Sight glass for fuel tank help

[NUTMEG]

Rhoda Rose has no fuel gauges. Fuel filler pipes have a dog-leg that makes dipsticks impossible. The two tanks are stainless steel and fitted in such a way that there is no access to the tank tops, but good access to the inboard sides. Neither tank has an inspection hatch nor are drain cocks fitted. Removing the tanks will involve,removing the engine so not an option.

I had the idea of fitting sight glasses to both tanks. Drill a hole in the lowest part of the tank, add a fitting, bit of pipe etc, maybe even a drain down tap.

Question is, is there anything like a Rivnut or similar that could be inserted into the hole that would accept a brass fuel fitting? Remember, no access to the inside of the tank. Considered simply tapping the tank side but am not sure how thick the s/s is, and wish to avoid as much swarf as possible.

Any ideas?

Thanks

 

[No Regrets]

Safer to dril a hole in the top and use a dipstick, with the option of plugging the hole in rough seas!!!

Self tapper with a gasket washer perhaps? Dipstick only needs to be thin...

 

[prv]

If there's no access to the top of the tank, then presumably the fuel feed comes out of the bottom?

I've never tried it, but perhaps a T-fitting inserted into the feed hose, with an upstand, would work as a sight gauge? At least when the engine isn't running, anyway. No need to meddle with the tank at all in that case.

Obviously the top of the gauge hose can't be closed, but you also need to avoid spilling diesel out of it, either due to rough weather or while filling the tank. Conventionally this is achieved by connecting it back to the tank, but we're trying to avoid that. You could just take it up very high (above the filling point), with a small drip-catching pot hung under it. Or if the height isn't available, a valve at the bottom which you only open (carefully) when you want to look at it. You can get press-button valves intended for this specific purpose on heating-oil tanks, so they can't be left open.

Pete

 

[pvb]

I'd be very cautious about drilling into the tank side, perhaps other than right at the top of the side. If the fuel feed comes out of the bottom, then a sight tube as prv suggests would work. If the fuel feed is drawn from the top via a dip tube, you might consider a pneumatic tank gauge. For this, you'd need to drill a hole, through which a flexible tube is passed, down to the bottom of the tank. If you can't access the top of the tank at all, this could be done as high as possible on the side of the tank, to minimise the risk of leaks. To read the level, you operate a little plunger on the gauge, and it shows the hydrostatic pressure which translates to the level in the tank. You can get these for less than £100 - cheaper than most other gauge options.

 

[prv]

If we're going for gauges rather than specifically sight tubes, then I believe you can get ones which work through the tank wall by some clever capacitive sensing. Often used for holding tanks because 1) loo paper tends to jam moving floats and 2) nobody wants to open up a holding tank to install things! I don't know whether they'd work on a metal tank and oil rather than water, but it might be worth a look.

Pete

 

[vyv_cox]

There are very many suppliers of simple sight gauges on the Internet, like this one http://www.centretank.com/products/detail/royal-push-button-sight-gauge. No drilling of the tank, simply attach to discharge nozzle of the tank. Normally closed, so risk of leakage minimised. I shall be fitting two of these to Cecilia this winter.

 

[Anchorite]

I have an identical problem with the same access complications. I couldn't find any non-intrusive measurement system. My tanks are mild steel, 3mm. However the vent pipe is on the (accessible) endwall, near the top. I can fit a one meter copper tube (4/6mm) and blow down till I hear bubbles: this is not a very satisfactory solution as it involves emptying and then climbing into the lazarette. There are few volunteers for this.
Current idea is to put a weighted flexible tube (2/4mm) in through the vent (1/2" ID) and down to the floor of the tank, then bend the length of flex outside in a "U" down to the floor and back up again: used as a syphon this should show the level in the tank. The outside (indicator bit) can be remote. The syphon can be blown clear after a measure.
Practical problem: how to weight the teflon/nylon tube so it will sink?

 

[NUTMEG]

Thanks for the helpful replies so far, some useful leads there.

Although there is only an inch between the tank tops and the floor of the wheelhouse both fuel supply and return are top mounted. I have no idea where the breathers exit the tanks but suspect from the top too.

I have pondered the idea of a 'flexible Pippett" sort of thing. Say a thin flexible plastic tube (fish tank airline or similar) and a fishing weight. Drill a central hole through the bomb shaped weight to take the tube. The lower pipe end, where it exits the weight, could be melted and flared to prevent the weight falling off. Drop the weight and pipe into the tank, lowering until you feel the weight contact the tank bottom. Place pinky over the upper end of the hose and withdraw. Fuel level could be read off the pipe, suitably marked/graduated. Cumbersome and awkward but would it work?

Sight tubes would be easier long term.

 

[James_Calvert]

I've got a sight tube. Works fine with red diesel but even after replacing the tube it is still really difficult to see the level of white diesel. I have to get down into the locker and shine a torch at it.

 

[rob2]

My tank has a bottom feed, so a tee piece and a modified oil tank sight glass from BES does the job. there is a press to open valve at the bottom of the sight glass, so you only risk spillage of the content of the sight glass. http://www.bes.co.uk/products/075.asp

A similar boat has a similarly rigged standpipe constructed of copper water pipes with a linear guage fitted to it. Of course, in both installations a breather tube has to be taken from the top of the guage tube to an elevated position to allow the column pressure to equalise and not slop out of the top.

Rob.

 

[Stemar]

I've got a sight tube. Works fine with red diesel but even after replacing the tube it is still really difficult to see the level of white diesel. I have to get down into the locker and shine a torch at it.

Could you find a small floating bead to drop in the sight tube? Cork might be better than plastic, as many plastics, especially less dense ones don't much like diesel.

 

[thalassa]

I've got a sight tube. Works fine with red diesel but even after replacing the tube it is still really difficult to see the level of white diesel. I have to get down into the locker and shine a torch at it.

I did it the same way, but it was still hard to see the level. Last year, I bought a meter of LED fiexible strip lights and stuck it to the tank behind the sight glass. It is a big improvement, no more guessing where the level is.

 

[Storyline]

Is it possible to buy an inline fuel flow meter ? If so, just fill up tank, zero the meter and subsequently subtract the reading from tank capacity.

Edit: Like this one - expensive but there may be cheaper ones
http://www.ebay.co.uk/itm/Digital-F...=AU_Car_Parts_Accessories&hash=item2c7003bfde

 

[NUTMEG]

Not sure a flow meter would work and, of course, I would need two :-( £££££££££££

Thanks

 

[Kylora]

I've got a sight tube. Works fine with red diesel but even after replacing the tube it is still really difficult to see the level of white diesel. I have to get down into the locker and shine a torch at it.

The sight tubes on a steam boiler would typically have a plate behind them, painted with black and white diagonal stripes ( like hazard tape ).

The difference in refraction would cause a perceived kink in the line at the level of the top of the liquid.

Ash

 

[Storyline]

Not sure a flow meter would work and, of course, I would need two :-( £££££££££££

Thanks

Can you not use the tanks independently ? Granted you would need a notebook to take readings when you switched over but some of the other methods sound more of a hassle. There are some other meters on ebay starting at £45 but these have large inlet/outlets so would need a reducer. Also maybe the resistance would slow down the fuel flow - am not expert enough to know .....

As an alternative could you cut an inspection hatch into the cockpit sole or whatever is above the tanks and then cut a hole in tank top and drop an electric gauge in ? Maybe swarf would also preclude this.

Agree that it is a problem that needs a solution. If I was in your shoes I would always be veering on the side of caution and constantly topping up the tanks !

Edit: even electric gauges are not cheap. Swmbo is almost obsessed when it comes to how much water we have onboard so I naively asked our boat yard to fit gauges in the water and fuel tanks and received a bill in excess of £1k !

 

[nigelmercier]

Not sure a flow meter would work and, of course, I would need two ...

Or four if you have an injection engine.

I've got a device similar to the one Vyv linked to on my domestic oil tank, it works well. However, I did wonder if you could get away with a very fine mesh, or perhaps just a pin-hole in the top of the tube, which would also give a damping effect.

 

[James_Calvert]

Some really good ideas here for making it easier to read a sight-tube. Thanks guys and I'll try one or two of them out next season.

 

[richardabeattie]

Just how dogged is the dog leg in the filler pipe? Could you not use a flexible dipstick?

 

[Storyline]

Just how dogged is the dog leg in the filler pipe? Could you not use a flexible dipstick?

+ 1 Maybe that type of plastic that boatyards use for pushing wires up masts .....