Most reliable level switch?

[TugboatEng]

A bit of background: I'm installing a centrifuge on a tug boat but it has no settling tank. I can't use the tried and true crew transfers from storage tanks to settler then centrifuge transfers and cleans from settler to the day tank. The day tank overflows back to the settler so you just leave the centrifuge running all of the time and it polishes the fuel as it circulates. What I plan to do instead is have the centrifuge draw from the storage tanks and fill the day tank to a certain level where it will switch to a recirculating mode and draw from the day tank instead.

What I need are some highly reliable level switches. While diesel fuel is relatively clean I have seen it darken sight glasses and grow bacteria sludge. This is also a high vibration environment so float switches are totally out of the question. What are your favorite level switches? I'm leaning towards tuning fork switches due to the heartbeat option. I also need it to fail in a shut down position. I'm also looking at using solid state relays. Failure is ok as long as it shuts down. I don't want to overflow the tank.

 

[MikeHalloran]

I've worked (on systems other than fuel) on quite a few tugboat-sized yachts. I don't recall seeing anything other than manually operated ball valves, on piping installed in an exposed, logical, functional arrangement, with sight glasses and pressure gages.

Are you sure you want to automate such a critical system?




Mike Halloran
Pembroke Pines, FL, USA

 

[itsmoked]

If there are sight-glasses associated with this setup you may be able to use capacitive switches thru the sight glasses to sense the fuel level. This would give the added benefit of being able to easily slide them up and down, visually setting the levels.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[roydm]

Tuning fork or ultrasonic gap would be my choice.
The day tank of course should overflow back into the main storage tank if possible.

Mount the switches from the top so it's possible to remove them without shutting down.

 

[georgeverghese]

You could also consider a combination of a top mounted ultrasonic and a side mounted remote sealed dp cell on the day tank, configured to stop the feed from the main storage tank on a 1oo2 voting arrangement.

 

[HCBFlash]

Well, just the expression "level switch" is interesting, and the stuff about "day tank", "centrifuge", "settler", etc tells us far more about you than the actual application of what most of us measurement and control types would think of as a sensor (as opposed to a switch). Your control scheme will determine the answer to your question. Ultrasonic and "tuning fork" devices are as reliable as their controllers. Floats work fine in environments at least as vibratory as yours. Oscillation, instability or tank overflows are caused by incorrect damping, time constants, as much or more than your selection of "level switch".

My favorite level "switch"? I like ultrasonics for powders in tanks. Load cells are great for bulk materials, which may not be consistently free-flowing, in bins. Water in tanks; I've had good results with floats, ultrasonics, pressure diff, IR photo, prox, refractory, and probably others I'm just not thinking of.

I'm no marine guy, but a harbor tug, a barge tug doing canal work, and seagoing all are much different environments. You may need to define your problems and needs a bit more.

.

(Me,,,wrong? ...aw, just fine-tuning my sarcasm!)

 

[buzzp]

I agree with HCB. A float level sensor should work as long as the electronics reading it compensate for the vibration. Shouldn't be an issue based on what was described.