I have an ice machine for my fish box that has us stumped. It has a pump for sea water that is used for condenser cooling and to make salt water ice if you select that option. The pump is March Mfg Model BC-3C-MD. Every time I start the machine I have to crack open a burp valve on the discharge side of the pump to burp it or it will not discharge. I use to have to do this once at the start of the season but now I have to do it every time I start the machine. It’s a PITA because I have to lift the fish box out to get to it which is a two person ordeal. Everything in this sea water circuit is well below the waterline. The hose from sea strainer to the pump is less than 6’ long and is straight shot into the pump. If I open the burp valve with the pump not running water comes gushing out. So I am 99.9% certain this is not a priming issue with water getting to the pump. Is it possible the clearances and condition of the pump have worn just enough that the pump can’t build pressure unless I open valve and then once it gets going it is able to maintain pressure? That’s the only thing I can think of. The only control circuitry from the ice machine to the pump is to turn the pump on which is working. The pump runs continuously if the machine is on. Any ideas other than replacing the pump? I thought about installing an actuated valve that I could open via switch to be able to burp it without lifting out the fish box but that seems kind of ridiculous to have to do.
I have great faith in that pump. So, next questions; Where is the raw water pickup, How high is the discharge outlet, This happens the next morning or when you splash? In my opinion, If that pump has a solid connection to the sea, it will pump,,, unless the output water is heavier than the first charge of raw water supply. Please tell us about the discharge path from that pump.
Raw water pickup is about 6’ from the pump, near stern of boat. Hose from strainer to pump is a straight shot as mentioned. Everything is well below waterline. This occurs any time I shut the machine off. Even if just for a few minutes I have to burp the discharge line or it will not discharge. Discharge path is maybe 18” of hose from pump to ice machine. It has a tee in center of discharge line that the burp valve is on. That’s pretty much it. Pump discharge goes into an Amot valve then into the machine. The discharge line does make a gradual loop so the burp valve is below pump in bottom of bilge. There does not appear to be any air in the line when I burp it. From the machine it goes to an overboard just above the waterline about 5’ from the machine. I am able to watch this discharge point and can see no water coming out until I burp it. Water discharges from the overboard almost immediately when I burp it. Again, a simple 1-2 second crack open of that burp valve and all is well.
You shut the ice maker off last, dock side. Then a few minutes later it will not restart? So not bubbles from the exhaust, running gear or anything else? Something is putting air on that impeller or the water against the pump is heavier that the start up flow. The next time you return to the dock, with the ice maker running, all else off, look at your strainer. Any air (one bubble) in there? OR,, air is coming back wards to the pump maybe. I may get a trip out of you yet, albeit living in your bilge watching your pump and strainer, but a trip..
Boat operating or not makes no difference. I tested it multiple times just sitting at the dock with nothing running to have any effect. Also tried while running. Same issue regardless.
One air bubble on that impeller can mess you up like this. Question; The discharge from the pump, pointing up and soft bent towards the ice machine?
The march pump heads and impellers are hard plastic that doesn’t suffer from erosion so it is unlikely to be an issue although I have had two fail over the years with a broken impeller piece. It did make quite a bit of noise though. when you say it’s a straight shot from the strainer to the pump, does it means uphill or is there a high spot like if going above a stringer? That’s a common issue although that would cause the problem after a haul out. Not once the system is primed and running not sure why you need a burp valve in the first place, I assume it’s just a valve you open to get air out. I ve never had to have one on any air con or water maker set up which would be no different from your ice machine I used to have a priming issue on a water maker which would loose prime after a run. Couldn’t figure it out everything running uphill, no high point, etc. The problem went away after we installed external scoop strainer. But in your case if it happens at the dock after the unit is shut down, that’s a different issue. As a band aid, can you extend the burp hose to a more accessible location?
The burp valve was installed to ease in priming after we are on the hard for the winter. Used to only have to do this once after we splashed then good all season. So something has changed but the plumbing configuration has not. I thought about routing a hose with the burp valve somewhere more convenient or using an electric ball valve with a convenient located switch. I may end up doing that but was hoping to solve the actual problem.
I would also look at a restriction somewhere in the system. A few dead shells could be restricting flow and causing priming issues yet allow the pump to run enough water once it’s going? how is the flow at the discharge? Are the coils running hot? have you made sure your diver cleans the thru hull? I be also seen shells stuck between the scoop and the thru hulls causing random issues. When was the system last descaled? You could also try to back flush the system to dislodge crap. as I ve said March pumps don’t suffer form erosion and performance drop with age but you never know …
There certainly could be a restriction somewhere. Doubt that it would be growth or shells but who knows what might have gotten in there. The AMOT valve is dialed down pretty far as it doesn’t take much of this cold water to keep it cool. Too much water and it shuts itself down hence the need for the AMOT. But this is same as it has been since installation. But I would think a restriction would cause flow issues continuously and not just at start up? But certainly can’t hurt to check it and back flush it to make sure. The thru hull is clean. Boat has only been in the water barely a month and we don’t get growth up here like you all do in that warm water. Suggestions and input are greatly appreciated - thank you!
AMOT valve ?? Can you open it up a lil more at a time and see if start up issues reduce or go aweigh? Like dead weight on a discharge line and the pump can not overcome it at start up. Maybe open the valve up some and install a lower flow pump.
I could see an air issue on the suction side but on the discharge side seems nuts to me. Must be the discharge air is actually accumulating in the impellor housing itself. The impellor housing gasket leaking, you'd think you would see a puddle. I always heard you could use shaving creme to find a suction leak. Messy but spray small amount on hose ends, pump impellor seal, etc and the creme will get sucked into the leak when it is running. I never had to try it though so maybe an urban legend ! What kind of head pressure can a March pump overcome ?
I had an issue where a big AC pump would not push water on start up intermittently. From the pump discharge, many dips in the 1" hose before the manifold that supplied water to 4 different AC stations, 15 feet aweigh and forward. These dips held water that the pump could not clear on start up. Leveled the hose and problem solved. My thoughts are this valve restriction is hard to overcome on pump start up. Water in the pump just churns. Re my post #11.
I think you guys are onto something with a restriction somewhere. I haven’t used this thing in salt water mode in a couple of years. So I flipped it over to Saltwater ice out of curiosity and the thing discharged and took right off without burping it. Now here’s the thing, the same March pump and AMOT feeds all the saltwater for cooling or making ice. So I don’t think the restriction is the AMOT valve setting as it still discharges thru the AMOT before getting to the machine. I’m going to let it run for an hour or so on saltwater ice mode then flip it back to fresh just to see what it does.
So I ran it on saltwater ice then shut it down. I started it on saltwater a second time and it kicked off just fine, no burping. I switched it back to freshwater and it started normally, no burp needed. So I’m not ready to declare victory by any means. We are headed out in the morning for a 3 day trip. I think I’ll run it on saltwater for this trip and see how it does. Upon return I’ll switch it back to fresh it try it as the manual says to flush it on fresh water mode after using saltwater anyway. I’ll report back upon our return.
Ice machine ran fine for three days on saltwater ice mode. We got back yesterday. Today I switched it to freshwater mode to flush it and it ran just fine. Go figure. Looks like I’m good for now. We’ll see what it does on the next trip in a few weeks.
So, Lets get to the important issues; What did you catch? How was it divided? Will I eat well when it comes in?
All the fish went to the vets. They caught Halibut limit all 3 days so 36 total over 3 days. Biggest were 84# and 68#. They took home about 175#'s of fillets. Sorry, I couldn't convince them to give up any to send to you
Ah heck yea, For the real guys. Certainly all and best to them. Looks like a bunch of big smiles. The land of the free, Because of the brave. God bless our service veterans.
I’m still fighting with my dang ice machine. Works sometimes then gives me fits other times and refuses to work. Doesn’t seem to be just a burp issue on the raw water pump now. I’m getting shutdowns on “High Freon Pressure” now. I’m going to get my local refer tech to take a look and see if he can figure anything out. Maybe a call to the factory as well. I do suspect my trouble is from the AMOT valve. Maybe not totally but pretty sure that’s contributing.
