No more cheapo float switches

dmmbruce said:
Yes, a disclaimer for legal reasons.

How often have you heard of bilge water, of whatever source, being as "clean" as distilled water?

;)

Mike
Click to expand...

my previous switch of a different make ( from a very honourable forumite :cool:) did 3 yrs trouble free
years. i only knew it was u/s when i went o/b to find the pump running with dry bilges.
the WW has sensors similar to the original & that worked ok ;)
 
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Thanks Winsbury.
Having designed electronics for most of my working life and developed a healthy mistrust for electronics near water, i'm using your float switch and relay circuit.
 
Chalker said:
Thanks Winsbury.
Having designed electronics for most of my working life and developed a healthy mistrust for electronics near water, i'm using your float switch and relay circuit.
Click to expand...

Excellent, let me know how you get on. It would be really interesting to see a photo of your finished item in situ when its done.
 
Switch Orientation.

winsbury said:
The problem as I see it is that all the bilge switches miss the fundamental point - they should turn on when the water reaches a certain level and turn off once its dropped to a certain level. All the arrangements with a single switch cannot do this so either keep switching on/off rapidly which rapidly wears out pump and switch, the more complex devices have a time delay which helps but may mean the pump runs longer than need be and possibly runs dry. My solution below - btw these switches are available on ebay for about £10 http://www.ebay.co.uk/itm/160804066289?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1438.l2649 though I dont know if they are suitable for marine environment, nevertheless any two switches appropriately spaced would do the trick. Remaining parts available for a few pennies.
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I might be wrong but is the labelling of the 'a' and 'b' switches the wrong way round in your diagram, in the first paragraph? You have labelled the lower one (turn off) as 'a'. Surely as soon as the level gets to this switch it will turn the pump on straight away before the level gets to 'b'?
 
captainboo said:
I might be wrong but is the labelling of the 'a' and 'b' switches the wrong way round in your diagram, in the first paragraph? You have labelled the lower one (turn off) as 'a'. Surely as soon as the level gets to this switch it will turn the pump on straight away before the level gets to 'b'?
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Ah, do I say "oops, well spotted", or do I say "it was a deliberate attempt to put anyone off that couldnt read a diagram therefore shouldnt be trusted anywhere near a soldering iron."

I think I'll go with well spotted. :)

PS: just for clarity: the diagram is correct, its only the letters 'A' and 'B' in the first paragraph which should be reversed to make the description read correctly.

The pump will switch on only once it reaches the upper switch and wont turn off again until it reaches the lower switch. So provided the vertical gap between the switches is larger than the wavelets normally found inside the bilge the system will prevent the pump overrunning (ie, wont go completely dry which is not good for impeller pumps ) and will not under-run (ie no short bursts) which can be bad for the motor and switches and is in efficient and might create unnecessary RF interference too.
 
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I don't think that it needs a 2 pole relay either. (Not just because I bought a single pole one!).
I'll fit a 'spike' diode across the supply as well to keep it off the boat supply
 
No. But the simplest to adjust as only 2 funtion screws. most others have 1/2 load level function as well and are pigs (From experience) to adjust for the low level bit.
 
VicMallows said:
What is the least depth of water you have been able to reliably detect? I'm sure it will work fine in a deep bilge, but I'd be surprised it it can detect 2 inch water depth, which is what I need in my shallow bilge.
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Just put an inverted funnel on the bottom end of the pipe, the pressure differential is larger for shallow depths.
 
fisherman said:
Just put an inverted funnel on the bottom end of the pipe, the pressure differential is larger for shallow depths.
Click to expand...

The funnel will increase the volume of air available to operate the switch. It will not increase the pressure. My question was whether 2 inches of water pressure is sufficient to reliably activate the washing machine switch. I was assuming that once the bilge was pumped dry, the pressure tube would be above water/open to air. If not, the differential becomes an issue and is likely to make reliable operation even more difficult.

I repeat: has anyone actually got it to work with a 2 inch bilge water depth?
 
VicMallows said:
What is the least depth of water you have been able to reliably detect? I'm sure it will work fine in a deep bilge, but I'd be surprised it it can detect 2 inch water depth, which is what I need in my shallow bilge.
Click to expand...
Can be set so low that the pump will run all the time. I set mine so that the pump grill is always covered and cuts in when I have 6" in the sump.
 
fisherman said:
Just put an inverted funnel on the bottom end of the pipe, the pressure differential is larger for shallow depths.
Click to expand...
I'm not sure that will work very well, the theory you are proposing is that of hydraulics as far as I can see, ie the large area of the open funnel will act as a large piston acting against the small actuator of the switch. The problem is that the air in the funnel is very compressable so the pressure increase will not be increased as much as one might hope and might not be sufficient to trigger the switch, it depends somewhat on the sensitivity of the switch of course. The same problem with pressure switches occurs when located remotely ( via an air tube ) , the longer the tube, the greater the air volume so the less effective the transfer of pressure.

It might be possible to create a lever which actuates a master cylinder to push a fluid/rod/wire to/from a remotely mounted switch but I'm not sure I see any advantage to making the system more complex mechanically.

I would have thought the only way to sensibly detect very low levels of water would be electrodes that sense depth, either simple 'water present or not sensor' or a continuous water depth sensor similar to a fuel level sensor and trigger the pump based on settings in the detector. This could be as simple as on/off or as complex as a processor controlled sensor that could incorporate hysteresis and removal of wavelets caused by the motion of the boat. With predictive programming it might even be able to pulse the pump to only work as a wavelet passes the inlet to effectively dry the bilge slightly below the level of the inlet.

A wise man once told me to get to the other side of a long high wall one could build a brick diminishing vacuum generator with reconstitution engine that would vapourise the bricks and then replace them after one passed through to the other side safely. Alternatively, one could use a ladder.... the moral is that we are in danger of over engineering a response to simple problem.
 
I had a pipe/pressure switch bilge alarm for years, it was very effective. The simplest bilge alarm/switch I've seen was a straight wire passing through staples or some such attached to a bulkhead, float on the bottom end, switch at the top. The stainless wire inside a morse 33c cable is very useful for this, and other random purposes.
 
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