Fuel tank sight tube valves

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jbloyd

jbloyd

Veteran Member
Joined
Dec 13, 2019
Messages
84
Location
United States
Vessel Name
Ardeidae
Vessel Make
Defever 44
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)?
 
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).
 
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.
 
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

Screenshot_20201116-180900.jpeg
 
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.
 
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.
 
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.
 
jbloyd said:
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.
Click to expand...
 
mvweebles said:
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

View attachment 110159
Click to expand...

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.
 
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.
 
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.
 
Cigatoo said:
jbloyd said:
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.
Click to expand...

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.
Click to expand...

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.
 
Last edited:
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.
 
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.
 
Ski in NC said:
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.
Click to expand...

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.
 
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.
 
rgano said:
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.
Click to expand...
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/pro...hBar=true&searchQuery=2EET3&suggestConfigId=6
 
Sight glass tube. Appears to be original from 1985. Replaced.
Valves now kept closed.
 

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Xsbank said:
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.
Click to expand...

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.
 
Last edited:
KnotYet said:
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.
Click to expand...

The valves are the kind that have to be screwed down to close. They are not 90 degree valves of any kind. They are like the ones you find on the water faucets that you connect your hose to in a marina (or house). I have repaired many of them as a home-owner.
 
There are many types of gate valves ranging from cheap & nasty to top of the line. In some high pressure applications they are preferred over ball valves.

I suspect these are the cheap discount hardware store type and you'd be better off with a decent quality ball valve. If you want to splurge, get fire-safe ball valves for the fuel tank outlets.
 
Not sure it was a European requirement to have self shutting valves...but did see a couple European boats with push button valves... similar to in the pic.
 

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Fuel Valves

It is a requirement in all the European regulations that I have seen, the sight glass valves be spring-loaded. Thus they are permanently closed and only opened when you push them to get a new sight glass reading. Any other type of valve is a fire hazard and is not allowed!
 
mikecambrai said:
It is a requirement in all the European regulations that I have seen, the sight glass valves be spring-loaded. Thus they are permanently closed and only opened when you push them to get a new sight glass reading. Any other type of valve is a fire hazard and is not allowed!
Click to expand...

That sounds like a great idea! It would help prevent newbies, like me, from doing stupid stuff.:):)
 
RoseLoper48 said:
Check your cross feed valve. If it is open the fuel can migrate between tanks.
Click to expand...

I have 3 tanks and a polishing system. I filled both port & starboard tanks and left the aft tank at 3/4 full. The manifold system valves are set so that only the aft tank feeds the engines and generator. The other tanks don't feed anything. When I want something from them it is only to run through the polishing system to the aft tank. I never cross feed from the port to starboard tank or vice versa. Loads are balanced by pumping fuel from either the port or starboard tank (through the polishing system) to the aft (centerline) tank. I will not use the external fill point on the aft tank for refueling. The sight gauges are only on the port and starboard tanks. The aft tank is dipped. Hope that helps with the mental image.

When I noticed that the port gauge was reading really low I just opened the top and bottom gate valves and the sighting zipped up to the top where I had expected to be (and, as the starboard gauge was reading). So, after filling both the side tanks to the tipity top and not running any of the fuel from either tank to the aft tank I took a five hour cruise from Anacortes to Semiahmoo using fuel only from the aft tank. The systems were then secured for some dock life. Part of system securing is making sure the sight tube valves (all 4) are closed. Two weeks later, while doing some routine engine rooms checks, I noticed the port sight tube reading low (as mentioned).

Thanks to all who responded. The take-away, from my original question, seems to be, gate valves are used just because someone wanted to use them, on my boat. Other boats may have had other builders, who didn't have any gate valves lying around and used whatever else was handy. And, some builders actually thought it all through and installed really good stuff for reading the fuel levels. After-market choices are available and I will be implementing one when fuel levels allow it.
 
Last edited:
Since it is most likely that the fuel leaked from the valve's stem seal (easily snugged)
which any replacement valve may also have, be sure to add checking that to your list.
 
Gate Valves

Not an answer to the OP question but just my own experience. My boat has the same, gate valves top and bottom for the site tubes, then two for the cross over tubes top and bottom, then two more on each fuel tank where the feeder hose goes to the filter. and then at least one more for the generator.

Due to the location and the fact that my boat holds 400 gallons of fuel, was almost full when I purchased it and has hard lined copper pipes to all, it's really not that simple to change these valves.. Sure a ball valve would be better but in 1985 when my boat was made and sold for probably under 70,000 dollars was anyone complaining about the fuel valves?
 
KnotYet said:
Since it is most likely that the fuel leaked from the valve's stem seal (easily snugged)
which any replacement valve may also have, be sure to add checking that to your list.
Click to expand...

:thumb:
 
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