One for plumbers or fluid engineers maybe?

Haych

Bit of a long story but I’m after some kind of small bore, 10mm or so, in-line hose fitting that can “tell” when there is water present in the pipe and send an electrical signal off to a relay to turn other circuits on, either via a relay or some other secondary switch. 

I’m basically trying to prevent a water heater element from burning out when the tank in which it is placed is empty. 

If the cold water feed to the tank is full then it can safely be assumed that the tank is also full. For space and practical reasons a float switch can’t be used. Ideally I need something small and robust.

I’m not sure there’s much pressure in the system so a pressure switch might not be suitable. 

Does such a thing exist?

Thanks in advance. 

ToneControl

Haych said:

Bit of a long story but I’m after some kind of small bore, 10mm or so, in-line hose fitting that can “tell” when there is water present in the pipe and send an electrical signal off to a relay to turn other circuits on, either via a relay or some other secondary switch. 

I’m basically trying to prevent a water heater element from burning out when the tank in which it is placed is empty. 

If the cold water feed to the tank is full then it can safely be assumed that the tank is also full. For space and practical reasons a float switch can’t be used. Ideally I need something small and robust.

I’m not sure there’s much pressure in the system so a pressure switch might not be suitable. 

Does such a thing exist?

Thanks in advance. 

most designs use a thermal cutout switch on the heater element I think

I have one that used a spring-loaded switch on the bottom of the tank - a bit flakier I think

Rocker

A float switch in the tank could activate a relay switch to switch off the boiler if there is not water in the tank.

Haych

Rocker said:

A float switch in the tank could activate a relay switch to switch off the boiler if there is not water in the tank.

It’s not something I can easily modify but I did think of the same idea. If it wasn’t so expensive to replace I might have a go but don’t want to make a pigs ear of it and be in a worse place than I am now. 

BahHumbug

I think the alternative to a float switch would be a conductivity switch.  I’ve seen them us3d in instrumentation schemes when I worked in the power industry.  They usually have two probes and work on the difference in electrical conductivity between water and no water.

I don’t think I’ve ever come across one in a small pipe fitting form, though.

BahHumbug

I must say that this idea of ‘if the water inlet is full, then the tank can safely be assumed to be full’, intrigues me a bit........

Haych

BahHumbug said:

I must say that this idea of ‘if the water inlet is full, then the tank can safely be assumed to be full’, intrigues me a bit........

The only way for the inlet to be empty is if the tank has been drained. Ergo, if the inlet is full the tank is full. Simples!

hywelg

I will actually  need something similar for my new brew setup. Waste hot water will go to an insulated tank used for washing equipment, but there will be a pump to deliver it at increased pressure and I need to ensure the pump never runs dry. I was intending using a float switch in the top if the pipe, but also considered looking for a flow meter type thing with a relay to cut the supply to the pump but the problem with that is the latency. Pump won't fire up until there is flow and that requires water to pass through the pump naturally. 

boogieman

We have a power shower that has a flow switch in the pipework. No water inlet flow = pump doesn’t run. Would that work? 

Simon_M

It is possible to purchase heating elements with a water level sensor integrated. They're installed on some of the newer immersion heater tanks however I couldn't point you to one but a local plumbers merchant should know.

However, depending on the application, a water sensor is very simple to make. Two conductive probes spaced apart and connected to the +/- terminals of a sensor circuit (you could use a Raspberry Pi or something). When there is water between the terminals it will close the circuit and you can trigger whatever event you want. When there is not water then it will be open circuit.

Danny1969

You can get all kinds of pre made sensors for water .... here's a common Kemo one 

http://www.kemo-electronic.de/en/House/Garden/M158-Water-Switch-9-12-V-DC.php

Your find it on CPC for about £15