AC loses prime

Anchor Management

Anchor Management

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Had this problem since I owned the boat. In fact, last owner put a petcock valve on helm intake line to let air out when it happens. Sometimes it re-primes on its own. The helm loses prime underway every time and the cabin occasionally. Never happens unless underway in either and there are no obstructions and they are placed towards the stern so never out of water. Both intakes are Searay factory installed. Boat has standard scoop strainers. Is there anything better to force consistent water flow? Thanks.
 
Does it happen only in rough water or smooth? Try keeping the bow down with the trim tabs.

Shouldn’t happen and it should reprime in its own anyway. Problem is that many builders don’t install pumps and hoses correctly. There should be no high point between the sea cock, strainer and inlet. Past the pump it doesn’t matter but not on the intake side. Often hoses are routed over stringers and back back down. Move the pump closer and inside stringers if that’s the case
 
Happens in smooth and rough waters. Strainer is 8” up from seacock and another 6” up from strainer to pump but all are very close in proximity. Never happens unless underway so I would think that the scoop would assist in driving the water. The intake just in front of drive shafts so I would not think the planing of the boat should come into play. Wondering if a more powerful pump would help.
 
Is the hose cheap ribbed bilge pump hose? If so replace it with smooth braided hose. It allows for higher prime hights for A/C pumps and greater output for bilge pumps. It's stronger and doesn't crack with age. Make sure you run it with softer bends so it doesn't kink. Don't buy the cheap stuff cuz it becomes tacky with age and isn't rated for below water line.
 
quote:
Originally posted by Stephen

Is the hose cheap ribbed bilge pump hose? If so replace it with smooth braided hose. It allows for higher prime hights for A/C pumps and greater output for bilge pumps. It's stronger and doesn't crack with age. Make sure you run it with softer bends so it doesn't kink. Don't buy the cheap stuff cuz it becomes tacky with age and isn't rated for below water line.

Click to expand...

Trident hose with very soft bends.
 
Could the pump be above the waterline on plane? How old is the pump and what type? Some of the cruisair with metal impeller loose suction as the impeller wears and cordless with age. March won’t have this problem
 
quote:
Originally posted by PascalG

Could the pump be above the waterline on plane? How old is the pump and what type? Some of the cruisair with metal impeller loose suction as the impeller wears and cordless with age. March won’t have this problem

Click to expand...

Since it’s only a foot higher than the seacock it should be below waterline under all circumstances but I will confirm next weekend. Not sure how old pump is but I’m just going to swap it out for a March and see what happens. Thanks for the advice.
 
Also some scoops have holes in the back to prevent pressure build up when used with generators Make sure yours doesn’t other wise plus the holes
 
Could be no scoop on the underside will create a vacuum that pulls air down. We had this issue in a Silverton and it turned out to be a twig had worked its way into the hosing that led to the strainer.
 
'Had this problem since I owned the boat. In fact, last owner put a petcock valve on helm intake line to let air out when it happens."
"The helm loses prime underway every time"
" and the cabin occasionally."
"Never happens unless underway"

Sounds like it was always a problem since the boat was built.
First place that may have some guidance is the Sea Ray owners site.
Sounds like you are saying that the one unit (helm) loses always and the other (cabin) sometimes.
Are they not both fed by the same pump and pickup which leads to a manifold of sorts?
Or do they have separate pickups and pumps?

If only underway and on plane I would look further forward on the hull for any other feature that could cause turbulance back at the pickups - I have found it takes very little to cause a large affect astern, much less than I would have thought.
 
quote:
Originally posted by smitty477

'Had this problem since I owned the boat. In fact, last owner put a petcock valve on helm intake line to let air out when it happens."
"The helm loses prime underway every time"
" and the cabin occasionally."
"Never happens unless underway"

Sounds like it was always a problem since the boat was built.
First place that may have some guidance is the Sea Ray owners site.
Sounds like you are saying that the one unit (helm) loses always and the other (cabin) sometimes.
Are they not both fed by the same pump and pickup which leads to a manifold of sorts?
Or do they have separate pickups and pumps?

If only underway and on plane I would look further forward on the hull for any other feature that could cause turbulance back at the pickups - I have found it takes very little to cause a large affect astern, much less than I would have thought.

Click to expand...

Separate pick ups and pumps but directly across from each other port and starboard and from what I just learned, it is fairly typical in this model so it could very well be too much turbulence. A friend recommended a positive displacement pump. I'm assuming losing prime is not an issue with this sort of pump??
 
quote:
Originally posted by Anchor Management

quote:
Originally posted by smitty477

'Had this problem since I owned the boat. In fact, last owner put a petcock valve on helm intake line to let air out when it happens."
"The helm loses prime underway every time"
" and the cabin occasionally."
"Never happens unless underway"

Sounds like it was always a problem since the boat was built.
First place that may have some guidance is the Sea Ray owners site.
Sounds like you are saying that the one unit (helm) loses always and the other (cabin) sometimes.
Are they not both fed by the same pump and pickup which leads to a manifold of sorts?
Or do they have separate pickups and pumps?

If only underway and on plane I would look further forward on the hull for any other feature that could cause turbulance back at the pickups - I have found it takes very little to cause a large affect astern, much less than I would have thought.

Click to expand...

Separate pick ups and pumps but directly across from each other port and starboard and from what I just learned, it is fairly typical in this model so it could very well be too much turbulence. A friend recommended a positive displacement pump. I'm assuming losing prime is not an issue with this sort of pump??

Click to expand...


Yes - positive displacement pumps have the ability to self prime within some reasonable limits but often have lower volumes. Please check that any pump meets the lower limits of volume flow for your AC applications.
 
quote:
Originally posted by Anchor Management

quote:
Originally posted by smitty477

'Had this problem since I owned the boat. In fact, last owner put a petcock valve on helm intake line to let air out when it happens."
"The helm loses prime underway every time"
" and the cabin occasionally."
"Never happens unless underway"

Sounds like it was always a problem since the boat was built.
First place that may have some guidance is the Sea Ray owners site.
Sounds like you are saying that the one unit (helm) loses always and the other (cabin) sometimes.
Are they not both fed by the same pump and pickup which leads to a manifold of sorts?
Or do they have separate pickups and pumps?

If only underway and on plane I would look further forward on the hull for any other feature that could cause turbulance back at the pickups - I have found it takes very little to cause a large affect astern, much less than I would have thought.

Click to expand...

Separate pick ups and pumps but directly across from each other port and starboard and from what I just learned, it is fairly typical in this model so it could very well be too much turbulence. A friend recommended a positive displacement pump. I'm assuming losing prime is not an issue with this sort of pump??

Click to expand...


Yes - positive displacement pumps have the ability to self prime within some reasonable limits but often have lower volumes. Please check that any pump meets the lower limits of volume flow for your AC applications.
 
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