Gate valve closing spontaneously

[bodgy]

Im wondering if anyone has seen this and can verify my theory of causation.

My 30 year old Volvo keeps overheating. The raw water cooling flow stops completely or drops in volume. This is intermittent and unpredictable. 10 minutes later, it may or may not flow again.

I have done all the usual things, checked filters, impellers, isolated the water heater, checked inlet strainer, inspected the anode etc etc.

I now suspect the 30 yr old gate valve. The shaft seems very loose but does close to a watertight seal but wobbly and leaky when fully open. My mechanic assures me that an engine internal blockage could not be intermittent.

I now suspect that the gate/barrel whatever in the valve is loose on the stem due to corrosion, will seat when pushed closed but will not draw back when opened, merely float around the chamber - gate is horizontal not vertical. Vibration and boats motion may allow it to be sucked closed

Im going on the slip to change to ball valves, however I need to motor there.

Any ideas out there??

Jon

[Tin Tin]

Have you got a length of hose long enough to reach another through hull, like the head?

[NYSail]

Shocked your” mechanic” did not advise to change those out in the first place. Also hoses can collapse internally if they are old and in bad shape.

Get rid of all the ball valves on your boat asap.

Good luck!

[Wotname]

Hmm...ball valves ain't so bad but gate valves on boats are the work of the devil.

Does it have an external strainer that might have trapped a ball of growth or some such that is getting caught in the thru hull. If it does have an external strainer, that needs to go as well; they are also the work of the devil.

[Mike Burch]

+1 for getting rid of all gate valves. Even the ones that claim to be bronze often have brass innards which of course rot away. And the handles are usually steel. I've never heard of a gate valve closing spontaneously, but I've sure experienced "bronze" gate valves corroding to the point where you can't close the wretched things when you need to. That's why I hate them.

Ball valves are certainly the way to go. Personally, I prefer glass-reinforced nylon ones, but I know some classification societies ban them on the grounds that they're not fire-proof. Of course, the hose connected to the valve is even less fire-resistant...

Talking of hoses, yes, you should also consider replacing them, especially the hoses on the suction side of the pump. These can get soft with age. You're probably aware that suction hose needs to be specifically designed for sucking. Most hoses are not, and if it's a old boat it's not unknown for some previous owner to have replaced the original with the a hose of the wrong type.

[bodgy]

Thanks all. The only other below waterline fitting is in the head at opposite ends of boat, no hose that long. The boat does have a strainer on the hull, that will go when slipped. I hadnt thought of the inlet hose imploding, Ill check that later today. The mechanic is due soon, so see what he has to say.

I think it will remain a mystery until she slips.

Ill start saving for a tow.

Jon

[Bycrick]

I needed to install a valve on the Genset exhaust to prevent occasional flooding of the motor. It’s above the water line. The only accessible place to put this valve was right at the exhaust manifold output, before the water injection. The valve gets HOT. I was worried about the plastic seal in a ball valve getting too hot, so I used a gate valve instead. One time the vibration of the Genset gradually caused the valve to turn itself closed. Fortunately, the motor stopped before any damage. Solution was a small wire hook for the valve wheel.

[Khaos13]

The "gate" typically has a threaded shaft that passes through it to open and close. The threads can corrode away leaving the gate to slide from one position to another. In some cases you can open the valve body and remove the gate completely assuring full flow until you can replace it.

[bodgy]

So I had the mechanic out yesterday, he changed the impeller which had a paddle arm about to tear loose and was completely ineffectual. With a new impeller the water volume increased.

I still cannot see how this could cause the intermittent cessation of the flow, however the mechanic said it maybe could've caused cavitation.

So, the two remaining suspects are the old and corroded gate valve and an obstruction between the water inlet strainer and the skin fitting, which floats around and may be sucked over the inlet.

All being well, which it rarely is, she should slip next week and the mystery solved.

If it is some weird internal blockage in the engine, Ill take out a second mortgage and put in a Beta (kubota).

[motion30]

Originally Posted by NYSail

Shocked your” mechanic” did not advise to change those out in the first place. Also hoses can collapse internally if they are old and in bad shape.

Get rid of all the ball valves on your boat asap.

Good luck!

What flavor valves would you have him replace the ball valves with?

[bodgy]

Originally Posted by motion30

What flavor valves would you have him replace the ball valves with?

Bit of confusion here.

I have gate valves and propose to replace with bronze ball valves.

Jon

[s/v Jedi]

Originally Posted by bodgy

Bit of confusion here.

I have gate valves and propose to replace with bronze ball valves.

Jon

I highly recommend you follow the guide from Rod Collins which you can find here: https://marinehowto.com/replacing-th...-and-seacocks/

[Wotname]

Ron Collins is the guru however for raw water inlet, I like to add a Tee to the delivery side of the ball valve/thru hull if access and space permits. The hose tail goes horizontal and a bung goes into the top of the Tee.

In the event of any obstruction in the thru hull / ball valve, pull the bung and rod it out.

[bodgy]

After removing the 2 old gate valves along with their skin fittings, they both seemed to work OK despite extensive corrosion, The seating of the open/close screw was loose but the barrel was firmly captured, and could not account for the spontaneous blockage.

To remove the engine inlet valve the raw water strainer had to come out too. The shipwright noticed that the lid of the Volvo filter had cracked about halfway around where it sealed to the cylinder. Consequently with little suction the water flowed freely but when revs increased the extra suction pulled in air.

Despite having checked the filter for detritus several times i never saw this, as when i unscrewed the lid the crack closed. When it was back on one could not see the side due to the position in the locker.

Thanks again for all the input, and I hope this may lessen someone else's misery one day, always assuming this was the root cause. She splashes tomorrow, so here hoping.

[bodgy]

All good