SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

That sounds good, except for the 30/50 psi range on the pressure switch will exceed your pumps performance, so you might as well start with a 20/40 psi model, and save some adjusting time. These switches all have a separate adjustment designed to increase only the cutoff pressure, so you can start with 20/40 and work it up towards 20/45, and you might even be able to shave a few psi from its cut-in point, and look towards achieving something like 15/45 psi. That 15 psi cut-in is somewhat theoretical, as I expect that switch has a minimum operating point not too far below 20 psi, but I mention it for the idea of gaining maximum pump operating time between cycles.

There is one brutally simple trick you can try for extending the runtime, at least for the moment, if the tank and switch don't get you there after making switch adjustments. That trick is to include a gate valve in the plumbing on the pump outlet, and closing it down so it limits flow. Gate valves are preferred for this, because you can always remove the handles from gate valves, to keep someone from messing up the adjustment. Of course that trick might just take away so much pressure that the pump won't support much of a sprinkler system. (You can work the tank-sizing calculator and see that it would take a 14 gpm flow to match your tank and a 20/45 pressure switch, to get that one minute of runtime)

Ok, I found a 34 gal Amtrol Champion tank that seems to be a good balance of quality, size and price. At 30/50 psi is has 11 gals of drawdown. I plan on installing this outside of the garage under the overhang, and out of the sun. I could jump up to 44 gal just to give myself the headroom, but the price jump is a tough pill to swallow.

I'll couple the tank with the Square D pressure switch. You recommended the FSG2, I assume the J20 (30/50). I'll go with that.

I'd like to try these first, before purchasing a CSV, in case I can get away without it.

Sound good?

"random intermittent small amounts of water" is what hose bibs are all about, and any good pro will design for the physical reality of a system, and not what anyone will say about using the hose bibs only in a certain way. But just how a hose bib will be used is not the issue. The issue is that the pressure switch will not be able to reliably distinguish the difference between the water pressure with your pump feeding a hose feeding a sprinkler, and the water pressure with your pump deadheading. Check the performance curve for your pump, and you can read that the pump output pressure at 3 gpm (one hose-end sprinkler) is about one psi lower than the deadhead pressure. That difference is not enough for pressure switch operation, which is bound to vary a tiny bit more or less than its set cutoff pressure.

And we aren't even getting into hose operation with a trigger sprayer on the end, which has to be foreseen by any designer, regardless of what anyone might say to the contrary.

So, in order to 'bulletproof' your present pump install to work reliably with a pressure switch, you might approach it from two directions. First, you look for a way to get constant pump operation when water is being used, while making sure the pump gets a full minute of run time whenever it turns on. Second, you make any tank selection compatible with straightforward operation with some future jet pump as yet not needed. The second one is easy, if you work the jet-pump curves into a gallons-per-minute number. I won't bore you with the details, or what other jet pumps may be had with higher flow capacities, that go into a tank recommendation. Suffice it to say that a precharge tank with a 30 gallon volume would handle the smaller two jet pumps without your having to do any advanced pressure switch adjusting. (the 1 HP pump has enough flow that you would have to do some fiddling with the pressure switch to get that one minute of runtime)

That same 30 gallon tank would give you enough capacity to work in combination with the smaller size of Cycle Stop Valve, and give your current pump a one minute minimum run time, as long as you can maintain a pressure switch cutoff point a few (very few) psi below the deadheading pressure of 47 psi. The way that valve works is that once you reach its built-in 40 psi pressure limit, it will only pass a flow of one gallon per minute, and it will be that low flow that will take time to build up pressure, and it will be that low-flow time in combination with a large enough tank, that gives the pump its minimum runtime. Up until the CSV reduces flow, the tank will be filling at a much faster rate, as you can see from the CSV1 pressure-loss graph.



You will note that the CSV1 flows top out at 30 gpm, and a more practical limit is 20 gpm or less. You will have to abandon the idea of a sprinkler system that uses all the possible flow of your centrifugal pump, if you want all-encompassing pump protection at anything near a reasonable cost.

Note that the tank sizing calculator page gives you the scientific theory that the calculator uses. If you want to try it yourself, remember that a pressure switch comes standard out-of-the-box with a range of 20 psi between cut-in and cut-off. Also, since there is no 1 gpm flow, you can use 10 gpm, and adjust the answers accordingly.

Ok, I think I see where the confusion lies... your statement "The problem for you is that you also want to have the ability to draw random intermittent small amounts of water from hose bibs" is not what I am looking for. When running the hose bibs, I am fully expecting the pump to be running continuously like it does today. We don't use the hose for random small amounts of water, we use it for running sprinklers. When I have the system fully operational the hose bibs will rarely be used. When they are, I am OK with the pump running.

Part of the reason I am thinking of a medium sized tank is because I do expect my pump will fail someday...when it does I am hopeful that I can replace it with a Jet pump without need to change anything else (except the pressure switch settings). I could probably get away with a smaller tank, but in trying to future proof it a bit, I feel a 30ish gallon tank would be a pragmatic choice.

Unfortunately I have run out of Summer, so I think it won't be until next Spring that I install the tank and switch. I will update this thread with how it goes.

Thanks for all your help!

You are both complicating and oversimplifying the situation. The over-simplification comes from your statement that you are pumping 60 gpm. What you are actually pumping is a flow rate that can be found on the performance curve. That curve starts at zero gpm and goes all the way to 88 gpm. In terms of your pump operation and pressure switch settings, your pump will begin operating at near to 80 gpm when it cuts in, and by the time it cuts out, you can hopefully have it fine-tuned to be pumping at 10 gpm or less. If you really wanted to mathematically work out precise cycling times from the performance curve, you would have to use calculus.

The complicating comes from assuming the tank is in place to deliver water. Not the case. It's just there to both provide some constant upstream pressure for the sprinkler zone valves, and to keep the pump from cycling too rapidly during operations other than lawn sprinkling. If you only cared about the constant upstream pressure, you could have a pressure switch and baby tank mounted right on the pump itself. The sprinkler system would be happy with only that.

The problem for you is that you also want to have the ability to draw random intermittent small amounts of water from hose bibs, fed by a pump that would cycle a pressure switch very rapidly, unless sufficiently sized pressure tanks are a part of the system. To have an install of your particular centrifugal pump that was proof against any and all possible operating situations might involve so much pressure tank capacity that it would actually be cheaper to replace the pump with a small jet pump, and work out the tank and pressure switch details from there.

It may work out that your best, and simplest, solution will be to employ a Cycle Stop Valve, and have it, the pressure switch, and the baby pressure tank on the pump itself or nearby. That will subtract some additional pressure, but you'll live with the loss, rather than have a tank farm.

{we interrupt this post for another teaching moment}

A jet pump is what this application really calls for, and we only need to see some jet pump performance curves to know why. Instead of unused overcapacity, you have a useful range of pressure and flow that graphs as nearly a straight line, for your calculating pleasure. The 1/2 HP jet pump would do fine in your application with a 20 gallon size precharged pressure tank, and there wouldn't be any agonizing over tweaking the pressure switch adjustment just right. And no Cycle Stop Valve needed.



{end of teaching moment}

And as for your own make and model of centrifugal pump, it possesses a key characteristic of all reliable electric pumps, which is a motor with a high service factor. More than anything else, that "service factor" is why some pumps endure and other burn out, assuming everything else is equal. The cast-iron jet pumps selected by conscientious professionals will also possess high service factors.

Thanks Wet_Boots. Very clear explanation of the situation and options.

I think I have what I need and understand the challenge I face depending on the choices I make.

The part I feel isn't being taken into account is that I WANT my pump to run. I don't "need" water delivered from the tank. My purpose for the tank is to keep the line pressurized when the pump is off. Without it my line pressure drops to zero and my valves won't function correctly. The calculators are geared towards trying to deliver a significant portion of the demand without having to run the pump.

For instance, the calculator you linked to has the first question "Pump output in GPM?". Mine is roughly 60+. If I enter that, is says I need to park a tanker truck in my back yard to match that volume without running the pump. This particular calculator tops off at 30gpm. If I enter 30gpm, 1.5 second run time (continuous isn't an option) and 30/40 cut in/out, it says I need a 250 gallon tank. So I then answer the pump output question with 5 gpm and I get a more reasonble sized tank (42). But that is just me knowing how to trick the calculator to give the answer I think I need. I understand my use is not what the calculator is designed for. Heck, I understand that my use is not what the tanks and switches are designed for. Typical recommendation for my setup is to use a Pump Start Relay.

If I had never tried to expand my sprinkler pump into a irrigation system pump, I would still have been using it to pump to a single sprinkler, so as far as "pump protection" goes, my worst case scenario is my starting point. With what I am trying to do I will eventually do the majority of my watering using the zones and valves which will be higher flow, lower pressure, happier pump. Given that, my goal is to simply introduce a tank/switch to pressurize the line when the pump isn't running, and wait patiently when it is.

So with the information you have provided, which I greatly appreciate, I understand that it IS possible but NOT guarenteed because I will likely be trying to balance very narrow pressure margins. Additionally, in my low flow situations my pump with be close to deadheading pressure (again I am already in this situation). I'm ok with that.

I feel compelled to say, for all those that may come across this thread because they searched for "sprinkler pump" or "centrifugal pump". This 1.5 hp, 110v, 2" intake, 1.5" output pump has been the best purchase we have made in the past 20 years for trying to water our vacation property. After countless headaches with burnt out pumps that lost prime and never really delivered enough performance, this pump has been rock solid, has never lost prime and delivers MORE than enough water to every corner of our property. If you are considering this pump for just running sprinklers via a hose (or multiple hoses) then I highly recommend it. If you are considering it for delivery to an irrigation system, then ask the pros before making a choice.

You have to remember that these threads are often read by others trying to learn about equipment choices, and it's for the now and future benefit of a wider audience that I stress some of these points, because every day, someone looks at a cast-iron "lawn sprinkler pump" and thinks that's just the item needed for a sprinkler system installation, not knowing the designation is either outdated or downright deceptive. Today's common rotor sprinklers need much more pressure than the simple brass spray heads of yesteryear, and a system greatly benefits from having a water source with more pressure than a centrifugal pump can manage.

So trust me, no one's beating up on you. It just happens that you walked into a teachable moment. Smile!

Meanwhile, your pump is going to be performing as its curve describes, and to make the combination of pressure switch and pressure tank work for you, you will be fine-tuning the cut-off pressure adjustment, so that you get a full minute of pump operation every time it starts, on the way to the tank pressure going back up to the cutoff point. This is where we get back to the script that was being read to you, and what the larger tanks make possible.

The larger the tank, the lower your cutoff pressure can be, so long as you are having the same cycle interval. You want an interval of at least one minute as a safe minimum, and a pro setting up a deep-well submersible can be thinking in terms of two or three minutes between pump starts. So this is where you have a tough choice to make, because this is an application where bigger is better. The only downside to a bigger tank is that it costs more money. The downside to a tank that is too small, is that it won't be able to give you a full minute of runtime for your pump.

The pressure switch itself is a fairly simple mechanical item (I recommend a Square D Pumptrol FSG2) and they have their limitations, in that if you set a cutoff point of 43 psi, it will most of the time cut off at 43 psi and at other times may cut off one or two psi higher or lower. This detail is important because the absolute maximum cutoff pressure you might set for your pump is 47 psi, the pressure that it would be deadheading at. (see the chart)

So the bigger the tank you buy, the more wiggle room you give to your pressure switch adjusting. And you need that wiggle room, because the difference in output pressure with you running a hose, and the pump simply deadheading is going to be a very small difference. What works in your favor, is that a cycling pump with you running a hose will take a bit longer to reach cutoff pressure (but not so much longer that it makes up for an undersized tank)

Here's a simpler calculator to play around with, but no online calculator will take into effect that your pump flow rate is going to start out big and end up small. The selection of a tank is going to come down to your budget and willingness to invest in a reliable level of pump protection. See what tanks are available in your area, and compare prices and capacities and reviews of quality. I think you should start the search with a 32-36 gpm precharged tank.

I don't know where the businesses that take pumps on trade-in are, but I am not aware of any in my neighborhood. The research I did pointed to the centrifugal pump as being the correct choice for irrigation/sprinkler applications. Sprinklerwarehouse.com has this exact quote when referring to centrifugal pumps... "A vast majority of all irrigation pumps fall into this category". I wish I would have posted the question on this forum before buying and using the pump, but I didn't. Can we move on from this?

I have used the pump for a three years now and am very happy with it. It has been supplying a single 3/4" garden hose for this whole time at a very low flow rate and hasn't deadheaded. I have been told that these pumps are used in this way frequently and do just fine, but are certainly capable of more.

I didn't want to use a pressure tank at all and would just rely on a pump start relay, however I learned the hard way that I need the lines pressurized to keep the valves closed. Without some pressure in the line, the zones will run for 5-10 secs every time I turn the pump on which is not desirable.

So I find myself in a situation where I have already made a commitment to this setup and am trying to make the most of it with some help from those experienced in this field. I'll understand if you do not want to help me, because you feel I have painted myself into a corner with bad choices, but beating me over the head about it isn't helping.

So not worrying about deadheading...should I be able to set up a pressure tank and switch in such a way (describe in previous post) that I will be able to have the pump come on when a demand event occurs (or shortly after) and run continuously until all valves are closed again (or shortly after)? I realize that the factory configuration and standard settings are not going to work for me, but I'm wondering if I can lower the pressure in the tank and narrow the range in the switch to make it work?

The "I Told You So Department" would like to take a moment to remind everyone that it was recommended that the centrifugal pump get traded in on a jet pump, which could become a stable water supply with the addition of a Cycle Stop Valve, a pressure switch, and a baby pressure tank, and all for less cost than was spent on the centrifugal and the flow sensor. The performance curve on that pump makes it a very touchy thing indeed, to have it operating at a pressure that would allow as little as a 10 gpm flow, since that pressure would be very close to where it would be deadheading. Maybe you will have to supplement the larger tank with some interface with the flow sensor you mentioned (make and model number, please)

I certainly don't want to add any additional devices to my system, ecspecially at that kind of price tag.

Doing the math will never replace real world experience which is why I turned to this forum, but I appreciate your point. As for building character, thanks for looking out for me, but I am doing fine

The online calculators are basically the same as the "script". They are designed to size a tank to deliver water to the system and reduce pump cycles (less run time is better). The calculators recommend very large tanks for my scenario, which I know is unnecessary overkill. I think the size you recommended is more practical, but the calculators would never have even come close to that unless I made up the numbers to get the answer I wanted.

Assuming the lowest psi when running a zone is 20, and the highest psi when runnnig just a spigot is 30, I "assume" I will be able to set a switch (Square-D for example) to cut-in at 30 and cut-out at 40, by adjusting the differential setting to tighten the range and then adjust the range to match the target. If I went with a 35 gallon Flotec tank it is charged at 40 psi, which is the top end of my range. I think I would need to bleed off about 20 psi to get its empty psi to about 10-20. It will likely require some tweaking to get the tank to be at about 30-35 gals and 40+ psi, but once I achieve this it should hold at the cut-off range (30-40psi) just fine for a couple of days before losing enough through attrition to require a "bump" back to the top by running the pump for a minute or two.

Now this is all just theory as I have never worked with any of this equipment before and I would certainly appreciate a "heads-up" if I am going to be dissapointed with the results after I spend hundreds of dollars and hours of time to install it.