More on Pumps, Flow & Maintence…Larger Pump ?


September 2, 2009 Facebook Twitter LinkedIn Google+ About,AC/Systems,Maintence Tips,Marine AC



Below is another copy of a  post I made in the Meridian Owners Forum...If you want the full jest...http://www.meridianyachtowners.com/forum/forums/thread-view.asp?tid=1957&posts=15#M18424

Hi Mark...Don't know if you are still watching this thread, or if you have seen my thread over in the "Introduce Yourself" forum but here's my take...

It seems that when the system was flushed, that it was flushed just well enough to break loose some stuff...Now it is floating around in the hoses and randomly blocking flow where it now lodges from time to time...
Once the pump shuts off the water drains back, and with it the loose stuff moves...Only to lodge again maybe somewhere else when the pump starts again...

If the water flow does not look right to you (and you obviously have been watching it since new) then it is not right, and will continue to get worse...Changing the pump will not fix a thing unless the pump had a problem...It can only pump water thru unrestricted passages, and that water it can pump will re-direct to the un-restricted passages...Like said...Path of least resistance.

From descriptions here & in the thread I started...It seems the 459 has what I would call a odd or improper A/C plumbing/pump setup...

This happens sometimes with boat builders...Generally speaking...In my experience the only way to get them to make a change in a poor setup is for enough customers to have a problem and complain...No amount of prodding from us A/C guys ever seems to help in effecting that change...It's a shame too because we are the ones dealing with this stuff everyday...They deal with building boats everyday...

So what is the fix ?...Well marine growth will always be a problem but there are a few things that can be done to help...

Over the years the A/C systems that boat builders install have gravitated to the Self Contained all in one units as opposed to the Split/Remote systems that most utilised for years...They don't need guys with refrigerant certification to install or buy these All in One units...They are easier to install, and freon leaks in connections of copper tubing line runs are no longer something they need to worry about warrantying....All they have to do now is run power, water hoses from the pump, and duct...

The problem with this is the water runs are now much further than when the "Central" type systems were installed all in one location close to the pump...Back then we had very little growth problems (just scale buildup in condensers that was easy to remove) and flow was much easier to plan & maintain...

What I have found since this change is that the further, and or higher you pump seawater...The more problems you will have with growth, and it has also created the problems I describe below with using larger pumps...

Directing a pumps flow to units of varying distance & height for even flow to each...Is a challenge to say the least !
Generally their answer is to install an oversized pump in an attempt to brute force flow...

No I have not seen a 459 but it has been described as having two units on the bridge and 2 down below...I don't care how they manifold this setup...It still going to be very hard to get the proper flow to each unit, and the least little restriction can and will upset any kind of balance they have designed into that system...The Pump has to overcome the height (Head) it needs to pump to the units on the bridge so it likely has been over sized just to do that with enough volume for those units...The remaining water can then supply the lower units...

Over sized pumps are never really the best answer over time (though it may be cheaper for them) because a over sized pump attempting to pump thru say four 5/8" condensers (in this case) is (even when the system is clean) likely not pumping it's rated flow which will cause it's impeller to cavitate...This causes cavitation burns to the bronze impeller & pump housing...Thus causing premature pump head failure.

Again having not seen the install...My answer would be to install two pumps...One for the upper units, and one for the lower units...
They both could then be sized for the job presented, the systems & pumps would be much happier with less overall maintenance.

Steve~