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Choosing the Correct Pump for Watering Automation

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This is a subject that baffles many gardeners. I, myself, have been trying to find the magic spot. There are so many factors to consider on this subject. Among these factors are desired gallons per hour/minute, number of plants being watered, and the height the water will have to be pumped to exit the reservoir and enter the lines (also referred to as head height). Keep in mind, at the time of writing this article, there is no magic formula I have found to calculate this. What we will be discussing is how pumps are rated and how that pertains to water flow in general.

First, let’s discuss the gallon per minute/gallon per hour rating. This rating on a pump refers to its ability to pump a specific amount of water over a specific amount of time. This rating is determined through factory testing by the manufacturer at zero feet of rise unimpeded by any reduction in size of delivery mechanism. Delivery mechanism in this case includes any hoses, drippers, or diffusion equipment.

Next we talk pressure produced by the pump (measured in PSI or pounds per square inch). This is important when deciding which type of delivery material to use. For example, with a pump that produces 10 PSI, it would be ok to use standard vinyl tubing; however, if your application requires a pump that produces 60 PSI, it is highly likely that the use of

vinyl would leave you with exploded delivery lines and a huge mess to clean up. In the latter application, it would behoove one to use PVC pipe or some type of braided lines.

Now let us move on to head height. Most pumps from reputable manufacturers with come with a chart that explains the PSI and flow rate at a given height. To explain this I have to assume that anyone reading this understands the basic concept of gravity (what goes up must come down), and that water has a specific weight by volume (8.34 pounds per gallon pure, and slightly more than that with dissolved solids). That having been said, we will imagine a six foot tube with a half inch diameter and our lung power as the pump. If that tube contains one inch of water, it would be easy to blow that water up that six foot height and out of the tube. If that tube was completely full of water, one would probably hope they had there beer-bonging skills fully honed to avoid drowning.

Finally, the number of plants being watered is a factor we must take into account. Consider this scenario. Your water reservoir is 200 gallons and is eight feet tall. The pump chosen is capable of pumping 22 gallons per minute at zero height, but will only pump sixteen gallons at four feet or eight gallons per minute at seven feet. You are trying to water 16 plants, one gallon each, in one minute of time. In this application the pump selected will fall short of meeting the gardener’s needs. If the dimensions on the reservoir were four feet shorter, this same pump that fails the test in the scenario above would function just fine.

I hope this makes the mud a clearer shade of brown where automation of watering is concerned. Based on the example above, I am sure you now have a basic grasp of the variables involved.

If you have any further questions regarding the subject, feel free to ask us on the web or pay a visit to Urban Garden Supply and ask one of our experts.

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