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  1. #1
    Join Date
    Jun 2019
    Location
    Scarborough
    Posts
    629

    Default Use a ball valve on the exhaust outlet?

    Can the nylon type material in a ball-valve type seacock stand continuous 80 degrees C exhaust gases, and warm water ?
    I think it might be useful to close the exhaust skin fitting sometimes, and it woukd help with fitting the hose tail.
    2" BSP thread with 51mm internal diameter hoses. The skin fitting has a male thread, and the hose tail has a male thread, and the valve has two females to conveniently join them together.
    ( You can get skin fittings in this size incorporating a hose tail, but thry're too short to go through the hull planks and internal pad)
    So I have two good reasons to use a ball valve, if the valve can handle it.
    Yes I must not carelessly start the engine with the valve shut

  2. #2
    Join Date
    Dec 2012
    Location
    Gone cruising
    Posts
    2,395

    Default Re: Use a ball valve on the exhaust outlet?

    From the data sheet for Tru-Design ball valves:

    operating temperature range
    o -40 to 80C (-40 to 176F)
    Their skin fittings go to 110C. They're resistant to many chemicals, including diesel fuel. No special mention of exhausts. They're definitely not designed for it, there's not a lot of safety margin, and if you ever have a cooling water interruption the plastic fitting will melt quickly, same as the plastic mufflers do. Exhaust hose is rated to 100C and 115C for short-term, so I would want anything else to have at least that much.

    Still a really bad idea to have a seacock on the exhaust though for obvious reasons. Also, wet exhaust skin fittings typically have a drip lip or tube to reduce hull staining, which standard skin fittings (plastic or otherwise) lack.

    In what situation is a closable exhaust useful, building a submarine?

  3. #3
    Join Date
    May 2007
    Posts
    38,236

    Default Re: Use a ball valve on the exhaust outlet?

    Not generally required, but I could introduce people to two individuals who've lost engines due to water up the exhaust in following seas while sailing.
    Personally, I'd rather have a non-return flap or put a bung in the transom fitting in such seas, but I appreciate that is not right for every boat.
    If you have some vintage yacht with a narrow arse-end, it may be worth considering.

  4. #4
    Join Date
    Jun 2019
    Location
    Scarborough
    Posts
    629

    Default Re: Use a ball valve on the exhaust outlet?

    Quote Originally Posted by lw395 View Post
    ...some vintage yacht with a narrow arse-end...
    Guilty as charged!
    Yes I have bungs etc, and I can't think why I shouldn't have a seacock in the exhaust, I have used a bung before for the reasons you mention. Can't do any harm.

  5. #5
    Join Date
    Jun 2019
    Location
    Scarborough
    Posts
    629

    Default Re: Use a ball valve on the exhaust outlet?

    Quote Originally Posted by Yngmar View Post
    From the data sheet for Tru-Design ball valves:



    Their skin fittings go to 110C. They're resistant to many chemicals, including diesel fuel. No special mention of exhausts. They're definitely not designed for it, there's not a lot of safety margin, and if you ever have a cooling water interruption the plastic fitting will melt quickly, same as the plastic mufflers do. Exhaust hose is rated to 100C and 115C for short-term, so I would want anything else to have at least that much.

    Still a really bad idea to have a seacock on the exhaust though for obvious reasons. Also, wet exhaust skin fittings typically have a drip lip or tube to reduce hull staining, which standard skin fittings (plastic or otherwise) lack.

    In what situation is a closable exhaust useful, building a submarine?
    Thanks for looking it up, 80 degrees C is fine.

    Yes a closeable exhaust is useful to keep water out..just like a submarine

    What are the obvious reasons it's a really bad idea? (Assuming I can remember to turn the seacock when needed, and it doesn't melt the nylon. Although if the nylon melted, it wouldn't block the exhaust.)

    I'm ok with a bit of hull staining, any protrusion would receive or inflict damage when springing off.

    I may indeed have forgotten something obvious, don't know what though.

  6. #6
    Join Date
    Jun 2013
    Location
    scotland
    Posts
    206

    Default Re: Use a ball valve on the exhaust outlet?

    Had one on a previous boat. I owned boat for 16 years and only ever closed it when laid up over winter incase wildlife used exhaust as a home. So it didn't come to any harm after 20 years or so. But if you have a decent gooseneck fitted in the exhaust you should be ok. Only problem I could see happening is the one time you close the valve will the time you forget to open it, then start the engine. You can buy a valve that contains a ball and a spring for the exhaust that prevents water from flowing back towards engine, but the increase back pressure slightly and may be more trouble than they are worth when they age.

  7. #7
    Join Date
    Nov 2001
    Location
    Me: Johannesburg South Africa Yacht: Richards Bay East Coast Africa
    Posts
    7,128

    Default Re: Use a ball valve on the exhaust outlet?

    This is a stainless steel ball valve in my engine exhaust that exits on the port side. I fitted it to allow me to beach my boat on its side.

    The seals are PTFE which has a higher temperature rating than nylon.

    Life is too short not to have a sea view
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  8. #8
    Join Date
    May 2001
    Location
    South Dorset/moored Poole/lay up Wareham
    Posts
    340

    Default Re: Use a ball valve on the exhaust outlet?

    Alternatively a large gate valve, provided it is above waterline & importantly, operated frequently, which is easier said than done in reality then no problem with high temperatures although a high loop at the transom is very much the best idea if it can go high enough.
    www.seasurveys.co.uk
    Surveying & Shipwright info on GRP, WOOD & so much more

  9. #9
    Join Date
    Dec 2007
    Location
    S.W. France
    Posts
    7,692

    Default Re: Use a ball valve on the exhaust outlet?

    Assuming a water cooled exhaust, why would you be concerned about the temp at the transom fitting? The hose to get there is subjected to the same temps, so after the water injection at the exhaust elbow point, it does not matter.

  10. #10
    Join Date
    Jun 2019
    Location
    Scarborough
    Posts
    629

    Default Re: Use a ball valve on the exhaust outlet?

    Quote Originally Posted by DownWest View Post
    Assuming a water cooled exhaust, why would you be concerned about the temp at the transom fitting? The hose to get there is subjected to the same temps, so after the water injection at the exhaust elbow point, it does not matter.
    Yes watercooled through a Vetus trap/silencer.
    I was thinking of the nylon type stuff in the ball valve not liking warmth from the exhaust gases. I don't now think it would be a problem heat-wise.
    But the valve was really just a way to join two male 2" BSP threads together, with the added benefit of being able to close the exhaust.
    Finally I have found a suitable female to female bronze fitting, (just by using the right search terms on ASAP..) so I'm not using a valve in the end anyway.. but thanks for all the suggestions!
    Attached Images Attached Images
    Last edited by Ohlin Karcher; 06-09-19 at 18:16. Reason: being clearer

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