Hi
guys,
The US Navy
seems to prefer bronze over stainless for saltwater. I use stainless for
welded components and bronze for bolt-on stuff. I also like to use ?liquid
tight? flexible electric conduit for exterior non ?pressurized systems like
ballast tank vent line. Liquid tight fittings are made to go through bulkheads
(like electrical enclosures) and come with both o-rings and NPT so you can
combine them with other NPT hardware. The hose-ends are union style and the
hose is easy to cut/ assemble. The plastic (PVC) is UV stable and made for
lengthy outdoor service. Best of all, it?s really cheap!
Greg
C
-----Original
Message-----
From:
owner-personal_submersibles@psubs.org
[mailto:owner-personal_submersibles@psubs.org] On Behalf Of
ShellyDalg@aol.com
Sent: Sunday, January 04, 2009 12:57
PM
To:
personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Soft ballast
venting valve
Hi
Brian. The stainless ball valves are the most common valve used for this, and
although they do get harder to turn after a while, they are easy and cheap to
replace. There are basically two kinds of ball valves. The more expensive type
are "repairable" and have little bolts holding them together, while the cheap
ones are simply replaced.
With
the repairable ones, a little adjustment is possible by loosening the bolts
slightly as the delrin seats age and the valve gets harder to turn. You can
lubricate the ball on both types to extend the life a bit, but replacement is
usually necessary after 3 to 5 years, depending on how often the valve is
turned and how many pressure cycles it has withstood.
Depending on where
you take the sub, that term can be shortened by how clean the water is, and of
course what maintenance schedule you have. Salt water with normal particulates
will reduce the life span, while sand or grit can ruin a valve very quickly.
The
plumbing system should be designed for ease of maintenance, with high quality
"unions" located in the line so replacement of individual components is
possible.
Swagelock fittings
and stainless tubes are good choices for the air system but very pricey in the
larger sizes so typically the ballast dump system is hard piped.
Another
choice is the use of "butterfly" valves located directly on the tanks, driven
by electric or hydraulic actuators. You could even have a mechanical rod drive
the valves, using the "block-V" seals where the linkage rod passes
through the hull.
The
number of through hull fittings is the same with both methods, two per tank.
I'll be
using the hard pipe ball valve method because it's simple and cheap.
I will flush the system after each dive with clean fresh
water. But because I'll be diving the sub near shore, I expect to
get some grit and sand in there and will probably need to replace the
valves fairly often.
A good
quality stainless ball valve at 1-1/2 inches runs about $150, while a brass
valve is about $25 to $50.
The
ball and seats are the same, just the body is different. Pressure ratings
typically are 600 psi. Exotic seats and high pressure ratings ( 1500 psi ) are
possible but not needed in my application.
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