We Replace Submersible Pumps

We just got done replacing another submersible pump. This pump was inside a 4" PVC well and was a 3hp (horse power) 50 gpm (gallons per minuet) pump that was hanging on 1&1/4" schedule 80 PVC drop pipe. This pump's power source was supplied with standard residential 1 phase power, not commercial 3 phase electrical which I have worked with on occasion.

Every 20 feet was an 1&1/4" galvanized threaded coupling. The well was approximately 360' feet and the pump was hanging 160' feet down in the well. The water table was approximately 60 feet. I would have used at least 1&1/2" or 2" PVC schedule 80 pipe instead of the 1&1/4" pipe. We got just under 40 gallons per minute from the pump at open discharge. The reason for this is because of the distance to water and the size of the drop pipe.

If the water table was higher, the 3hp 50 gpm pump would deliver more (or a higher volume of) water. Also, the drop pipe is restricting the volume and thus pressure. To top this all off, the irrigation system was over-sized. What I mean by this is that most of the zones were demanding too much water or more water than the pump could keep up with.

There are a couple of possible solutions to this problem. The 160' feet of 1&1/4" drop pipe can be replaced with 2" schedule 80, or all the zones demanding too many gallons per minute can be lowered by changing nozzles and/or sprinkler heads. For example, there is one particular zone with twelve 3.0 (three gallons per minute per head) that demanding about 36 gpms . By changing just half of the nozzles to 2.0's, I can lower the demand of this zone by 6 gallons per minute.

Of course, you want to try and achieve matched precipitation, but in practice it is difficult to get it exact and imitate mother nature's precise even watering. So, you want to do your best to design, layout, and build a sprinkler system that will water as evenly and efficiently as possible. Some irrigation contractors can do this better than others...

The system also operated with a pressure tank, specifically a bladder or diaphragm tank and uses a 30/50 psi pressure switch. We also installed a new pressure tank which came pre-charged with air. I lowered the psi in the tank to 28psi before installing and filling it with water. So, the system actually operates on a 28/48 psi cut-on and cut-off range.

Submersible pumps are powerful because the push directly rather than having to create a vacuum or suction like a centrifugal pump, or use hydraulics to force water to the surface like a jet pump. Replacing your submersible pump can be easy or hard depending on your knowledge, skill, tools, and strength. If you have never replaced a sub-pump, I do not recommend doing it. You should only do it if you have had replaced these types of pumps with an experienced person with you to help teach you.

Scott
http://www.autolawnsprinklers.com

Pulling and Replacing Submersible Pumps

Today we replaced a 3hp 50 gpm (3 horse power/ 50 gallons per minute) submersible pump. The well the 362 feet deep. The pump was hanging on the standard 20 foot sticks of 1&1/4" schedule 80 PVC. The pump / drop pipe was only hanging 160 feet. The depth to the water table was close to 90 feet.

We replaced the old pump and 12-gauge solid strand twisted 4 wire. The colors are red, black, yellow, and green. The type of sub pump that we use is called a "3 wire motor" even though there are four wires, they don't count the green ground wire I guess! There are also two wire submersible motors available (actually have three wires including the ground), but I do not use them and recommend against them.

The three wire motor has the main advantage of utilizing a piece called a control box which contains the starter capacitors and relays and this box is installed above ground. A two wire motor has the start capacitor together with the motor. The reason why this is bad is because the most common thing for to go out on a sub is the start capacitor or relay and if your system only has a three wire motor, you will have to extract and replace the whole pump! If you use a three wire motor, when the start capacitor or relay in the control box goes out, it is easily replaced above ground without having to remove 200, 400, 600 feet of pipe or even more!

If you do not have a specialty truck with a wench and proper pipe clamps this process can be a labor intensive task, but can be done with the use of another specialty tool. A pipe pulling clamp will help hold the pipe has you pull it up and remove it. Every twenty (20ft) feet there will be a threaded connection that you must undo. The pipe pulling clamp help hold the weight of the rest of the pipe and sub pump so that it does not fall to the bottom of the well!

Be prepared do get covered in water because every 20 feet you will have to unscrew the metal or galvanized coupling and water will rush out fast on you! I have seen a few sub pump hanging with schedule 40 PVC, on glue fittings, but the majority of subs are on 1&1/4", 1&1/2" or 2" schedule 80 male threaded pipe ends.

When replacing submersible pumps, we normally replace all the wire just to be on the safe side. You can end up nicking the wire as the pump is pulled up and removed, plus the wires could have a short in them, so it is best to put new wire in. I don't replace the drop pipe unless it looks in horrible shape, or is the wrong type.

It's not an easy job, but a satisfying one, that is for sure. If you ever have any questions regarding sprinklers, irrigation, and pumps, feel free to contact me and I'd be glad to help you!

Scott Young
http://www.autolawnsprinklers.com