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Old 11-16-2020, 05:14 PM   #1
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Question Fuel tank sight tube valves

On my Defever 44, the two side tanks have sight tubes that each have a gate valve at the top and bottom. I've had the boat for about a month and the weather has been foul when any captains have been available to do drivers ed so I've been doing chores/maintenance. The first thing I did before starting the trip to home port (under supervision) was to fill the tanks. Recently, I closed the valves to the sight tubes. Yesterday I happened to glance at the sight tube on the port tank and noticed it showed less than half a tank. Check stb and it showed full. The port lower gate valve had some diesel on the handle (not dripping) but no showing of diesel in the bilge. Opened both port valves and the sight tube filled again to full. Closed valves. I'll check again in a few days. Maybe there's a slow leak in the tube junction. I'll find it. My question is, why are gate valves used at all? Isn't that a violation of best practices for fuel valves? Should I consider changing them out for ball valves when I can (I know, it's got 300 gallons of fuel sitting on it with nowhere to go)?
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Old 11-16-2020, 05:54 PM   #2
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Valves are used on sight tubes to limit fuel leaking from the tank into the bilge, especially during a fire situation. The tubes will easily melt and if no valve, release the tank contents to help fuel the fire. Keep them closed except when actually checking the fuel level in the tank. As soon as both valves are open, the level of fuel in the tank will show (match) the level in the tube. When you have finished taking your measurement, close both valves (top and bottom).
If you had no sign of dripping fuel, or any sign of diesel lying (or staining) below your valves, you probably don't have a leak (or much of one).
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Old 11-16-2020, 05:59 PM   #3
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If the sight glass dropped its level with the tank full and the valves closed, the only explanation is leaking to the outside. It's a very small quantity of fuel so you didn't see accumulation in the bilges.

The valves are there to allow you to clean/replace the sight glass. Other than those occasions, they're normally left open in most applications, though the bilges of your boat is not normally one of them. Whereas gate valves are verboten for use as seacocks, their use in sight gauges is common.
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Old 11-16-2020, 06:16 PM   #4
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Valves top and bottom can be handy as you can close them, run for a known number of hours, then open and measure the drop in sight glass level. Gate valves are common as are needle valves.

I recently installed LDI encased sight gauges on my newly constructed fiberglass tanks.

If OP has a weep, possible the valves need servicing. Perhaps in the Taiwan yard, getting fully diesel tolerant valves was difficult. In the US, purpose built valves such as the attached are easily available. I purchased 24 inch versions of the attached for about $175 each

Peter

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Old 11-16-2020, 06:23 PM   #5
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The actual question

It seems I wrote too much in my initial post. Here is the actual question (as seen at the end of my first post):
"My question is, why are gate valves used at all? Isn't that a violation of best practices for fuel valves? Should I consider changing them out for ball valves when I can?"

The question is NOT "why are valves used?".
Also, as mention previously, I do close them after fueling and after getting a new sighting.

Thank you for responding.
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Old 11-16-2020, 06:38 PM   #6
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My guess is gate valves are more commonly available in 90 degree configuration. If you used a straight valve, either it extends far from the tank, or, if placed vertically, would make the actual sight gauge portion very short. But that's just a guess. All I can say is I found many options with traditional gate valves, none with gate valves, and the best ones seemed to have needle valves.

My hunch is replacement would be a hassle. Unless you have a strong reason to do so, wouldn't worry about the gate vslves. If I were to replace, I'd go with a purpose built system such as the LDI one from Grainger I showed pictured.
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Old 11-16-2020, 06:39 PM   #7
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Could be the bottom valve has an internal leak, leaking through the valve back into the tank. That would explain no fuel seen in the bilge. Gate valves may more prone to this than ball valves, I don't know for sure but it sounds logical. Back in the old days the tubes would be glass, so of course you would need valves in case you broke one. Now days they're likely plastic, but over time they'll cloud or craze, and then you need valves so they can be replaced. I like the idea of keeping them closed when not actually being read. The dinner boat I run used to have a sight tube, but the CG had a rule change and they made us cap it off. There were no valves so that was not an easy job. Now we have to stick the tank, the sight tube was a lot easier. Of course this was commercial vessel rules so not applicable to pleasure boats.
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Old 11-16-2020, 06:39 PM   #8
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[QUOTE=jbloyd;943471]It seems I wrote too much in my initial post. Here is the actual question (as seen at the end of my first post):
"My question is, why are gate valves used at all? Isn't that a violation of best practices for fuel valves? Should I consider changing them out for ball valves when I can?"

The question is NOT "why are valves used?".
Also, as mention previously, I do close them after fueling and after getting a new sighting.

Why???? Who knows.
I had gate valves in my full tanks when we bought our GB. Took forever to get the tanks down to a manageable level so I could remove the gate valves and replace with ball valves.
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Old 11-16-2020, 07:00 PM   #9
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Quote:
Originally Posted by mvweebles View Post
Valves top and bottom can be handy as you can close them, run for a known number of hours, then open and measure the drop in sight glass level. Gate valves are common as are needle valves.

I recently installed LDI encased sight gauges on my newly constructed fiberglass tanks.

If OP has a weep, possible the valves need servicing. Perhaps in the Taiwan yard, getting fully diesel tolerant valves was difficult. In the US, purpose built valves such as the attached are easily available. I purchased 24 inch versions of the attached for about $175 each

Peter

Attachment 110159
That's a nice looking gauge. Mine are just a reinforced flexible plastic tubing connected to an upper and lower brass gate valve. And, there would be no way to repair or replace the lower valve without finding a parking space for 300 gallons of fuel. When I get back to the boat I'm hoping there is no problem or that the problem is a very slow and fixable clamping between the tube and the brass. Your gauge looks really rugged. Mine could easily be damaged by carelessness and should always be closed up when not being sighted.
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Old 11-16-2020, 07:02 PM   #10
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Nothing wrong with a gate valve in that app. Not what I would prefer, but should work fine. A globe valve is sorta nice as it naturally forms a 90deg fitting which is good for sight gauges. I prefer ball valves for just about anything on the boat, but on a sight hose the fitting stack may render the last few inches of tank level unreadable. There I would use a 90deg globe.

If gate valve is leaking at stem, try snugging the valve packing gland.
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Old 11-16-2020, 07:11 PM   #11
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I just keep the lower valve closed. Why? I have no idea.
It would hurt to keep the upper valve closed.
I have a "plastic" (Tigon) sight glass on my AT.
My N46 had armored glass which I did not like the glass.
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Old 11-16-2020, 07:13 PM   #12
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Quote:
Originally Posted by Cigatoo View Post
Quote:
Originally Posted by jbloyd View Post
It seems I wrote too much in my initial post. Here is the actual question (as seen at the end of my first post):
"My question is, why are gate valves used at all? Isn't that a violation of best practices for fuel valves? Should I consider changing them out for ball valves when I can?"

The question is NOT "why are valves used?".
Also, as mention previously, I do close them after fueling and after getting a new sighting.
Why???? Who knows.
I had gate valves in my full tanks when we bought our GB. Took forever to get the tanks down to a manageable level so I could remove the gate valves and replace with ball valves.
Yes, I guess I was overwhelmed by all the newness (even thought it's a 1983 boat) to deal with and the valve thing escaped my notice until after the top off on fuel. Pete's gauges look really nice and $175 doesn't seem like too much for peace of mind. My tubes are fiber-reinforced flexible clear tubing clamped to a fitting on the valves. At least they won't shatter if hit but, I really wish I had noticed, when the tank was really low and I could transfer the remaining fuel to the starboard tank (which was also almost empty), so I could have replaced those gate valves. Oh well, there are many other projects I need to address that should keep me busy for the next year.
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Old 11-16-2020, 07:45 PM   #13
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One caution: DO NOT use a knife to remove the tubing. You could/will scour the AL fitting and then, you put replace the fitting to prevent leaks.
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Old 11-16-2020, 08:46 PM   #14
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I am amazed at some of the responses and hope that in at least one case it was a typo that suggested the valves be left open - the OP already knows how to handle his valves. And so much pontificating about what a sight gauge is and why it is used just indication of paying little attention to the OP's question about why gate valves were used. They were likely used because they were available (already mentioned) and a lack of wisdom about their faults, leaking valve stems. They are a ridiculous valve to be used in a boat fuel system. Gate valves have a seal in their stem which must support the pressure of the system Try tightening the stem packing nut just a little bit (quarter turn maybe) to slow stop the leak. As intimated by the OP, I strongly suggest removed all the sight gauge gate valves and replacing with ball valves as time and tank levels allow. Nothing worse than that lingering diesel smell in a boat.
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Old 11-16-2020, 08:53 PM   #15
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Quote:
Originally Posted by Ski in NC View Post
Nothing wrong with a gate valve in that app. Not what I would prefer, but should work fine. A globe valve is sorta nice as it naturally forms a 90deg fitting which is good for sight gauges. I prefer ball valves for just about anything on the boat, but on a sight hose the fitting stack may render the last few inches of tank level unreadable. There I would use a 90deg globe.

If gate valve is leaking at stem, try snugging the valve packing gland.
As Ski notes, a gate valve is appropriate for that use.
Are you in fact sure it is a gate and not a globe valve as they can appear similar.
Any leak is most likely at the packing and can be easily addressed.
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Old 11-16-2020, 09:09 PM   #16
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Such frustrating reading!

Rgano nailed it. Even what I am about to write is probably redundant.

Gate valves are a pita to use and therefore I have changed all mine to ball valves. Gate valves work fine, until they age then they leak. They use packing around the shaft and use a seal/gasket/washer (remember those in your parent's house? Changing washers was always annoying as the correct size was missing).

Ball valves good, gate valves bad. Oh, forgot to say IMHO for the liberals on here.
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Old 11-16-2020, 09:10 PM   #17
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Quote:
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I am amazed at some of the responses and hope that in at least one case it was a typo that suggested the valves be left open - the OP already knows how to handle his valves. And so much pontificating about what a sight gauge is and why it is used just indication of paying little attention to the OP's question about why gate valves were used. They were likely used because they were available (already mentioned) and a lack of wisdom about their faults, leaking valve stems. They are a ridiculous valve to be used in a boat fuel system. Gate valves have a seal in their stem which must support the pressure of the system Try tightening the stem packing nut just a little bit (quarter turn maybe) to slow stop the leak. As intimated by the OP, I strongly suggest removed all the sight gauge gate valves and replacing with ball valves as time and tank levels allow. Nothing worse than that lingering diesel smell in a boat.
Rich - the sight gauges I've seen on older boats appear to be exactly as you say - likely scavenged from available parts with pvc hose, etc.

But I observe that gate valves (globe vales?) are made for use in a sight gauge application. The attached are Apollo valves good to 125 psi. As mentioned in my post, use of a straight ball valve would usurp vertical space otherwise used for visual sight gauge.

https://www.grainger.com/mobile/prod...gestConfigId=6
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Old 11-16-2020, 09:24 PM   #18
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. As mentioned in my post, use of a straight ball valve would usurp vertical space otherwise used for visual sight gauge.

https://www.grainger.com/mobile/prod...gestConfigId=6
A minor loss of reading at the bottom if used in line with the gauge hose. If a ball is plumbed in line with the lower port from the tank and with a simple 90 barb to mate with the gauge line, you're golden.
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Old 11-16-2020, 09:51 PM   #19
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Sight glass tube. Appears to be original from 1985. Replaced.
Valves now kept closed.
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Old 11-16-2020, 10:09 PM   #20
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Such frustrating reading!
Rgano nailed it. Even what I am about to write is probably redundant.

Gate valves are a pita to use and therefore I have changed all mine to ball valves. Gate valves work fine, until they age then they leak. They use packing around the shaft and use a seal/gasket/washer (remember those in your parent's house? Changing washers was always annoying as the correct size was missing).

Ball valves good, gate valves bad. Oh, forgot to say IMHO for the liberals on here.
Not only redundant but if you are referring to faucet valves, wrong.
In general old houses would have either globe or spool valves.
Many ball valves have stem seals, too.

I suspect the OP's valves are actually globe valves that commonly come in 90 degree versions.
For all those that want to exchange a 90 degree globe valve for a ball valve,
those are also available in 90 degree versions.
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