{Stus-List} Valves - a primer

Dennis C. captbuy at yahoo.com
Mon Jun 8 08:57:20 EDT 2009

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 carburetor?)
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 boat.
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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