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Seacocks are often awkward to get at, awkward to open and close, and often ignored. Should they fail, the results can prove disastrous.

Most seacocks are sited well below the waterline, so they cannot be ignored if your vessel is to remain safe. If seacocks are always left open and neglected they can eventually seize which will prove a serious threat to boat safety should a connecting hose fail and the seacock refuses to close. There are three main types of seacock – ball valves, cone valves and gate valves.

Servicing seacocks

All through-hull fittings, including seacocks, should be serviced at least once a year. As well as cleaning and re-greasing the seacocks themselves, the condition of the hoses and stainless steel clips need to be checked and replaced as necessary. Make sure two hose clips are used at each end of the hoses connected to seacocks.

  • Ball valves – ball valves are hard wearing, but can stiffen and seize if they are not kept greased, which will also make them more likely to corrode. If a ball valve has become very stiff or seized, the first thing to do is use penetrating oil to try and loosen it. Even if it the valve is moving reasonably satisfactorily, it will still pay to take it apart and check it for corrosion, give it a clean and apply fresh waterproof grease to help keep it in good working condition. If on inspection the valve looks seriously corroded, then be prepared to replace it with a new one, even if it is still working, as trouble could be brewing. Remember to order a marine grade valve as they are also made for domestic systems.
  • Cone valves – cone valves are usually made of bronze. They have a conical tube or plug that fits inside a cylindrical body which connects to a hose. The plug has a whole in one side and as it is turned by a handle the seacock is opened and closed. Although bronze is hard wearing the plug needs to be kept greased so that it can turn smoothly and to prevent corrosion. The plug is held in place by a keeper plate with two bolts and locking nuts which need careful adjustment to allow the valve to operate smoothly.

To service the valve, undo the keeper and remove the plug. Clean the plug and housing using a degreasing agent. Check the condition of the plug. Use grinding paste or fine wet and dry paper to polish the plug smooth before adding fresh seacock grease – note that any old grease is not recommended, it is best to use the manufacturer’s recommended waterproof grease, even if this is pricey. If the plug is badly pitted then it might need replacing.

  • Gate valves – gate valves should also be greased and inspected annually. They are usually made of brass with a circular handle connected to a threaded rod which moves up and down to open and close a gate in the valve. They are more prone to failure than cone and ball valves, being very susceptible to corrosion in the marine environment. The handles can get very stiff to operate and if they seize they will most like need to be replaced. If so, it would be best to replace with a ball or cone valve, which are considered more reliable. A big drawback with gate valves is there is no way of knowing whether the valve is open or closed when it is seized.

To service a gate valve, remove the valve body and dismantle it. Check for corrosion, clean and re-grease. Also check for damage to the bottom part of the gate which is quite common.

  • Jammed seacocks – seacocks can seize through lack of maintenance, corrosion or through lack of use. If a seacock is seized, start by spraying it with penetrating oil and leave it for an hour or two. Applying heat from a hot air gun also works. Resorting to a hammer is not good.

International Standard

The international standard for metal seacocks and through-hull fittings is ISO 9093-1:1998. When replacing a seacock check the replacement complies with this standard. Sub-standard fittings are more likely to corrode and fail.

Tips:

  • Make a note of where all seacocks and through-hull fittings are located.
  • Ensure all hoses attached to seacocks and through-hull fittings have two stainless steel hose-clips.
  • Tie a tapered softwood plug to each seacock and fitting. Plugs can be hammered into a hole in case of a fitting failure.

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