There are three main methods to achieve Dry Run Protection on your valuable pumps:

1: A float switch in your supply tank.                                    (most common way)

2: A pressure switch on the suction side of pump.   (supply tank must be least
                                                                                                           6meters above)

3: A Level probe in supply tank.             (suitable for a very shallow supply tank
                                                                                                  18inchs deep or less)

A level probe would be used when a float switch can't work because of depth of tank, and tank at same level. 
Float switch requires about 24inchs, probe 1inch.

Also handy for accurately controlling a sump pump.

It controls a relay or contactor which actually handles the pump electrical load.

Would only use if necessary, behind other 2 methods.

You would use a pressure switch on suction side of booster set if the supply tank was sufficiently above the pumps, at least 6 metres, or mains pressure fed, you would use a pressure switch with a very small differential (on/off gap) .3 bar.
Set very Low .2 bar.
It would be wired to cut out the control circuit of pump when there was no water available.
Float switch installed in supply water tank (break tank).
By far the most common and reliable way to save your pumps from running on air.

It's vital that installation is correct.

1= Attach weight about 10inchs back along cable.
2= Hang switch down so it's just above the outlet pipe.
3= Attach cable tie just below ceiling of tank.
4= Drill hole in tank ceiling near hatch.
5= Place all in tank and thread cable back out through gland, pull until cable tie hits on inside, then tighten gland to secure position.

Again load power does not run through float switch, only the control circuit power, usually 24v ac.

Some of the self controlling domestic water pumps will have dry run protection built in.

Copyright © 2010
Copyright © 2010