A/C Raw water pump size

[Kquaine]

Anybody know what the factory raw water a/c cooling pump flow rating is? I have a shipyard telling me that the current units are undersized and that I should increase the flow rate. I have a 1988 67’ CPMY. Thank you

 

[Captain Ralph]

Anybody know what the factory raw water a/c cooling pump flow rating is? I have a shipyard telling me that the current units are undersized and that I should increase the flow rate. I have a 1988 67’ CPMY. Thank you

There is a spec;
GPM per BTU.
You probably have 2 AC raw water pumps, one each for half of your ACs.

We need the pump size-model and total BTU that each pump supplies water to.

I'll dig up that spec if another member does not recall it of the top of their head.

 

[firbanks]

I have same boat same year. I have run for 6 years in South Florida with AC going continuously all seasons with March AC-5C-MD pumps, nominally 1,000 gallons per hour. Keep the strainers clean and barnacle bust the condensers when needed. Two things made a big improvement. First, I replaced the hose run from the strainers to the pumps to the manifolds in the generator room - what came out was in rough shape and impaired flow. Second, after having some challenges on the electric motor side of the march pump, I found that the start capacitors were failing (2-3 over one year) but that the motors we actually fine (based on taking it to a motor rebuild shop each time). I now leave the hatch cover off the small bilge area where the pumps sit so they get better air flow and no more capacitor issues...just have to make sure not to break an ankle walking in the port engine room. If the water temp there is much higher than south fla or if you have tons of silt, you might need more velocity/flow rate.

 

[Kquaine]

I have the 17.2 gpm(1032 gph) rated pump. Pm-1000-115, I have already replaced the suction (input) side hoses and strainers. I actually rotated the strainer so that the cap is pointing vertically up instead of horizontal to the side. I am in the process of replacing the discharge (output) hose between pump and manifold. Hopefully that clears thins up.

 

[Pascal]

Basic formula is 180 gph per ton/12k BTU

Note that pumps with bronze body and impellers (cruise air / oberdorfer or Scott) suffer from erosion with time and will loose flow

I monitor the coil temperatures to spot trends and avoid high pressure shut downs. Most of the time when temps start going up it s not the pump but restrictions on the system due to growth and shells. Shells have become a big problem in summer is sofl. I have rigged my chillers with fresh water back flush which help reduce the frequency of barnacle busting sessions

 

[Kquaine]

There is a spec; GPM per BTU.You probably have 2 AC raw water pumps, one each for half of your ACs.We need the pump size-model and total BTU that each pump supplies water to.I'll dig up that spec if another member does not recall it of the top of their head.

The nominal flow rate is 3 gpm per ton (or per 12,000 btu)

 

[Kquaine]

Basic formula is 240 gph per ton/12k BTUNote that pumps with bronze body and impellers (cruise air / oberdorfer or Scott) suffer from erosion with time and will loose flow I monitor the coil temperatures to spot trends and avoid high pressure shut downs. Most of the time when temps start going up it s not the pump but restrictions on the system due to growth and shells. Shells have become a big problem in summer is sofl. I have rigged my chillers with fresh water back flush which help reduce the frequency of barnacle busting sessions

How did you provide the flush functionality? What type of fittings did you use? Where in circuit did you place it?I would think you would place it near the pump discharge so that you flush from pump to thru hull.

 

[Pascal]

It all depends on how your air cons are setup.

I added a Tee and two valves on the discharge side of each units so I can hook up a water hose from the ER faucet. When I need to back flush, I shut off that chiller, shut off the valve at the manifold, disconnect the hose at the manifold and put it in a bucket. Then switch the valves on the discharge side and hook up the hose. Whatever shells are trapped in the system get flushed in the bucket

I use the same setup when I need to descale.

I set up a similar system on the 116 I run with 3 chillers except that I was able to hard plumb into the fresh water system. No garden hose. I also have valves and tees on the other end to collect the debris

Every boat is different but the key is to set it up to back flush so anything trapped at the coil intakes gets flushed out

 

[rwaldrop13]

I have same boat same year. I have run for 6 years in South Florida with AC going continuously all seasons with March AC-5C-MD pumps, nominally 1,000 gallons per hour. Keep the strainers clean and barnacle bust the condensers when needed. Two things made a big improvement. First, I replaced the hose run from the strainers to the pumps to the manifolds in the generator room - what came out was in rough shape and impaired flow. Second, after having some challenges on the electric motor side of the march pump, I found that the start capacitors were failing (2-3 over one year) but that the motors we actually fine (based on taking it to a motor rebuild shop each time). I now leave the hatch cover off the small bilge area where the pumps sit so they get better air flow and no more capacitor issues...just have to make sure not to break an ankle walking in the port engine room. If the water temp there is much higher than south fla or if you have tons of silt, you might need more velocity/flow rate.

I had same pumps in Pau Hana and when I had the OOTB problem with the second MarineAire unit I installed, they told me it was too high a flow rate with that pump. We were in Ft Myers, FL and after I got that unit repaired from the factory-installed problems, I had 3 single-piece units running off 2 pumps. I had pumps on continuous run, and weekly I flushed the lines from the strainer with dock water pressure. They cooled beautifully. I doubt the pumps are the issue, try replacing the hose from the intakes and strainers.

 

[firbanks]

I have the 17.2 gpm(1032 gph) rated pump. Pm-1000-115, I have already replaced the suction (input) side hoses and strainers. I actually rotated the strainer so that the cap is pointing vertically up instead of horizontal to the side. I am in the process of replacing the discharge (output) hose between pump and manifold. Hopefully that clears thins up.

Also shifted my a/c seawater strainers to vertical - makes it alot easier and keeps the bilges dry.

 

[rwaldrop13]

Also shifted my a/c seawater strainers to vertical - makes it alot easier and keeps the bilges dry.

Depending on your strainer type (I had Groco), you can get a flushing cap on Amazon that lets you attach a washdown hose to the strainer and flush thru the system. That was how I flushed my lines weekly. I never even considered aligning the strainers horizontally. AC systems took up a lot of my maintenance time on a weekly basis but paid off in comfort when we were hitting 95+ degrees with 99% humidity... at night!

 

[Pascal]

Flushing from the strainer forward isn’t going to help much as whatever is restricting flow, usually at the coils inlet or at fittings, will just be pushed tighter against the fitting flanges. You want to back flush instead and remove the pieces from the system

 

[Kquaine]

Flushing from the strainer forward isn’t going to help much as whatever is restricting flow, usually at the coils inlet or at fittings, will just be pushed tighter against the fitting flanges. You want to back flush instead and remove the pieces from the system

That makes sense. Also explains why the hose fitting is on the discharge side of condenser. Thank you

 

[pmacFL]

I enclosed a few photos from the starboard replumb of the ac pumps. I like the groco strainer much better than the old. The port side still has the perko mounted horizontally, which spills seawater everywhere when cleaning. And tends to render the pump un-primed.The pump is a march te5.5c MD

 

[Pascal]

Next haul out just put an external strainer aka South Bay strainer and you ll Never have to clean the internal again

I ve put them on my boat and every boat I ve run. What a difference!

 

[rwaldrop13]

Flushing from the strainer forward isn’t going to help much as whatever is restricting flow, usually at the coils inlet or at fittings, will just be pushed tighter against the fitting flanges. You want to back flush instead and remove the pieces from the system

I would backflush if needed, just a matter of hooking my homemade hose connector to the discharge side line where I had a t-valve for this purpose. The weekly dock water flush pushed loose stuff thru, and I ran each leg for about 30-40 minutes. If I had to backflush, it was usually from the strainer to the thru-hull where something had sucked up against the hull. At least once doing this I got outside in time to grab a boathook and snag a grocery bag that came up on the bubble.

 

[rwaldrop13]

Next haul out just put an external strainer aka South Bay strainer and you ll Never have to clean the internal again

I ve put them on my boat and every boat I ve run. What a difference!

I'm putting this in my future-boat notebook Pascal... Thanks.