Bob NH
In the Trades
You could do it with a reverse action pressure switch and a time-delay relay.
Install a pressure switch on the suction of the pump that will open when the pressure drops below the point where you want to operate the pump. Reverse action pressure switches are available from different sources. For example, The FRG52 (links below) can be set to a cut-out pressure (switch opens) as low as 1 psi and a cut-in pressure of 6 psi. The FRG32 has a cut-out pressure as low as 4 psi and a cut-in pressure adjustable from 6 to 20 psi above the cut-out pressure.
http://ecatalog.squared.com/catalog/173/html/sections/20/17320014.html
http://ecatalog.squared.com/catalog/173/html/sections/20/pdf/17320014.pdf
Then install an On-delay relay such as the SSAC TRU Series using the "Delay on make" function where the output contact is closed at a set time up to 1000 minutes (16.67 hours) after voltage is applied.
http://www.ssac.com/standard/ff-tdr1.htm
http://www.ssac.com/catalog/TRU01A01.pdf
When the pressure drops below the set pressure (for example the 1 psi setting of the FRG52) the power is removed from the relay and the pump stops. If the pressure dropped because the pump was drawing water, then the pressure might be immediaely restored, applying power to the relay. However, the relay contact would not close until the delay setting had elapsed.
For example, it would be possible to set the delay for one hour, in which case the system would "try again" every hour to see if there is anough water to supply the pump.
Install a pressure switch on the suction of the pump that will open when the pressure drops below the point where you want to operate the pump. Reverse action pressure switches are available from different sources. For example, The FRG52 (links below) can be set to a cut-out pressure (switch opens) as low as 1 psi and a cut-in pressure of 6 psi. The FRG32 has a cut-out pressure as low as 4 psi and a cut-in pressure adjustable from 6 to 20 psi above the cut-out pressure.
http://ecatalog.squared.com/catalog/173/html/sections/20/17320014.html
http://ecatalog.squared.com/catalog/173/html/sections/20/pdf/17320014.pdf
Then install an On-delay relay such as the SSAC TRU Series using the "Delay on make" function where the output contact is closed at a set time up to 1000 minutes (16.67 hours) after voltage is applied.
http://www.ssac.com/standard/ff-tdr1.htm
http://www.ssac.com/catalog/TRU01A01.pdf
When the pressure drops below the set pressure (for example the 1 psi setting of the FRG52) the power is removed from the relay and the pump stops. If the pressure dropped because the pump was drawing water, then the pressure might be immediaely restored, applying power to the relay. However, the relay contact would not close until the delay setting had elapsed.
For example, it would be possible to set the delay for one hour, in which case the system would "try again" every hour to see if there is anough water to supply the pump.
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