Presure Sensors to Measure Tank Fluid Level ?

[twistedtree]

Is anyone using pressure sensors as a way to measure the content level in a tank? I was talking to Maretron at the Ft Lauderdale show and they have sensors that screw into a port at the bottom of a tank and wire to an N2K gauge unit. They can then be calibrated for different fluid types to read fuel level, water level, etc. I've been wanting to get my tank gauges on N2K, and this seems like a straight forward way to do it while keeping my existing gauges in place and active as a backup.

The only downside I can envision is if crud in the bottom of the tanks plugs up the pressure sensor, but if I have that much crud in my tanks, I need to deal with that problem anyway.

Does anyone have gauges based on pressure sensors of any king and how do they work?

[delmarrey]

Water would be fine but you don't really want a fitting at the bottom of any other fluid. Any seepage would be a problem. If it came in from the top then IMO would be OK.

This would be my choice.

[GordMay]

If like this? ➥ About Tank Tender
They’ve been around for ever.

[twistedtree]

Originally Posted by GordMay

If like this? ➥ About Tank Tender
They’ve been around for ever.

Same concept, but without the need to pump air. It just measures the pressure at the bottom of the tank. With that, and knowing the specific gravity of the fluid, it's straight froward to calculate the head (depth) of the fluid.

[twistedtree]

Originally Posted by delmarrey

Water would be fine but you don't really want a fitting at the bottom of any other fluid. Any seepage would be a problem.

Why? Just curious. My fuel tanks already have at least two plugs at the bottom, and of course the fuel line comes off the bottom too. In fact, my entire fuel system (lines, joints, valves, fittings) are all below the tank bottom. If I replace one of the plus with a pressure sensor would that represent more exposure than I already have?

My thinking is that if something is seeping then it needs fixing.

[delmarrey]

I'm surprised I'm the first to respond to this. And that the tank was installed this way on such a quality vessel.
Fuel tanks are not to ABYC or USCG code with fittings below the top, with exceptions noted below.

§*58.50-10***Diesel fuel tanks. :: PART 58--MAIN AND AUXILIARY MACHINERY AND RELATED SYSTEMS :: CHAPTER I--COAST GUARD, DEPARTMENT OF HOMELAND SECURITY :: Title 46 - Shipping :: Code of Federal Regulations :: Regulations :: Law :: Justia

46 C.F.R. § 58.50-10 Diesel fuel tanks.
Title 46 - Shipping
(4) Openings for fill and vent pipes must be on the topmost surface of a tank. There must be no openings in the bottom, sides, or ends of a tank except as follows:
(i) The opening for the fuel supply piping is not restricted to the top of the tank.
(ii) An opening fitted with threaded plug or cap may be used on the bottom of the tank for tank cleaning purposes.
(iii) Liquid level gages must penetrate at a point that is more than 2 inches from the bottom of the tank.

Fittings coming off the bottom of a fuel tank is asking for trouble. What would happen if it came loose, or even caught fire in the bilge?

As for waste tanks; it's up to you if you want a seeping septic system inside your boat. And seeping may not show up until one is out in the rough seas, exercising the integrity of it's construction.

[twistedtree]

Interesting, thanks. When I say "bottom of the tank" that's actually low on the side of the tank. I'd guess they are the requisite 2" above the bottom, but will check.

If I remember correctly, there are three taps in total at the "bottom" of each tank. One is the main fuel pickup, and on one tank a second is used for the gen set pickup. So one tank has one free tap, and the other tank has 2 free taps. I think it might be rigged for site glasses as an option, but I'm not sure.

Can anyone point me towards one of these automatically closing valves referenced in the ABYC specs?

[GordMay]

Originally Posted by twistedtree

... Can anyone point me towards one of these automatically closing valves referenced in the ABYC specs?

Which valves?
ABYC "H-33" Diesel Fuel Systems ➥ http://newboatbuilders.com/docs/H-33_Diesel_2005.pdf

[twistedtree]

Originally Posted by GordMay

Which valves?
ABYC "H-33" Diesel Fuel Systems ➥ http://newboatbuilders.com/docs/H-33_Diesel_2005.pdf

Oh, sorry. It comes from the full ABYC text.

"Where liquid level indicating devices are attached to the tank, they shall be of heat resistant materials adequately protected from mechanical damage and provided at the tank connections with devices which will automatically close in the event of rupture of the gage or gage lines."

[Greggegner]

I have seen ads for this and would like more info. The sensor I saw goes between the tank and the feeder hose. While an additional hole in the tank is not required two additional fitting are required. Please keep us updated. I also need a fuel gauge.

[twistedtree]

Originally Posted by Greggegner

I have seen ads for this and would like more info. The sensor I saw goes between the tank and the feeder hose. While an additional hole in the tank is not required two additional fitting are required. Please keep us updated. I also need a fuel gauge.

I'd be cautious with the sensor in or off of the fuel flow path. As your fuel pump circulates the fuel, you will get slight increases and decreases in pressure depending on where you are in the fuel path, plumbing sizes, etc. I don't know if the pressure variations would be enough to impact the gauge readings in any significant way, but I'd want to convince myself it wouldn't before taking that approach to installation.

[GordMay]

Originally Posted by twistedtree

Oh, sorry. It comes from the full ABYC text...

That's the Code of Federal Regulations, not ABYC standards.
Code of Federal Regulations, Title 46, Shipping, CFR 58.50-10 - Diesel fuel tanks,
Paragraph 6 ➥ Electronic Code of Federal Regulations:

[twistedtree]

Originally Posted by GordMay

That's the Code of Federal Regulations, not ABYC standards.
Code of Federal Regulations, Title 46, Shipping, CFR 58.50-10 - Diesel fuel tanks,
Paragraph 6 ➥ Electronic Code of Federal Regulations:

Thanks for the correction. I was following the link that Delmarrey posted without paying attention to the source. My bad.

I'm trying to understand what it would take to comply with that reg/code. My read is that the tap needs to be 2" above the bottom of the tank, the pressure sender needs to be fire proof and in a physically secure location, and there needs to be an automatic shutoff between it and the tank. It's this last piece that I'm trying to understand. I haven't come across such an automatic shutoff valve before.

[delmarrey]

Originally Posted by twistedtree

Is anyone using pressure sensors as a way to measure the content level in a tank? I was talking to Maretron at the Ft Lauderdale show and they have sensors that screw into a port at the bottom of a tank and wire to an N2K gauge unit.

I'm curious, why do you want a pressure sensor vs a fluid level gauge. They are normally not installed on tanks unless the tank is sealed, which it shouldn't be in a recreation vessel. Or do you have an irregular tank shape.

Maretron : Marine Electronic Instruments

http://www.maretron.com/products/tla100.php

[twistedtree]

Originally Posted by delmarrey

I'm curious, why do you want a pressure sensor vs a fluid level gauge. They are normally not installed on tanks unless the tank is sealed, which it shouldn't be in a recreation vessel.

A variety of reasons. It's not definite that I'll go that way, but I'm trying to scope it out completely so I can compare it to the alternative. Here are the attractions:

1) The tanks are irregular, but other gauges can deal with that so it's a consideration but not a critical thing.

2) All my electronics are on N2K and NavNet (Ethernet) except tankage. I really want tankage on N2K so I can display it at both helms, view it the way I want to see it, etc, etc. This is a must-have for whatever approach I take.

3) I might change them over incrementally rather than all at once. There are two fuel tanks and two water tanks. If I do it incrementally then keeping the existing metering in place in parallel with any new system has it's attractions. It also provides a measure of redundancy which is nice.

My tanks are currently gauged with a Computank system, and I don't really like it very much. I can't see everything on one screen and have to sit in front of the display waiting for it to scroll through all the tanks, totals etc. to get the info I want. It's also only at the lower helm and I want full metering from the upper helm too. So I'll be replacing the computank.

The Computank senders are proprietary, so I can't just use a Maretron meter that connect to the existing senders - I would have to replace all the senders, plus get the meter units, and it starts to add up to some big $$. As I recall, the meters are good for one tank each, so I'd need 4 senders, 4 meters, and N2K Tees and cables for 4 drops. It's probably $500 per tank, maybe more.

The pressure sender approach strikes me as simple and elegant. A single N2K meter can handle all 4 senders so it's one N2K drop rather than 4, and the senders are inexpensive. The whole thing is probably $500 total.

So that's where I'm coming from.