Gate Valves

I had interesting yesterday surveying a 30 year old Pearson 424. The boat was in remarkably original condition and had been very well cared for. There was very little wrong with the boat although I did find the usual suspects of sea cocks that were frozen open and this little beastie which the new owner will be replacing before recommissioning the boat.

Gate valves should never be used as skin fittings for a number of reasons. They are often, think usually, made of brass, which will dezinctify when exposed to salt water turning them to a soft mush from the inside out and it is impossible to tell if the valve is open or closed at a glance. A proper sea cock will have a lever style handle which will clearly show when it is open as the handle will be in line with the pipe, moving it 90 degrees closes it. A gate valve on the other hand can only be checked by screwing down the handle and if there is anything under the seat of the gate then it will not fully close thus making it impossible to shut off the water. Gate valves are often fitted by well meaning DIYers who think that they can save money by popping in to Home Depot and picking up a valve for a fraction of the cost of a proper sea cock. But this may well be a question of penny wise and pound foolish. If the sea cock fails the boat could well sink costing the owner dearly.

Also closer inspection of the picture above highlights several other problems with the installation, there is no backing block to the skin fitting and the hoses should be double clamped with the screws at 180 degrees to each other.

Comments

[Bill Parks]

Mark you are right on. I've seen a lot of failed gate valves used just like that. It is always the stem that fails inside the valve where you can't see it. Another thing I don't like about this installation is that the valve is just screwed onto the thru-hull. Thru hulls can and do break. Someone stepping on that valve or hitting it whith something heavy could snap the thru-hull right off. Where is the tapered wood plug to jam in the hole? A fellow from the ABYC told me it was ok to use a ball valve instead of a gate valve but I will only use a flanged sea cock with the flange fastened to the hull. That way if the thru-hull fails, water still can't get in. I'm not crazy about that gray plastic hose to pipe elbow either. Why is there a hose clamp around the thru-hull fitting?

[DT]

An equally if not more important consideration regarding seacocks is contained in the ABYC Installation standard H-27.7.1:

"A seacock shall be securely mounted so that the system will withstand a 500 pound static force applied for 30 seconds to the inboard end of its connecting fitting, at any point in its most vulnerable direction, without the system failing to perform as intended."

I wonder whether the installation shown would meet that test even if the gate valve and fittings were brand new.

[DT]

By the way, can anyone reference the standard for double hose-clamping in ABYC Standards? I'm curious about where it's listed.

[mark]

DT

You are right about the ABYC standard. I debated if I should have included that when I wrote the post but deceided to leave it out for the sake of clarity and anyway it does not alter the fact that this is not a proper sea cock.

As to you other point, double clamping is just good practice, if one were to rust through there is a back up and also the pipe especially if it is a little oversize on the barbed connection can pucker a little. Installing a second clamp at 180 degrees ensures that this potential source of leakage is closed.