March Pump- Refrigerator-new data

[DayDream2]

Hello Hunter Owners-
I was on the phone with March Pumps today. Great folks--they hooked me up to the engineering department and the guy was very friendly and helpful.

The challenge I've had is that the Model 893-04 I use to cool my Gunert Polarmate fridge keeps burning out. I'm on the third one in three years.
New data (to me): These are rated for 125 days (3000 hours) of continuous usage. Of course the fridge is not supposed to be on 24/7, but it seemed remarkably low for a $300 pump. Turns out the new 893-09 has a 50,000 hour rating, for an additional $70.

I also called Hunter-Marlow and they said they'd never heard of these burning out. That was baffling. Has no one ever mentioned this common problem to them?

Three issues:
1- I occasionally lose the prime to this pump and can't figure out why. Sometimes when sailing. As I read the documentation, it appears this is the primary reason it has a short life. Everything is carefully installed according to the diagrams.
2- Does anyone know if there is another option for pumps with more life, that could run dry without burning out?
3- Is there an alarm system that could warn me when the pump loses it's prime? The only way we know to check is to keep sticking our head over the port side to see if water is coming out.

I'd love to hear updated info from others on this issue.

 

[scottdube]

I have read of using a forward facing scoop on the through hull check page 5 of this http://seafrost.com/pdfs/BD-TW/BD-XPX airwater-pcb.pdf

 

[DayDream2]

I have a forward-facing scoop- checked it this spring and it's not clogged. System is installed according to the instructions you sent. Thanks Scott. Hope to unravel this mystery some day.
I did learn that these pumps work best submerged, as it cools the motor. And this one is not submerged, so it has to have water running through it to help cool it.

 

[justsomeguy]

I did learn that these pumps work best submerged, as it cools the motor. And this one is not submerged, so it has to have water running through it to help cool it.

In fact, Defender states it must be submerged.

 

[DayDream2]

I know! Crazy huh? But the engineer at March Pumps said it was optional.
I know very little about pumps. Don't a/c pumps run continously for years without burning out once a season? What am I missing?

 

[Gunni]

I assume this is the cooling water for your compressor condenser system. Do you really need the massive flow rate of that pump? There are continuous duty 12vdc pumps that don't need cooling and should give you all the heat extraction you need. In fact my A/C system warns against too high a cooling water flow - messes with the refrigeration cycle.

 

[DayDream2]

Thank you Gunni. I've wondered the same thing, so grateful to hear it's possible to find another solution. Do you have any examples? I've spent tons of hours searching through different manufacturers trying to find one.

 

[scottdube]

I assume this is the cooling water for your compressor condenser system. Do you really need the massive flow rate of that pump? There are continuous duty 12vdc pumps that don't need cooling and should give you all the heat extraction you need. In fact my A/C system warns against too high a cooling water flow - messes with the refrigeration cycle.

I don't think this is considered a high flow rate pump. It is in fact very small. I have to believe you have an issue with getting air into the line somewhere between the through hull and the pump. Here is the pump specs in case you haven't seen it.

 

[DayDream2]

Right now I have the 893-04, but will upgrade to the -09 next since it has a 50,000 hour life expectancy.

The first problem is losing it's prime, so you're right Scott. When I put it back in the water in the spring I'll search for leaks. The pressure from the through hull is significant, as you can imagine with a 10 ton boat pushing down into the water!

Has anyone heard of an alarm for when it stops pumping water?

Any other suggestions for how to troubleshoot this?

 

[Gunni]

Any circulation pump will have problems with losing it's prime as you sail the boat and drain the intake hose. Shurflo makes a 12vdc continuous-duty diaphragm pump which can prime itself. Defender sell it for $125.
http://www.defender.com/product.jsp?path=-1|2061076|2061077|2234240&id=3214615

 

[Don Lucas]

I also called Hunter-Marlow and they said they'd never heard of these burning out. That was baffling. Has no one ever mentioned this common problem to them?

Well all that means is the person you spoke to had not heard it because they are too new to have heard about all of them amd by now most owners have changed to air cooled units. When I researched my 410 (sister to your 420) the #1 complaint was the water cooled refrigeration. Maybe that is why my 2001 model has an air cooled unit (OEM) even through the owners manual has it being a water cooled unit.

 

[pateco]

by now most owners have changed to air cooled units. When I researched my 410 (sister to your 420) the #1 complaint was the water cooled refrigeration. Maybe that is why my 2001 model has an air cooled unit (OEM) even through the owners manual has it being a water cooled unit.

I always wanted to ask someone, where do you vent the heat created by the air cooling on an air cooled unit? I would not want to heat my cabin any further.

 

[Gunni]

I always wanted to ask someone, where do you vent the heat created by the air cooling on an air cooled unit?

Into the bilge. I have an add-on ducted fan with an intake low in the cabin.

 

[pateco]

Into the bilge. I have an add-on ducted fan with an intake low in the cabin.

Does it vent outside the boat? or just heats your bilge area?

 

[scottdube]

I always wanted to ask someone, where do you vent the heat created by the air cooling on an air cooled unit? I would not want to heat my cabin any further.

Mine vents into the saloon under the table through the settee base.

 

[DayDream2]

Thank you everyone. Grateful for all of your input. This points me in the right direction.

 

[Gunni]

Does it vent outside the boat? or just heats your bilge area?

Actually it drys the bilge under my galley. And the hull is between 50 and 70 degrees so it absorbs the heat. I have developed a procedure for our refrigeration. In preparation for a trip I arrive at the boat early, start the refrigeration and place three 2 gallon rectangular potable water jugs into the freezer. The leaves plenty of room for frozen items and frozen jugs create a huge reserve of cold for my spillover system, allowing me to turn off the compressor while sailing and have the circulation fan keep the refrigerator cold. Sort of like a thermodynamic flywheel. ...and an emergency drinking water source.

 

[JamesG161]

On my H430 the thru hull is located amidships aft of the keel. Our 13 Ton boat's pump is about 24" below water line so no priming needed. When the pump is off, your line water will flow backwards until it matches the water level of your boat. The discharge in Stbd Aft and should be above a heeled boat water line.

We have to clean our pump suction strainer 4 times a year. A restricted flow through the strainer will cause cavitation and loss of pumping. Have you cleaned yours recently? We have found baby crabs and minnows in our strainer. Pumping crabs is not good for your pump.

keeps burning out.

I assume you mean the motor. The lowest amp use is when it is NOT pumping water.
If you mean the pump housing is burnt, then a dry pump may cause this.

Although we don't sail with the refrigerator running, I have never lost the pump prime. In fact yesterday, I did my annual city water "blow out" of the lines to clean and look for leaks. I forgot to open the seacock, when verifying all was reassembled right. Oooppps! I quickly opened the seacock and the pump primed instantly.

Your refrig compressor will cut off on High pressure without cooling water.

Tip: Higher flow rate pumps don't add much flow since your line size/length limits the flow rate.

If it is loosing prime when at berth, it would have to be a small air leak on the suction (if strainer is clean). You can check for leaks "on the hard".
1) Put a shore water hose into the discharge vent until you see water flowing backwards through the seacock intake.
2) Close seacock while putting hand pressure on the water hose to pressurize the line a bit.
3) Look for leaks. I use a dry paper towel to wipe all down. Towel damp, small leak.
Jim...

PS: Our Gunert compressor is located Port Aft under the shallow lazarette (above the water line) and thus minimal heat is vented by cockpit drafts.

 

[SG]

As others have mentioned:

The Marsh units are not "positive displacement" pumps. (i.e., They don't like to suck water up. or they can't be counted on self-priming except in the least challenging situations. Therefore, it's important that they should ALWAYS be located at or below the natural water line and should NOT have any reverse "traps" in the hoses or path to the pump where air could collect and block flow to the pump. The Marsh pumps do fine with working pressure AFTER the pump (within reason.)

Also locating one off of the center line of the boat risks "drying it out" when the boat is on an opposite tack. Further, in a pounding seaway (where say, you're boat is launched off of a wave and you "shiver your timbers" with a crash) you can induce an air pocket. On our boat, if we are beating or motoring into short, pounding 5'-6' waves, we have to reprime one of the Marsh pumps that handles two of our AC units, the optional water condenser for our Sea Frost refrig/freezer compressors; and, our water maker. (The simple one that is dedicated to one AC unit never has lost its prime in seas that we've been pound over and through.)

A forward scoop helps (if you're moving forward). That's probably has made our loss of prime less of an issue -- but it doesn't solve the problems. That's even at 9-10+ knots of scooped water flow.

Do you have a filter in line between the intake seacock and the pump. The filter has to be sufficiently large or it creates a problem with occluding the flow; and, needs to be clean enough also or it can be an issue.

I have never heard of a properly installed Marsh pump having a one season "life span" by design. We've had multiple Marsh pumps over the years on two boats -- they occasionally will have to be replaced for a variety of reasons. If they are properly installed and function well.

As Gunni says, there are positive displacement pumps which will work. I'm not sure about their power use compared with the Marsh. In my experience they are noisier.

When I've asked our AC guy about switching, he just looks at me and says, "[He] wouldn't do that." I'm not sure of his reasoning except that the Marsh Pump works well and doesn't seem to be destroyed by dry running (within reason).

 

[DayDream2]

I'm taking away a wealth of wisdom from these posts. We do have a strainer between the seacock and pump, and there are no opportunities for air lock based on hose positioning. I will definitely add the 2.5 gallon ice water idea, I really like the thermodynamic flywheel idea. Plus my 5'4" wife can't reach the bottom of the freezer anyway, so we can stack frozen items on top of the water containers.

What's strange is that we've never had any substantial amount of weeds or particulate in the strainer. A few small pieces is all. I will watch for leaks in the lines though.

The most obvious answer is that we're losing prime while sailing. Have never lost it at the dock that I remember. We're at the boat every weekend May 1- Mid-October, so we'd like to be able to leave the fridge running during the week with supplies. Hauling everything back and forth is a routine we did for ten years and thought we were done with.

Continue to be grateful for this sailing community. Thank you.