Letters to the Editor Web Extra
CO DETECTOR SAFETY
I love reading Steve D’Antonio’s articles and hope he can answer my question about his newsletter article on CO detectors (Channels Jan. 2011, Vol. 1). His statement that the density of CO gas is “neutral” raises a question regarding the mounting of detectors. We know that propane is heavier than air, and therefore propane detectors need to be mounted low in the boat, but at what level should I mount my CO detector? Should it be low to the floor, middle-of-the-bulkhead height, or at the same level as, say, my pillow when I’m sleeping? Or doesn’t it matter?
North Saanich, British Columbia
All carbon monoxide detector manufacturers include guidance for choosing an installation location in the instructions that come with the detector. For detectors specifically designed for marine applications, most suggest installing the units at eye level, although it’s not uncommon to see them on overheads. Areas that should be avoided as installation locations include corners and other places where air movement may be impeded, such as lockers or closets. Areas adjacent to ports or other ventilation inlets, where incoming fresh air may skew readings, also are less than ideal.
CO detectors that are combined with smoke detectors, such as those designed for homes, must be installed high, preferably on the overhead. These units are very sensitive, and because CO has nearly the same density as air, they are likely to work nearly anywhere they are installed, with the exception of the aforementioned locations. Follow the manufacturer’s instructions, and the CO detector you install is likely to work reliably.—Steve D’Antonio
WORRIED ABOUT WATER INTRUSION
An oil analysis on my 1989 200bhp Volvo turbo diesel found salt water in the oil. Because of the damage incurred, I had a certified Volvo mechanic rebuild the engine. When he replaced the exhaust pipe elbow, it did not have a valve to stop water intrusion. He said Volvo does not sell the exhaust elbow with the valve, because it will corrode and fail, as mine did. I now have to rely on my exhaust flapper to stop water intrusion, and I am concerned that I will have further water problems. What else can be done, or am I protected adequately?
I really enjoy PMM and have saved every issue since the first one.
Your mechanic is correct; few engines rely on a check valve to prevent water intrusion, nor should they. The environment inside a water-cooled exhaust is a hellish one indeed. With near-1,000° exhaust gases making contact with cold, corrosive sea water, it’s a wonder they last as long as they do.
The primary method of preventing water from traveling the wrong way—back up your exhaust and into your engine—is ensuring that your exhaust system’s design complies with the requirements set forth by the manufacturer (Volvo, in your case). Virtually every marine engine manufacturer establishes guidelines for this design, instructing the boatbuilder or engine installer as to how the exhaust system should be built and installed. (Some guidelines are more specific than others.) Exhaust systems are nearly always designed, built, and installed by the boatbuilder, rather than the engine manufacturer, and as such, the builder carries the full weight of responsibility for making certain the installation is compliant. Many exhaust systems I inspect, both used and new, are not.
I strongly advise that you obtain the installation instructions for your engine and make certain your exhaust and other critical systems are fully compliant. Doing so will prevent a recurrence of the unfortunate episode you experienced. Finally, while the rubber flapper installed on the exhaust outlet may be beneficial, it should not be relied upon as the only means of preventing water entry into the exhaust system and into the engine. (For more on properly setting up a wet exhaust system, see “Gearhead” PMM Oct. ’10.)—Steve D’Antonio
WHICH CHECK VALVE IS BEST?
I’m making a few improvements to the domestic water system on my boat, a Nauset 35, and I have a question about check valves. My original 3/4-inch NPT brass Strataflo Products check valve is a spring-loaded valve and was connected directly to the cold-water inlet side of my water heater. I suspect the valve was not working well, as we often got hot water at the cold tap after running the engine.
At home-improvement stories, I could only find brass check valves that have a swinging “flapper,” which seems less than ideal in this situation. I bought a 1/2-inch SHURflo inline check valve, only to find that the instructions inside the package say “Do not use for water heaters.”
Can you suggest an appropriate check valve to use for this application?
Harvey McChesney III
You were on the right track with the brass swing check valve. These are commonly used in water heater installations, and, for the most part, they work well and are long lasting. If you purchased the valve in the domestic plumbing section of a home-improvement store, you can be reasonably certain the valve is suitable for potable water. Remember that not all plumbing is appropriate for potable water; some alloys contain lead or other metals that could be harmful to users.
Certain caveats should be noted when using a check valve in a raw-water or seawater application. In these cases, check valves are prone to becoming lodged in the “open” or “closed” position, reducing flow. Brass valves used in raw-water applications are prone to corrosion through dezincification. However, these issues are of little concern when check valves are used at water-heater inlets or elsewhere in potable water systems.
The primary reason for installing a check valve in a water-heater inlet is to prevent the water heater from emptying itself in the event that the vessel’s water tanks run dry. If this happens and the water heater isn’t protected against such an occurrence (some water heaters have a burnout protector), the water heater’s electric heating element will almost certainly burn out.—Steve D’Antonio