Stick-on Holding Tank Level Sensor

[Hudson Force]

I favor the scan of the tank level from the top, but if I were to have such a device for my tank, the sensor would need to have a low profile. Most tanks are installed with a minimum amount of space above the top of the tank compared to what space is often available at the sides. I would require a product that could have the bulk of the mechanism at the side of the tank with only a small vertical clearance of a sensor on the top.

[rwidman]

Originally Posted by Nicholson58

I use sticks with notches carved on that correspond to actual gallons in these odd shaped tanks - water and diesel. All of our 9 tanks are 3/16" SS welded. I gave up on the electronic sending units- too many to keep up with. Dowels are really cheap and seem to be reliable. So far, no failures.

That's fine but are you willing to use a notched stick on a holding tank?

Do you plan on throwing it away after each use or cleaning it?

And what about tanks that don't have an access hole in the top? How do you "stick" them?

[Nicholson58]

The system totally infallible is the manometer type. These are advertised in the back of boating magazines classifieds. It is a small air source to a dip tube in any tank. The pressure required to push diesel or water to the bottom of the dip tube is read on a gauge/manometer. Great - but they want way more than any of this is worth and each additional tank is not a reasonable increment but a pile of bucks. This should be really cheap to build yourself. You could even blow into the tube to make it work.

[rwidman]

Originally Posted by Nicholson58

The system totally infallible is the manometer type. These are advertised in the back of boating magazines classifieds. It is a small air source to a dip tube in any tank. The pressure required to push diesel or water to the bottom of the dip tube is read on a gauge/manometer. Great - but they want way more than any of this is worth and each additional tank is not a reasonable increment but a pile of bucks. This should be really cheap to build yourself. You could even blow into the tube to make it work.

We are talking about a holding tank here. A tank used to hold raw sewage until it can be pumped out on shore or at sea where it's legal.

The difference between a holding tank and a water or fuel tank is that the contents are not pure liquid and the solids tend to coat or clog measuring devices. Think of a piece of undigested corn in your dip tube.


In theory, the infallible way to determine the level of the contents would be to weigh the tank but that presents its own problems on a moving, rocking boat.

[fguptill]

My holding tank is Vee shaped, with a horizontal cross section that varies in area from 0 when its empty to 100% at the full mark. Programming a customizable lookup table into the app that converts tank level to tank volume would be a nice feature.


Sent from my iPad using Cruisers Sailing Forum

[Nicholson58]

Originally Posted by rwidman

We are talking about a holding tank here. A tank used to hold raw sewage until it can be pumped out on shore or at sea where it's legal.

The difference between a holding tank and a water or fuel tank is that the contents are not pure liquid and the solids tend to coat or clog measuring devices. Think of a piece of undigested corn in your dip tube.


In theory, the infallible way to determine the level of the contents would be to weigh the tank but that presents its own problems on a moving, rocking boat.

I am afraid you do not understand how the manometer type works. Sewage is close to the same density as water. In the manometer system, a positive flow of air is pumped to the bottom of the tank through a dip tube. The flow circuit is pump - check valve - gauge - dip tube. The pressure required to force air to the bottom of the dip tube is registered on the gauge as inches of water pressure. Simply put, it measures the liquid head height in the tank by back pressure of the air. No Poo enters the dip tube. The measuring device never sees anything but air, even if the air flow is turned off. It is absolutely honest. The gauge can be totally mechanical and could even be a heavy liquid manometer. In the old days, mercury was used. Today, I would use an air gauge calibrated in inches of water pressure. Commonly available for HVAC systems.

If you have multiple tanks, you can use the same air pump with a tiny air valve bank to switch from tank to tank BUT, the Poo measuring circuit needs to be isolated by check &/or shut-off valves for obvious reasons.

This is precisely how this HART TANK TENDER works. Note the ridiculous price tag for a 6-station push-button air valve and a gauge. (or we would have one) Air pump not included. You can buy all the components from McMaster Carr or Grainger for well less than that AND the air pump. I suggest one could use a bike pump and it would be zero power. consumption. Hart Tank Tender 6-Tank Monitor System

On our boat, I took one step back and use a sticks with notches for every 5 gallons. I made the sticks for each tank by adding fuel or water in known increments at dockside. This also accounts for the odd shapes of all of our tanks. The poop tank is translucent plastic. You can see black water inside so no need for any measurement.

[Dave22q]

I have no idea how exterior holding tank electrical sensors work bit it appears that they do. Certainly the build up of solids do not prevent pump outs from the top from working on my boat. Build up on the sides is a nice theory but lots of theories sound nice. I based my decision on what I did not see. I did not see lots of cruisers complaining foil sensors do not work. I did not see reputable suppliers no longer selling exterior sensors. Radar might work, dipsticks will always work but I see nothing to tell me the inexpensive foil exterior sensors are unreliable. Maybe those with bad experiences are too shy to post but I kind of doubt it.

[rwidman]

Originally Posted by Dave22q

I have no idea how exterior holding tank electrical sensors work bit it appears that they do. Certainly the build up of solids do not prevent pump outs from the top from working on my boat. Build up on the sides is a nice theory but lots of theories sound nice. I based my decision on what I did not see. I did not see lots of cruisers complaining foil sensors do not work. I did not see reputable suppliers no longer selling exterior sensors. Radar might work, dipsticks will always work but I see nothing to tell me the inexpensive foil exterior sensors are unreliable. Maybe those with bad experiences are too shy to post but I kind of doubt it.

If you'll go back and read my previous post, you will see that my foil sensor works on fresh water but not the holding tank. I am not too shy to post it.

[Hudson Force]

Originally Posted by Dave22q

I have no idea how exterior holding tank electrical sensors work bit it appears that they do. Certainly the build up of solids do not prevent pump outs from the top from working on my boat. Build up on the sides is a nice theory but lots of theories sound nice. I based my decision on what I did not see. I did not see lots of cruisers complaining foil sensors do not work. I did not see reputable suppliers no longer selling exterior sensors. Radar might work, dipsticks will always work but I see nothing to tell me the inexpensive foil exterior sensors are unreliable. Maybe those with bad experiences are too shy to post but I kind of doubt it.

My foil tape impedance system worked well for a number of years, but it has presently failed. My foil strips have separated from their attachment to the plastic tank. I believe that I'll be able to repair it successfully, but it has not yet made it to the top of my list of projects. I only work on my top priorities and I always have a list!

I am able to see the level within my tank by holding a bright flashlight behind the corner of the tank.

[Nicholson58]

Originally Posted by rwidman

That's fine but are you willing to use a notched stick on a holding tank?

Do you plan on throwing it away after each use or cleaning it?

And what about tanks that don't have an access hole in the top? How do you "stick" them?

No - never. I don't need to. We can see the level through the walls of the translucent tank.

[Hudson Force]

Originally Posted by Nicholson58

No - never. I don't need to. We can see the level through the walls of the translucent tank.

As I said, I have the same ability to visually note the level in my tank; however, I like the convenience of the sensor. I need to raise a mattress, remove some panels and do some contorsioning to hold my flashlight!

[HappyMdRSailor]

Originally Posted by Nicholson58

The system totally infallible is the manometer type. These are advertised in the back of boating magazines classifieds. It is a small air source to a dip tube in any tank. The pressure required to push diesel or water to the bottom of the dip tube is read on a gauge/manometer. Great - but they want way more than any of this is worth and each additional tank is not a reasonable increment but a pile of bucks. This should be really cheap to build yourself. You could even blow into the tube to make it work.

The magnehelic's on ebay are $20... cheap enough to have one for every tank... They have cheap digitals too... $25...

Dwyer Magnehelic 2015C Pressure Gage 0 15 inches of Water | eBay

[Holding Tank]

Greetings; Thanks for the input.
Radar is the size of a pack of playing cards.
Looks down through the plastic top of the tank.
Battery lasts more than 1 year. (mostly sleeping; wakes up to take a measurement and then goes back to sleep.)
Smartphone can keep statistics and estimate time to full, # flushes remaining, warn user as it gets close etc.

[Dave22q]

Seems like the difference between absurd and ridiculous is getting blurred. Radar to monitor waste tank? Given your unlimited funds why not have a lackey use a dip stick or put it on a scale and track the weight?
Real folks choose between invasive and noninvasive sensors. Having just invested in non invasive I am assuming there is no experienced based case for making holes in a **** tank!

[Holding Tank]

Originally Posted by Dave22q

Seems like the difference between absurd and ridiculous is getting blurred. Radar to monitor waste tank? Given your unlimited funds why not have a lackey use a dip stick or put it on a scale and track the weight?
Real folks choose between invasive and noninvasive sensors. Having just invested in non invasive I am assuming there is no experienced based case for making holes in a **** tank!

Friends; ... the holding tank radar can be made smaller than a pack of cards and the cost can be less than $50 in parts. Modern chips are amazing, and are being made in quantities because of automotive applications (so becoming cheap).
Remember; I am an old retired radar scientist (and a sailor), so I really do know how to do this cheaply.