Long distance pump control

Electromatic

Electromatic

Senior Member
Location
Virginia
Occupation
Master Electrician
I've been asked to help reconfigure a municipal water pump booster station. There is a pressure tank about 2,000ft from the pumps. The water (not electrical) engineer wants a simple pressure switch at the tank to tell the pumps to turn on or off.
What are the difficulties with using a dry contact at this distance?
Alternatively, we could use a pressure/level transducer and a 4-20mA signal. I understand the theory of loop impedance limitations, but I've never had to completely design a transmitter, sensor, cable system. What do I need to look out for at this distance--or would most equipment be fine?

TIA
 
Would a 4-20mA signal with shielded, twisted pair be feasible? Would I have to be extra careful in selecting a sensor and input based on impedance? We wouldn't need a true analog signal--we could just set low and high mA values as on and off.
 
I’ve done one using a 120.volt cube relay controlled by a level sensor at a water tower about a quarter of a mile away. Very little voltage drop because of the low current of the cube relay. It in turned controlled the starters for the pumps. Same could be done with the pressure switch. Kinda old school though, most nowadays use variable speed pumps for better pressure control.
 
Electromatic said:
Would a 4-20mA signal with shielded, twisted pair be feasible? Would I have to be extra careful in selecting a sensor and input based on impedance? We wouldn't need a true analog signal--we could just set low and high mA values as on and off.
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I have done industrial 4-20 mA instruments loops that were that long without issues. Most of the ones I worked with were limited to 750Ω, with the PLC input having 250Ω, leaving 500Ω for the wiring.
 
If either site is or was wired for plain old phone service (POTS) there were ways of doing it over a phone line, around here you cant order new service, but they maintain the existing for the towns the use it for stuff like that.
The service was called a 'dry pair' or a 'dry loop', the service was just a pair or wires (or two pairs) from point A to point B, no dial tone.
 
tortuga said:
If either site is or was wired for plain old phone service (POTS) there were ways of doing it over a phone line, around here you cant order new service, but they maintain the existing for the towns the use it for stuff like that.
The service was called a 'dry pair' or a 'dry loop', the service was just a pair or wires (or two pairs) from point A to point B, no dial tone.
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Our local village used it for years. Updates to systems and the need for more information required changes. That and the telephone system service went downhill. Drastically.
 
We actually have a similar booster pump and tank pair of sites on another side of town that uses a POTS connection and an old Wheelock relay to control the pump site from the tank site. (Apparently there's only one good pair left in the old phone line. Who knows what we'll do when/if that fails.)
The situation I'm currently working on has an existing booster pump site on the side of a (modest) mountain. At the top of the hill--about 2000' away--is a bladder tank, but that tank is getting replaced with a larger one. The new tank site will get power for a convenience light and receptacle, but otherwise there is nothing existing between the pump site and the tank site besides water piping. Currently, the pumps are controlled by pressure measured at the pump site, but they need to be controlled by pressure or level at the tank site.
 
I have done a lot of pump control for reservoirs. AC at that distance may pull in a contactor but no release. DC can be run for that distance easily. A pressure switch would require calibration, have good sensitivity and be protected from freezing.
Float switches are easy to set up and test.
One float can be used, with a long cord, but better is a low float and high float wired in a basic pump up control.
If you use a pressure switch make sure the reservoir has an overflow that safely discharges the max water.
And there are many companies that make spread spectrum license free radios, Banner is one of them
 
electrofelon said:
It will be fine just using a simple setup with a relayer/contactor, let's not make it into a Rube Goldberg device here.
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Those simple set ups did not work when farmers started trying to put start/stop buttons 1/4 mile from their pump panels. No doubt part of it may have been because they were laying the control wires in the same ditch as the power. It was trouble often enough.

Wireless control can verify that the pump has actually started, it is at pressure or has shut down for whatever reason. They can stage several pumps as needed. Not all that expensive and really fairly simple. We did it by just RFM.

On/off may be all that's needed, but the option is there.
 
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