning the RW circuit.

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Old 14-01-2010, 06:55   #10
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Every one of your sinks and heads are connected to thru-hulls below the water line. Do you close those every time you leave the boat?

Even with the raw-water strainer (the Groco is the best) above the water line, once the air is removed you will have the potential of a siphon effect if there is any breach of the raw water lines below the water-line. So long as there is no breach, and the discharge line is above the water line, you have no issue. You will allso have no issue if you simply close the through-hull when you are not aboard the boat.

Your selection of the March Pump is a good one as these are air cooled units and are less prone to failure as are Cal Pumps. One thing to keep in mind as you install the pump is to ensure that the two lubricating holes at either end of the pump motor case are oriented upward. (If necessary you can ease the mounting brackets on the pump and rotate the motor until the lubricating holes are up-ward when the pump is in the mounted position. The pump assembly on the end of the motor itself can be re-oriented without difficulty to suit the discharge direction). The pump bearings need be lubricated roughly every 3 to 6 months, depending upon use, by injecting some 3-in-1 oil (ie 20 weight lube oil) into the lubricating holes. As these can be hard to spot in the awkward--dark--mounting positions that the pump is likely to be in, put a little white paint around each hole--use a Q-tip to keep paint out of the hole itself--before you bolt the pump in place. With that it's not so difficult to see where to inject a squit of oil. (I actually keep a little bottle of 3-in-1 oil in a hook next to the pump to ensure its always there.)

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Old 20-01-2010, 22:37   #11
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Hylyte thanks for the tip on the white paint and keeping the 3-1 oil next to the pump. Good idea.
I went from a march water cooled pump, to a air cooled, going to install it in a month or so... I will follow that advice.
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Old 21-01-2010, 03:23   #12
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I agree with the Groco filters being the best, but I selected the Raritan (tough plastic) filter because of huge size of the filter basket. If your cruising in places like the Chesapeake in the summer, you'll need the largest size filter basket or jellyfish willl be clogging your filter very frequently. The alternative is to install a "sea chest" as a resevoir for your influent cooling water. 'take care and joy, Aythya crew
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Old 21-01-2010, 05:28   #13
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Raw water cooled A/C heat exchangers should always drain back, and leave no salt water, to cause electrolosys, in the unit. This is the reason the pumps are not self-priming, and the installation drawings always ask for the unit to be at the highest point in the system to facilitate draining. Mr Kollman has emphasized this a number of times in past threads.

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