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View Full Version : Installing a pump for irrigation?


jphag
08-27-2004, 01:09 AM
Where I live in Colorado we only use city water and tap into a main from inside the house. How do you install a pump from a well and get the recommended amount of pressure to operate your sprinkler.

John

jerryrwm
08-27-2004, 02:47 AM
John,

Using pumps is a bit different, but getting the pressure is not the problem. A pump can be found that will put out the pressure you and much more.

The main factor when using a pump is the available water flow. How much water will the well produce at the wellhead?

Once that is known, and how long you can pump from that well (draw-down) you design the system around the available GPM, and the pump can be sized accordingly. If it is already downhole, then you are limited by the pumps performance.

This is quick but Pumps are a lot longer subject and not enough time to discuss now.


Jerry R

SprinklerGuy
08-27-2004, 09:39 AM
Jerry...I have a need to learn the well/pump relationship as well....in my rural area there are many of them and not many guys that service them.

Also, they use them for sprinklers.

Experience the biggest learning tool? Other?

Common sense?

jerryrwm
08-28-2004, 01:42 PM
erry...I have a need to learn the well/pump relationship as well....in my rural area there are many of them and not many guys that service them.

Tony,

Wells and pumps are closely regulated by most states water agencies. You must have a well driller's license to service any of them, and if you don't have the equipment to do so, it becomes one helluva task.

As for using them on irrigation systems, there are several ways to do so.

1. A well that is existing without a pump can be used for irrigation, but there are several things to take into consideration. You are going to tell the well driller what performance you need and he will make it happen or tell you it can't because of factors downhole.

How much water is available? This is a factor of drawdown - how far the water table is lowered during pumping. If it is a good water sand, the drawdown will not drop much, but on tight sands, it may draw considerably.

If the static water level in the well is say 100' then the pump will need to produce 43.3 psi (100 ft of head) in order to get the water to the surface. You will not have enough pressure to water anything though so the pump must be sized to overcome the verticle lift and then provide pressure for the system to operate. If you need 40 psi to operate the system, then the pump will need to be sized to pump at 83.3 psi (191 ft of head)

Now drawdown comes into play. If after pumping for a period of time, the water table drops due to pumping. Let's say that it drops 20 feet and holds. Now the pump has to overcome the additional lift caused by drawdown.
Instead of a pump requiring 191 ft of hd, we now need a pump capable of producing 201 ft of hd (87 psi) or your system will be operating at 31.3 psi.

Have the homeowner contact the well driller and get a copy of the well report. It will have all the information needed. ie. static water level, drawdown level, pump depth, etc.

On the other hand, you may have a well that has been in use for a while with pump installed and operating. The well driller will be able to tell you how many GPM at what pressure the pump will produce. Then you can design the system using that data the same as you would with domestic public water meters when you have the meter size, service size, and static pressure.

The other way to use wells for irrigation is to have the well pump into a storage tank or cistern and then install a centrifugal pump. This will be sized based on the system requirements - GPM and required pressure. The well will replenish water in the storage tank by using float valves (like the toilet tank float) or with a set of level switches and probes. Then when the system starts using water from the tank, the well will start refilling the tank. You will still need to know the output of the well to determine how long you can water.

ie. 1500 gal tank full at cycle start. Well pumps 10 GPM (pressure here is not important on the well pump, only volume) Your system is designed to run at 15 GPM. (Don't worry about pressure just yet) In this case you have a deficit of 5 GPM replenishment rate. Assuming that all zones are 15 GPM (for clarity) you will be able to run the irrigation system for 260 minutes before you run out of water. This doesn't add up to 1500 gallons, but you don't want to run the tank dry, so I left a 200 gallon reserve in the tank. (This can be monitored by the level probes.) Now the well pump will take 130 minutes to refill the tank, and then it is ready for another cycle.

Sizing the centrifugal pump for this application is fairly simple. Design the irrigation system for 15 GPM and determine your total pressure losses. Let's say the total pressure losses are 38 psi. You will need a pump that produces pumps 15 GPM at 40-45 psi. A little bigger for miscalculation. This information is available from most pump manufacturer's for every pump they make.

I recommend getting to know a good pump supply house in your area. They will be able to help you size the pumps. And become friends with a well driller. They can be a valuable resource.

Hope this helps. Pumps are nothing to be scared of, but they can be very complicated. Especially when using jockey pumps, multiple pumps, variable speed pumps, submersible pumps, etc, etc.

Jerry R