Air pressure gauge setup in septic tank

[coopersim]

I have a sewage treatment plant that is buried in my garden

Last week I noticed a part had failed causing the treatment of effluent to stop, I'd like to have some pre warning if this happens again and want to know how I could add some air pressure gauges to the setup.

There are three circuits I'd like to be able to remotely monitor, two that blow in to the treatment reactors and one that moves sludge from one settlement pool to another.

What in thinking of doing is fitting thin airlines to the 19mm air hose and 40mm solvent weld pipe and running these back to the garage where I will mount three air pressure gauges - problem is I don't know what fittings I need to buy to be able to install this setup - especially how to tap these in to the existing pipes?

Thanks for reading

 

[bernardgreen]

You could use air pressure diferential switches to detect if fans are blowing. These are used, among other applications, in boilers to detect if the fan is operating correctly. While they will not provide a pressure reading they will close a contact to say the fan is running. They can be fitted locally to the tanks with a cable back the garage. Running fine bore air lines some distance would have problems with condensation in the pipes and possible freezing in winter.

Sludge depth can be sensed as being too deep by a float switch. The Kari 3YE float switch in our pumped sewage system proved totally reliable. It had stert, stop and over filled switches

The full Kari range can be found at http://www.kari-finn.fi/eng/e_pintakytkin.html

 

[Agile]

I agree, but washing machine fill sensors are air pressure switches and probably cheaper than boiler ones which tend to be expensive. But you do need to know what air pressure you have.

You can make up a bodge "U" gauge with some plastic tubing. Or even hosepipe. It does not even need to be clear as you can move the open end up and down until you can see the water at the end.

 

[bernardgreen]

I agree that the air pressure switches in boilers cost a lot of money to buy as boiler spares but can cost a lot less when sold for some other purpose.

Washing machine sensors are looking for pressures between ( approx ) 200 and 1000 Pascals ( 3/4 inch of water to 8 inches ) which is probably a lot more than the differential pressure of a blower fan.

As you say without knowing the prissures involved it is not possible to suggest the optimum solution.

 

[coopersim]

I hadn't thought of the condensation issue.

The problem with digital switches is that I want to know if there is a drop in pressure rather than just knowing if there is some or none.

What about an electronic gauge?

 

[bernardgreen]

Electronic pressure sensors are relatively cheap. Les than £10 for a device that when supplied with 5 volts DC will provide a voltage proportional to the pressure Feed the voltage to a cheap voltmeter and you have a low cost indicator. Feed the voltage to a simple comparator ( such as a PIC micro ) and you can have two logic outputs saying whether the pressure is too high or too low. Add a control signal that tells the PIC when the fan is ( or should be ) running and the too high and too low signals will only operate ( as alarms ) when the fan is running. Otherwise the too low will be an alarm when the fan is not required to be running.

 

[Agile]

I always like to use simple ways!

Use a 741 op amp as the comparator and power it from the fan supply so that its only powered when the fan is powered!

Tony

 

[coopersim]

Thanks for the advice on this one. I could do with a bit more help on what I need to buy, I'm struggling to find a voltmeter that displays below 3v and I don't know what sensor I need specifically. Thanks