You are looking at a pair of magnetic “reed” switches. The lower unit turns the bilge pump on/off, while the upper gives an alarm signal if the pump fails to keep up. The gray plastic floats contain the magnet which controls the reed switch making the electrical contact.
In the case of the bilge pump, the reed switch is used to trigger a relay through which the current for the pump flows.
We have been using this combination of reed switch and control relay for 25 years and it has proven to be extremely reliable (much better than moisture sensors and mercury float switches).
Posted by Steve Dashew (February 4, 2010)
February 12th, 2010 at 9:47 pm
Hi Steve,
Well thought out, as always. I’m guessing, therefore, that you have a time delay built into the bilge switch system somewhere to take care of rapid on-off and to allow the pump to pump to ‘the bottom’. How do you do this? I have one of the electronic switches with time delays. I like the delay aspect a lot, but have problems with the continued reliability of the switch sensors.
February 14th, 2010 at 10:35 am
Hi Steve:
We’ve used these at times in the past, but for the last ten years have stayed with a simple, relatively foolproof reed switch. The benefit of the timer module is not great enough in our application for the increased complexity. With manual overrides at the helm it is easy to quickly pump out the last little bit if required.
If you know of a 100% reliable timer we’d like to know about it.
February 14th, 2010 at 2:01 pm
The pumping-dry aspect is nice, but the main advantage of the timer is in preventing the pump from constantly ‘false starting’ and stopping from the sloshing. Do the reed switches in your setup take care of this without a timer? I’ve used reed switches a number of times in static-water situations (on land), but not on boats.
Am I correct in guessing that you are using reed switches with mercury contacts? I’ve not had that much success (reliability wise) with regular contact-type reed switches. The contact points still get pitted over time if the carry much current at all (athough I guess there’s no need for them to carry much current since you are probably using a relay to power the pumps).
February 14th, 2010 at 5:07 pm
Hi Steve:
The two areas where we can accumulate water have the shape or sumps to accumulate so short cycling is typically not a problem. The reed switches we use are magnetic, and I don’t think mercury is involved. We use these to trigger a control relay through which the pump current flows. On Beowulf (seven years) and Wind Horse (five years) we have yet to replace one of these reed switches.
February 24th, 2010 at 11:49 am
Can you tell me who makes the reed switches you use. Thanks, Mark
February 24th, 2010 at 4:21 pm
Hi Mark:
http://www.nationalmagnetic.com/ is their website.