{Stus-List} Valves - a primer

Nate Flesness nate at isis.org
Mon Jun 8 14:31:40 EDT 2009

Thanks to all for the in-depth lesson in valves...  

I have replacing the original (gate) valves on my long todo list, looks
like I'll move it higher.

Freshwater gives us old boat owners more time then salt does, but not



"Sarah Jean"

1980 30-1


From: cnc-list-bounces at cnc-list.com
[mailto:cnc-list-bounces at cnc-list.com] On Behalf Of Dennis C.
Sent: Monday, June 08, 2009 7:57 AM
To: cnc-list at cnc-list.com
Subject: {Stus-List} Valves - a primer


FWIW, just a brief primer on valves.  Probably more than most want to
know.  See the bottom for commentary on usage of valves in boats.


1/4 turn valves - lever type handles; generally open when handle is
aligned with flow; closed when handle is perpendicular to flow

*	Plug valve - has a cylindrical or tapered plug with a hole which
is either aligned with flow (open) or across flow (closed)
*	Ball valve - has a ball with a hole which is either aligned with
flow (open) or across flow (closed)
*	Butterfly valve - has a "wafer" which is either aligned with
flow (open) or across flow (closed)

Gate valves

*	True gate - has a round handle.  Rotating the handle causes the
gate to move up or down a threaded shaft into (closed) or out of the
flow (open)
*	Swing gate - has a lever which swings the gate across the flow
to open or close.  

Knife valve

*	Similar to a gate valve but the "gate" is very thin.  These are
commonly seen as sluice gates in drainage applications.  Rotating round
handle, threaded shaft

Globe valve

*	Globe valve - has a rotating handle and threaded shaft like a
gate valve but instead of a gate it uses a disc which either sits hard
on a seat (closed) or rises off the seat to allow flow (open).  Many
older bathroom fixtures are a form of globe valve.  I suspect most
residential garden hose spigots are globe valves.  If it has a round
gasket and a seat, it's probably a globe type valve.

Pinch valve

*	Pinch valve - Rotating handle which squeezes a flexible tube to
stop flow. 

Needle valve

*	Rotating handle inserts or extracts a thinly tapered plug along
a tapered seat.  Think carburetor idle adjust valve (I know, what's a

Ball valves (and possibly plug valves) are, IMHO, the best choice for
boats and are standard for many OEM applications today.  Assuming the
handle stem doesn't break, they will always close.  If there is debris
or marine growth in the valve, the ball will either slice through it and
close or not close at all.  It's obvious whether they're open or closed.


Gate and globe valves can present boatowners with a couple of issues.
First, because they are a "seating" type valve, debris or marine growth
can foul the valve seat.  When this happens, the gate may crush the
debris onto the seat and the valve may fail to completely close.
Without disassembling the valve, you usually cannot resolve the issue.
Second, if the stem corrodes and shears off or the threads corrode, the
handle can spin freely and the gate not move.  The boatowner will not
know if the valve is open or shut.  I had this problem on a previous


Touche' had several swing gate valves when I bought the boat.  One of
them got debris in it and would not fully close.  I have replaced them
with ball valves.


Dennis C.

Touche' 35-1 #83

Mandeville, LA



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