Seacocks and Ball Valves

2 posts in this topic

Posted Image

A seacock is made to fit a thru-hull fitting which is NPS (national pipe straight) threads.  The top of the seacock is NPT (national pipe tapered) thread to take a hose barb fitting.  It is important that the thru-hull fitting fit all the way onto the base of the seacock which will be significant threads seating in the base providing a strong leak proof seal.



Ball valves: Posted Image

Ball valves have NPT tapered threads on both ends and should not be used with a thru-hull fitting below the waterline.  Since the thru hull fitting is straight thread and the ball valve is tapered, when screwed in, there will only be about 3 to 4 threads before it binds up.  In a thru hull situation, there is only a small amount of the thru-hull fitting on the ball valve and with time and corrosion, any pressure placed on opening or shutting could cause the fitting to fail.

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