This part of the Pump Tutorial Series. The 1st page is at Pumps: Selecting-a pump step-by-step.
There are numerous types of pumps designed for various purposes. Pumps commonly used for irrigation fall into two broad categories: Displacement Pumps and Centrifugal Pumps. Within those categories there are sub-categories that further define the type of pump. This tutorial will focus on those types of pumps most often used for irrigation.
Continue reading Types of Water Pumps for Irrigation Systems
Q. My irrigation pump runs fine when the system is operating, but after it turns off it cycles on for 5 seconds every 10 minutes or so.
A. If you are using a pressure switch and pressure tank to turn the pump on and off my first guess would be that you have a water leak in your irrigation system. The water leaks out, which cause the water pressure to drop, then the pump kicks on and recharges the pressure. Then the pump shuts off again. That would cause exactly this symptom.
Knowing the problem is the easy part. Finding the leak, that could be harder to do. It could be a zone valve that isn’t turning off all the way or it could be a leaky pipe. You can narrow the search area a little, the leak will be someplace in the pressurized part of the system, that is, between the pump and the zone control valves. Start by looking for obvious dripping, then look for someplace that seems wetter than it should. If it is a leaky zone valve then the water will be leaking through the valve into the sprinkler zone pipes and will dribble out at the lowest sprinkler head. So look at the sprinkler heads. There will be a small “swampy” area around the lowest sprinkler head that is controlled by that valve.
Q. I am currently in the process of converting my entire lawn irrigation system into an electronically controlled system using a control and relay setup for the pumps. I currently have two centrifugal pumps that pump water from a pond about 150 yards away. The system has seventeen zones and I have already ordered all the valves needed as well as the controller and pump relay and am in the process of installing it all. I am concerned with the fact that if one of the valves fail to open then I may have a problem with too much pressure and would like to know what kind of setup you suggest in order to overcome this. I researched pressure relieve valves and such but I feel that a flow sensor combined with a high pressure sensor to turn the pumps off would be the safest route in order to minimize damage to the pumps. How could this be done to cut pumps off if there is too much pressure or no flow at all?
A. They make flow sensors that use paddle wheels, they can actually measure the flow rate in the pipes in GPM or cu ft/min. They are a great way to go for this. They require that you have a fancy irrigation controller that can work with them, so you may need to return your controller and upgrade it. The irrigation controller measures the flow and compares it to the pre-programmed flow that should be present in the system for the valve that is currently open. The controller then makes a decision based on that flow. If the flow is too low or too high it can shut down the pumps or close a master valve that shuts off the water to the entire system.
The sensor needs to be installed in a tee on a straight length of pipe. The length of the straight pipe should be 5x the pipe diameter before the sensor and 5x after it. This is to reduce water turbulence in the pipe caused by turns, the turbulence can cause inaccurate pressure readings.
You can also use a pressure sensor and pump logic controller to turn off the pumps at high pressure or very low pressure. You should be able to get what you need at a specialty pump supplier. The sensor is a bit different from the typical pressure switch. A standard switch turns the pump on at low pressure and off at high pressure. The logic controller is basically used as a detector and timer. The timer would only turn off the pump if the high pressure was present for maybe 4 minutes or so. It is normal to have a pressure spike as the system changes from one valve to another, you don’t want the pump to shut off during the switch of valve zones. You also need a delay to allow the pump to start up, since there will be no pressure until it gets going (so the switch would never allow the pump to start!) The pressure sensor also needs to be on a straight pipe section like the flow sensor.
If you wnat to use a pressure sensor you should also do a quick test to make sure your pumps are capable of producing a high enough pressure to detect. Some pumps don’t produce very much increased pressure, even at no flow. So you need to make sure your pump will, if it doesn’t you need to use a different method of detecting no flow, like a flow sensor. Run the pump as normal with the smallest valve circuit open and check the pressure. Now shut off the valve and watch the pressure (don’t let it run for more than 3-4 minutes without flow! Don’t want to overheat the pump.) Ideally you want to see a pressure increase of 5 or more psi. The more pressure increase you have the less likely you are to get a false alarm caused by a small pressure spike.
If the pump doesn’t produce enough pressure to measure the increase at no flow you will need to use a flow switch to detect flow. A flow switch is nothing more than a paddle that sticks down into the pipe. When the water is flowing it presses against the paddle and the switch opens/closes (depending on how you have it set.) It’s very simple. Unfortunately flow switches also break pretty easy, so they have to be frequently replaced. That’s why I don’t use them as my first choice.
Q. I have a shallow well that was drilled this summer and a centrifugal pump pulling up about 15 gallons/min (HAPPY!). The problem, it will only produce somewhere around 30psi (sad!). Am I able to add a booster pump to this setup to produce more psi or should I just forget it and go for a submersible pump? Obviously the booster pump would save me $…
A. You can add a booster pump but it is tricky. The flow range of the booster pump needs to match that of the existing well pump. Using two pumps will probably use considerably more electricity than a single new pump, especially if it is a submersible. Submersibles are by nature more efficient than a centrifugal pump at the top of the well and now you are adding the friction drag of two pumps rather than one. I can’t tell you how much the electricity cost difference would be, that’s beyond my knowledge level. But ongoing electricity cost is certainly something to look at.
Essentially when you couple two pumps together they are going to have to play nice with each other. You don’t want one to over-power the other and do most all the work while the other just causes drag. Plus you need to deal with the wiring issues and how you will start the two pumps. Hopefully they would both stay primed so, in most cases, you could start them both together using the irrigation controller connected to a relay connected to the pumps. You might need two relays if the pumps exceed the capacity of the relay.
Finally you will need to deal with figuring out if and how you will handle problems such as the malfunction of one of the pumps. If one burns out the drag created by the burned out pump could very quickly burn out the other. Hopefully you would quickly notice the problem, since the irrigation system would not work well at all if only one pump was running. But what if you were on vacation when it happened?
You probably should get a local pump professional who knows his/her stuff and has experience with two pump systems to help you if you use two pumps.
Basically if you want to keep this a simple do-it-yourself project I’m thinking buying a new submersible for your well would be the better way to go.