Float switch

[howardm]

Hi,
I am sat here at work, trying to work out how to get reed switches to operate a sump pump.!
How do I get the switch to keep operating while pumping out, yet not operate whilst the level rises to the pumpout level.?
It's a puzzler.!


Howard

 

[normspanners]

Are Reed switches called that coz they switch on the reeds when the swamp fills up?
Seriously You could use a mercury type switch when the float is upright ie floating the mercury makes the contact when the float falls over ie container empty, the mercury runs from the contacts and switches off the motor.
Or is it that you are replacing a mercury switch due to legislation?
because in theory they are banned but you can still buy them!
A mercury switch is far more reliable than any other

 

[rtbcomp]

How critical is it? Have you already got the float switches? If you have a couple of normally open float switches you can use a relay to make a latching circuit so the pump starts at high level and stops at low level.

 

[normspanners]

sorry I didnt read your question properly what about a shelf at an adjustable level that the floatswitch lands on earlier

 

[rtbcomp]

As the level rises B closes and then A closes at high level

RLA calls and starts the pump via RLA/2

RLA/1 also closes

As the level drops A opens but RLA/1 holds RLA called

At the lower level B opens and drops the relay

The pump stops.

 

[Luke]

Is this for a boat, or something else?

Most off-the-shelf float switches will handle this to an extent, due to switch hysteresis, friction and the characteristic of the buoyancy of the float itself.

 

[pidgeon chit welder]

Just use a pole end of a small bar magnet fixed to a float that has a verticle rod so that when it passes the reed operated relay it opens or closes the circuit as the case may be . Put the pump on a timer so that in a timed empty you can set it to empty the sump .

Another very simple & reliable way is to use a float with a tall upright running through a pair of guide rings and a pair of collars that trips a long lever on a mechanical switch set on a fixed arm as the float rises or falls the switch is turned on or off . ( Used to have such a set up in the cellar of my house in Germany ) Once in place put a protective box over everything .

You could also use a water proof switch and a float arm set up like on the sump pumps you see in Machine Mart .

 

[howardm]

Thanks folks,
I should have explained.
I have dug a hole for my new workshop foundations and had to go below the water table to find firm ground.
The effect of pumping out the water has had a miraculous effect of drying out a major part of my soggy garden. So, when the workshop is up, I want to continue pumping out to make the garden more useable.
I will be pumping out through a one inch pipe inside a length of 4inch drainpipe reaching 1.2metres to the bottom of the hardcore fill. Hence, the float switch needs to be purely vetrical and fixed to the suction pipe.

Thanks for the diagram Norm, I think I understand it.!

Howard

 

[rtbcomp]

........
Thanks for the diagram Norm I think I understand it.!

Howard

Ahem!

 

[the snooper]

all you need is the type of float switch you get with a dirty water pump, the pump holds the switch on a cable which floats horizontal but when the water rises to the set level the float becomes vertical and switches on.

aslo maplin sell a large float switch that you could mount on a pole at whatever height you want it to operate / cut in at

then as ron points out use relays to handle the higher power switching

 

[DrNik]

surely just buy a pump with a float attached. or am i missing something???

 

[rtbcomp]

"the float switch needs to be purely vetrical and fixed to the suction pipe."

Would one of those pressure switches they use in washing machines do the job?

Just need a vertical pipe with the upper end sealed and the switch unit plumbed in. The lower end is open so the water can rise up the tube.

They use microswitches so there should be a decent bit of hysteresis, it may even be adjustable.

 

[the snooper]

"the float switch needs to be purely vetrical and fixed to the suction pipe."

Would one of those pressure switches they use in washing machines do the job?

Just need a vertical pipe with the upper end sealed and the switch unit plumbed in. The lower end is open so the water can rise up the tube.

They use microswitches so there should be a decent bit of hysteresis, it may even be adjustable.

that would be perfect, never thought of that

 

[normspanners]

Thanks for the diagram Norm, I think I understand it.!

Wasa me!

 

[normspanners]

Good idea! washing machine switches usually have 3 different pressure settings/ switches on them, and each one is adjustable and they take the reading from each one seperately depending what depth of water it requires

 

[normspanners]

vetrical

Should that read vertical?
because vetrical is something completely different!

 

[J_K]

You need one of these.

The float can move up and down the string until it hits a weight at the bottom which switches the pump off or the toggle at the top of the string which switches the pump on.
I've used these a few times for filling water tanks and the work really well.

 

[CompoSimmonite]

I've got a float switch intended for boat bilge pumps.

 

[captain-destructo]

why not get hold of a plastic 45g (or smaller) drum drill lots of holes into it dig a big hole plonk it in backfill with gravel buy the cheap submersible pump from machine mart wich has a float switch fitted and you are sorted

dont forget to insulate the outflow pipe if its above ground or next winter

 

[KemppiFrog]

Fitted quite a few of the electronic controls with two sensors. The sensors are put at the upper and lower levels. Internal relay good for 16amps and the module fits a DIN socket. Rarely had to replace one. Useful for borehole pumps to avoid them running dry.