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Old 01-12-2020, 15:56   #1
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Washdown pump - suck or blow?

Dumb question of the day. I will be installing a wash down pump on my Catalina 36. I can put the pump either close to the through-hull or close to the outlet forward. Does better sucking (close to the outlet) or better blowing (close to the inlet) make more sense or does it not really matter?
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Old 01-12-2020, 16:49   #2
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Re: Washdown pump - suck or blow?

Depends on if the pump will even suck

I would plan that it is better to have the pump below or at least close to the waterline depending on pump type
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Old 01-12-2020, 19:41   #3
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Re: Washdown pump - suck or blow?

Most pumps suffer more from inlet restrictions than outlet restrictions. So put the pump closer to the thru hull.
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Old 01-12-2020, 19:45   #4
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Re: Washdown pump - suck or blow?

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Originally Posted by rslifkin View Post
Most pumps suffer more from inlet restrictions than outlet restrictions. So put the pump closer to the thru hull.
Yes, This
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Old 02-12-2020, 11:40   #5
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Re: Washdown pump - suck or blow?

Putting almost any pump with its intake under positive pressure improves its performance.

Any leak on the suction side (which if you mount your pump above the water line will be under negative (relative to atmospheric) pressure and will admit air.
Air bubbles in your suction line will greatly degrade pump performance.
Think of positive pressure on the suction side as supercharging your pump
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Old 02-12-2020, 11:47   #6
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Re: Washdown pump - suck or blow?

Place it close to your intake. Much less likely to have a priming problem.
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Old 02-12-2020, 11:50   #7
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Re: Washdown pump - suck or blow?

I can't help myself. Suck, blow is only a figure of speech.
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Old 02-12-2020, 11:51   #8
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Re: Washdown pump - suck or blow?

Also don’t forget to put in a place that’s easily accessed, but below the water line is best.
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Old 02-12-2020, 12:58   #9
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Re: Washdown pump - suck or blow?

Mine (installed by PO) had a long intake run from the forward head intake, through the forward cabin into the sail locker. Over time (and a couple of blocked inlet events) the nearly right-angle bends in the hose began to flatten out. Moving it was impractical (I really tried) so I replaced the hose with a spiral reinforced type that won't (so far) crush. My aft washdown also has a long run, but it's T'd from the aft head intake with only a foot of hose. In other words, blow, definitely blow.
Also consider how you will be getting power to the pump - sometimes more hose is easier than more wire.
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Old 02-12-2020, 13:17   #10
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Re: Washdown pump - suck or blow?

Quote:
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I can't help myself. Suck, blow is only a figure of speech.

...and it eventually comes down to personal preference.
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Old 02-12-2020, 14:13   #11
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Re: Washdown pump - suck or blow?

Seems unanimous (which is rarely the case on CF). Now on to anchors to have onboard.
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